Knob and tube electrical wiring questions & answers:

Frequently-asked questions (and answers) about knob and tube electrical wiring.

This article series answers questions about Knob and Tube electrical wiring. We define knob and tube wiring, we include photographs that aid in recognition of this generation of electrical wiring, and we describe both proper and improper K&T wiring installations, repairs, or circuit extensions.

This website provides information about a variety of electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards and on proper electrical repair methods for unsafe electrical conditions. Our page top photo shows a home inspection client pointing out knob and tube electrical wiring in an older home.

Knob-and-tube wiring questions & answers on inspection, troubleshooting, repair, extension, abandonment

Knob and tube electrical of wiring has been installed in homes from the 1920s right up into the 1970's in some jurisdictions. The photo shows knob and tube electrical wires passing through a wall top plate in a 1920 New York home.

These questions & answers about knob and tube electrical wiring were posted originally at KNOB & TUBE WIRING

[Click to enlarge any image]

On 2021-05-29 by Hamp - Why is knob and tube wiring more-likely to overheat than modern electrical wiring?

Question: Why is the knob and tube wiring more likely to overheat if you insulate over it than today's modern wiring? Thanks.

On 2021-05-30 by danjoefriedman (mod)

@Hamp,

Thank you, that's a helpful question.

The original wire insulating jacket on knob and tube wiring and the wiring current or amperage rating presume that the wiring is installed as originally intended: was spaced in air.

That is, air could circulate freely around the wire, removing heat.

And where the wire passes through wood framing, of course, it runs through a ceramic tube; and of course it's supported off of surfaces by a ceramic knob.

Now if you're surround that same knob and tube wiring with insulation, it no longer has free circulating air around it.

The heat that is produced will not be so easily dissipated and therefore the insulation in fact may fail.

Now covered by insulation, the wiring overheats, thus there's an increased risk of a fire.

As a different example take a look at modern non-metallic electrical cable and you will see that the insulation is much more robust.

For any electrical wire, its insulating jacket is rated and intended to handle the heat that may be produced by the wire when the circuit is in high use without becoming hot, deteriorated and failing.

Failing wire insulation and overheated electrical wire is, of course, a fire hazard.

 

On 2021-04-03 by dennis stobinski - I just wanted to say that I find this site to be an excellent resource.

I just wanted to say that I find this site to be an excellent resource. I wish more rehabbers would read this article to understand knob and tube wiring.

On 2021-04-03 - by (mod) - Thank you for the kudos

@dennis stobinski, Thank you so much for your very nice note. It means a lot that you took the time and trouble to comment as you did, and of course I'm very happy that our information proved helpful to you.

Indeed we have worked hard for over twenty years to make information at InspectAPedia.com accurate, in-depth, and without bias, so I am of course very grateful when a reader reports that our website has been useful.

To that end, I would much appreciate hearing any comments, critique, suggestions, or further questions that you may have about any of our diagnosis/repair articles.

We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions. Working together and exchanging information makes us better informed than any individual can be working alone.

On 2021-02-12 by Bob - Some of my knob and tube wires have no juice

In my 1925 home I have these knob and tube wires in the ceiling that have no juice even though everything else on the circuit works OK.

Before tearing out plaster to follow and inspect the wires, do you have any other troubleshooting recommendations?

On 2021-02-12 - by (mod) - watch out that "dead" electrical wires might be live in some areas - and dangerous

Bob

Watch out: If the wires test as "dead" you still need to take great care during demolition to treat the wires as "live" until you have visually traced the entire wire length.

I recall pushing my way into the attic of a 1920's home in New York - a space that had not been entered for many decades. I saw what looked like a pile of loose wires coiled up on the attic floor and figured

"Gee these must be dead old wires someone left here" and on touching one of them got a terrific electrical shock.

Since then, when I've had to abandon rather than remove old un-used wires in a building, I tie the hot and neutral wires together, figuring that if someday someone finds another wire end that I didn't locate and if that someone connects that wire to a live source, the breaker or fuse will blow immediately.

You going to want to test each wire with a multimeter or voltmeter to be sure you know where the incoming hot leads are. It looks as though there's a dimmer controlling a light somewhere and an on-off switch controlling a light somewhere.

But from just the drawing I don't know what's the incoming hot wire what's the neutral wire and where the light fixtures are.

If you're not familiar with using a voltmeter or digital multimeter safely you need to take care of because making a mistake could shock you or burn the place down. I suspect from what you already said that you know that perfectly well.

In its original installation knob and tube wiring insulation was black indicating hot wires and gray lighter color or including some white in its woven insulation to indicate the neutral wire.

Remember, there is no grounding conductor wire.

Reader question: thanks a lot for all the info on the site, it’s very informative. Help me figure out my K&T wiring

Hi, thanks a lot for all the info on the site, it’s very informative. I just opened a wall in our 1915 house and discovered this.

We already did some major renovations in the other part of the house and I knew we had K&T. I’m trying my best to understand how this is wired but it’s too hard...

On the right it ends with 1 switch (still connected in the back of the wall) and the one with wire nuts was a dimmer.

What I can’t figure out:

- is this is all K&T or was this modified at some point (it looks too messy and it’s missing tubes)

- are the two cables exiting on the left coming from the panel and powering all this or if the power coming from the 4 ceramics on the right stud?

Thanks a lot! On 2021-01-12 by Lucas

On 2021-01-12 by (mod) - has this K&T wiring been modified or is it original?

Lucas

I can't see enough to tell you exactly what is being wired in your photo but I can say that I see what looks like a lot of knob and tube wire all jammed together in a small area, perhaps entering a junction box that I can't see.

And at the left of your photo I see new metal that suggests there have been modifications or additions to the wiring and I see what looks like an exposed splice that of course would be improper.

