[OP]
Contributor
It's my understanding that a circuit controlled by a 20 AMP breaker, should have wire, receptacles, and switches on it that are also rated for at least 20 AMPs. Are light fixtures an exception to this principle? The typical light fixture has small stranded wires and no fuse. Is the bulb in a fixture regarded as a fuse?
Contributor
I believe it is permissible to have 15 amp outlets in a multidrop off a 20 amp breaker. I expect you need 12 gauge wire, not 14.
The breaker is designed to protect the wire, not the devices on the end of the wire. So I expect you could have very small lights, say one amp, on a 20 amp breaker as long as you use 12 gauge wire.
But I'm certainly not a code expert.
Mike
Last edited by Mike Henderson; 12-15-2019 at 9:25 PM.
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That is why you can plug your led Christmas lights or a night light into any 120 volt receptacle.Originally Posted by Mike Henderson
Lee Schierer
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Contributor
The common lamp cord or what some call zip cord is not sufficient to carry a 20 AMP load. It may heat up a bit before a dead short drops the breaker or blows a fuse.
This kind of reminds me from something some of the older guys used back in the 1950s, a Jim Dandy Fuse Blower. It was basically a plug, cord and button so they could get the lights to go out at a party. The things guys would do to get a girl in the dark.
jtk
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Contributor
The lighting fixture itself will have wiring that can handle that individual fixture's current draw. An individual fixture shouldn't be seeing the same current as the breaker is rated for. A 100 watt fixture is only drawing 800-850 maAC for example, so the fixture's wiring is sized for 1 amp and less.
You'll also notice that small fixtures, such as lights and fans, are listed in watts, not current draw.
Last edited by Mike Cutler; 12-16-2019 at 4:51 AM.
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I think the fixture wire is contained inside the fixture enclosure for safety. The pigtail, or what ever it is called that sticks out of the fixture and connects to the line voltage, is kept inside the junction box for safety. I don't know about the light cord or toaster cord that plugs into a receptacle. Maybe it just burns the house down when it shorts.
Contributor
This kind of reminds me from something some of the older guys used back in the 1950s, a Jim Dandy Fuse Blower. It was basically a plug, cord and button so they could get the lights to go out at a party. The things guys would do to get a girl in the dark.
My aunt told me when she was in high school in the 1930's waffle parties were the thing. The girls brought waffle irons from home to one house. They made the waffle batter and turned them on until the light went out from the current draw. This was before circuit breakers so it took a while to find th fuses and fuse box in the dark.
Bill D.
Contributor
your device only uses the amount of current it needs, there is no need for the wire on the device to be sized for anything more than what the device will use. the circuit wire/breaker/outlet/ are all sized for a maximum current, in this case 20 amps, but there is only ever the amount of current required by the devices plugged into it flowing in the circuit. could be 1 amp, could be 15.
Member
I think that if the wire serving the fixture were to short out that it would draw more than fixture uses. More likely the wire would be in a race with the breaker to see if it melted through or the breaker tripped first. In either case there would be a very hot spot where the wire shorted. If it was a wimpy short then maybe the wire or plug cord between the short and the receptacle would just heat up until it melted the insulation and a fire started?
Contributor
The light is in PARALLEL with any other loads on the circuit. Whether it's a 5 watt light or 5000, only the current it draws passes through its wiring. If it were in SERIES with all or part of the rest of the circuit and the load didn't fry it, the loads in the series would reduce the voltage available to all of them. It don't work that way.
Moderator
I am neither an electrician nor an inspector. I do all of my own wiring, some of which has been inspected. What I know is a 20 amp breaker needs a minimum 12 gauge wire to the receptacle. The job on the breaker is to protect the wiring in the building. I always use 15 amp 120 v receptacles and when I wired where it was inspected the always passed. I disassembled some and found the gauge and quality of the internals were identical in 15 and 20 amp receptacles, the only difference was the dual orientation for the common to accept either a vertical or horizontal prong.
What gets plugged in to the receptacle can be any gauge. Any light fixture can be used on either circuit, according to the inspector I asked. The opinion of others may vary.
I wire lighting circuits with the thinner 14 gauge wire since it is cheaper and a lot easier to work with. I never put lights on a circuit that has receptacles although I have found some existing work where this was done. One reason is safety - if the breaker pops with some tool plugged into a receptacle the lights don't go out.
But as always, for any question call your local electrical inspector and ask. Regardless of what the code states or how it is interpreted or opinions you read on a forum the inspector is the authority.
JKJ
Contributor
I think the OP is asking why the internal wiring of a permanently-installed light fixture does not need to be the same size as would be required for a receptacle fed by a given size of breaker.
The answer is that they're rated by the manufacturer based on use conditions and failure risks. Receptacle rating and wire size requirements are specified based on the risks that show up when the wire is buried in hot attic insulation, receptacles are connected to worn, loose-fitting plugs, users daisy-chain power strips together to draw lots of current from a given receptacle, etc. So those are adverse situations that the ratings are designed around.
With a light fixture, the risks are different. Fixtures will have a maximum bulb wattage rating. Bulbs are unlikely to fail dead-short. The wires are usually contained in a metal light fixture housing that prevents fire spread. Users aren't connecting random loads - just light bulbs that are also designed around certain failure modes and risks.
This difference in risks is what explains this. It's the same reason that aluminum wiring may be allowed in a light fixture but not in receptacle wiring.
Guest
Wiring size is directly related to the amp draw of the fixture.
My 150w high bay leds are on 20 amp circuits, at 1.25 amps each that's 15 per 20amp circuit. the wires are tiny.
Contributor
A 20A circuit with a known load like lighting would be 16A max, and would require 20A switches if over the 80% rule for 15A rated switches, it all depends on the load.
Guest
Every switch an outlet I install is a commercial 20a rated device. No use for cheap junk.
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