NEC Article 310-15(B)(2)(a) Conductors derating

[ronnieg1025]

Under the NEC, article 310-15(B)(2)(a)- Adjustment Factors. More than three current-carrying conductors in a raceway or cable exceeds three, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(A).

I am looking for an interpetation for the Neutral Conductor as described under 310.15(B)(4)(a) - A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(2)(a).

Here is the situation, the contractor ignored the electrical plans that called for no more than 3 branch circuits per homerun and ran a total of 6 branch circuits with 6 phase conductors and anywhere from (2) to (4) neutral conductors as well as equipment grounding conductors. In most cases, the branch circuits were rated 20 amps, 120 volt. Also, the contractor did not de-rate the conductors and ran # 12 wire. One of the conduits was a 1-1/2" and had 7 phase conductors, 6 neutral conductors and 4 equipment grounding conductors.


If the neutral is considered a current carrying conductor, the contractor will have to replace the #12 wire with # 8 wire since Table 310.15(B)(2)(a) states that 10 to 20 current-carrying conductors must be adjusted by 50%.

Any opinions as far as if the neutral conductors should be considered current carrying conductors?

 

[LarryFine]

Here is the situation, the contractor ignored the electrical plans that called for no more than 3 branch circuits per homerun . . .

It shouldn't require plans to know that rule applies. One hot per phase max.

. . . and ran a total of 6 branch circuits with 6 phase conductors and anywhere from (2) to (4) neutral conductors as well as equipment grounding conductors. In most cases, the branch circuits were rated 20 amps, 120 volt.

In this case, only a neutral which serves all three phases may be uncounted; one serving one or two phases (technically not a 'neutral') must be counted.

Also, the contractor did not de-rate the conductors and ran # 12 wire. One of the conduits was a 1-1/2" and had 7 phase conductors, 6 neutral conductors and 4 equipment grounding conductors.

That's obviously not good.

Any opinions as far as if the neutral conductors should be considered current carrying conductors?

See above.


Oh, and welcome to the forum. :smile:

 

[infinity]

Also, the contractor did not de-rate the conductors and ran # 12 wire. One of the conduits was a 1-1/2" and had 7 phase conductors, 6 neutral conductors and 4 equipment grounding conductors.
If the neutral is considered a current carrying conductor, the contractor will have to replace the #12 wire with # 8 wire since Table 310.15(B)(2)(a) states that 10 to 20 current-carrying conductors must be adjusted by 50%.

The required use of #8 conductors may be incorrect. If the conductor type has 90 degree insulation then a #10 conductor would be fine after derating for use with a 20 amp OCPD.


#10 THHN = 40 amps*50%= 20 amp adjusted ampacity.

 

[cschmid]

wow can you spell NO Profit.....I would be curious of his reasoning for this action..

 

[steve66]

If the neutral wires only carry the unbalance of 3 phase conductors from different phases, and there aren't harmonics present, then you only need to derate 70%. (For 7 phase wires).

And like Infinity said, if the conductors are rated at 90 deg., then #12 wire would be good for 30 * 0.7 = 21 amps.

So there may not be a problem.

Edit: I just realized: 7 phase wires, and 6 neutral wires, the neutrals have to be counted. But the contractor might be able to fix this by combining neutral wires.

Steve

 

[infinity]

If the neutral wires only carry the unbalance of 3 phase conductors from different phases, and there aren't harmonics present, then you only need to derate 70%. (For 7 phase wires).

And like Infinity said, if the conductors are rated at 90 deg., then #12 wire would be good for 30 * 0.7 = 21 amps.

So there may not be a problem.

Steve

I was referencing the 7 phase conductors, 6 neutral conductors and 4 equipment grounding conductors.

In a WYE system with that scenario you will have 13 CCC's so you would have to use the 50% derating value.

 

[charlie b]

One of the conduits was a 1-1/2" and had 7 phase conductors, 6 neutral conductors and 4 equipment grounding conductors.

Just in case this is not already obvious, you never count the EGC. So this situation has, at most 13 CCCs. Depending on the connections, it might have as few as 8.