Most serious is that although the photos a bit blurry, it looks to me as if the wires in poor condition in some cases exposing legs of bare copper that I would consider to be unsafe and also an indicator that the wiring may have been damaged by overheating, rodents, or something else. I hope that you're planning to replace all of it.

Normally I like knob and tube wiring it I don't rush to replace it but if it's in poor condition or has been extensively modified or extended it's more likely to be unsafe.

On 2021-01-12 by Lucas

Here is a diagram of the connections. Thanks!

On 2020-10-17 by John - what is this old wiring in my house?

I recently removed the last part of an abandoned knob and tube wiring system and found this. Anyine know what this is called?

On 2020-10-17 - by (mod) - don't mistake old telephone wiring for knob and tube electrical circuits

I can't quite make out the photo, as it's a bit blurry John but it looks a bit like resistors and connectors I've seen in older homes where the telephone wires came into the building.

 

On 2020-05-17 by Jessica - is this knob and tube wiring?

I was replacing my outlets with tamper resistant outlets when I came across the following. Is this k&t?

Thanks

On 2020-05-17 by (mod)

Jessica

That looks like a transformer, though I can't see all the wires;

I cannot see into the wall or ceiling from which this was pulled; take a look at the article above and note those white ceramic knobs and tubes -

if you find those anywhere in your home then you've confirmed that it at least had and may still have this type of electrical wiring

 

On 2020-01-16 by William J. Petersen - How do I use existing Knob & Tube wiring where insulation has been added and other modifications made?

I have knob and tube wiring going into my second story of my home as it enters the walls from below at the basement I want to safely secure those wires and finish wiring the first floor and basement with the proper wiring.

How do I incorporate this wiring to accommodate the wiring going to the second story . The walls have blown in insulation.

Someone had changed the electric plug ins to three prong outlets but no ground, could I run a separate ground wiring and connect it to my other electrical services that are grounded to the water pipe. I plan on adding a separate ground rod to make sure the safety of the ground.

On 2020-01-16 - by (mod) - safety concerns even where knob & tube wiring remains legal

William

First, in my OPINION, while existing, un-modified K&T wiring is perfectly legal in homes ain general, and thus it can be used, there are some important safety considerations that you should think about before continuing, some of which I think you're already thinking about given your question.

1. an existing knob and tube circuit can be used but it cannot be extended -

that is to add to it wires for lights, more receptacles, etc.

2. the existing K&T, as you note, is not grounded,

so it is important to use un-grounded receptacles so as not to fool users into thinking a ground is present (and possibly creating an unsafe condition by allowing plugging-in of a device that requires grounding for safe use) OR you'd have to run a ground wire along that circuit and into every electrical box on it.

3. Local grounds to water pipes is not a safe "solution:

While grounding water pipes is a good safety feature (so you don't get electrocuted when a toaster falls into the sink) you would not simply rely on pipes here and there in a building as a safe electrical ground - the pipes may be interrupted by a diaelectric fitting or may otherwise not provide a continuous ground;

Some communities permit using an existing water main entering from underground to serve as one of the two grounds required; the other is a grounding electrode. Look in the ARTICLE INDEX under GROUNDING to see details.

4. If insulation has been added the knob and tube wiring is unsafe:

This is my opinion and is the worst news.

Knob and Tube wiring was in my opinion an excellent and safe wiring method in that it used ceramic knobs and tubes plus running wires in open air to provide wiring that wasn't likely to overheat or short together.

BUT now everything has changed: when insulation is blown into walls, the wiring therein that used to run in open air now is covered by insulation. It can not possibly run as cool as it did originally; the insulation on the wire and its approval as "safe" presumed the wires were in open air.

So the insulated circuit is less safe and at greater risk of overheating.

I'm not sure about your question:

"I want to safely secure those wires and finish wiring the first floor and basement with the proper wiring. How do I incorporate this wiring to accommodate the wiring going to the second story ."

But you can either leave the existing K&T but make it comply as we've outlined in this article series, and risk overheating in insulated cavities - (keep fusing to 15A or less and take care not to tax the circuit, e.g. by running electric heaters on it)
or
you can abandon the circuit and run a new one or multiple ones to upper floors.

On 2019-11-13 by Arnold - knob and tube wiring blew a fuse that won't re-set

Hi there i have knob and tube in a section of my house which my inspector considered safe when we bought the property.

Not too long ago i overloaded the circuit by plugging a laptop into an outlet on the ground floor so now all my outlets and lights in my master bedroom and porch are not working. Is there a way to reset this without having to go through a costly overhaul.

I dont intend to use the outlet that started this any more. Many thanks

On 2019-11-14 - by (mod)

If there is simply a fuse that's blown or a circuit breaker that stripped you can reset the breaker or replace the fuse.

It's also possible that a limited error such as a damaged electrical receptacle caused the fuse to blow or circuit breaker to trip: and the short circuit that occurred remains un-repaired; in that case you can't re-set the circuit breaker, you have to find and repair the fault - often a small, local electrical repair.

If, for example a short occurred at an electrical receptacle it's possible to remove the receptacle and, if the wiring itself isn't damaged, make necessary splices to keep the circuit active.

But keep in mind that when you eliminate an electrical receptcle, your home's electrical wiring may no longer be code complaint - for example if you have too much distance between the remaining receptacles.

Watch out: However if the electrical receptacle itself is damaged and causing a short circuit that it needs to be replaced. Leaving it in place without that would be unsafe.

I'm a bit surprised for the laptop alone would possibly be enough to trip a breaker or blown fuse. There's something else going on there. Most likely it's a defective receptacle. Replace it.

 

On 2019-10-01 by RosieF - which agency would be an authority on knob and tube wiring?

Does anyone know who/which agency would be an authority on knob and tube wiring?

