[RE-wrenches] Rooftop wiring methods between multiple subarrays

[Mark Frye]

Hey Folks,
 
I don't want to dicourage anyone from doing good work that meets or exceeds
Code requirements.  But I am a little quizzical about the how we all seem to
be ignoring what the Code actual says about this.
 
"250.97 Bonding for Over 250V Volts....
 
Exception: Where oversized, concentric, or eccentric knockouts are not
encountered....the following methods shall be permitted:...(3) Fittings with
shoulders that seat firmly against the box or cabinet, such as electrical
metallic tubing connectors..."
 
This tells me that if I run PV source conductors in EMT from one metal box
to another, I don't nessecarily need to bond the EMT as if it were part of a
service.
 
Mark Frye 
Berkeley Solar Electric Systems 
303 Redbud Way 
Nevada City,  CA 95959 
(530) 401-8024 
 <http://www.berkeleysolar.com/> www.berkeleysolar.com  
 

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of August Goers
Sent: Friday, October 09, 2009 12:57 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Rooftop wiring methods between multiple subarrays



All -

 

PVC doesn't hold up well in the Bay Area - Here's a photo of  some ~4 year
old PVC browned PVC from Marin County:

 

PVC (Small).jpg

 

You can see that the straps melted resulting in the conduit sliding down.
Thank goodness we didn't install this. PCV seems like a good option for
shaded areas. 

 

As Bill pointed out, if we use EMT we need to bond both ends of the conduit
to comply with NEC 250.97. My issue is that it is hard to find outdoor rated
bonding bushings - that's why we've just been installing cast metal boxes
with threaded connections (complies with NEC 250.92(B)(2)).

 

As William point out, EMT is robust and reliable. I still think that there
must be more efficient way to go between arrays. Maybe that's why commercial
low profile racking systems are often fully integrated systems with built in
wire raceways.

 

-August

 

 

August Goers

 

Luminalt Energy Corporation

O: 415.564.7652

M: 415.559.1525

F: 650.244.9167

august at luminalt.com

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of William
Miller
Sent: Friday, October 09, 2009 12:07 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Rooftop wiring methods between multiple subarrays

 

Ray:

Good question.  We do use PVC in coastal zones to avoid corrosion.  We try
to keep it in the shade, paint it where exposed to UV and support it in
close intervals.

William


At 10:57 AM 10/9/2009, you wrote:



Except for coastal installations.... where  EMT is NOT  recommended
outdoors, PVC browns out and warps, and we should therefore use product X???

R. Walters
ray at solarray.com
Solar Engineer




On Oct 9, 2009, at 11:38 AM, William Miller wrote:




August:

I suggest the use of EMT with proper fittings to protect high voltage, high
amperage DC Wiring on rooftops.  Sure it is time consuming, but high
quality, reliable craftsmanship will always be thus.

William Miller





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