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Short question, long NEC answer

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West Pittston, PA
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[#1] Posted: 10/08/2009 - 04:34:52 AM
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I belong to the NFPA and get an NEC newsbrief newsletter. There is always a question that the NFPA officially answers. I thought this one was a no brainer but the detailed, long answer was enlightening.

Question:

Can 14-2 wire be used for the switch leg of a light fixture where the branch circuit is protected by a 20-amp circuit breaker? If this is prohibited by the Code, why can 15-amp switches and receptacles be used on 20-ampere circuits?


Answer:
The conductors from a switch location to the lighting outlet it controls are considered branch-circuit conductors, not tap conductors connected to branch-circuit conductors. These conductors are subject to the general overcurrent protection requirements of 210.20(B), which points to 240.4 for the specific overcurrent protection requirement. Section 240.4(D) specifies that 14 AWG copper conductors are to be protected by an overcurrent protective device with a rating or setting no higher than 15 amperes. Table 210.24, which summarizes the requirements for branch circuits with two or more outlets or receptacles, specifies that the minimum conductor size for a 20-ampere-rated branch circuit is 12 AWG.
Section 210.21(B)(3) permits a 15-ampere receptacle to be connected to a 20-ampere rated branch circuit. The terminals of feed-through type receptacles rated 15 amperes are tested for the heating that will result from the full load of a 20-ampere branch circuit. In addition, the attachment caps of cord-and-plug-connected appliances are configured based on the appliance load. If the appliance is rated greater than 15 amperes, its cord cap will not be compatible with the configuration of a 15-ampere receptacle.
Snap switches installed on branch circuits are subject to the load requirements specified in 404.14. For ac general-use snap switches controlling resistive or inductive lighting loads, the minimum rating cannot be less than the load it supplies. In other words, a 15-ampere switch installed on a 20-ampere circuit can supply a load of 15 amperes. For switches controlling lighting outlets supplied by 15- and 20-ampere branch circuits, it is the load controlled by the switch and not the rating of the branch circuit that determines the switch's minimum ampere rating.

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Linn, OR
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Short question, long NEC answer
[#2] Posted: 10/08/2009 - 08:11:59 AM
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Quote: Originally posted by Jeff Remas
...If the appliance is rated greater than 15 amperes, its cord cap will not be compatible with the configuration of a 15-ampere receptacle...

...it is the load controlled by the switch and not the rating of the branch circuit that determines the switch's minimum ampere rating...


In the case of the outlet, the amperage is limited by the plug type of the appliance, however with light fixtures, there is nothing to stop someone from installing higher wattage bulbs!

So on the one hand they are saying you can't exceed 15 amps with an outlet...

But on the other hand they don't seem to realize someone could replace the originally installed bulbs with higher wattage bulbs that would exceed the 15 amp capacity of the switch.

Then of course there is the present day reality of the situation. I know many people and businesses are doing the exact opposite - That is installing lower wattage bulbs wherever possible to save on their electric costs.

But there are always these gizmos which could add a bit of amperage to a lighting circuit...



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Short question, long NEC answer
[#3] Posted: 10/08/2009 - 08:54:17 AM
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Is there such a thing as a lightbulb that exceeds 1800 watts and had the normal sized socket? Any huge draw lights that I've ever seen have huge sockets.

I've used 1500 watt heaters on 15-amp circuits that were loaded up with lighting, radios, computers and such and have never even tripped a breaker. I'm not sure why this is such a big deal.

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Mike

Linn, OR
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Short question, long NEC answer
[#4] Posted: 10/09/2009 - 08:45:00 AM
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Quote: Originally posted by hausdok
I'm not sure why this is such a big deal.


Well keep in mind the NEC covers all situations, not just homes. Also light switches which control many lights per switch in a commercial situation.

So this would include high-rise buildings, commercial buildings, industrial buildings. something like the Pentagon (6.5 million square feet), etc. Or a housing development where they are building 100 homes. That's a lot of wire!

Then you get a large building with thousands of light switches and circuits for those switches. Imagine being able to use a smaller gauge wire or less expensive switches in a situation like that. It could mean a lot of money!

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Short question, long NEC answer
[#5] Posted: 10/09/2009 - 09:18:26 AM
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Yeah but... The Pentagon has paid $300 for a toilet seat, you really think they care about saving a few bucks on switches?

Tom

Tom

http://clearcreekhomeinspection.com/

Life is tough enough as it is, it's tougher when you're stupid. Don't do stupid things.
Dr Joe Lstiburek
   
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