I live in a building over 100 years old whose unscrupulous landlords never bothered to update the wiring. It caught on fire a few years ago and the landlord blames one tenants for an overcharged power strip. While the power strip no doubt was the spark, the fact that it spread so quickly and pervasively was most-likely due to the faulty wiring, whose conditions were questionable.

On 2019-10-01 - by (mod) - which agency is an expert on knob and tube wiring?

Rosie

Your local building code enforcement department's electrical inspector should know about Knob and Tube (K&T) wiring.

Indeed use of extension cords and power strips can easily overload a circuit - that ought to cause a breaker to trip or fuse to blow, but over-fusing, damaged wiring, damaged power strip or something else might indeed start a fire.

OPINION: in such a case, there remains an indirect relation ship between the primary cause (bad power strip or line cord or plug - for example) and the secondary cause of the fire that might include

- an inadequate number of electrical circuits

- overloaded individual electrical circuits

- over-fusing of those circuits to stop what an occupant or owner regards as "nuisance" tripping of breakers and fuses, in turn leading to overheated wires and a building fire

- absence of an electrical grounding conductor on those K&T circuits - meaning that a typical power strip that includes receptacles for three-prong "plugs" or grounded plugs is misleading since no ground is present, and in fact the
power strip's own plug may have been modified or adapted to fit into the two-prong K&T wall receptacle

FYI K&T is legal and is not required to be removed from a building provided

- the circuit has not been extended (extensions are not approved)

- the circuit is not damaged

- the circuit is properly fused

But as you'll read in this article series, the assumption that an old K&T circuit is "safe" might be a mistake. For example, simply blowing insulation into a wall or ceiling where K&T was run changes the environment of that wire: it is no longer suspended in air, therefore it may overheat.

 

On 2019-06-13 by Joe - can an appliance that uses justa 2 prong plug - without a ground - be plugged into a 2-prong outlet on a knob and tube wired circuit?

Is it still considered acceptable to plug an appliance with a 2 prong cord into an ungrounded 2 prong outlet with knob and tube wiring? If so, where is the line between what is ok and what becomes questionable?

On 2019-06-14 - by (mod) - Yes, it's OK to use un-grounded wall plug appliances in un-grounded electrical receptacles & knob and tube wiring

If the line port on your appliances a two prong plug them it's not looking for a ground and so you're not getting anything up by using it on a knob and tube circuit. Of course that is assuming that the circuit is safe and has not been damaged or is not unsafe for some other reason.

If the line cord on your appliances a three-pronged plug then it wants to be in a grounded receptacle so it needs to be on a circuit that includes a grounding conductor.

 

On 2020-01-1 by Logan

I am working on a house remodel. There is existing K&T. Currently working on the kitchen, however, the K&T wiring on this circuit covers(at least) the kitchen, a hallway and the back porch; possibly another room.

I can't/dont want to tear into anything beyond the kitchen at this time. What's the safest way to cut the kitchen off this circuit, leaving the other rooms still working. Am I able to just splice the hot and the neutrals together in a junction box prior to the kitchen? Then start the kitchen with a new circuit, with romex.

On 2020-01-13 by (mod) - never connect live hot to neutral wires

Logan,

It's possible that I misunderstood you, but no. If you connect hot and neutral of a live circuit together you're creating a dead sort that ought to blow the fuse or trip the breaker.

If you mean you're going to disconnect the K&T where it enters the kitchen area and then tie together the kitchen side of that circuit to prevent its re-use later, that might make sense. But the live wires where you cut them at the kitchen entry just get capped with twist-on connectors and left in the junction box.

The only time I wire hot and neutral together is when I am abandoning an electrical circuit that has been connected at both ends, but am leaving wires in place. In that case I wire the two together so that in the future if someone mistakenly tries to hook up the circuit (whose other end may be unknown) it'll trip the breaker.

Then yes, a new circuit to the kitchen is in order. Actually you want 2 20-A circuits supplying the kitchen so that occupants can run multiple appliances without tripping the breaker. I like to run 2 circuits and put a couple of quad outlets over the main counter workspace, with each receptacle in the quad on a different circuit.

On 2019-03-25 by Sean

I have three Knob and Tube related questions. In my 1920s house all but two K&T circuits have been replaced. One circuit powers the built in lights on my second floor. I'd like to start by replacing the second circuit which powers a series of built in wall light fixtures on my ground floor and a chandelier.

My first question has to do with the wall lights. I removed the fixtures and found that they used a metal 4" pancake style junction box to mount the lights. Behind the boxes is what looks like 2x8 boards which span the width of each stud bay.

The 2x8s are drilled in two locations for the K&T and the wires were passed through the holes and into the box via a knockout. The 2x8s and holes look original. The box itself is lag bolted into the wood in two locations, so the boxes are very secure and running the romex down the stud bay and into the basement is going to be fairly straight forward. However I'm not sure what to do with the old K&T leads. I can't pull the wires out of the wall.

From a previous project I know that the wires are tied into the stud bays with at least two knobs. For the old K&T wires, should I simply put wire nuts on them and leave them in the small junction box? I'm also a little paranoid about if for some reason the wires arc or connect in the junction box.

That would leave me with an energized wire in the wall or where the wire exist in the basement.

My second question. I'm planning on cutting the K&T wires in my basement until I get to where the wire goes vertical into a wall cavity. How should I treat this wire? Should it be in a junction box of its own or is a simple wire nut and electrical tap good enough to meet code?

For the chandelier there is no easy way to run a wire. The ceiling is highly decorative and I can not access from above. My plan was to run a new romex line to the light switch.

From the light switch on would be K&T. My plan would be to also connect the chandelier's neutral K&T wire to Romex at the closest point possible. Does this sound like a good plan or would this be a code violation?

