FAQs about how to make proper & safe electrical wiring splices & connections:

Frequently-asked questions & their answers on how to splice or join electrical wires in building circuits. What connector to use, how connections are made, different types of "wire nuts" or twist-on connectors.

This article series answers most questions about how splices (connections between two or more electrical wires) are made to connect & secure electrical wires together in residential or commercial building electrical wiring systems. We also discuss the use of electrical splices or wiring connectors outside of electrical boxes.

Electrical Wire Splicing Questions & Answers

The following questions & answers about electrical wiring splices and using twist on or "wire nut" connectors were posted originally

at ELECTRICAL SPLICES, HOW TO MAKE

Watch Out:  Do not attempt to work on your electrical wiring, switches, or outlets unless you are properly trained and equipped to do so. Electrical components in a building can easily cause an electrical shock, burn, or even death. 

Even when a hot line switch is off, one terminal on the switch is still connected to the power source. Before doing any work on the switch, the power source must be turned off by set­ting a circuit breaker to OFF or removing a fuse.

See SAFETY for ELECTRICAL INSPECTORS

and ELECTRICAL WIRING BOOKS & GUIDES

Sketch of a twist on connector splicing two wires together was provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing firm.

On 2019-01-20 by (mod) - ALL in-wall wiring (whether high voltage or "low") MUST be rated for "in wall use"

Scootz

Thank you for making some excellent points I'll be sure to keep them with this article.

I agree that the claim never had a problem is a ridiculous one both because it has no statistical basis
And because it ignores the problems our experts have already discovered that have led to the codes and standards it served as our guide.

An analogy I use is driving around in your 65 Mustang convertible with a seatbelt that's worn to a mere thread.

But the thread is under the seat where you don't see it.

You buckle your seatbelt and you think it's perfectly fine. After all it's been fine up to now. But then you've never been in an accident. Yet.

On 2019-01-19 by Scootz - ALL in-wall wiring (whether high voltage or "low") MUST be rated for "in wall use"

Speaker wire...

Since you mention speaker wires (and b/cthis is such a great resource) I'll throw in the comment that ALL in-wall wiring (whether high voltage or "low") MUST be rated for "in wall use". Non-rated materials are accelerants in event of fire.

And while I'm on my rant, the in-wall speakers must be rated for such use, and unless explicitly exempted they must be installed in a "box" (drywall box or designated enclosure), and the wires must pass through a panel/plate.

I mention this because I've seen so many handiman jobs where people run "regular" speaker wire (lamp cord) or networking cables through walls, and carve out large holes in drywall, then say it's fine because "it's never been a problem".

On 2018-04-05 by (mod) -

Posting reader comment rec'd by private email to editor

Mar 25 2018 The table of wire colors shown on the following web page may have an error in it.

<inspectapedia.com/electric/electrical_wiring_splices.php> Theerror to which I refer is the description of the use of the color ORANGE.

The language which says "Excepted voltage" is used in some texts and manuals to name what the National Electric Code (NEC) calls the "Conductor having the higher voltage to ground." The NEC requires that on Delta Connected Three Phase Services that all of the splices and terminations to the "Conductor having the higher voltage to ground" will be colored ORANGE.

Yellow is not acceptable for that coding under the NEC.

Please advise why the language "these wires may be hot when main disconnect is switched off" is in the table. Under the US NEC that"Conductor having the higher voltage to ground" must disconnect with the other 2 phase conductors When the Service Disconnecting Means is opened.

On 2018-03-19 by (mod) -

Apologies Mark but I do not fully understand the situation. I don't understand why we would be talking about extending building sheathing into an electrical box.

On 2018-03-19 by Mark Weglin

I just ahad a hood vent fan installed by my general contractor and he cut the sheathing off about one “ from the wall then added wire nuts to extend the wires into the provided j box. I should call this on him to put aprox. 1/2” sheathing into the j box? Also didn’t hook up the ground wire mrweglin@gmail.com please reply.

 

On 2017-08-16 by Dean

Can I use a Quick Splice Connector on led lighting under a kitchen cabinet without the use of a junction box? I have want to take out a few lights so I need to join the old cables together, is that legal to do under electrical regulations.

On 2017-07-03 by (mod) - If you splice 2 number 12 wires in A J Box do they have to be twisted before you put a wire nut on ?

