Derating Auxiliary Gutter over 41 conductors

[Finite10]

PROBLEM:

20% fill not exceeded but there are over 41 conductors and need to derate per 2008 NEC table 310.15(B)(2)(a).
So, per table 310.16: 90 degree column; THHN #12 AWG Cu has an ampacity of 30 amps.
30A derated at 35% = 10.5A.

On a correction situation, would one prove each branch circuit's load within that ampacity?
OR-
Upsize the conductors?

 

[GoldDigger]

PROBLEM:

20% fill not exceeded but there are over 41 conductors and need to derate per 2008 NEC table 310.15(B)(2)(a).
So, per table 310.16: 90 degree column; THHN #12 AWG Cu has an ampacity of 30 amps.
30A derated at 35% = 10.5A.s

On a correctio situation, would one prove each branch circuit's load within that ampacity?
OR-
Upsize the conductors?

The only thing you could "prove" would be the size of the source breaker size or the internal overload protection of a single mo
tor load.

Upsize.

 

[GoldDigger]

Or relocate some wires.

 

[Finite10]

Or relocate some wires.

Thanks GoldDigger.
Say this was in the middle of an entire pipe rack run to restart the 360 degrees of bends limit, or to transition somehow.

I'd say the suggestion to upsize would be best, unless there were a ton of single load utilization devices - or many easily proven/calculated loads.
For the 'source breaker' proposition;
240.6(A) says the smallest standard breaker is 15A. Since this still doesn't protect the conductor from an ampacity (load) over 10.5A is there still a way to apply this?

I'm thinking- if it was a big job with engineered electrical prints, it may be easy to provide design loads on each branch circuit. Would that be a solution too, in that situation?

 

[GoldDigger]

Thanks GoldDigger.
Say this was in the middle of an entire pipe rack run to restart the 360 degrees of bends limit, or to transition somehow.

I'd say the suggestion to upsize would be best, unless there were a ton of single load utilization devices - or many easily proven/calculated loads.

IMHO calculated loads do not matter only the OCPD for the wires.

 

[texie]

PROBLEM:

20% fill not exceeded but there are over 41 conductors and need to derate per 2008 NEC table 310.15(B)(2)(a).
So, per table 310.16: 90 degree column; THHN #12 AWG Cu has an ampacity of 30 amps.
30A derated at 35% = 10.5A.

On a correction situation, would one prove each branch circuit's load within that ampacity?
OR-
Upsize the conductors?

If the conductor count does not exceed 30 at ANY CROSS SECTION, I would argue that derating is not required.

 

[kwired]

If the conductor count does not exceed 30 at ANY CROSS SECTION, I would argue that derating is not required.

And don't forget you wouldn't have to count neutrals that only carry unbalanced current of a MWBC, or any art 725 conductors that may be permitted in there and of course equipment grounding conductors.

 

[Finite10]

And don't forget you wouldn't have to count neutrals that only carry unbalanced current of a MWBC, or any art 725 conductors that may be permitted in there and of course equipment grounding conductors.

Yep, agree of course. I should have stipulated that in my scenario but wanted to keep it short.
> 41 conductors that need to be counted for derating.

So, how to handle a 10.5A ampacity with a standard size breaker?

 

[GoldDigger]

Thanks GoldDigger.
Say this was in the middle of an entire pipe rack run to restart the 360 degrees of bends limit, or to transition somehow.

I'd say the suggestion to upsize would be best, unless there were a ton of single load utilization devices - or many easily proven/calculated loads.
For the 'source breaker' proposition;
240.6(A) says the smallest standard breaker is 15A. Since this still doesn't protect the conductor from an ampacity (load) over 10.5A is there still a way to apply this?

I'm thinking- if it was a big job with engineered electrical prints, it may be easy to provide design loads on each branch circuit. Would that be a solution too, in that situation?

Offset some of the pipes to a second parallel aux gutter?
For OCPD use fuses?

 

[infinity]

Derating begins when you exceed 30 CCC's at any cross section not 30 conductors. Since you have a derated value of 10.5 amps you could go up to the next standard size which is 15 amps if you can meet the conditions of 240.4(B).

 

[qcroanoke]

PROBLEM:

20% fill not exceeded but there are over 41 conductors and need to derate per 2008 NEC table 310.15(B)(2)(a).
So, per table 310.16: 90 degree column; THHN #12 AWG Cu has an ampacity of 30 amps.
30A derated at 35% = 10.5A.

On a correction situation, would one prove each branch circuit's load within that ampacity?
OR-
Upsize the conductors?

Have you thought about dividers?

 

[kwired]

Yep, agree of course. I should have stipulated that in my scenario but wanted to keep it short.
> 41 conductors that need to be counted for derating.

So, how to handle a 10.5A ampacity with a standard size breaker?

Just like you would any other conductor.

Determine what minimum ampacity the load needs, if it is equal or less than 10.5 amps next size up overcurrent device can protect it.

If it is supplying multioulet circuits, particularly receptacle outlets, it will require a minimum of a 15 amp conductor if on a 15 amp overcurrent device, see 210.19(A)(2). If that is the case your derated 10.5 amp conductor needs to be increased in size.

 

[Finite10]

Just like you would any other conductor.

Determine what minimum ampacity the load needs, if it is equal or less than 10.5 amps next size up overcurrent device can protect it.

If it is supplying multioulet circuits, particularly receptacle outlets, it will require a minimum of a 15 amp conductor if on a 15 amp overcurrent device, see 210.19(A)(2). If that is the case your derated 10.5 amp conductor needs to be increased in size.

Yes, 240.6 -> next size up breaker protecting that circuit.
210.19(A)(2) does establish the floor for conductor sizing.

This is not my situation -in reality - somebody else has issues and I can't see a way out aside from....
separating his CCC's out inside the aux. gutter and allowing the separated boats, with associated neutrals, to exists in the adequate volume. It's a big gutter, so no reason to pole vault over a mouse turd.

This is not a concrete, technically code-sound fix, but it would meet a reasonable interpretation of the NFPA's intent -IMHO.

Thanks for your reply - thanks to all responders!

 

[don_resqcapt19]

Can you apply the exception to 310.15(A)(2) to your installation?

 

[kwired]

Yes, 240.6 -> next size up breaker protecting that circuit.
210.19(A)(2) does establish the floor for conductor sizing.

This is not my situation -in reality - somebody else has issues and I can't see a way out aside from....
separating his CCC's out inside the aux. gutter and allowing the separated boats, with associated neutrals, to exists in the adequate volume. It's a big gutter, so no reason to pole vault over a mouse turd.

This is not a concrete, technically code-sound fix, but it would meet a reasonable interpretation of the NFPA's intent -IMHO.

Thanks for your reply - thanks to all responders!

All the conductors are still in the same gutter no matter which ones you bundle together within the gutter. I do see your logic, but code is not written that way.