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14_2_NMB_electrical wire (C) D FriedmanElectrical Wire Size FAQs
Questions & answers on how to choose the proper wire size for typical building electrical circuits

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What size electrical wire should you use when hooking up an electrical receptacle (wall plug or electrical outlet)?

Here we explain the choice of No. 14 or No. 12 copper wire for 15A and 20A electrical circuits where receptacles are being wired.

This article series describes how to choose, locate, and wire an electrical receptacle in a home. Electrical receptacles (also called electrical outlets or "plugs" or "sockets") are simple devices that are easy to install, but there are details to get right if you want to be safe.



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Electrical Wire Size & Run Length FAQs

Common house electrical wiring sizes (C) Carson Dunlop Associates

Question: Is 14/3 wire ok to use to wire between the light switch and the light? What about an electrical outlet on the same circuit as the ceiling light fixture?

Is it okay to use 14/3 wire for power to light to switch to receptacle?

[Click to enlarge any image] Sketch at left provided courtesy of Carson Dunlop Associates, a Toronto home inspection & education firm.

Reply:

Anon:

If you are asking about using a shared neutral wire on a lighting circuit combined with an electrical receptacle circuit, see (search InspectAPedia.com for) our article on "multi wire branch circuits" or "shared neutral electrical wiring".

In general we'd use 14-2 wire on a 15 amp circuit to power electrical receptacles and a SEPARATE circuit to power the lighting fixtures. If we lose power on one circuit we want the other still working so that there is safe lighting in the area.

For a light fixture such as a ceiling light, in addition to bringing power to the junction box where the light fixture is to be mounted (using 14-2 copper wire) we'd use a separate length of 14-2 wire to run from the light switch to the junction box to control the light. Tape the white wire at both ends of the switch circuit with black tape so that the next worker knows that this is a switch circuit and that the white wire is not a neutral wire.

Watch out: we do not wire fixed lighting fixtures such as ceiling lights on the same circuit as electrical receptacles ("wall plugs"). If one of the two circuits should be switched off by a circuit breaker (perhaps detecting a fault or overcurrent) we want the other circuit to remain on so that room occupants are less likely to be left in darkness.

Question: how is an electrical outlet wired to the electrical panel?

how do wire the outlet plug to the electrical panel - Anon

Reply:

Anon, the electrical circuit that powers an "outlet plug" or receptacle is connected, usually through building walls, ceilings, or floors, from the first receptacle in the particular series back to a fuse or circuit breaker connection in the electrical panel. The fuse or circuit breaker, by its connecting mount in the electrical panel, receives electrical power from the income electrical service.

Question: connecting 14-3 to 14-2 wires & to the junction box

How do you connect 14-3 to 14-2 to a junction box - Moe.

Reply:

Moe, twist on connectors are used to connect the incoming and outgoing hot, neutral, and ground wires, and a single pigtail length in that same twist-on connector can connect the ground to the local junction box.

Watch out: when mixing 14-3 and 14-2 wires on an electrical circuit.

If the 14-3 wires are the hot wires entering the box, and if only 14-2 is leaving the junction box, cap off the unused (typically the red) hot lead.

Do not just bond it together with the outgoing hot wire in the 14-2 group. Making that mistake would short two hot leads together, would be improper, unsafe, and a fire or shock risk.

I recently moved into a 3 1/4 story home, and I have a basement that I am trying to finish with drywall. The room is down to the studs and the electrical receptacles are about 4' up the wall. The Romex wiring is stapled, and there isn't enough wire to lower them. It is way to much work for me to replace all of the downstairs wiring right to the breaker box, so I'm wondering if it is possible to add onto the existing wires and attach wire screws or marrets within the walls before I start adding drywall, or whether I should add some kind of junction box to contain the marreted wires in between. My building code stipulations would differ in some cases because I live in Canada, but I just want to do the job right, and I do not want to take the chance of having any fire hazards, as I also have small children. - Dave 2/10/12

Reply: if you have to move an entire string of electrical receptacles complete re-wiring is faster and cheaper than adding a splice box for every device.

