Is a Junction Box a Raceway?

For reasons I'm not going to describe, we ended up with a generator supplied circuit that comprises of 150' of (3) 600 XHHW kcmil/phase in conduit, transitions to (3) 4/0 RHW-2 cables inside a junction box for a length of about 6ft then transitions back to another 200' of (3) 600 kcmil/phase in conduit. It's protected by a 1200A breaker.

One interpretation is that the junction box is not considered a raceway and the free air rating of 405A is applicable for each of the 90C RHW-2 with its 90C rated terminations.
Others do consider the junction box a raceway, with each RHW-2 only good for 260A.

A third opinion is that the raceway vs not a raceway question is irrelevant based on the 310.A.2 exception for the 6ft of RHW-2.

I'm curious where the experience here falls with this question.

Thank you!
 

jim dungar

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One interpretation is that the junction box is not considered a raceway and the free air rating of 405A is applicable for each of the 90C RHW-2 with its 90C rated terminations.
The conductors are not in free air if they are in an enclosure, unless there is sufficient ventilation. I know of no way to calculate the air flow requirements, so I would just use the 'in raceway" rating.
 

roger

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The conductors are not in free air if they are in an enclosure, unless there is sufficient ventilation. I know of no way to calculate the air flow requirements, so I would just use the 'in raceway" rating.
:thumbsup:

Roger
 

jap

Senior Member
How is this run allowed to be protected by a 1200 amp breaker with the 4/0 RHW-2 in place?

JAP>
 

charlie b

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How is this run allowed to be protected by a 1200 amp breaker with the 4/0 RHW-2 in place?
One interpretation cited by the OP used the 90C rating of 405 amps. Three of those would have an ampacity over1200. But I agree with Jim that the free air rating would not apply.
 
Thank you all for the responses. I thought I was losing my mind....


I would add that a junction box is not a raceway.
Trying to think why this matters now based on the info provided by all above.

Is this why we don’t necessarily derate for a parallel run with 2 conductors per phase that could have 6 conductors in a junction box but only 3 in each raceway?
 

infinity

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Thank you all for the responses. I thought I was losing my mind....




Trying to think why this matters now based on the info provided by all above.

Is this why we don’t necessarily derate for a parallel run with 2 conductors per phase that could have 6 conductors in a junction box but only 3 in each raceway?
Yes, that would be one example of why it's not a raceway. Another would be 24" nipple>junction box>24" nipple >junction box, etc, no derating required.
 
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