On 2019-03-25 by (mod) - tie together hot and neutral of completly abandoned circuits left in place

Sean

My OPINION which means it's not the last or only word on this is that safest when we can't remove wires for an abandoned circuit is to
tie the hot and neutral together with one twist-on connector.

That way when someone foolishly finds and tries hooking up those wires to power somewhere else in the building the fuse or breaker will respond right away. Tie the two together, install the twist-on, and if you're scared as I am, maybe add a bit of electrical tape to be sure the connector is extra-secured to the wires.

I prefer to box all dead wire ends and treat them as I described above. You could label them too but that's probably going further than most would do.

Leaving "dead" wires out of a box risks that someone later activates the circuit from somewhere else in the building - risking a shock or fire.

This is not a mere theoretical speculation.

I pushed my way into the attic of a 1920's house in Poughkeepsie NY through a newly-cut hole in a ceiling (there was no access) and found my head coming up through a rats nest (here in Mexico we say a "lata" of "abandoned" electrical wires left as a little gift by Bill the previous owner and a DIY handyman. Except one of the wire pairs was live and I got a nasty bite. While standing atop a ladder.

Never trust that old wires you find hanging around are "dead" - test every one; and be grateful if someone left them capped and boxed safely as you will do.

About continuing to use knob and tube wiring -

Despite an recent but error-filled or at least safety-inadequate (IMO) "electrical safety" article in the New York Times saying K&T was abandoned in the 1960s it remained legal in NY and in original installation was a very safe wiring design: the hot and neutral wires are widely separated and are supported on fireproof ceramic knobs or run through ceramic tubes when passing through wood framing.

However when my Poughkeepsie house was built in 1920 heat was inexpensive and homes were uninsulated; Those K &T wires ran IN AIR through walls and ceilings and attics and floors. Later when people added insulation the wire's operating temperature was naturally increased - risking overheating the insulation and creating possible fire hazards.

So even when remaining K&T wires are "code legal" that doesn't mean that those circuits are actually safe or that they will perform as safely as they did originally.

When wiring your chandelier, if the ceiling is insulated the wires should best be replaced with a new circuit; an experienced electrician can drill and snake wires without wrecking the whole ceiling.

On 2018-04-24 by Anonymous

have a home that has KnT.. but all of the home has been rewired to code new panel etc..none of the working outlets or lights are using knob and tube.. and none of the KnT is near the new panel... but i am putting in a bathroom on 2nd floor and have run into some KnT in the floor where i need to run some plumbing.

I tested with pointer tester it beeps and lights up red for a few seconds and then goes quiet..then lights uo red again then goes quiet etc.. both runs do it.. i can not find any wire coming from any box that is possibly connected to the KnT .however appears to go quiet when the main is off..

again nothing in the house is in use that uses the KnT..so my question is do you think i could shut off the main cut the knt... cap it so i could run the pipe ?? any response would be helpful

On 2018-04-24 by (mod) - Some voltage detectors will pick up stray current that is *induced*

Anon

I don't know what "tester" you are using. Some voltage detectors will pick up stray current that is *induced* in an inactive (not connected to anything at either end) electrical wire that runs close to or parallel to live wires.

I'd check for voltage between the K&T wire ends and ground.

"Abandoned" electrical wire circuits are sometimes not properly disconnected and abandoned. I pushed my way up into a small attic space of a 1920's Poughkeepsie bungalow through a newly-cut attic access (the old one had been removed and ceilinged-over. On pushing into the attic space I found a rat's nest of old BX wire including bare wire ends. It was live. And shocking.

When I used to re-wire homes and was leaving abandoned wire in place - as was often necessary - I would tie the ends of the wire (hot and neutral) together. That made darn sure that if in the future some dope tried to hook up the other end of wire somewhere the circuit would short and immediately trip a breaker or blow a fuse - forcing discovery of the problem.

On 2017-05-26 by Mary

We have a mixture of knob and tube and newer wiring in our 80 year old house. We found an unused ceiling light fixture which had been filled with plaster. The two wires in it are still hot. With all the circuit breakers in the box on, only one wire of two shows voltage with a ncvt tester.

When either of two different breakers are turned off, both wires show voltage. We have not tried to shut off the "main" breaker, as our box has four breakers labeled as main, in addition to a fifth labeled as main range and a sixth labeled as main lights. How do we troubleshoot to find the source of the voltage?

On 2017-05-27 by (mod) -

Mary:

There are tools and approaches for tracing circuit wiring through buildings - some suggestions are at ELECTRIAL CIRCUIT ID, MAP & LABEL https://inspectapedia.com/electric/Electrical_Circuit_ID.php

I test wires with a neon tester and with a VOM or DMM.
I test:

- wire to wire

- wire to known ground

USUAL SITUATION:
If with all breakers on

Wire A has 120VAC between wire A and Ground
and

Wire B has 120VAC between wire B and Ground
then

IF A and B are on two different phases (opposite sides of the panel or that is taking power from two separate service entry wire leads)

And if both are properly wired

THEN you might see 204VAC when measuring current between A and B

YOUR SITUATION
…
With all the circuit breakers in the box on, only one wire of two shows voltage with a ncvt tester.
When either of two different breakers are turned off, both wires show voltage.

I'm puzzled by this too and worry that there are defective breakers.

Can you tell me the electric panel brand and send me photos of the panel and its labels and its breakers?

On 2017-05-25 by David

Does old black knob and tube wiring (single conduit, going through porcelain) ever have asbestos in it?

On 2017-05-26 by (mod) - Does old black knob and tube wiring (single conduit, going through porcelain) ever have asbestos in it?

David.

I don't know, and haven't seen an authoritative answer to that question. I will look further.

It is certainly true that electrical wiring from the era that use knob and tube included some installations in which asbestos wire insulation was used, such as in theater electrical lighting

See ASBESTOS ELECTRICAL WIRE INSULATION for complete details

On 2017-05-26 by David

thanks. my sense is that no one tests it even for a whole house removal.