Thanks for the question, VB.

No pre-twisting wires before connecting them with a twist-on connector (like a "wire nut") is not required, but the wire ends should be
clean of oxide, and rather straight as a single bent wire can prevent good secure contact.

Using the Ideal Corporation's installation instructions for its Wing Nut twist on connectors, "Pre-twisting acceptable, but not required. For pre-twisting; strip wires long, hold wires together with insulation even, twist wire ends together, trim to recommended strip length."

Ideal's Wire Connector catalog describes its Wire Nut (R) connectors as: No pre-twisting required — positive grip design provides
fast, easy installation.

3M's Performance Plus connectors brochure is perhaps deliberately ambiguous - there are no instructions there but a photo shows wires that are slightly twisted as might occur during the natural torquing when the twist on connector is applied to straight wires.

Experts opine that the twist on connector will grip the wires better if they are straight, not pre-twisted; also the actual electrical connection between the spliced wires will be better if the wires are straight than if they're pre-twisted

- I think that's because there is more and more-reliable wire to wire contact area. You do NOT want electrical current passing through the spring of the connector (causing overheating and failure) - rather it should pass directly wire to wire by wire-contact.

For special cases, such as repairing aluminum electrical wire ( a fire hazard unless it's properly repaired) a functional but now-obsolete repair method described by Aronstein at SCOTCHLOK 3M REPAIR CONNECTORS

discusses making a very-secure twist-on connector wire splice by

- pre-abrading the wires through an antioxidant

- further coating with antioxidant

- pre-twisting the treated wires

- then applying a Scotchlok 3M Twist On connector

so pre-twisting is used in some cases but is not generally required.

In making copper wire splices using a twist-on connector you should:

Cut away damaged or nicked wire ends that might break off, causing a splice failure

Strip back insulation 3/8" yp 7/8" - depending on wire size and connector size

An Ideal Wingnut 451 requires stripping 3/8"

An Ideal Wingnut 452 strips to 1/2"

An Ideal Wingnut 454 Strips off 7/8" of insulation

Be sure the wire ends are straight and un-damaged and of equal length

If one of the wires is a multi-stranded wire such as for a light fixture, let that end extend about 1/8" past the solid wires

Twist on the twist-on connector tightly.

Hold the wires closely together

Twist on the connector (clockwise) until tight. Some electricians (and I) twist firmly until the wires themselves begin to twist together below the connector.

See: Ideal Corporation" Wing-Nut® Wire Connector Instructions" https://www.idealind.com/content/pdfs/instructions/wing-nut-connector-instructions.pdf

On 2017-07-03 by vb

If you splice 2 number 12 wires in A J Box do they have to be twisted before you put a wire nut on

On 2017-07-02 by Jan

I was hanging a new ceiling light. Directions were terrible about how to put the peices together and threading the 3 wires through the fixture.

After 3 attempts I figured out how they wanted it done but by then the ends of the wires on the light fixture were pretty sparse. So my question is this: the sparse wires were the black and white on the fixture, (the black and white from the house were one solid wire)

after I connected white to white and black to black, I twisted on the wire connectors (included securing the ground) finished the installation and turned on the breaker. Switched on the light and it works, but is the sparseness of the one set of wires going to b a problem?

On 2017-07-03 by (mod) re: pre-twisting of electrical wires not required before splicing with a twist on connector or Wire Nut®

Thanks for the question, VB.

No pre-twisting wires before connecting them with a twist-on connector (like a "wire nut") is not required, but the wire ends should be clean of oxide, and rather straight as a single bent wire can prevent good secure contact.

Using the Ideal Corporation's installation instructions for its Wing Nut twist on connectors, "Pre-twisting acceptable, but not required. For pre-twisting; strip wires long, hold wires together with insulation even, twist wire ends together, trim to recommended strip length."

Ideal's Wire Connector catalog describes its Wire Nut (R) connectors as: No pre-twisting required — positive grip design provides
fast, easy installation.

3M's Performance Plus connectors brochure is perhaps deliberately ambiguous - there are no instructions there but a photo shows wires that are slightly twisted as might occur during the natural torquing when the twist on connector is applied to straight wires.

