Q&A on how to inspect & repair old house or old building electrical wiring.

This article series answers basic questions about assessing and repairing the electrical service, capacity, wiring type, condition, and safety in older homes.

Old House / Building Electrical Wiring Q&A

These questions and answers were posted originally

at OLD HOUSE ELECTRICAL SYSTEMS - be sure to review the information there.

Photo: an 1920's vintage ceiling light fixture box.

When did electricians stop using cloth insulated wiring and add a grounding conductor?

When did they stop using cloth for insulation

What year did they add ground wire to residential wiring On 2020-03-20 by Mark

by (mod) -

Mark

Thank you for the helpful questions about the history of types of electrical wire used in residential buildings. Here is a nano-history of types of electrical wire use:

The shift to popular use of plastic-insulated NMC or "non-metallic-cable" electrical wire in residential and light commercial use began in the late 1950's in North America, but you will not find any date or year in which cloth- or fabric-insulated electrical wire use ceased completely.

In fact some fabric-insulated electrical wire use continues into the present day.

Your question about dating the use of ground wiring in electrical circuits has a similar answer.

Pure un-grounded knob and tube circuit wiring began in North America around 1890, waned in popularity by the 1950s but continues to be legal in many jurisdictions even today in 2020.

Metallic-sheathed "BX" electrical wire entered popular use in North America as early as 1920 and was widely-used in the 1940s and in some jurisdictions is required for new wiring even today in 2020.

Non-Metallic (NMC) electrical wiring was used in North America beginning in the 1930s first as fabric or fabric-and-rubber insulated wire and later - by 1965 - was commonly installed as plastic-insulated wire. Plastic NMC pretty much replaced fabric NMC in branch circuit wiring by 1975, and it continues in use today. Some early NMC wire did not contain an electrical ground.

Metal conduit-wired electrical circuits were used in North America as early as 1940 and continue to the present.

And all of these answers depend on and vary among the country and city where the building is located.

Porcelain "cleats" for electrical wire date fro mlate 1800s in Massachusetts

That open wiring usually has porcelin cleats holding it in place on the wall.in older homes built in late 1800 Charlestown and Boston Ma. Area ! On 2020-02-14 by Mario Di russo

by (mod) -

Thanks for the note, Mario. Indeed porcelain knobs or "cleats" were used to hold knob-and-tube electrical wire off of wood surfaces.

How can I reattach the porcelain wire knob that was accidentally knocked off

How can I reattach the porcelain that was accidentally knocked off putting up drop ceiling tiles, the wire is cut in half
On 2019-12-1 by Steve Houze

by (mod) -

Steve,

Sure you can reconnect knob and tube wires that were accidentally cut.

Back in the day when that wiring was new the electrician would have simply splice in a short length of additional wire sufficient to make the reconnection and she would have tipped joint thoroughly with electrical tape.

However in modern practice any such place would be enclosed in a metal or plastic electrical box.

I wouldn't consider that a modification or extension of a knob and tube circuit and I would expect your local electrical inspector to approve such a repair.

I can't tell the hot from the "cold" (Neutral) wires in my house

Can't tell hot wire from cold. Cloth insulation.want to wire electric box On 2019-08-04 by Mark

by (mod) - figuring out which wires are hot and which are neutral

If you know how to use a voltmeter or digital multimeter and how to work on electrical wiring safely you can test to see which is the hot wire.

Watch out: if you don't know how to do that work safely you could be shocked or killed.

Sometimes there are other Clues available to identify which was a hot and which was a neutral wire such as noting the color of the screws to which wire's at the junction box or fiction were connected.

• Neutral wires will be connected to the silver screw and
• the hot wire would be connected to the Brass colored screw.
  

Trouble identifying hot and neutral wires in old house.

I just started working on old home wiring, 1910ish. can not tell which one is common or hot.

Both have identical wrap. When u test them separately u get 55 - 60 volts each?

I can find the hot one with a tracer, but connecting to another receptacle to provide power i cant tell between hot and common. Or is it just hot with ground? This is in Rochester, NY On 2019-03-01 by Dean

by (mod) - Testing from hot wire to ground you should be seeing 120V not 55 or 60V -

Dean

Testing from wire to ground you should be seeing 120V not 55 or 60V - sounds like there's a short.

The hot wire to ground would show 120V or close to it

The neutral wire would show nothing if there were no short.

