15 amp wire in 20 amp cir

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nankipoot

nankipoot

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If a 15 amp wire is used a switch leg on a 20 amp cir (all other wires on cir are 20 amp), does the whole cir need to be 15 amp protected?
 
Yes. Absolutely. Every conductor in a circuit must be protected against overcurrent. The overcurrent protection must be set no higher than the ampacity of the conductor (or sometimes, the next higher standard setpoint). There are times (i.e., the Tap Rules) in which a wire can be protected at a level much higher than its ampacity. This is not one of those times.
 
I know a inspector that will allow it to be fused at 20amp if the cir goes to the fixture first and not the switch first. I think it does not matter. I feel ANY part of the cir is 15, then it should be fused 15

Then others will say "Its just a switch leg"

I know another inpector that does not like any "mixed size wire" because of the difficulty in enforcement. (other than voltage drop provisions)
 
nankipoot said:
Then others will say "Its just a switch leg"
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Feel free to remind those others that that "switch leg" is going to carry the full circuit current, during those times the switch passes current its way. And since that current might reach 20 amps and sit there forever (i.e., it wouldn't trip a 20 amp breaker), this situation sets up an opportunity for the 15 amp wire to exceed its limits. The result could be damaged insulation, and maybe even a fire. That is the reason for 240.4.
 
I am currently in a code meeting in Murfreesboro tn and this question just came up.

Basically the question
Can 15 amp wire be mixed with 20 amp (not allowed regardless of fuse size, as some inspectors are saying)


The speaker just said the below:

210.19 A (4) list rules that would apply in this condition,

“Only if exception 1 a-e or 2 were present could 15 amp wire be allowed on a 20 amp fused cir. Additionally 15 amp wire should not be allowed,”

but he did not address if it was fused at 15 amp.

If I understand correctly; 210.19 A (4) would NOT apply if the entire cir was fused at 15 amp, and nothing is wrong with mixed wire! IMO

This whole thing has been a big deal around here.
I allow 15 amp wire and 20 amp to be mixed,, IF its fused 15. (of course not on a cir that has to be 20 amp, small app ect.) They are suggesting to stop allowing this. (Some reasons , no real cost savings, diffcult to enforce)

What do you guys think?
 
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Mixing wire sizes is perfectly fine if the circuit or feeder OCP is at the smallest conductor ampacity. (for motors and and a few other areas this is not always true)

Mixing wire sizes is sometimes neccessary when installing conductors for Voltage Drop correction.

Roger
 
This is a good expaination of the question.

Necdigest ?, February 2007

Compiled by Jeff Sargent and the NFPA Electrical Engineering Team

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

A. 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 Section 210.20(B), which points to Section 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. And 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 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 Section 404.14. For AC general-use snap switches controlling resistive or inductive lighting loads, the minimum rating may not be less than the load it supplies. In other words, a 15-ampere switch installed on a 20-ampere circuit may 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, not the rating of the branch circuit, that determines the switch?s minimum ampere rating.
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Sometimes i read things here that say some inspectors need to find another job.They are trying to type in exceptions that are not there.Regardless of if it can work or not we need to follow nec.What is there liability in allowing this violation ?
 
nankipoot said:
This whole thing has been a big deal around here.
I allow 15 amp wire and 20 amp to be mixed,, IF its fused 15. (of course not on a cir that has to be 20 amp, small app ect.) They are suggesting to stop allowing this. (Some reasons , no real cost savings, diffcult to enforce)

What do you guys think?
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First off, I hate to mix sizes... it confuses me :wink: If I'm going to use #12 on 15A for VD purposes, I'll go with it all the way if at all possible.

Nevertheless, this is plain nuts... Do they enforce the NEC, or just what they think should be how it's done?

Secondly, regarding "difficult to enforce" -- I fail to grasp this entirely? Does this mean that if it is mixed then they don't know what the OCPD should be? That should be elementary. Does it mean that if it might be mixed they are worried that they'll miss an improper OCPD? If so, how is that any different than finding the "mixed wire" violation they propose?
 
fixture wire

fixture wire

then you would be violating 402.11 :)
would you not ?
 
mix

mix

nakipoot,
You may have inspected in TN longer than I, but in the decades I've been there, this issue has been muddied considerbly.
Many years ago, the DEI supervisors announced at a State meeting that #14 should be allowed as a "switch leg" on a 20 amp circuit, stating it was a long accepted practice. A few years ago, they stated it was acceptable as a "true switch leg" (their definition:--no neutral, feeding one fixture).. with the incorporation of the individual inspectors, I have found fewer are accepting this as it is considered by most a direct code violation. Hopefully the "practice" will die out as do the old inspectors and old electricians. (spoken by an olddddd inspector) :)
 
Chris,
I'd tag you on 240.5 and 240.10. But what do I know?
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Did you read 240.5(B)(2)? 50' of #18 fixture wire on a 20 amp OCPD.
I have no idea how 240.10 would apply to this...no one said anything about supplementary overcurrent protection.
Don
 
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