Experts opine that the twist on connector will grip the wires better if they are straight, not pre-twisted; also the actual electrical connection between the spliced wires will be better if the wires are straight than if they're pre-twisted - I think that's because there is more and more-reliable wire to wire contact area. You do NOT want electrical current passing through the spring of the connector (causing overheating and failure) - rather it should pass directly wire to wire by wire-contact.

For special cases, such as repairing aluminum electrical wire ( a fire hazard unless it's properly repaired) a functional but now-obsolete repair method described by Aronstein

at SCOTCHLOK 3M REPAIR CONNECTORS

discusses making a very-secure twist-on connector wire splice by

• pre-abrading the wires through an antioxidant
• further coating with antioxidant
• pre-twisting the treated wires
• then applying a Scotchlok 3M Twist On connector
  
  so pre-twisting is used or permitted in some cases but is not generally required.

See details at ELECTRICAL SPLICE WIRING DETAILS

On 2017-07-03 by vb - do I have to pre-twist wires before installing a wire-nut?

If you splice 2 number 12 wires in A J Box do they have to be twisted before you put a wire nut On

On 2017-07-02 by (mod) re: are those thin or "sparse" light fixture or ceiling fan wires safe to use?

Jan:

I too have noted rather thin No. 16 and even no. 18 electrical wires on some light fixtures and celing fans I've installed.

You can see those "thin" wires protruding from the ceiling fan to be installed in my photograph. (No that's not me in the painting.)

The manufacturer specifes that the device be installed on a 15A properly wired and fused circuit (that will usually be No. 14 gauge copper wire).

The heavier solid No. 14 copper wire is spliced using a twist-on connector to the multi-strand lightter No. 16 wire or perhaps No. 18 wire for the fixture.

We can assume that for a "listed" light fixture or ceiling fan, (e.g. UL listed or CSA listed) the manufacturer has determined that the total current draw of the actual fixture makes the lighter, or as you put it, more sparse, wire is adequate and safe provided it is properly installed and connected.

On 2017-07-02 by Jan: is the sparseness of the one set of wires going to be a problem?

I was hanging a new ceiling light. Directions were terrible about how to put the pieces together and threading the 3 wires through the fixture.

After 3 attempts I figured out how they wanted it done but by then the ends of the wires on the light fixture were pretty sparse.

So my question is this: the sparse wires were the black and white on the fixture, (the black and white from the house were one solid wire) after I connected white to white and black to black, I twisted on the wire connectors (included securing the ground) finished the installation and turned on the breaker.

Switched on the light and it works, but is the sparseness of the one set of wires going to be a problem?

On 2017-06-25 by (mod) re: Metal boxes need to be connected to ground

Metal boxes need to be connected to ground, and of course, contrary to the photo shown below, 120V and 220V circuit electrical splices must be made inside of a properly-sized and rated box.

Details about our question and our suggestions on how to proceed as well as about how to make the ground wire connection and on several options for connecting the ground to the box are given at ELECTRICAL BOX GROUND WIRING.

Also see ELECTRICAL GROUNDING in OLDER HOMES

On 2017-06-24 by TheDude

Preparing for rough in. All outlet and switch boxes are spliced with appropriate pigtails.

Light fixture boxes were not touched but I have been told so strip and splice them.

Do I need to pigtail the grounds like the electrical boxes? Do I need to strip the wires and wirenut them as well? That seems like excessive work.

State = Minnesota

On 2017-02-18 by (mod)

Right, Laura. But loose wires might sometimes connect as temperatures change or vibration affects the connection, so the circuit might behave oddly.

On 2017-02-16 by Laura

What will happen if the wires are separately put together with a crimp connector and electrical tape, not making connection? Wouldn't it just not work?

On 2017-01-25 by Dave

Never mind, found it: Article 110.14 (B): Splices. Conductors shall be spliced or joined with splicing devices identified for the use or by brazing, welding, or soldering with a fusible metal or alloy.

Soldered splices shall first be spliced or joined so as to be mechanically and electrically secure without solder and then be soldered. All splices and joints and the free ends of conductors shall be covered with an insulation equivalent to that of the conductors or with an identified insulating device.

On 2017-01-25 by Cal

I am connecting a #14 to a #12 wire. the 14 is going into a wall receptacle. The plug shows good power connect, but when I plug in my appliance or light, it does not work.

On 2017-01-25 by Anonymous

Sorry, dont know why it double posted.