On 2017-05-27 by (mod) -

I think that's right, David. Remember that if there is a hazard from asbestos it is from friable materials. When you consider the low probability that ordinary house circuit wire is high in asbestos and that it's not particularly friable as wire insulation, the risks probably don't justify testing.

On 2017-11-23 by Freddie

Hi, I work for a company that wants me to replace old Knob and Tube wiring in attics, but I can't find a recommended procedure for safely doing so; tying into the existing K&T in the walls.
Do you know where I could find one, as well as a prescribed method of testing the wiring in the walls to make sure it's still safe?

On 2017-11-23 by (mod) - how to connect new attic re-wiring to existing knob and tube circuit

Freddie,

A quick summary of some points we make in the KNOB & TUBE WIRING article and in this article series on knob and tube wiring:

1. it is not, in most jurisdictions, required to remove K&T circuits provided the wiring is un-damaged

2. You are not permitted to extend an existing K&T circuit

3. You cannot safely "update" a portion of existing K&T circuit with new wiring if grounding is required, since the feeding K&T circuit would not provide an incoming ground.

4. Your local electrical inspector will probably be OK with you bringing the end of the existing circuit into a junction box where it enters the attic, then running new wire in the attic, presumably for attic lighting, but beware that any attic that also includes electrical receptacles as those won't be grounded (and should not mis-lead occupants by sporting receptacles with grounded-plug connector - that is a three-pronged plug receptacle)

5. I would be nervous about doing you are being asked to do. There is NO safe way that you can "test" the safety of existing K&T wiring where it passes through hidden spaces like walls and ceilings.
You can do continuity tests and tests for shorts but you cannot see the condition of the wire.

For example, where K&T was run originally in an uninsulated wall cavity it might have performed well and safely but decades later after people added insulation by blowing it into the same wall cavity that same wire is now overheating. It is no longer running in open air.

So later when someone in an attic plugs in an electric heater and starts a fire in the building walls below where squirrels chewed the insulation off of the wire you and your employer are likely to be blamed.

 

On 2017-03-14 by southernmunkey

Have knob and tube getting my 120v but the ceiling fan isn't working pretty sure I found the neutral and hot but still isn't working how do I go about troubleshooting

On 2017-03-14 1 by (mod) -

ceiling fan not working

Check the voltage,
then review the fan connections and switch controls

 

On 2017-02-25 by Kp

Anyone familiar with the color coded ( red,white,black) knob and tube wiring to n the 1950's

On 2017-02-25 by (mod) - color coded ( red,white,black) knob and tube wiring

Red & Black would normally be hot wires and white, the neutral wire.

On 2016-09-20 by dave conifer

Hi. I just bought an older house and found a run of knob and tube in the basement. However, the house also has a modern panel of breakers. I painstakingly flipped breakers and checked outlets/fixtures, and determined that every one of them can be turned off in the modern panel. Does that mean that none of the knob and tube wiring I found is currently active?

In other words (I guess, being a novice), can knob and tube wiring be connected to a modern panel?

Thanks!

On 2016-09-21 by (mod) - is the knob and tube wiring active?

Dave:

What you did was what I'd have tried too, but given that you could be killed if there's a mistake, and given that over at a companion article inspectapedia.com/electric/Old-House-Electrical-Systems.php#Abandoned_Wiring

I warn about having nearly got fried by assuming a circuit was really "dead" or "off", you want to do a bit more.

I've even found live circuits as a building when the main breaker was off, supposedly shutting off all power, and even when the meter was pulled (there was a circuit wired over from an adjoining building).

So never assume. Test before touching.

There are several types of voltage detection devices, some inexpensive, that will buzz or light up if held near or touching an electrical wire that carries current. Some of these along with some scary photos are at inspectapedia.com/electric/Electric_Shock_Hazards.php.

 

Question: the circuit I was working on does not seem to be connected to a circuit breaker - it only turns off when main power is off

Our home has a combination of 14/2 and knob and tube wiring - with an updated circuit breaker box. I wanted to change a kitchen light fixture and when I went to shut-off the breaker found that the light I wanted to change wasn't connected to a breaker? When I shut-ff the main breaker,the light circuit was off? Don't understand - help! -Mike - Joyce.k.smalley@gmail.com - 8/12/2011

Reply:

Mike - Joyce, this is not good, and if you cannot quickly see what's going on I strongly recommend hiring an experienced electrician to trace down your wiring.

From your description, and assuming you correctly identified your main breaker and have only one such in the home and panel, then I suspect your main breaker is defective and did not turn off internally.

Here are some other possibilities:

1. Switch off the MAIN circuit breaker in the home. If that does NOT turn off ALL power in the home then one of these problems is happening:

- you have not correctly identified the main breaker, or in some older panels, there may be multiple "Mains"

- your main breaker is a brand that often fails to actually turn off inside even if the switch is in the "OFF" position, such as FPE Stab-Lok (search our website for Federal Pacific Electric ) for details.

- your home has more than one electrical service or (as I have found on some old buildings in very dense urban neighborhoods, usually now used as businesses) on occasion someone has wired one or more circuits in a building by "borrowing" a circuit or power from a neighbor.

If on closer inspection your MAIN breaker turns off the light in question, but the individual circuit breaker that you thought controlled that light does not, then either you've not correctly ID'd the individual circuit breaker, or as I described above, the breaker is defective and is not turning off the circuit in question.

