Home>Discussions>ELECTRICAL & LIGHTING>Would it be okay to put 2 Ceiling Fans on one circuit???
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JLMCDANIEL
Re: Would it be okay to put 2 Ceiling Fans on one circuit???
deadshort wrote:

I'd prefer to stick to NEC requirements rather than than Jacks "engineering' calculations and would agree with Doug.

I always recommend sticking to NEC requirements but think it is important to know why they are requirements and what exceptions there are. I find it interesting that NEC says the breaker must match the weakest component. If you run 12 ga to a J-box then run 14 ga out of the J-box you have to protect the circuit with a 15 amp breaker but you can use a 20 amp breaker and run 12 ga wire to a J-box and connect a light fixture with 18 ga wire.
Jack

DougLanglois
Re: Would it be okay to put 2 Ceiling Fans on one circuit???
JLMCDANIEL wrote:

I always recommend sticking to NEC requirements but think it is important to know why they are requirements and what exceptions there are. I find it interesting that NEC says the breaker must match the weakest component. If you run 12 ga to a J-box then run 14 ga out of the J-box you have to protect the circuit with a 15 amp breaker but you can use a 20 amp breaker and run 12 ga wire to a J-box and connect a light fixture with 18 ga wire.
Jack

My understanding of that is that the breaker is there to protect the house's wiring system, not the fixture.

canuk
Re: Would it be okay to put 2 Ceiling Fans on one circuit???
DougLanglois wrote:

My understanding of that is that the breaker is there to protect the house's wiring system, not the fixture.

The breaker ( or fuse -- for that matter ) is an over current safety disconnect for the circuit --- which includes devices plugged in or hard wired.

Does it protect the house's wiring ? --- Sure -- if you are over amping the circuit which leads to over heating the wiring.
But --- importantly is a fault protection --- say a short between the hot and neutral or ground ---- whether the fault is the device itself or along the circuit wiring.

However --- it's allowable to run 12 ga wiring connected to a 15 amp breaker.
So --- one would think over taxing the wiring wouldn't be much the concern --- the fault protection is.

JLMCDANIEL
Re: Would it be okay to put 2 Ceiling Fans on one circuit???
DougLanglois wrote:

My understanding of that is that the breaker is there to protect the house's wiring system, not the fixture.

Minimal fault protection and some over heating protection. I say minimal because you can have a high resistance ground fault that causes a draw of say 10 amps which will not trip the the breaker but posses a deadly situation due to shock and with 1200 watts of heat dissipation at a single point that can pose a fire hazard.

It should also be pointed out the length of run and the load must be taken into account when sizing wire. For instance a 12 amp continuous load circuit 200 foot long would require 12 ga wiring. If 14 ga were used you would have about a 12.5 volt drop (a little over 10%) and generate almost 1500 watts of heat loss in the wiring alone. While the voltage drop would have minimal affect on incandescent lights or resistance heating it would fall outside the allowable tolerances for most other devices. The 1500 watts of heat loss is not likely to cause a fire as in the example above because it is spread over the entire 200 feet of wiring.

With a circuit the rating stops at the outlet. You can plug a lamp or other device rated at much less into the receptacle. The same applies to the fixture but it being hard wired as part of the circuit it appears to be contrary to other provisions of the NEC.
Jack

DougLanglois
Re: Would it be okay to put 2 Ceiling Fans on one circuit???
canuk wrote:

The breaker ( or fuse -- for that matter ) is an over current safety disconnect for the circuit --- which includes devices plugged in or hard wired.

Does it protect the house's wiring ? --- Sure -- if you are over amping the circuit which leads to over heating the wiring.
But --- importantly is a fault protection --- say a short between the hot and neutral or ground ---- whether the fault is the device itself or along the circuit wiring.

However --- it's allowable to run 12 ga wiring connected to a 15 amp breaker.
So --- one would think over taxing the wiring wouldn't be much the concern --- the fault protection is.

I could be wrong, but I believe you'll find the stated purpose of the breaker is protection of the home circuit. A device or fixture could burn out at much lower current than the home circuit (as evidenced by 18ga. wire on a light fixture, previously mentioned), so it won't be protected as much as the home wiring. Of course, the breaker tripping at very high draw will protect everything on the circuit as a side effect.

The allowance of running 12ga on a 15A circuit is an invalid retort to the home circuit protection argument. A 15A breaker protects 12ga as much, in fact more so, than 14ga because it will trip before 12ga approaches anywhere near it's capacity. If you had an entire 12ga circuit on a 15A breaker, the worse you'd introduce is nuisance trips, since it would trip while the circuit was still well within tolerance. If you have a mixed circuit, then the 15ga breaker is protecting the 14ga through which power is flowing to reach the 12ga.

If code allowed for 14ga. on a 20A circuit, then I would accept your argument.

Of course, we are now arguing intent and stated purpose - not real world maximums. The reality is, as mentioned, that pretty much any product on the consumer market is engineered with incredible margins of error. I'm sure that if you took a piece of 14ga wire you could run many multiples of 15A through it. But just because you can doesn't mean that you'd want to have a single 200A circuit in your house that is constantly one light switch flick away from catastrophic failure.