 

[infinity]

Just in case this is not already obvious, you never count the EGC. So this situation has, at most 13 CCCs. Depending on the connections, it might have as few as 8.

Charlie, how could 7 phase conductors and 6 neutrals in one conduit ever be 8 CCC's?

Best case scenario from a 120/240 volt system would be 12 CCC's.

 

[charlie b]

Charlie, how could 7 phase conductors and 6 neutrals in one conduit ever be 8 CCC's?

Two full boats, one 2-wire circuit, and 3 unused conductors. Keep in mind that we do not actually know how any of this is really connected.

 

[infinity]

Two full boats, one 2-wire circuit, and 3 unused conductors. Keep in mind that we do not actually know how any of this is really connected.

Don't you find that response in a discussion about derating to be somewhat misleading?

 

[charlie b]

Don't you find that response in a discussion about derating to be somewhat misleading?

Not misleading, but rather intended to forestall a misleading situation. My point is that the OP should not presume any knowledge of what is inside the conduit, or how it is used. The actual configuration should be verified, before any conclusions are drawn with regard to code compliance, and before any decisions are made with regard to corrective measures.

 

[infinity]

Two full boats, one 2-wire circuit, and 3 unused conductors. Keep in mind that we do not actually know how any of this is really connected.

I'm curious why you chose 8 CCC's and not say just 2 or 3 or 5 or...?

 

[charlie b]

I'm curious why you chose 8 CCC's and not say just 2 or 3 or 5 or...?

Because I didn't want to do the extra work to figure out how to make it nine! :grin: (Nine, of course, is the limit above which the #12 conductors would not have been acceptable.)

 

[cschmid]

Under the NEC, article 310-15(B)(2)(a)- Adjustment Factors. More than three current-carrying conductors in a raceway or cable exceeds three, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(A).

I am looking for an interpetation for the Neutral Conductor as described under 310.15(B)(4)(a) - A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(2)(a).

Here is the situation, the contractor ignored the electrical plans that called for no more than 3 branch circuits per homerun and ran a total of 6 branch circuits with 6 phase conductors and anywhere from (2) to (4) neutral conductors as well as equipment grounding conductors. In most cases, the branch circuits were rated 20 amps, 120 volt. Also, the contractor did not de-rate the conductors and ran # 12 wire. One of the conduits was a 1-1/2" and had 7 phase conductors, 6 neutral conductors and 4 equipment grounding conductors.


If the neutral is considered a current carrying conductor, the contractor will have to replace the #12 wire with # 8 wire since Table 310.15(B)(2)(a) states that 10 to 20 current-carrying conductors must be adjusted by 50%.

Any opinions as far as if the neutral conductors should be considered current carrying conductors?

Just in case this is not already obvious, you never count the EGC. So this situation has, at most 13 CCCs. Depending on the connections, it might have as few as 8.

Two full boats, one 2-wire circuit, and 3 unused conductors. Keep in mind that we do not actually know how any of this is really connected.

wait wait here if they are in the pipe hooked up or you you need to derate them..they will be used in the future that is for sure and then they are wrong.. he is wrong to start with the plans said no more than 3 home runs..that is 9 wires total..3 hots 3 neutrals 3 grounds..ignoring the plans for your own profit is wrong..no excuses wires need to be pulled out and new pipes installed..


dang this is nice and easy now..this is with google chrome and vista..

 

[roger]

wait wait here if they are in the pipe hooked up or you you need to derate them..they will be used in the future that is for sure and then they are wrong.. he is wrong to start with the plans said no more than 3 home runs..that is 9 wires total..3 hots 3 neutrals 3

What is the definition of "3 home runs"? A multi-wire branch circuit is "one circuit", this could / would mean that up to 12 conductors could be "3 home runs".

Roger

 

[cschmid]

okay you got me there..

Yet when I read the question and the concerns I assumed that the prints did not specify multiwire branch circuits..I have found that allot of the time contractors will bid a set of prints and include multiwire circuits to cut costs even if the drawings do not show multi wire circuits..