On 2017-01-25 by Dave

I'm installing 3 outlet boxes on a 50A multiwire branch circuit - in order to do three receptacle boxes on the circuit that contain both a 240v and a 120v receptacle (in a two gang box) I need to make pigtails that have three 6 gauge and one 10 gauge wire in it. They dont make twist on connectors that big and even if they did I dont know if I'd trust it.

How can I make a 2014 NEC code pigtail with wires that big? I'd like to twist it, solder it, coat in liquid electrical tape, and wrap that in cloth backed electrical tape but I can't find a provision in the code that allows it.

On 2016-11-28 by James

When both screws are bronze does it matter what the hot and neutral are wired to a plug .

On 2016-10-16 by Anonymous

Jim as long as the splice meets UL and NEC standards it doesn't matter what method you use. Just as important is, what is going to happen with the box you splice in. This box must be accessible according to the NEC.

(Oct 9, 2016) Jim said:

I need to move my electric range about 8 feet and cannot replace the entire run of 6 AWG 220v service cable because it runs throughout a finished space from the service panel. I prefer to use compression sleeve splices in heat shrink inside a J box. Burndy, AMP, Ilsco all make them along with their associated crimpers. I'm a licensed aircraft mechanic and use compression splices in my field, so I find the split bolt and other screw down methods to be hokie. Any opinion of the crimp splices I'm considering?

On 2016-10-16 by Scoobe re: EU wiring colour code guidelines:

Brown = hot. Blue = neutral. Yellow/green = ground. This is a standard that comes from across the water. Also the plugs are not polarized.

(Apr 16, 2016) danjoefriedman (mod) said:

Sorry, Louise, but this does not sound like proper, safe electrical wiring to me.

Just so you are aware, we are getting more of this from EU countries.

Brown would be hot.

Blue would be neutral.

Yellow/green would be ground.

If you notice on these applications the cord cap is not polarized.

(Apr 16, 2016) Louise said:

I need to join brown, blue and yellow/green (water feature pump) to 2 flex cord (colourless) - which goes where? Or should I rather get 3 flex cord?

On 2016-10-09 by Jim

I need to move my electric range about 8 feet and cannot replace the entire run of 6 AWG 220v service cable because it runs throughout a finished space from the service panel. I prefer to use compression sleeve splices in heat shrink inside a J box. Burndy, AMP, Ilsco all make them along with their associated crimpers. I'm a licensed aircraft mechanic and use compression splices in my field, so I find the split bolt and other screw down methods to be hokie. Any opinion of the crimp splices I'm considering?

On 2016-06-22 by (mod) re: range hood fan wiring

Range hood fans are typically nominally 120VAC (or "110 Volts" more or less). The 3 wires are typically hot (black) neutral (white) and ground (bare).

On 2016-06-22 by Gretchen

Hi! We are replacing our under cabinet microwave with a range hood (over our cooktop). The hood I bought came with three wires sticking out of it rather than the three-prong plug our microwave is currently using. I have been told to use a three prong replacement cord of 14 gauge/15 amp. The range hood says that it's 110 volts, which doesn't seem typical. Does this sound safe to you? We live in a track home in CA that is about 20 years old.
Thanks for your help! :)

On 2016-04-19 by (mod) re: use weatherproof boxes and wiring outside, provide GFCI protection

Sophie:

WATCH OUT: making a mistake in electrical wiring can kill someone, particularly outdoors and undergound where water adds to the risk.

There are waterproof exterior-use electrical boxes rated for underground use that can assure that, if properly installed, the wiring repair splice is safe.

Power must be OFF when working on electrical equipment, as your electrician will demonstrate. If she finds that in testing there is no power on the outdoor light circuit, she'll first check that the circuit breaker is working properly, then look for another break in the wiring, in lamp post, or in the light fixture itself.

Be sure the circuit is on a GFCI protected breaker or receptacle. That could be what's tripped off.

On 2016-04-19 by Sophie

Front yard lamp post wire underground in front yard up by house got cut in half by gardening tool. tried to splice it back together. THICH gauge copper wiring. NOT WORKING. can you not splice this type of wiring back together? I really dont' want to have to dig up my yard and re-wire the lamp post. two wires one white and one black the black is HOT. Spliced black to black and white to white. What gives? thank you

On 2016-04-16 by (mod)

Sorry, Louise, but this does not sound like proper, safe electrical wiring to me.