Question: how would you track down knob and tube in the walls of an old house

If you were an insulation person, how would you track down knob and tube in the walls of an old house so you could generally ascertain which bays NOT to insulate. I am thinking you begin in the basement -- though some of our insulation guys start in the unfinished attic and go down. I am a novice at electricity -- and having trouble identifying a proper plan of "attack." - MBT 9/7/2011

Reply: Tracking down just where knob and tube wiring is found in a building: tips

There are several electrical test instruments that can spot metal running through a wall, including both metal pipes and metal wiring. The trouble with the idea of leaving some bays uninsulated to avoid overheating the K&T wiring is that in walls wiring typically runs horizontally - through most or all stud bays.

I'm not sure, other than tracing wiring, how you could reliably infer that wiring in building cavities is the original knob and tube or if some areas have been re-wired. Certainly if you open a junction box and see that there is a ground wire entering the box, or if you see armored cable entering the box, at least right there it's not knob and tube.

But we may not know exactly where new circuits were installed and where old ones remain.

For example, I would not rely on seeing grounded receptacles as an indication that the wiring is newer than K&T. It's just too easy for someone who is uninformed about good practice to have installed grounded electrical receptacles even though the circuit may not include a ground (and may be knob and tube).

In sum: make visual inspection of the entire building to identify where knob and tube wiring is visible, trace those circuts as far as you can into individual rooms; use instruments (such as the Tic Tracer) to trace down wiring paths in walls, ceilings, floors.

Reader follow-up:

Thanks, Moderator for your suggestions. I had been told that there was also something that you could plug into the electric panel --then go around the house to see where knob and tube (or at least ungrounded stuff) was. Have you heard of this -- and do you recommend it?

Reply:

MBT there is a variety of circuit tracing tools including what you describe. The simplest is a stand-alone device like the tic tracer by Tif that senses electrical wires in walls; schemes using transmitters also work though where I've seen them used more often it was to track down a specific circuit. Yes, it's a useful approach.

Question:

Do you know what they call the knob and tube ceramic junction box above the light bulb fixture that supplies neutral & hot to a drop light bulb fixture. My teacher said the word starts with R - Ray 10/21/2011

Reply:

Electrical junction box. Let me know (page bottom CONTACT link) what the rest of your teacher's "R" word is.

Question:

Love your site.

I am in Los Angeles in a house that was built in 1921. It has knob and tube and is still running electricity that way. We've had a licensed electrician come and inspect all the wires, install a brand new breaker box and ground all the outlets. We asked him if cellulose could be blown in over the knob and tube in the attic only and he said that'd be fine because the wires are still in good shape.

I called an insulation company with experience in knob and tube and they said it's fine, as well. Especially because cellulose is non-flammeable.

I still have reservations, though. A lot of forums say to replace the knob and tube completely.

Should I be worried? We are planning on only blowing in the cellulose in the attic, not the walls.

Thank you! - Richard 10/28/2011

These questions were posted originally at KNOB & TUBE WIRING

Question: is it ok to run romex wire off of a knob and tube circuit?

isit ok to run romex off knob &tube - Jack 7/11/2012

Reply: No. Do not extend knob and tube electrical circuits

Mixing knob & tube with romex is not safe - Bruse

k&t should never be spliced into to extend the circuit. When k&t was around it was used primarily only for lighting and other light load on the wiring. Don't even think of using it for bathrooms, hair dryers, coffee makers, kettles and toasters, etc. With the age of the wiring (splices were taped), the splices are brittle and often deteriorated.

Adding a new circuit as illustrated above can be very dangerous, depending on new load added to the circuit. Splices overheat and can be a potential fire hazard. Many insurance companies in Quebec Canada will not insure a home with k&t or charge and insane premium for it.

If they do insure it, they demand that the system be inspected by an electrician prior to insuring the home. I believe in Ontario Canada if you have a home with k&t it has to be replaced, they will not insure your home! (Can someone confirm this?). The insurance companies are doing this due the the higher risk of fire with homes that have k&t (statistically).

I personally would never add a circuit modify the wiring or cover it with insulation. It can be performing well right now, but the modification can over heat the wiring and cause a fire. I would make a plan to slowly replace the wiring. If insulating an attic replace the wiring, its just safer, why take a chance.

This is my personal opinion based on past experience. Always consult an expert. - Kosta (professional home inspector)

- Kosta Trivlidis Home Inspector (AIBQ) National Home Inspector (NHICC) CSI Inspections Inc. csiinspections.ca kosta@csiinspections.ca

Thanks Kosta, we agree that extending K&T electrical circuits is improper. Most jurisdictions permit homes to continue to use K&T circuits but as you will see in the article above, even though as originally installed (widely separated hot and neutral wires, ceramic knob and tube support with no direct wood contact, suspension in air for cooling) made these circuits perform well, in older homes where conditions have changed, the circuits, even legally in place, may not be as safe and reliable. Reasons that K&T circuits cannot and should not be extended include:

• the absence of an electrical ground
• the added electrical load on an old circuit whose wiring, particularly where it passes thorugh hidden spaces, may no longer be as fire-safe as when new
• electrical code prohibitions

Question: how do I get this unsafe knob and tube wiring out of my home?

(Nov 18, 2012) mr419247@youtube said:
this is a good start, but i know what k&t is and that i should get that old fire hazard out of my home!

how the wire was ran was great now i need to know how to pull from my old plug up to the top of the home. after that how to find the chase to run all my lights and plugs back to the secret breaker box in the basement of the home
this is not easy for the pro's but not ever one can pay there hard cash but they know its only a matter of time with k&t for the elc.
i looked on youtube for videos and found only junk vid's

well i have a 1924 home and working on it found alot of k&t that i need to pull out
just wist there was a good how to rerun wire from the k&t system
thank you for your info it will help

going to pull one from the plug or light to the top of the walls and chase that all the way back to the box
doing one line at a time once i run in to a splice wire "soldered and also taped" i will put a box in.
also chase the splice k&t to it outlet
also i have a wire sniffer that will let me know if the wire is live or not
hope i am doing things right!

is there a good video or a easy way to get all this k&t out of my home
also have updated s/b box looks like every thing is new but up stairs its all knob and tube
even in the bath room thats how i found it all
some one put new wire with wire nut to make is look like new but behind the wall's is the truth
i dont want to rip every wall down to get it out
wish some helpfull hint like dont buy that home lol but to late now

Reply:

Mr41

If old electrical circuits are found to be damaged or otherwise unsafe and beyond economical repair, most folks just disconnect the old wiring and leave it in place- harmless in that case. Old wires are capped, enclosed in junction boxes and labelled as "OFF" or "DEAD" or "DO NOT USE".