Old house has black and green wire and a red wire: which is doing what?

in my ceiling rose wiring I have a cable with one black & one green wires in it and one cable with one red wire in it, could you tell me what these are for please. On 2020-01-13 by richard milnes

by (mod) -

Richard: apologies but no, I can't say for sure what those wires are; an electrician would tell us immediately by use of a VOM or DMM to determine the hot, neutral and ground.

Color code conventions would say

Green - ground

Black - hot or line voltage

Red - an alternative hot or line voltage

but more likely if your building is using 120VAC wiring one of those, perhaps the red, is acting as the neutral.

When I plug in a vaccum cleaner into the knob and tube circuit the lights flicker and power went off but fuse didn't blow

Older house built in the 20s found a lot of knob and tube being fed from Romex... plugged in a vacuum cleaner ran for a bit lights flickered circuit went out did not trip a breaker went up in the attic to see if there were any issues with animal chews or whatever and found that the neutral is also carrying 120 volts

and unlike some knob and tube I've seen the hot is being switched but again did not trip a breaker ....curious as to where to look I've already eliminated all the ceiling fans and anything plugged into that circuit and all of the constant hot wall sconces On 2018-09-11 by JeanO

by (mod) -

Jean

Watch out: what you describe sounds dangerous, with the risk of both fire and shock.

It's not something that I can diagnose from just your brief a text.

To be safe you should turn the circuit off. Electrician would doubtless trace a hot and neutral lines looking for a short between them or within or inside of a connected device.

Figuring out hot and neutral wiring in an old ceiling fan electrical box

I removed a ceiling fan to hang a new one I purchased and found a confusing array of black and white wires coming from the same point in four places. They have some brown paper that I believe originally wrapped the two together.

My house was built in 1960 but I cannot figure out what each set of black and white wire is neutral, ground and hot. Please advise. Picture attached On 2019-12-05 by Patty

by (mod) - figuring out 1960 house wiring

Patty:

I see fabric exterior sheathing on plastic covered electrical wired: black is normally "hot" and white is normally "neutral" but one pair of wires could have been used to wire up a switch to turn the fan on and off;

Watch out: if you are not familiar with proper electrical wiring you ought not fool with these wires - you could be shocked or killed or start a house-fire.

An electrician would use a DMM or VOM (multimeter) to identify which wires are hot, neutral, and intended for a switch, or that are being used to power other devices "downstream" from this over-crowded junction box.

As an aside I see the metal box isn't properly connected to the electrical ground wires and the ground wires themselves are simply twisted together - no connector was used: not a safe, reliable practice (though it's common).

 

 

Does metallic sheathing make aluminum (or copper) wire safe?

Does non metalic sheathing make a conductor of copper and aluminum safe? On 2019-10-27 by Catherine

by (mod) - insulation alone does not make an electrical wiring system "safe"

Catherine

IF the wire insulation or sheathing is in good condition on an electrical wire it's doing its job: preventing a short circuit between conductors or between conductors and other building components like pipes.

But insulation alone does not make a wiring system "safe" as there are plenty of other snafus that could be present.

And no type of insulation or sheathing makes ALUMINUM branch circuit wiring "safe" - see details at

ALUMINUM WIRING HAZARDS & REPAIRS

 

What is this antique electrical outlet thing with four parallel slots?

My house was built in 1918, I have a couple of receptacles that I would love to replace (maybe using wire mold boxes and GFCI receptacles. When checking the prong holes I get hot on two, low voltage on one (probably the neutral) and nothing on the fourth. What is this thing? On 2019-06-21 by Pauly -

by (mod) -

Pauly

at ELECTRICAL RECEPTACLE TYPES

you'll see a photo of and discussion of the receptacle that I think is yours in your photo.

 

What's this insulation on old wiring: what is it's age?

I inherited 2 old shop tools from my dad, They are craftsman with capacitor start motors. both units have strangely silver wire. Doubting that my dad had that kind of money back in 1960 or so, they both probably were purchased used.

The other indication that these machines are very old is that the outer insulating cover is black, probably rubber based, while the black and white inner insulation is still quite good. Any guess as to the span of years this was used? On 2019-06-17 by darrell

by (mod) -

Thanks for the photo and question, Darrell.

Wiring such as shown in the line cord in your photo was widely used in North America as early as the 1940s and continues to the present.

In trying to date a tool it's always helpful to include details such as

- a photo of the tool and of each of the data tags or nameplates whose data is always critical

- the country and city where the tool was found or used

- any records of repairs or modifications to the tool (that can include line cord replacement)

 

How safe are exposed ends of "abandoned" or "dead" electrical wires

I'm a new homeowner needing some advice. I Found old wiring in my crawlspace. Looked cloth wire with ends tattered but the middle spliced to copper ?lamp wiring that leads to house. Third pic was the middle that was spliced. I'm assuming it's all dead since both ends were laying on the crawlspace floor.

