Tap Rule

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  #1  
Old 06-08-01, 07:13 AM
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I have this friend, (no - honest it's not me!) who has used #14 on a 20 amp circuit which consists mainly of #12. He has fed a couple receptacles here & there with the 14.

Aside from the fact that 240-21(b)1 requires tap conductors to be in conduit and he used NM cable (romex), the article specifies that the tap conductors allowed terminate at a switchboard, panelboard, disconnecting means or "control device". Article 100 doesn't define control device, but I'm guessing that a receptacle doesn't qualify. Before I tell this guy he has to re-wire I was hoping to get some feedback from the good folks in the forum.

Appreciate your input.

Juice
 
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  #2  
Old 06-08-01, 08:20 AM
resqcapt19
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Juice,
First look at 240-21(b)(1)(a)(2). This requires that the tap conductors terminate in an OCPD having a rating not greater than the conductor ampacity. This is a branch circuit so you also have to look at Article 210. 210-19(b) says that conductors of a branch circuit serving more than one receptacle for cord and plug connected loads must have an ampacity of not less than the branch circuit rating. The OCPD (overcurrent protective device) rating is the branch circuit rating. Remember that a duplex outlet is 2 receptacles.
Don(resqcapt19)
 
  #3  
Old 06-08-01, 08:37 AM
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I have a dumb question....what is meant by "tap conductor"?
 
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Old 06-08-01, 09:45 AM
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Thanks Don. Yes I am aware that the OCPD rating is the branch circuit rating. But by using the term "Control Device" I thought that the termination of the tap conductors was not necessarily limited to an OCPD. I was fairly certain that my friend had done something incorrectly, because with a 20 amp breaker protecting this circuit, he can pull 20 amps through a 15 amp conductor.

I will recommend that he reduce the breaker size or re-wire those portions of the circuit that utilize #14 wire.

Dave, a tap is a set of conductors connected to a feeder anywhere along a circuit between the fuse or breaker (OCPD) and the end of the feeder run. The NEC permits you to branch off the feeder with smaller gauge wire than the main wire you're tapping into without installing a breaker at the intersection of the two if the other end of the smaller gauge wire has overcurrent protection of not greater than the ampacity rating of the smaller wire. This isn't particularly useful in most home wiring, since the cost difference between #14, #12 and #10 is minimal. It's used more with commercial and industrial electrical systems where very large conductors are used and a lot of money can be saved using smaller gauges on the branch circuits.

Juice
 
  #5  
Old 06-08-01, 10:11 AM
resqcapt19
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Juice,
The words "control device" appear in 240-21(b)(1)(b) but the requirement for an OCPD is in 240-21(b)(1)(a)(2). All of the conditions listed in (a) through (d) of 240-21(b)(1) must be complied with.
Don(resqcapt19)
 
  #6  
Old 06-08-01, 10:35 AM
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240-21(b)(1)(a)(2) seems ambiguous in that it says "or". "Not less than the rating of the device supplied by the tap conductors OR not less than the rating of the OCPD at the termination of the tap conductors." It gave me the impression that an OCPD at the end was not necessarily required, and that if you use a 15 amp rated receptacle you were OK if the other conditions were met. This didn't seem like such a good practice to me but there are certainly those that would say "Well, if it's good enough for the NEC it's good enough for me!". Of course as many of us realize, the NEC is only a minimum requirement, and not necessarily a good electrical design.

Anyway, I appreciate your reply, and feeling a bit more confident that I was correct in my opinion that my friend should not have tapped off 12/2 with 14/2 I went to chat with him. Turns out that he protected this entire circuit with a 15 amp breaker in the first place. He was relieved to find out that he didn't have to re-wire. But I cautioned him that with #12 terminating at the breaker some future owner might assume the whole circuit is rated 20 amps and upgrade that 15 to a 20 amp CB. My advice is always to label the breaker of such circuits with a warning of "Max. breaker 15 amps". Thanks again for your help.

Juice
 
  #7  
Old 06-08-01, 08:09 PM
Wgoodrich
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Juice, look at 210-19, I think you will find your answer there concerning branch circuits and taps.

Notice that multioutlet branch circuits is reqired to size the breaker by the smallest conductor on the circuit.

Considering "other loads" branch circuits you should find the tap rules to be limited to 18" in length.

I also think you will find that 240-21-B refers to feeders not branch circuits. 240-21-A refers you to branch circuit rules as resqcapt19 suggested in his first reply.

Hope this fulfills your quest

Wg
 
  #8  
Old 06-12-01, 09:18 AM
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Thanks Don & Wg.

Juice
 
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