Dave,. you are correct to be careful about moving outlets or any other device when the existing wires are too short. The temptation is to just splice on an extension and bury that in the wall or ceiling: an illegal, improper, unsafe as well as really aggravating approach.

The proper approach is to add a junction box at each splice - we never splice 120/240V wires without including them in a box. You can reduce the wiring work a little by using plastic boxes instead of steel - avoiding having to also connect the box to the ground wire.

The proper approach also means that you don't then bury any of these splice-boxes in the walls either. Each box has to be brought to the surface and covered.

The result is a lot of work and expense and an ugly wall with an extra junction box and blind cover all along the wall over each of the now moved or lowered electrical receptacles.

Frankly I figure that especially as you've already got the wall open to the studs, if there are more than one or two receptacles to be moved you'll probably find it is actually much less total work to re-wire the entire circuit, allowing proper lengths of wires for each box. You might carefully remove and re-route the existing wire lower in the wall or you might buy all new electrical wire - depending on the age and condition of the existing materials.

Watch out: when removing wire that appears to be in good condition, if you nick the insulation you've created a new hazard.

Question: armor around wire through concrete?

I am running a new 15A outlet into the back of a bookcase in a 50 year old house with updated electrical. The wire runs out the back of the retrofit box and down through the concrete foundation into the crawlspace to a wire I plan to splice into. Do I need to put armor around the wire run through the foundation? It goes through open air for about 2 feet and there is no way to secure it to anything.

Thanks!
Tom - 7/19/12

Reply:

You need to look at the type and rating of the electrical wire to determine if it is permitted to bury it in concrete or not.

Question: Am I allowed to add one more outlet onto an existing string?

I have an existing outlet being used for lamps I wanna run one more outlet shares from the hot on is it okay? - Phantom 113 8/1/12

Reply:

Usually, yes provided all safe and proper wiring code procedures are followed.
If the circuit is overloaded already, no.
If the circuit is knob and tube wiring, no - we don't extend knob and tube.

Question: is it legal to convert a split receptacle into two separate receptacles

Is it legal to change a spit receptacle to two separate receptacles? - Gord

Reply:

Gord,

unless I've missed something, sure. You see this all the time. Instead of a single receptcale that has been split-wired to feed from two different circuits (usually using a common neutral and properly wired in the panel etc), you often see a 4" box with a pair of receptacles that side by side are run from different circuits instead of up and down different circuits in the same box.

Watch out about overloading the circuit however.

Question: I've lost electrical power to the whole room after testing power at the light switch

I've lost elec to the whole room.

I tested the wiring at the light switch.

If I turn the switch off I get elec to the switch,If I turn it on I get no elec.to the switch. I've lost electricity to the whole room - Dave

Reply:

Dave, your wiring or perhaps the switch itself is unsafe; sounds as if it's shorted. Leave the circuit off until the wiring has been traced, lest you start a fire or zap someone.

Question: I need to add a light, fan, and fan switch to an existing bath - I can't find where to kill the power

very informative article thumbs up . I have a question nevertheless:


I am renovating a customers bathroom and need to install another light as well as a fan witch requires a larger box to be installed in the wall.

When i checked the existing switch there was a black and a white wire on the switch and when i attempted to shut the power off to the light and switch at the panel there is no breaker that kills the power to the light

What is the likely cause of this and how do i fix this problem - Blinden 12/12/12

Reply:

Blinden,

It would be odd for a bath light circuit to be wired with no over current protection, and very dangerous too. Try each breaker in the panel in turn to find the one controlling the circuit.

As the switch is interrupting only the hot wire it is common practice to run a standard 2-wire line from the light to the switch. In meticulous electrical work the installer would wrap black tape near the ends of the white wire to indicate that in this use it is a hot lead not a neutral wire.

Depending on the light location, such as near a shower, it may need GFCI protection as well.

Question:

I have one line with power coming into a box that will have one two way switch, one three way switch and one power line exiting. Is it proper to splice the incoming black wire to make 3 black wires by pig tailing with wire connectors and doing the same for the white wire and ground? - is it ok? 12/13/12

Reply:

I'm sorry but I'm confused by the question. I think it's safe to say that in general it's common practice to use a twist-on connector to splice pigtails or individual wires at an individual hot or neutral wire where more connections are needfed than fit with the original wire.