I pulled off the tattered wire from the copper lamp wiring but couldn't not yank the copper wiring out of the floor of the house. I covered the end with electrical tape.

Theres no way the wire can be live right? The ends of the tattered aluminum wires it was spiced with were just laying there. The rest of the house is wired pretty well with yellow updated Romex to a 200 panel. Thank you! 2019/04/29 Anonymous

Reply: never say "there's no way the wires can be live" before you've traced the entire circuit

Watch out: It's best to err on the side of caution when we don't know the status of old, supposedly-dead electrical wires.

I certainly wouldn't assume that old wiring is not live. I have often found supposedly dead wires that have been connected to power.

A concern is that even if wires are disconnected at both ends of their original installation, unless the wire ends are properly-treated, someone might, in the future, erroneously connect the wires at one end, making the other wire end dangerous.

 

That's a good way to set the building on fire or to electrocute someone who touches them in the future.

Also the sort of electrical work that you described such as lamp-cord wiring is indicative of very inexperienced electrical work.

It's safest if all such wiring is removed, and if those lamp-cord wired circuits that are needed, you need to have them correctly installed by an electrician.

I agree that you don't always have to remove all dead wires but they need to be joined spliced and capped wherever those ends can be found and certainly lamp cord that runs through your building needs to be absolutely dead. Don't leave any of that live.

If "dead" or "abandoned" electrical wires must be left in place (as can be the case where the wires are fastened within an enclosed wall or ceiling, I like to cap the "dead" wire ends with a twist-on connector after joining them together.

That assures that if someone connects the other wire ends to a live circuit in the future they'll immediately trip a circuit breaker or blow a fuse - indicating that something's wrong - and unsafe.

Reader follow-up:

Thank you for your advice! Having the electrician take a look. ...

The wire was dead and the electrician pulled it. It was the old wiring from long ago. He said it was connected to nothing on both ends! Phew. I couldn't sleep for a few days worrying the house would set on fire.

Moderator Reply:

Thanks for the follow-up - I'm relieved too - having once gotten shocked right off of a ladder when I accidentally touched the ends of a supposedly-dead electrical wire.

In my old house lights flicker, breakers don't trip

Older house built in the 20s found a lot of knob and tube being fed from Romex...

plugged in a vacuum cleaner ran for a bit lights flickered circuit went out did not trip a breaker

went up in the attic to see if there were any issues with animal chews or whatever and found that the neutral is also carrying 120 volts and

unlike some knob and tube I've seen the hot is being switched but again did not trip a breaker ....

curious as to where to look I've already eliminated all the ceiling fans and anything plugged into that circuit and all of the constant hot wall sconces On 2018-09-11 by JeanO

by (mod) -

Jean

Watch out: what you describe sounds dangerous, with the risk of both fire and shock.

It's not something that I can diagnose from just your brief a text.

To be safe you should turn the circuit off. Electrician would doubtless trace a hot and neutral lines looking for a short between them or within or inside of a connected device.

Suspected electrical short circuit increasing electricity usage in an older home?

Hello, thank you for the wonderful website, it has been of great help to me for years now.

I have a 1974 home in Maine, a ranch with 200 amp breaker box service. I also have power bills around 50% higher than they should be.

I have not been able to afford to have the kind of exploratory work done to find the problem, but I did find some thing odd in a wall outlet the other night. It is mid circuit in a metal box in the wood paneling by the brick chimney.

The top of the box is clean, but the inside of the bottom has some white corrosion.

The lower hot and neutral pair are dark from age but also have green corrosion where they wrap around the terminal screw, but the upper pair do not.

I thought water or perhaps mouse urine from the attic, but then the top outside of the box would be corroded too, as would the top pair of hot and neutral wires.

A simple circuit tester shows the wiring to be double green correct. Here is the weirdest part, the power strip/protector plugged into he TOP outlet, the blades are clean, but when I unplugged it the ground pin is a corroded mess.

At some point the the upper hot must have touched somewhere because there is a bright brass splash in the screw, and it has not darkened over time--it looks polished.

The inconsistencies make no sense to me but I hope they might to you, and maybe a solution to my many thousands of dollars in power I have never used. Thank you for reading my lengthy post--I can send pictures if that would help. Bruce E 30 Jul 2015 Bruce E

Reply: simple DIY observation to identify the main users of electrical power in a home

Bruce

Find our email at the page bottom CONTACT link to send me some sharp photos and we can comment further.

