Immediate response requested

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Martin County

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I have a contractor with 21 current carrying conductors in a raceway.
The conductors are #12 thwn-2 and are installed on 20 amp breakers.
I have failed this job and cited table 310.15(b)(2)(a). The contractor states that the load on the branch circuit conductors do not exceed the derated values and that this table is not for sizing overcurrent protection. Please advise and reference as soon as possible as I will not release power to this new business. I may be reached by PM

Sincerely:
In the interest of public safety
Mike R.
 
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The load isn't the issue in 310.15(B)(2)(a) adjustment factors, and his conductors are only good for 13.5 amps, he may be able to use 240.4(B) for 15 amp breakers but without more information this would be hard to say.

Roger
 
The ampacity of the wires are now 13.5 amps, so using 240.4(B) you must protect the wires with no greater than a 15 amp overcurrent device.

Chris
 
Martin County said:
The contractor states that . . . this table is not for sizing overcurrent protection.
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True, but irrelevant. The table is used for part of the process for determining the ampacity of conductors. However, the conductors must be protected at their ampacity. A 20 amp breaker cannot protect a conductor with an ampacity of 13.5 amps. You have a violation of 240.4.
 
Based on the information given you made the right call.


What type of racewaye is it? and what is the length?
 
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Martin County said:
I have a contractor with 21 current carrying conductors in a raceway.
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Wow!

Just curious. Are all the cccs ungrounded and not a 3 phase system? What's the total number of conductors in the raceway? What size is the conduit?
 
Hope I'm not too late?!?! How many of the 21 are "current carrying conductors" - it only applies to them..... If that number is 20 or below he could easily and without question stick to 15A. Otherwise remind him that the "Magic number is 9" to without question avoid loss of rating for the conductor and still use the typical breaker sizing without upsizing to #10's.

IMO I would tell him to invest in 10's, maybe some more conduit too, and call you back....
 
e57 said:
Hope I'm not too late?!?! How many of the 21 are "current carrying conductors" - it only applies to them..... If that number is 20 or below he could easily and without question stick to 15A. Otherwise remind him that the "Magic number is 9" to without question avoid loss of rating for the conductor and still use the typical breaker sizing without upsizing to #10's.

IMO I would tell him to invest in 10's, maybe some more conduit too, and call you back....
Click to expand...

Mark, per the OP all 21 are CCC's

Martin County said:
I have a contractor with 21 current carrying conductors in a raceway.
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Roger
 
I agree with the others? Curious to know the size of the raceway?
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Why, if the size of the conduit is increased it makes no difference in respects to determining or obtaining a better derating as presented.

Now wireway and trough would be different matter, and I don't think this was their raceway.
 
cadpoint said:
Why, if the size of the conduit is increased it makes no difference in respects to determining or obtaining a better derating as presented.

Now wireway and trough would be different matter, and I don't think this was their raceway.
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I thought the same while reading those post but they may be thinking about raceway fill rather than derating.
 
cadpoint said:
Why, if the size of the conduit is increased it makes no difference in respects to determining or obtaining a better derating as presented.

Now wireway and trough would be different matter, and I don't think this was their raceway.
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Technically the size of the raceway could also be it's length. Probably not what he was asking but possible.;)
 
Well I think length would be the third or fourth thing they might even consider if there ducks are in a row to get there! :grin:

I've heard it on the job before it's listed for X number of circuit! Hello !
Number 9, #9, #9...
 
e57 said:
IMO I would tell him to invest in 10's, maybe some more conduit too, and call you back....
Click to expand...

10 AWGs are the way to go IMHO. :smile:

Where I am we have relaxed derating rules so 10 AWGs combined with multiwire branch circuits allow me to install 21 current carrying conductors (7 MWBCs) in a single raceway. So can get away with just two 2" conduits out from a 42 circuit panel. :cool:
 
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