Just watch out to avoid violating the space or number of connectors permitted in a junction box of the particular size you're working on.

Question: comment

Electrical wiring are the devices that are used to generate electricity. There are different types of electrical wiring that are usually vary according to three factors - purpose, quantity of electricity to be carried, and location. All the above three factors are really very important while doing electrical wiring. - Bella Cruse, Dublin electrical contractor

Reply:

Thanks Bella.

Question: which circuit is better to use when adding a closet light

If I want to add light to closet, which circuit is it better to pull from? I have access to 120 plug and switches in outside wall facing away from closet that could be pulled into closet. Also, can you help explain the two different wiring configurations on my non GFI plugs. On two different plugs on different walls the plugs are 8 wire push in style (4 hot and 4 common), but the wiring config is different between the two plugs. One one all white and black are inserted in the bottom 4 connectors with tabs in place. On another same style plug, one set of 4 wires (2 blk and 2 white) are inserted in bottom left row, and other set of 4 wires are inserted in opposite side top row. These plugs are not controlled by switches. Thank you. - Chris 12/30/12

Reply:

Chris,

In my OPINION, it's best to connect a closet light to the room lighting circuit if possible.

About your other question, I'm a little confused by the query, but in general, receptacles and switches often have more than one permittted connection point, such as under a screw terminal, on older devices via a back-wiring push-in connector (something we do not recommend using), or on newer devices a side-clamp operated by a screw.

In all events, regardless of which connection point you are using, receptacles and switches have a designated side or screw or connector set for the white (neutral wire) (typically the side that has a silver colored screw and that is marked NEUTRAL on the device) and for the black (hot wire) (typically the side that has a brass-colored screwe and is marked LINE or HOT or BLACKI).

Question: floor receptacle not working

(Aug 21, 2015) Steven C said:
I used some electrical wire I had in my workshop to add an electrical outlet in the floor. It will light up a lamp, but anything requiring more power (blender) won't work from this outlet. I am not sure of the size of the wire used. Is the size of this wire causing this issue?

Reply:

Watch out: turn off the circuit and leave it off lest you cause a fire, shock, or injury. I can't know from your e-text if the wire is undersized or if there is damaged insulation or a current leak. It sounds unsafe to me.

Question: match the fuse or circuit breaker to fuse size?

(Oct 8, 2015) bill said:
My mobile home has 12/2 15 amp receptacles. Is that ok? Should i replace them with 20 amp receptacles.

Reply:

Good question, Bill. IF the fuse or circuit breaker is a 20-A unit then the wiring needs to be 12/2 to match.

But if your wiring is #14 copper (that's rated for 15-amp circuits) the right thing to do is to change the fuse or circuit breakers to match the #14 wire: make the breakers 15-amp units.

The electrical wire used for the receptacle circuit must be the proper type in size (thickness or gauge) and number of conductors for the ampacity of the electrical circuit

Note1: it's safe and OK to use a smaller (lower ampacity) fuse or circuit breaker, such as a 15-amp fuse protecting a circuit wired with #12 copper wire.

Note2: it's generally safe and OK to use a larger size electrical wire, and a larger wire size may in fact be required for longer wiring runs. Generally you want a 3% or less voltage drop across the wire from source to point of use. For the U.S., electrical wire sizes vs. circuit ampacity are given in National Electric Code Table 310-16.

Watch out: in complex circuits that have many connections within a single junction box you could get into trouble: the number of connections that are allowed within an individual junction box depends on the wire size and the size of the box itself. So increasing just the wire size could require that you use a larger electrical box. Sketch courtesy of Carson Dunlop Associates.

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Continue reading at SIZE of WIRE REQUIRED or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see ELECTRICAL OUTLET, HOW TO ADD & WIRE

Or see NUMBER of WIRE CONDUCTORS needed

Or see COPPER-CLAD ALUMINUM WIRE for information about copper clad aluminum wiring

Or see SE CABLE SIZES vs AMPS for more wire size guidelines

Or see SPLICING WIRES

Or see UNDERGROUND SERVICE LATERALS for more wire sizing guidelines

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