On 2016-04-16 by Louise

I need to join brown, blue and yellow/green (water feature pump) to 2 flex cord (colourless) - which goes where? Or should I rather get 3 flex cord?

On 2016-04-13 by (mod)

re-posting

Dan said:

hello! It is very important information that everyone should know more over if he works with wiring. I didn't know it while doing wiring work in my house. I wanted to install these lighting [fixtures that were] quite expensive. As a result it lead to short circuit...

On 2016-03-18 by (mod) re: spliced wires for alarm system

Veronica:

I can't really see what's going on with your wiring. Normally electrical connections that are wire splices are made using a mechanical connector such as a twist-on connector or "wire nut". That device covers exposed wire ends and is itself enclosed in an electrical junction box.

But if your tech wired LOW-VOLTAGE wiring (12VAC or 24VAC for example) it's common to leave those splices and their twist-on connectors out of an electrical box.

Still if she made the connection with tape alone it may not be reliable.

On 2016-03-18 by Veronica

Hi,

I had my alarm system upgraded to a wireless system. The technician (without informing me first) spliced some wiring in order to get power to the transformer box. The spliced wire was wrapped with electrical tape and is in clear view. Do you see hazards/issues with this? Thanks!

On 2016-03-18 by (mod) re: typical reasons for wiring connection failure

Mike:

Typically electrical connections fail because of

- mechanical movement that loosens the connector - such as in a frequently-used wall receptacle

- corrosion

- overheating from overloading, aluminum wiring, or from corrosion just cited

- poor original work

- occasionally, aging insulation leading to a short as insulation deteriorates or even falls off

- something else I've not thought-of

On 2016-03-18 by Mike

Thanks for posting all this info. Am wondering if you would be able to tell me why a connection would fail - I wanted to run a plug from an existing live wire so made a "tap splice" into the existing live no matter what I done the plug remained dead while the original wire outlets were OK/Live

It was not a bad connection problem - am I missing something?

Any advice you can give me on this appreciated.
Thanks
Mike

On 2016-02-12 by (mod)

Steve I probably don't understand the question. Splices are legal if properly made and enclosed. If you are asking about the number of receptacles on a circuit that's a different matter.

On 2016-02-12 by Steve

How many times can I jump/splice from outlet box to outlet box 110v

On 2016-01-11 by Esther

I'm splicing two groups of wires together the first group of wires are black, red, white and the second group of
wires are brown, green, and white what colors go together

On 2015-12-11 by (mod) re: splicing No. 10 wire - what connector to use

Yes if the splice is properly enclosed in an electrical box. Be sure to use a properly-sized twist on connector for the wire size and number of connectors specified by your connector's manufacturer.

For example, if you are using a Wing Nut® twist on connector made by the Ideal Corporation, you could use a No. 452 Red Wing Nut® or a 454 Blue Wing Nut® but not a 451 yellow wing nut tojoin No. 10 coppe wires. The red Wing Nut can join up to 4 #10 copper wires. The Blue Wing Nut can join 3 #10 wires.

On 2015-10-02 by jake

is it safe to splice 10 ga wire for a dryer.

On 2015-09-06 by (mod) re: extending an electrical circuit

Rene for life safety reasons such extensions should be made by a licensed electrician who will in turn select the proper wire gauge, connectors, splice boxes, and if required, obtain the permits and inspections your local electrical inspector demands.

On 2015-09-05 by Rene

I need to extend 3 Gauge wire by about a meter for my electric furnace (20KW, 240V). How do I make the connection

On 2015-07-17 by (mod) re: splicing any-old-thing together?

Anon:

Watch out: I wouldn't do that at all - I'm afraid your suggestion is going to electrocute someone.

On 2015-07-11 by Anonymous

How do you safely splice 3 wires into 1 for outdoor garden lights?

Splices in electrical wire that carries electrical current in a building (such as for lights or electrical outlets) must be completed using an approved mechanical connector and must be enclosed in an approved junction box which itself is secured to the structure. In addition, the NEC and other electrical codes specify lots of precise details describing the number of wires of various sizes that can be enclosed in junction boxes of various sizes, where these boxes must be located, how they can be covered, etc.

...

Continue reading  at ELECTRICAL SPLICES, HOW TO MAKE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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