You can find the energy users in your home quite easiy if somewhat subjectively.

Stand at the meter and watch the dial spin rate (or time it to be more accurate) or on a digital meter note the number change rate per second or 30 seconds.

Start turning off circuits in the home. One or two of them will usually define the main energy users in the home when you see the electric meter spin rate drop significantly.

Make a note of what appliances (or in your theory current shorts to ground) that are located on that circuit and you've got a good idea who's using the juice. Typically these are air conditioners, refrigerators, electric heaters.

An electrician can perform a similar but more precise task using an ammeter.

Bruce E said:

Thank you for the speedy response. I will take the pics today and send them to you. I have the ammeter now, so I will use the circuit isolation method you suggest and then check the items on that circuit specifically. I will also check for "leaks" at the same time by turning everything off and doing a circuit by circuit test.

We have gone digital here for a meter, but we are certain the original meter was part of the problem (it was taken, tested, and destroyed). In our first two weeks, with virtually everything still in boxes. we were billed over $900 for electric--in July with no AC.

Now bills average $100 to $120, double the going rate for a small house like ours--gas stove, oil fired boiler. Thanks for the interest and advice.

(mod) said:
Bruce,

First step if I had your hypothesis, would be to shut off at the panel the circuit that you suspect is the trouble - not just to save electricity but to avoid electrocuting someone

 

How can I tell if a shell type fuse is blown?

(June 20, 2016) Anonymous
How can i tell if a shell type fuse is blown

Reply:

Sorry I don't know what you mean by shell fuse. If you are referring to an artillery fuse, or a pyrotechnic fuse using aerial shells,

Watch out: do not touch nor fool with artillery shells unless you are a trained expert. The risk is an explosion, fire, death.

Generally an electrician might "test" for a bad or blown fuse first by simply replacing it to see if that gets things working again.

Often the visual inspection of a fuse will show that it has blown, as a fusible link will be visibly burned. But cartridge fuses may look the same whether blown or intact.

Separately, one could pull a fuse out of the electrical panel and use a DMM or VOM to test the fuse for continuity. If there is no continuity then fuse has "blown".

WATCH OUT: fooling around with fuses or in a fuse panel if you're not trained risks death by electrocution.

Electrician replaced knob and tube in the attic by extending the circuit from a floor below

The knob and tube wiring in our attic was replaced. I think the electrician powered it from a circuit on the 2nd floor. Now there is no power in the attic but everything else is OK. Does the attic need a separate circuit breaker? Thank you. (July 17, 2016) Ellen

Reply:

Ellen:

It sounds as if there is an open connection in wiring to your new attic wiring circuit. I'd ask the installing electrician to return and find and fix the problem. It could be as simple as a poorly-made spice or connection on a single wire - hot or neutral.

About the circuit breaker: the extension off of a lower floor circuit means that the extended wiring should be protected by the same circuit breaker that protects the second floor circuit that is serving as its power source.

There is a separate question of whether or not the 2nd floor source circuit is now overloaded because of what was added to it.

 

Is my old fuse panel safe or should I replace it?

I'm buying a house and it looks like this kind of electric box and fuse's I was wondering do I need a new electric panel or with breakers will be safer or is this ok to keep in the house 2016/07/31 Benjamin Dowd

Reply:

Benjamin

I cannot guess at what is installed in your home and less whether or not it's safe from an e-text; it's just too dangerous to bet the fire and shock safety for you and other occupants on a wild guess.

If you're buying a home and hire a home inspector who is working for you not for the realtor or seller, then she or he is required by virtually all standards, even the most lightweight state licensing code stanards, to inspect the condition of the electrical system: wiring, devices, panel, fusing, etc.

Old electrical panels that use fuses are not innately unsafe and in some cases fuses may be safer than circuit breakers;

but old panels in old houses are very often overloaded and not able to support the number of circuits and total amperage of electrical consumption that most people use in contemporary situations.

That alone will often argue for panel replacement as well as for adding electrical circuits in some areas.

How do you remove old electrical wire clips installed before Romex type?

how do you remove clips used in 1950 before romex connectors were made On 2015-01-23 by Anonymous

by (mod) - remove clips used in 1950 before romex connectors were made

Anon not sure what "clips" you mean - use our email found at our CONTACT link to send me some photos for comment.

