Temp derating of service drop

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Toros

Senior Member
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Tujunga, CA
Hi
my question about wheater I need to derate paralleled horizontal ran service drop installed on the roof
servicing 600A 1 phase 3 wire service
I would install 2sets of 350 mcm if it was not subject to the California sun

thank you
 
electrofelon said:
Is this service drop subject to the NEC?
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Me thinking same thing.

According to art 100 definitions:

[h=5]Service Drop.[/h]The overhead conductors between the utility electric supply system and the service point.
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NEC definition of service drop is describing conductors that are outside the scope of NEC

If these conductors are on the load side of the "service point" then the NEC does apply to them, but they are not a service drop they are -

[h=5]Service Conductors, Overhead.[/h]The overhead conductors between the service point and the first point of connection to the service-entrance conductors at the building or other structure.
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It sounds to me like service conductors running in raceway across a roof.

If the NEC does not apply I will be very surprised.
 
iwire said:
It sounds to me like service conductors running in raceway across a roof.

If the NEC does not apply I will be very surprised.
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Well the title of the thread says service drop, so that gets one thinking of overhead style conductors right out of the gate.
 
Rather curious "service", 600 AMPS, SINGLE phase?

Just keep it several inches above the roof using timber, or better using Versablocks or Dura-Blok, and such to minimize derating issues. Timber will rot quickly, even if treated. I always put on my drawings for the installer to coordinate with the roofing contractor to avoid roof damage (CYA).

RC
 
Ragin Cajun said:
Rather curious "service", 600 AMPS, SINGLE phase?

Just keep it several inches above the roof using timber, or better using Versablocks or Dura-Blok, and such to minimize derating issues. Timber will rot quickly, even if treated. I always put on my drawings for the installer to coordinate with the roofing contractor to avoid roof damage (CYA).

RC
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600 single phase may not be all that common to see a single 600 amp disconnecting means, but I can show you many places that have 600+ amps of incoming service conductors and/or sum of disconnecting means ratings.

If the actual demand for 600 amps is there and it is not some remote location where three phase is not present it may not always be the best option though.
 
electrofelon said:
Look at 310.15(B)(2)(c) "conduits exposed to sunlight on rooftops" Dont forget you can derate from the 90 degree column as long as the final ampacity does not exceed the value in the 75 degree column.
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I agree
thats what I thought
servicing conductor running across the roof needs temp de- rating
and since it is nonFuse not protected , it must be encased in high PSI concrete
 
Toros said:
I agree
thats what I thought
servicing conductor running across the roof needs temp de- rating
and since it is nonFuse not protected , it must be encased in high PSI concrete
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Though it is not a bad idea, on top of the roof is not inside the building. The requirements for having the service disconnect and overcurrent protection inside the building only kick in once you enter the building. Run same set of conductors through the attic instead of on the roof and you will need service disconnect and overcurrent protection ahead of those conductors- and an additional EGC as they are now feeders instead of service conductors.

I would also say that if it were encased in concrete you may not be subjected to the same ambient temp as you are above the roof, but not certain just how you would determine what the ambient temp is. Would depend on exactly how this was done.
 
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