ECN Forum Forums General Topics of the Trade General Discussion Area 14-2 on 20 amp circuit

It is acceptable if you live in Canada

30-412 allows #14 copper conductors on a 20A lighting circuit providing the luminaires they are supplying don't exceed its ampacity, and isn't over 7.5m in length.

The "ha-ha" is that we can't use a 20A lighting circuit in a dwelling unit.

Randy said:

I don't get it. I assume you already have the roll of 12 AWG wire...so what difference does a few extra feet of 12-2 down to the switch make?

Isn't it just easier to follow "the good book" and be done with it?

If you cannot even pigtail #14 Cu. to a 15 amp receptacle outlet on a 20 amp circuit, you certainly cannot use #14 Cu to run to a switch.

Fixture wire won't be used to power up anything else but that fixture. Your switch may be called upon to power up something extra, one day.

Re-reading the rules for 'tap conductors' as permitted by 240.4(E) made me gasp a couple of times. This is probably the most convoluted and non self consistent section of the code...and I think that one _could_ argue for 14ga wire on the switch loops for lamps with circuits protected at 20A.

240.4(4) references 210.19(A)(3), which says in exception 1 that a tap conductor in a 50A range circuit can be rated 20A if that is sufficient for the load served...which I take to mean that I could have a 14ga wire protected by a _50A_ breaker as long as the appliance served required less than 20A in this case. Note: looking at 210.19(A)(4) and table 210.24 seems to suggest that the authors of this article consider that a 20A rated tap conductor requires 12ga...which is not consistent with article 310... but even this interpretation clearly allows 12ga conductors protected with a 50A breaker.

240.4(4) also references 210.19(A)(4) which is just Byzantine. 210.19(A)(4) references 210.2, which basically identifies the various special purpose branch circuit articles. 210.19(A)(4) says that branch circuits other than the special purpose branch circuits or the cooking appliance branch circuits can be used with tap conductors. " Branch-circuit conductors that supply loads <other than special purpose or cooking appliances> shall have an ampacity sufficient for the loads served and shall not be smaller that 14AWG. IMHO this is explicit permission for running 14ga conductors to lamps on 20A circuits.

What follows is an Exception with a list of specific conditions for taps. This is pretty convoluted, because in general, you have a rule that creates a restriction, and then you have an exception that lifts the restriction in specific cases. But with this rule there seems to be a very broad allowance (you can use tap conductors wherever they will supply the load), followed by an exception that restricts the allowance to specific cases. Based upon the exception, 14ga taps on 20A circuits would be limited to 18" lengths, with the additional allowance in 410.67 for conductors used to connect lights requiring higher temperature wires...these taps could be up to 6 feet in length.

Needless to say, I am rather confused about how to apply the tap rules, but I rather think that the authors of the article were similarly confused about how to write the tap rules

-Jon

P.S. to earlydean: the tap rules clearly differentiate between known loads and unknown receptacle loads. If a switch for a single lamp is being connected to a much larger circuit, that should be done by someone with sufficient skill to recognize the current circuit configuration and be aware of the limitations...but anyone can plug something in.

It's kinda out there... but 551.43(B) says you can use 14AWG taps to 6' for recessed lights on rec vehicles

-Randy

Well, what if a dead short should happen on the far end of the switch leg, or at the light fixture itself? You will need wire heavy enough that won't get fried by the fault current passed by the 20 amp breaker.

Another example of this is the outlet over the sink (near the ceiling) in the kitchen for the electric clock. Such clocks draw only a few watts, and thus around 30ma. Does that mean that you can run 24 gauge wire to that outlet? No, because if a short circuit ever happened at the clock, that thin wire would burn up and the breaker would think it's only someone making toast. The house might be toast....

what is the amp rating of 14 gage wire Wa2ise?

Randy, the ampacity of a conductor is not really relevant, we would have to look at resistance of the conductor and then the impedance of the combined contributors.


Roger

[This message has been edited by Roger (edited 05-04-2004).]

If I recall correctly, 15 amps. Much higher and the insulation will start to melt or burn. Or have I missed something?

Wa2ise,

I'd suggest taking a look at table 310.16 and 310.17. If the question is 'what is the current which can be safely carried without overheating the wire', then this NEC section allows 24A for 14ga THHN wire (with appropriate terminations, etc. etc.), and 35A for 'single conductors in free air'... even the worst case for 14ga wire, 60C insulation in a raceway allows 20A.

There is also a note referencing 240.4(D). This restricts the overcurrent protection used on 'small conductors' to 15A for 14ga wire, 20A for 12ga wire and 30A for 10ga wire. If I recall correctly, this is not to protect the wire from overload during normal operation, but instead to protect the wire during overload and short circuit conditions.

The 'unused ampacity' is available if you are in situations which require derating, say because of a large number of current carrying conductors in a single conduit, or high ambient temperatures.

-Jon