Running new circuits in an existing building uses several tricks of the trade

Plan the runs by careful study of building layout and the directions of floor and ceiling joists as well. Wires are snaked through wall, floor, ceiling cavities using a few holes to give access, and drilling, and fish tapes.

Check with your building department to see what permits and approvals are needs, and what work requires a licensed electrician. Some electricians will also allow you to do certain tasks that will cut your costs.

Requirements for permits, approvals, licenses are not just tonirritate you, they are to keep you, your family, and future occupants of the building safe.

Question: big "POP" when installing a microwave on K&T wiring

(Dec 3, 2012) Bailey Ragsdale said:
I was trying to instal a microwave and our knob and tube wiring (black and white wires) crossed and there was a big pop and bright light and now nothing on that circuit works. I thought I was turning off the right breaker but Im guessing it wasn't the right one. How can I fix it?

Reply:

Bailey: it sounds as if you either crossed a hot to ground or moved a wire with damaged insulation so that a hot lead shorted to ground. Turn off and leave off the circuit until your electrician has diagnosed and fixed the problem. Proceeding as you describe sounds dangerous, risking shock or fire.

Question: ok to use a compressor, refrigerator or computer on a Knob and tube circuit that has been extended?

(Mar 22, 2013) Robert said:
Is it unsafe to use compressors, refrigerators, computers, etc with knob and tube wiring that has been extended with three wire insulated wiring in an old building built in the 1920's and used as a fire station?

Thanks

Reply: extending K&T circuits is unsafe; also you're missing a required ground.

The wiring you describe is unsafe and probably violates electrical codes in that while it is permitted to continue to use K&T wiring that is in good condition, extensions and additions to the circuit are not permitted.

And computers or other devices that are sold with a grounded electrical plug at the end of their power cord must be connected to an electrical circuit in which an electrical ground is provided - a feature not included with knob and tube wiring.

Question: lights go off in my house when it's cold

(Mar 13, 2014) diego said:
the lights in my second floor house which are K and T go off when it is cold in the middle of night and back on when the house heats up in the day .
how do I trace he problem

Reply:

Diego: look for a loose or corroded electrical connection at one or more splices in the circuit, starting at the panel and working forward. OR when lights are "off" trace the circuit to see if part of it is live as the fault lies at the end of that run.

Question: adding a bath fan and switch to a knob and tube circuit: which is the hot wire?

(Mar 24, 2014) Anonymous said:
I have knot and tube wiring in my bathroom I want to add a fan and a new switch for the light how do I no with is the hot wire thank you

Reply:

Anon,

Sorry for the bad news, but while it's legal to continue to leave in place and use existing knob and tube electrical wiring, it is not acceptable nor permitted to extend or add to those circuits.

Question: does knob and tube wiring that was wet need to be replaced?

(Aug 18, 2014) Petra said:
If K&T wiring gets wet, can it be dried out or does it need to be replaced?

Reply:

Petra,

You can read about wet electrical wiring hazards in documents that address flood damage to homes. Generally if wiring has been wet there may be shock and fire hazards. Usual procedure is to have the wiring inspected by a professional. The wiring does not necessarily have to be replaced.

However with old, fabric-covered wire such as was often used with knob and tube systems, the inspector might opine that the insulation has been caused to deteriorate so might want wiring replaced.

Watch out: As the Underwriters Labs point out in their flood advice, "... this is not a do-it-yourself project"

Leave electrical power off and don't even touch the electrical panel until an electrician has inspected the system and let you know that it's safe to do so.

You don't say just what sort of "wetting" occurred nor its extent. After building flooding, it is common to have to replace electrical circuit breakers, fuses, switches, receptacles, and even wiring as well as electrical equipment such as motors that were flooded or soaked.

On the other hand, if someone opened a can of carbonated water and accidentally splashed a section of K&T wiring, most likely it'll be ok.

Comment: opines that the hazards on K&T wiring are just at the splices

Thomas said:
If splices are soldered, then they are safe. A properly soldered splice is safer than any wire nut or quick connector made today (those are dangerous). IF K&T is 12 gauge, it can definitely be used for heating appliances, if all of it is 12 gauge. I'd trust K&T over old crumbly Romex, where both wires are right next to eachother. That stuff is scary. Ungrounded wiring is only dangerous if you try to use grounded appliances, or otherwise appliances with conductive housings that aren't properly insulated (lamp sockets, where the paper gets damp in the summer, or crumbles).

Reply:

Thanks for your comment, Thomas. But I'm unable to find an authoritative citation or source that agrees with you. The issues with knob and tube wiring are not generally the splices in any case but rather

1. extensions to the existing circuits - not permitted

2. damaged wiring from being exposed to rodents, foot traffic etc.

3. change in wire conditions that mean overheating, such as the addition of insulation to building cavities where the wire was originally installed in open air space.

4. Connection of "grounded" receptacles to un-grounded circuits, which is unsafe and in most jurisdictions a code violation. I emphasize the term "receptacle" or in popular parlance "wall plug or wall socket" - the existence of a wall receptacle with a ground opening when wired to an ungrounded circuit is unsafe and illegal: we cannot control who may come along later and connect to it a device that presumes the presence of an electrical ground connection for its safety.

