for the electricians in here: what wiring guage is acceptable for 110v lights?

[dv416]

In several places where people have asked this question, a very intelligent response claims that 14 guage wire is required for anything 110v AC household lighting. However, most of the standard, medium base sockets I see online use 18awg wiring. I recently purchased 12 such sockets for a project I'm working on and the safety "ratings" printed on them say 660w, and up to 250v. The factory issued wires attached to them are 18 guage.

What's the deal? Is 18awg good for up to 660w @ up to 250v, despite the claims of electricians and the NEC? Why this discrepancy? My project is admittedly VERY low wattage (36w total), but I will need to use some additional wiring other than the short ends that come with the sockets. So, can I buy 18 guage wire, or should I go with 14?

 

[Razz16mm]

In several places where people have asked this question, a very intelligent response claims that 14 guage wire is required for anything 110v AC household lighting. However, most of the standard, medium base sockets I see online use 18awg wiring. I recently purchased 12 such sockets for a project I'm working on and the safety "ratings" printed on them say 660w, and up to 250v. The factory issued wires attached to them are 18 guage.

What's the deal? Is 18awg good for up to 660w @ up to 250v, despite the claims of electricians and the NEC? Why this discrepancy? My project is admittedly VERY low wattage (36w total), but I will need to use some additional wiring other than the short ends that come with the sockets. So, can I buy 18 guage wire, or should I go with 14?

Proper wire gauge varies with the power cable length and maximum current draw. What works for 600 watts with an 8 or 9 foot cord wouldn't work with a 50' cord. You would get too much voltage drop from the cable resistance. NEC minimum ratings are for maximum breaker loads at typical panel to outlet wiring distances to prevent insulation damage and fires. 14 gauge is the minimum for 15 amp breaker circuits rated for 1800 watts and loaded to no more than 1400. 20 amp circuit breakers require 12 gauge. My old house still has one original 30 amp glass fuse panel and is wired with 8 gauge.

 

[Paul F]

Razz has it right. But for lamp cords, extension cords and other non-structural electrical (in the walls) wiring, the 12 gauge and 14 gauge don't apply. An appliances can be designed and rated for a specific limited current consumption. UL.CSA will allow an appliance to be sold with a smaller gauge because it is rated for a lower power consumption.

A wall socket has no idea what will be plugged into it. So it has a breaker and wire gauge that work together to help prevent fires.

But a lamp is a specific use and so if it is rated for X watts, in only needs gauge y. You will see a label on the appliance that says what the biggest bulb (in watts ) that can be used. Of course, you can ignore the label and start a fire, but then, that's your problem.

 

[dv416]

I understand, 14 awg for 15amp, 12 awg for 20amp. and that refers to BREAKER -> OUTLET. However, from OUTLET -> LIGHT / DEVICE, the wire just depends on the power draw? In this case 36w, so low amperage, about .3 amperes. So I would be fine with 18 guage it sounds like then. For what its worth, my outlets I believe are wired with 12 guage wire, but the receptacle itself I think is only a 15amp one.

Is there any guage wire that is inherently not able to handle 110v AC, or is it dependent on the load? Can 110v AC somehow "overload" a short wire and cause a risk? OR... is it as you were saying, a factor of the distance of the wire? Ie, longer wire = more voltage lost to heat = greater risk of fire?

 

[Paul F]

I understand, 14 awg for 15amp, 12 awg for 20amp. and that refers to BREAKER -> OUTLET. However, from OUTLET -> LIGHT / DEVICE, the wire just depends on the power draw? In this case 36w, so low amperage, about .3 amperes. So I would be fine with 18 guage it sounds like then.

Yes.

For what its worth, my outlets I believe are wired with 12 guage wire, but the receptacle itself I think is only a 15amp one.

15 amp and 20 amp receptacles look very much alike. The only difference is that a 20 amp receptacle has an additional horizontal slot in one of the two connections.

Is there any guage wire that is inherently not able to handle 110v AC, or is it dependent on the load?

No, not when talking about current. But the insulation has to be able to safely protect that the voltage does not arc over to another conductor (like you or a piece of metal) and must be resistant to heat. The insulator is rated for both voltage and heat rating. You will see this printed on the wire.

Can 110v AC somehow "overload" a short wire and cause a risk?

Yes. Long wire or short wire does not matter (ok, I'm going to confuse you saying that). Fire hazard is due to arcing or the wire got too hot. A wire gets too hot when too much current is running though it. It doesn't matter if it is an inch long or 100' long. 100 amps running through 1' of 18 gauge wire or 100' of 18 gauge wire will have the same effect.

 

[dv416]

Thanks Paul, great help!

 

[RyanT]

Yes. Long wire or short wire does not matter (ok, I'm going to confuse you saying that). Fire hazard is due to arcing or the wire got too hot. A wire gets too hot when too much current is running though it. It doesn't matter if it is an inch long or 100' long. 100 amps running through 1' of 18 gauge wire or 100' of 18 gauge wire will have the same effect.

Maybe you meant to say something else, but running 100amps through 1' of cable and 100' of
cable is two very different things. I did these calculations with 12 gauge cable, but with 100' of cable and a 100a load you would have 33% line loss, which is about 30% more allowable by the NEC. 1' of cable with 100a would be a .3% drop in voltage. The reason for all of this is everything has resistance, even copper. The more copper you put in line the more resistance and the more voltage drop you'll experience.

If you had that 33% line loss, your 100a load would actually be more around 119 amps at 84 volts. Of course with such dramatic line loss, your cable starts to overheat, once it overheats you have more resistance in your line, which in turn creates more line loss, which creates more heat....you get it.

So this is why you can't just run 1000' of cable and expect your lamps to perform as expected. This is why we have to run oversized conductors and double up runs to spread the load out amongst a few different pieces of cable. Then even more specific to your problem dv416 is the attempt by the studios to get rid of zip cord(18/2 I believe) runs longer than 6'. With such thin gauge wiring, you are much more prone to line loss over long distances and the potential for fire is much greater.

 

[Bruce Watson]

I understand, 14 awg for 15amp, 12 awg for 20amp. and that refers to BREAKER -> OUTLET. However, from OUTLET -> LIGHT / DEVICE, the wire just depends on the power draw?

Close. Not the power draw, but the current draw. It's the flow of current in the wire that makes the wire hot and causes the fire. The voltage is pretty constant (or your local electric utility is hosed), so what varies with power is current, as in P=VI.

 

[Paul F]

Your point is well taken. Indeed when discussing gauges and capacities, cable length and resistance must be considered.

In the context of the discussion, 100 amps flowing through 1' of cable is identical to 100 amps running through 100' of cable. Any 1' section of wire, no matter how long the wire is, will heat up the with same speed to the same temperature. I picked 100 amps as a failed condition, assuming there was some sort of shorting condition that caused the 100 amps to flow. Of course, if 100amps was flowing through 18 gauge wire, it wouldn't be doing it for long. Either the breaker would trip or there would be one heck of a big stink from the wire burning until it fried open.

I didn't provide the assumptions I was making and that's why I said "ok, I'm going to confuse you saying that".

It's a good discussion. These questions come up often on the forum. A sticky with some electrical FAQ might be useful.