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Old 03-03-2013, 11:40 AM   #1
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Raceway fill on rooftop


Hello!

Per my research I determined that a 3/4 raceway (EMT or IMC) would sized sufficiently to hold 4x 8 AWG THWN-2 wires (BK, RD, WT, GN).

Now, I am not 100% sure how the fact that this will be installed on a rooftop effects the fill calculation.

Could you help me in verifying if this will be ok? Could I possible even go with 1/2" raceway?

Thanks

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Old 03-03-2013, 12:07 PM   #2
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Raceway fill on rooftop


I would not use 1/2" it's better to go larger than small, #8 wires are not easy to work with.

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Old 03-03-2013, 12:11 PM   #3
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Raceway fill on rooftop


4 #8's would not be compliant in 1/2".

We would have to know the distance above the rooftop the conduit was running and the area you are in. I'm guessing you will have to upsize the conductors. How much, don't know yet.
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Old 03-03-2013, 01:00 PM   #4
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Raceway fill on rooftop


Fill has the same issue along the wall, floor or rooftop.
Derating factors come into play on a rooftop install.
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Old 03-03-2013, 01:15 PM   #5
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Raceway fill on rooftop


Thanks a lot for you comments so far!

The run will originate at the main service panel on the exterior building wall. From there it runs straight up (about 5ft) and will penetrate through the eave onto the top of the roof. At about 4 inches above the roof surface it will turn 90 degrees (will probably use an LB) and run horizontally over the roof surface for about 3ft max. to a junction box.

This will be for a solar PV system. Currently the load will only be about 17A but:

1) I have lots of 8 AWG lying around which I can use
2) using 8 AWG will have the benefit of having a little room for further expansion of the PV system

Thoughts?

Thanks
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Old 03-03-2013, 01:48 PM   #6
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Raceway fill on rooftop


Quote:
Originally Posted by Jaxx View Post
Thanks a lot for you comments so far!

The run will originate at the main service panel on the exterior building wall. From there it runs straight up (about 5ft) and will penetrate through the eave onto the top of the roof. At about 4 inches above the roof surface it will turn 90 degrees (will probably use an LB) and run horizontally over the roof surface for about 3ft max. to a junction box.

This will be for a solar PV system. Currently the load will only be about 17A but:

1) I have lots of 8 AWG lying around which I can use
2) using 8 AWG will have the benefit of having a little room for further expansion of the PV system

Thoughts?

Thanks
You might want to read up on the NEC for all the requirements for installing a PV system... not just wing it...
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Old 03-03-2013, 02:07 PM   #7
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Raceway fill on rooftop


Quote:
Originally Posted by Jaxx
Thanks a lot for you comments so far!

The run will originate at the main service panel on the exterior building wall. From there it runs straight up (about 5ft) and will penetrate through the eave onto the top of the roof. At about 4 inches above the roof surface it will turn 90 degrees (will probably use an LB) and run horizontally over the roof surface for about 3ft max. to a junction box.

This will be for a solar PV system. Currently the load will only be about 17A but:

1) I have lots of 8 AWG lying around which I can use
2) using 8 AWG will have the benefit of having a little room for further expansion of the PV system

Thoughts?

Thanks

Are conduit fill rules the same for DC as they are for AC? I assume PV output is DC current.
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Old 03-03-2013, 03:04 PM   #8
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Raceway fill on rooftop


Quote:
I assume PV output is DC current.
In most cases it is. But, there are systems that are installed with microinverters on each panel. The output from these would be 240V AC.

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