wire size for grounding panels

73 Posts
Jun 28, 2009 11:13 am
wire size for grounding panels

when grounding panels, should the grounding conductor wire size be sized for the total Isc x 1.3 of all the panels being connected to the grounding rod?

(3) Kyocera KC40t panels that I'm going to ground on one conductor.

Individual panels rated at 2.65amps x 3 x 1.3 = 10.34amps

the grounding conductor would then need to be able to carry say 12amps min?

OR would a larger wire be more better..Smiley
 
Jun 28, 2009 03:19 pm
Re: wire size for grounding panels

This is from the 2002 NEC. The NEC is revised every three years.
http://photovoltaics.sandia.gov/docs/PDF/PV_grounding_CC_HP_102.pdf
 
9 Posts
Jul 17, 2009 12:52 pm
Re: wire size for grounding panels

There are a few considerations when figuring the grounding wire size.  First, are you talking about the PV source circuit (before combiner or junction box) or the PV output circuit (after the combiner or junction box going to the inverter or charge controller).  

According to the 2008 NEC Article 690.46 equipment grounding conductors (EGC) must be 6 AWG unless they are protected....in other words if you are using unprotected grounding wire for your modules, it must be 6 AWG or larger.

Otherwise, the EGC is dictated by the source and output circuit overcurrent protection in accordance with Table 250.122 of the 2008 NEC.  

Hope this helps....it can get quit complicated.
 
578 Posts
Jul 17, 2009 12:59 pm
Re: wire size for grounding panels

here is the link to the newest version of pv and nec code, suggested practices. 

#6 bare copper with lay in lugs or split bolt lugs is commonly used in pv source circuits to a combiner or pass thru box, and after a combiner or pass thru the same size conductor as the largest current carrying conductor is typically used.

http://howto.altestore.com/Reference-Materials/National-Electric-Code-and-Solar-Electric-Systems/a45/

james,
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73 Posts
Jul 18, 2009 10:20 am
Re: wire size for grounding panels

so sorry guys..I should have been more clear with my original post. I'm just grounding the frames of the panels..so sorry for the confusion. So what I need to know is the wire size needed for the EGC to the ground rod.

With that said, if Alt-E ever has a class on grounding, which seems to be the most esoteric item in fabricating a system, I would definitely fly across the country to attend!

James
 
9 Posts
Jul 22, 2009 01:01 pm
Re: wire size for grounding panels

so sorry guys..I should have been more clear with my original post. I'm just grounding the frames of the panels..so sorry for the confusion. So what I need to know is the wire size needed for the EGC to the ground rod.

With that said, if Alt-E ever has a class on grounding, which seems to be the most esoteric item in fabricating a system, I would definitely fly across the country to attend!

James

James - you cannot run the equipment ground as you propose....According to NEC Article 690.43, the equipment ground must be run the same raceway as the circuit conductors.  Basically the whole system is grounded together.

-BF

 
73 Posts
Jul 22, 2009 01:18 pm
Re: wire size for grounding panels

interesting..I could have sworn that I can have a separate ground rod out at the panels that takes care of all the equipment grounding and then another rod for the neg side of power...at least this is shown in most every book & article I've read...
 
578 Posts
Jul 22, 2009 02:53 pm
Re: wire size for grounding panels

hi bruce,

nice post.  the one thing i would like to add is that in some cases it is possible to have egc and grounding electrode separate from that of the remainder of a system, although not for james j with his modules on a building (that contains the bos).

here is a link to an old john wiles article that describes the "seperately derived system" in which i believe in cases of physical distance between array and the building which it serves, the equipment grounding may occur at the array, go to its own grounding electrode while not carrying egc in the conduit to the building.  upon reaching the building the BOS equipment is all bonded as appropriate and tied in with the building's grounding system and electrode(s).

http://www.nmsu.edu/~tdi/pdf-resources/cc74.pdf

looks like this is still valid in 690.47D 2008 version, but eager to hear others' thoughts on this.

cheers,

james
altE staff

AltE
"Making Renewable Do-able"
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Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854
 
9 Posts
Jul 22, 2009 03:14 pm
Re: wire size for grounding panels

I was assuming the panels were roof mounted....If they are ground mounted or otherwise remotely mounted away from a dwelling unit, that is different. 

BF
 
578 Posts
Jul 22, 2009 04:14 pm
Re: wire size for grounding panels

right on. 

in james j case they are roof mounted, so in theory at site of first enclosure (combiner or pass thru)on roof,  the egc, along with pv source circuit wires, transition from bare copper and use-2/rhw-2 respectively, to more "normal" conductors like thhn or so run together in conduit as pv output circuit, as Bruce F suggests.

james
altE staff

AltE
"Making Renewable Do-able"
http://www.altEstore.com/

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854
 

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