Raceways exposed to Sunlight on Roof

[Dennis Alwon]

Another thread made me think of this question. I am assuming that raceways on a rooftop do not have to be adjusted if the raceway falls under 310.15(A)(2)-- any arguments there????

If the above is true and I have 100' run of conduit and say 10' outside to the disconnect and then 10' or less to the unit can I still use 310.15(A)(2) for the feeder to the disconnect and then have to use the adjustment factor on the run from the disconnect to the unit (RTU).? or because the run outside is 20' then the entire run must be sized with the adjustment.

MY opinion-- is the first part- bold section.

 

[GoldDigger]

When this section was discussed recently, I think that the consensus was that it applies to a continuous run of wire rather than a circuit which is composed of seperate runs of wire separated by device connections. Whether the same separation exists at simple splices in a J-box was not clearly stated.
In the situation you set out, the first 10 feet are definitely exempted, allowing the continuous run of wire to be the smaller size. Since the next part of the run beyond the disconnect offers an opportunity to change the wire size, IMHO the exemption would not apply even if there had not been a 10 foot outside section just upstream of it.
So much for logic, now what does the Code actually say?

One other point: In your discussion you mention the length of the raceway. I would instead say that what counts is the length of the conductor.
If you have a continuous run of wire and the type of raceway changes or the number of conductors changes, I would still say that the temperature factor for the ampacity correction for the wire stays at the factor for the 100 (or less) part of the wire run.

Tapatalk!

 

[Dennis Alwon]

When this section was discussed recently, I think that the consensus was that it applies to a continuous run of wire rather than a circuit which is composed of seperate runs of wire separated by device connections. Whether the same separation exists at simple splices in a J-box was not clearly stated.
In the situation you set out, the first 10 feet are definitely exempted, allowing the continuous run of wire to be the smaller size. Since the next part of the run beyond the disconnect offers an opportunity to change the wire size, IMHO the exemption would not apply even if there had not been a 10 foot outside section just upstream of it.
So much for logic, now what does the Code actually say?

Tapatalk!

Sounds like you agree with what I was saying. The code basically says 10% of the run or 10' whichever is less-- IMO that means that the 10' does not get to use the exception and it must be a larger wire. The fact that the wire is going thru a disconnect doesn't really change much so I wasn't sure how that was looked at. I can see it going either way... just wondering what others think.

Unfortunately the code does not helps us o interpret this situation-- code proposal????

 

[GoldDigger]

Whether the wire passes through a disconnect enclosure does not seem significant to me.
Whether the wire terminates at a terminal on each side of the disconnect does.

Tapatalk!

 

[Dennis Alwon]

Whether the wire terminates at a terminal on each side of the disconnect does.

Tapatalk!

That is probably because the disconnect allows the wire to breathe some since that section is not in a raceway. It makes sense and thus it should follow that the second part from the disconnect to the unit should not be able to use art. 310.15(A)(2).

 

[GoldDigger]

I guess we will just have to differ on that. To me the effect of the exception is to keep you from having to use a larger conductor size for the whole run just because of the ampacity calculation for the short segment.
Any time you have an opportunity to change wire sizes the exception is no longer necessary and does not apply.

Tapatalk!

 

[Dennis Alwon]

I guess we will just have to differ on that. To me the effect of the exception is to keep you from having to use a larger conductor size for the whole run just because of the ampacity calculation for the short segment.
Any time you have an opportunity to change wire sizes the exception is no longer necessary and does not apply.

Tapatalk!

I don't think we differ. I agree with you- not sure why you think we differ. I understand the exception and why the 90' inside we allow the wire to cool sufficiently. I also see that the 10' to the unit does not qualify for the exception-- I was saying I can see why people don't see it that way.... Am I reading you incorrectly?

 

[GoldDigger]

All I am saying is that I don't see the relevance to the outcome of any cooling effect or lack of it in the disconnect box.

Tapatalk!

 

[GoldDigger]

Ran out of time to edit ....
All I am saying is that I don't see the relevance to the outcome of any cooling effect or lack of it in the disconnect box.
I do agree with you that the 10 feet to the unit does not qualify.
Where I am not sure whether we agree is that if there were no wire in rooftop raceway before the disconnect the exception would still not apply.
And if the disconnect were inside at the point nearest to the roof penetration the exception would still not apply. I feel that it is the presence of the disconnect between the two sections of wire that counts and not what the temperature is at the disconnect.

Tapatalk!

 

[ActionDave]

I don't think we differ. I agree with you- not sure why you think we differ. I understand the exception and why the 90' inside we allow the wire to cool sufficiently. I also see that the 10' to the unit does not qualify for the exception-- I was saying I can see why people don't see it that way.... Am I reading you incorrectly?

Ran out of time to edit ....
All I am saying is that I don't see the relevance to the outcome of any cooling effect or lack of it in the disconnect box.
I do agree with you that the 10 feet to the unit does not qualify.
Where I am not sure whether we agree is that if there were no wire in rooftop raceway before the disconnect the exception would still not apply.
And if the disconnect were inside at the point nearest to the roof penetration the exception would still not apply. I feel that it is the presence of the disconnect between the two sections of wire that counts and not what the temperature is at the disconnect.

Tapatalk!

The two of you either need to add some graphics or get together in St. Louis and calibrate your thermometers.

 

[Dennis Alwon]

The two of you either need to add some graphics or get together in St. Louis and calibrate your thermometers.

What I am saying is that a 100' run of wire from a panelboard to an rooftop disconnect does not have to use T. 310.15(B)(3)(c) if the outdoor run is 10' or less.

I am also saying that the run from the disconnect to the rtu does need to use T.310.15(B)(3)(c) since it is only 10' and has no indoor section to disperse the heat.

Now the fact that the 10' from the disconnect to the rtu is connected to the 100' run (thru the disconnect) may make someone believe that the entire outside run is 20' and thus the entire run would need to use the table mentioned.