DougLanglois
Re: Would it be okay to put 2 Ceiling Fans on one circuit???
JLMCDANIEL wrote:

With a circuit the rating stops at the outlet. You can plug a lamp or other device rated at much less into the receptacle. The same applies to the fixture but it being hard wired as part of the circuit it appears to be contrary to other provisions of the NEC.
Jack

Thank you, that is precisely my point. Devices plugged into the circuit are on their own when it comes to overload protection from currents higher than normal operation of the device, but lower than the circuit rating.

canuk
Re: Would it be okay to put 2 Ceiling Fans on one circuit???
DougLanglois wrote:

I could be wrong, but I believe you'll find the stated purpose of the breaker is protection of the home circuit.

Isn't a device or appliance plugged into or hard wired part of the circuit?

There is a need for something to complete an otherwise open circuit with only potential current flow. Not saying only those items can complete the circuit but that is the intended purpose.

A device or fixture could burn out at much lower current than the home circuit (as evidenced by 18ga. wire on a light fixture, previously mentioned), so it won't be protected as much as the home wiring. Of course, the breaker tripping at very high draw will protect everything on the circuit as a side effect.

So -- if said device or fixture with 18 gage was shorted --- say a light fixture socket --- would burn out before the breaker limit tripped ?

The allowance of running 12ga on a 15A circuit is an invalid retort to the home circuit protection argument. A 15A breaker protects 12ga as much, in fact more so, than 14ga because it will trip before 12ga approaches anywhere near it's capacity.

I think we are saying the same thing here.

If you had an entire 12ga circuit on a 15A breaker, the worse you'd introduce is nuisance trips, since it would trip while the circuit was still well within tolerance.

It wouldn't be a "nuisance trip " since the circuit limit is 15 amp governed by the breaker not the heavier gage wire.

If you have a mixed circuit, then the 15ga breaker is protecting the 14ga through which power is flowing to reach the 12ga.

It's protecting the circuit of which the 12 gage would be part of.

If code allowed for 14ga. on a 20A circuit, then I would accept your argument.

Of course, we are now arguing intent and stated purpose - not real world maximums. The reality is, as mentioned, that pretty much any product on the consumer market is engineered with incredible margins of error. I'm sure that if you took a piece of 14ga wire you could run many multiples of 15A through it. But just because you can doesn't mean that you'd want to have a single 200A circuit in your house that is constantly one light switch flick away from catastrophic failure.

I'm thinking more of discussion rather than arguing --- albeit maybe a little off topic.;)

DougLanglois
Re: Would it be okay to put 2 Ceiling Fans on one circuit???

We're down to semantics now. When I say 'home circuit' I mean wiring from panel to outlets and light boxes. I know that to be rigorously correct it's not a circuit until completed, but I'm using generally accepted language.

My point is that if you plug something into an outlet that will overload at much lower currents than would trip your breaker, then your breaker is not protecting it. If you plug your table saw into a 20A outlet with 40ga copper wire, there's a good chance that 40ga wire is going to melt - but the breaker will not trip. Unless of course the melting of the wire causes a short that endangers the house wiring.

If you plug in a device that shorts, then the breaker will trip before there is damage to the home wiring.

Hence the breaker is there to protect the home wiring, not the devices plugged into it. Any protection of devices is a happy side effect.

JLMCDANIEL
Re: Would it be okay to put 2 Ceiling Fans on one circuit???

Actually a breaker limits the capacity of the circuit and provides little protection other than over capacity. Loose connection or high resistant connection can cause receptacles and switches to burn and never trip a breaker. This was a pretty common occurrence with house fires when Al wiring was being used. A breaker will also not trip if you have a loose connection that is arching which can cause a fire. A breaker provides no personal safety, a ¼ amp will kill you so you would be long dead before a 15 amp breaker trips. That is why newer devices such as GFCI and AFCI devices are now required by code.
Jack

jvande7471
Re: Would it be okay to put 2 Ceiling Fans on one circuit???

Man! You guys are touchy! :D

I can certainly see where AWG can be critical and why electricians always seem upset when they're working in an old home where homeowners have added to circuits over the years.

I can see the senario where an old house has 2 or 3 bedrooms on one circuit with a couple plugs per bedroom. Owner 1 adds a couple more outlets per bedroom for convenience. Owner 2 makes one bedroom into an office and has multiple multi-plug cords to power the computer, printer, monitor, fans, space heater... No shorts, but the extra equipment now overloads the 15A circuit.

No problem. Just swap out the 15A breaker for a 20A. "It'll probably be okay". And in most cases, probably will considering the safety margins built into code.

Owner 2 has some issues and calls in the electrician who opens up boxes and finds AL wiring tied to copper plugs or wirenutted to copper for the new outlets, and the wirenuts are black from overheating and the box shows char.

I couldn't figure out why I had to run 12AWG thhn to fan circuits that I then spliced to 18 AWG vinyl coated at the appliance. I've realized through this series of posts that it's because people will add to the circuits, and that it's the fire inside the wall that you can't see that will kill you. That 18 AWG at the appliance will not have anything added to it.

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