Question: cover up knob and tube to improve safety?

(July 30, 2015) Carl said:
Why can't an insulation barrier be made out of non-conductive, heat resistant material, perforated with ventilation holes that can be attached to a joist and covers k&t wiring, allowing insulation to be inserted in the joist bay but along side of the dam and away from the wiring that remains cooled from the perforations in the top of the shielding?

A material that is inexpensive, easy to cut to different lengths & fast to install (a 10' long piece that can be screwed or nailed to the top of a joist, extends out just far enough to surround the k&t wiring and rests on top of the gypsum/sheetrock/plaster ceiling of the room below so that a 12" piece of insulation can be covering the 16" joist bay between the shielding and the adjacent joist.) At least in this manner you can still insulate a majority of your attic while keeping the insulation away from the k&t wiring.

Reply:

Carl

You could insulate the stud or joist or other framing bays through which no wiring is run. Insulating around wiring, if it's close enough to raise the wiring temperature, will raise the issues of heat deterioration of the insulation and a resultant fire risk.

What's missing is the beef of your suggestion and also of my reply, that is, we don't know the clearance distance that would in all circumstances (building variations, weather, temperature, air movement, current flow) would keep the wiring temperature within its rated temperature range.

Question: I have 35 volts from hot to neutral.

(June 2, 2016) Bill said:
I have 35 volts from hot to neutral.
When I bring in a 120 v hot it jumps to 240v
Any suggestions

Reply:

I suggest you need an electrician to find where someone has crossed wires - not to be a smartypants - but a mistake can kill you or burn down the house.

When you see 240V I suspect that you're touching two hot wires from opposite panel buses or phases together - that'll give 120V

When you see voltage to neutral if nothing is connect to or running or drawing current on the circuit then you have a short somewhere in the wiring.

Question: changing a light fixture on knob and tube circuit that was called "in remarkably good shape" blew a fuse

(July 12, 2016) Dan said:
I have an old home with knob and tube that has been inspected and rated as "in remarkable good shape, the best I've ever seen" as the inspector. The box in the basement is new, the basement and kitchen has been updated and into the new box. In the entrance we went to replace a chandelier that was working perfectly-just wanted a different style.

When we put up the replacement it blew a fuse. We tried everything and kept blowing the fuse, so we took another light that we had use before and went to hang it instead and blew the fuse.

Both chandeliers after blew a circuit breaker when tested at another hookup/outlet.

My question is this-it could be possible both lights I went to hang were bad because they had both been used in other applications but now I'm afraid to hang anything! How do I test to make sure it's not the wiring in the ceiling where I was trying to hang it. I really don't want to start ripping the ceiling down to trace it when the previous light worker perfectly there for years.

Reply: This scares me, really.

Your inspector sure makes me scared, Dan. Any inspector who sounds as if he is giving a sales pitch for the home makes me worry that he's working for the seller or realtor, not for the client who's paying him. That in turn makes me worry that hazards may be under-reported or mis-reported - putting the buyer at risk of a nasty surprise later.

That editorial finished, knob and tube wiring in good condition is not required to be replaced, though it cannot be extended, and it is less safe than modern wiring in that there is no electrical ground on the circuit.

When you put up your replacement light fixture and a fuse blew, that suggests that there is a wiring error - a short circuit somewhere is most likely. It's easy to have a sneaky, hard-to-find short when working on older wiring: a connector made too tight that cuts into a wire's insulation at a metal box, or a wiring error during hookup can be the cause.

Keep in mind that your light is not grounded - so an error that connects power to the metal of the light fixture presents a serious shock hazard.

Start by removing the light fixture you installed
Then inspect the wiring for damage
Then review the installation connections and try again.

Question: can I assume the knob and tube wiring in this home is all inactive or "off"

2016/09/20 dave conifer said:

Hi. I just bought an older house and found a run of knob and tube in the basement. However, the house also has a modern panel of breakers. I painstakingly flipped breakers and checked outlets/fixtures, and determined that every one of them can be turned off in the modern panel. Does that mean that none of the knob and tube wiring I found is currently active?

In other words (I guess, being a novice), can knob and tube wiring be connected to a modern panel?

Reply: no

Dave:

What you did was what I'd have tried too, but given that you could be killed if there's a mistake, and given that over at a companion

article KNOB & TUBE or OTHER ABANDONED ELECTRICAL WIRING

I warn about having nearly got fried by assuming a circuit was really "dead" or "off", you want to do a bit more.

I've even found live circuits as a building when the main breaker was off, supposedly shutting off all power, and even when the meter was pulled (there was a circuit wired over from an adjoining building).

So never assume. Test before touching.

There are several types of voltage detection devices, some inexpensive, that will buzz or light up if held near or touching an electrical wire that carries current. Some of these along with some scary photos are

at TOUCHING ELECTRICAL EQUIPMENT

Also See SAFETY for ELECTRICAL INSPECTORS for a more complete treatment of electrical inspection safety procedures for inspectors.

...

Continue reading  at KNOB & TUBE WIRING - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see KNOB & TUBE WIRING FAQs-2 - more-recent Q&A about knob and tube wiring.

Or see these

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  • KNOB & TUBE WIRING PROPERTIES
  • KNOB & TUBE WIRING ILLUSTRATIONS
  • DAMAGED KNOB & TUBE WIRING
  • EFFECTS of INSULATION on KNOB & TUBE CIRCUIT SAFETY
  • KNOB & TUBE WIRING EXTENSIONS ELECRICAL CODE CONCERNS
  • ADVICE on IMPROVING KNOB & TUBE WIRING SAFETY
• OLD ELECTRICAL WIRING TYPES
• OLD HOUSE ELECTRICAL SYSTEMS
• WET SUBMERGED K&T WIRING

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