If you refer to the strain relief used on metal boxes sporting BX or armored cable, there are three connecting devices:

2 screws that tighten a sliding clamp against the exterior of the BX cable

1 large nut inside the electrical box that secures the clamp body to the electrical box - removed typially by tapping a screwdriver against the notches in the nut to turn it counter-clockwise - leftie-loosie as my daughter Mara says.

Electrician says using old pipes as electrical conduit is illegal

Hi I had recent electrical work done in old house. Apparently a new wire for light switch has been fed down the old steel pipe. Electrician says this is illegal if it hasn't been earthed! Is this correct and I don't understand then why the electrician hasn't fixed this issue when he saw it. On 2014-10-17 by Lea

by (mod) - Using old abandoned gas piping to run electrical wires was common in older buildings ?

Lea

Using old abandoned gas piping to run electrical wires is common in older buildings might pre-datescurrent celectrical odes.

Watch out: when the ground wire is missing or if the pipe itself is being used as a grounding conductor the installation is improper and unsafe.

And in either case the re-use of existing gas pipes to run electrical wires may not be approved by your local building electrical code compliance inspector. So it'd be smart to check before attempting the work.

Old gas pipes used for electrical conduit is crazy

comment on using old gas pipes as electrical conduit.
Are you NUTS ?? First of all the color of Gas piping is BLACK- this signifies that this is indeed GAS. It has been this way since gas was first brought into homes even OLD homes. Today they also use a YELLOW flexible gas line the color also signifies GAS.

Secondly if this had been inspected the IOR ( Inspector of Record) would have not allowed this wiring method.I have read through some of the other comments listed on this page and you seem to give sound advice in regards to electrical safety to the homeowners that inquire to the issues they face. The best way to deal with any electrical issue is

FIRST turn the POWER OFF,

then call a Certified knowledgeable and qualified electrician.

His services may cost you in the front end,but you will be taking your chances with life safety when you hire your neighbor or HANDYMAN who claims to know how to wire up your pool motor,3 way light switch, A/C unit Etc. On 2015-04-09 by Anonymous -

by (mod) - what is in place may not be what would be "approved" by code officials - writer says "hire an electrician"

Anon

Please do not confuse a description of "what is" or what building practices were common with what is recommended or approved by current building officials.

And let's keep nuts and insults out of the discussion

What do I do if nobody will tell me how old my building and wiring are?

What if the apartment owner, or management group won't tell me how old the building is (at least 50 years old), or the voltage of my outlets? How do I get this information? Wiring is not done by a certified electrician.

What do I do? I'm at my wits end. I've 8 electrical outlets, with a refrigerator, stove, televisions, stereos, computer, printer, lamps, hair dryer and hair iron, and iron, which are used. On 2014-02-23 by Marilyn

by (mod) - how do I find out the age of my house?

Marylin we have published a series of articles that help determine the approximate age of a building by looking at its components and features, comparing them when those were first used; Just search InspectApedia for "AGE OF HOUSE"

Or go to AGE of a BUILDING, HOW to DETERMINE - home page

Your local tax department or building authority and registrar of deeds have actual documents on the building.

But I'm not sure why we're barking up this tree of age.

If the wiring is unsafe, improperly installed, or damaged it needs to be repaired by a qualified person; your municipality may or may not permit electrical work to be done by other than a licensed electrician - just ask your building department;

If you feel that the apartment is unsafe you should notify the owners in writing of the conditions you've observed, giving them the opportunity to make an expert assessment. It's surely not in the building owner's interest to permit actual unsafe conditions to persist.

Have I found old electrical wires or something else?

Found two pieces of metal coming out of wall beside a door frame upstairs in an older home. It is two pieces of flat metal with round ends and they move up and down in the hole in the wall and it clicks when you do so. I have seen this before but never knew what it was. On 2011-11-19 by Cindyloohoo

by (mod) -

Cindy

Using a volt-ohm meter you can test for voltage to see if the stuff you found is electrical and live.
I'd like to see some sharp photos (use the CONTACT link found at page top, left, or bottom) and I may be able to comment further. Watch out for electric shock hazards.

I found the gbround conductor used as a neutral wire in a sub panel

ground conductor being used as neutral at sub panel On 2011-11-14 by gilgonzalez2000

by (mod) -

Gil Gonzales,

See the article LOST NEUTRAL SHOCKS HOMEOWNER "Case History:Loss of Neutral Shocks Homeowner" using the ground for neutral at a sub panel is improper and risks shock or fire.

...

Continue reading  at OLD HOUSE ELECTRICAL SYSTEMS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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