Module Grounding [RE-wrenches]

[William Miller]

Friends:

I apologize for the lengths of these posts, but the rules are complex on
the subject.  My goal is to find the safest, quickest and easiest way to do
a given job.  To do this requires research.  If we collaborate on these
subjects, we all end up with the "ammunition" to support our practices to
the local AHJ inspectors.  Let me know if these lengthy discussions are not
appropriate.

William Miller


At 12:06 AM 10/30/02 -0600, you wrote:
>
>I am out of town and don't have my NEC along, but I thought that every
>panel was required to be hit with the ground wire and that it had to be
>done in such a way so that the removal of any one module from the array
>will not un-ground any other module in the array.

This is true for the grounded conductor (usually but not always the
negative), not the grounding conductor:

	690.4 (C) Module Connection Arrangement. The connections to a 
	module or panel shall be arranged so that removal of a 
	module or panel from a photovoltaic source circuit does not 
	interrupt a grounded conductor to another photovoltaic source 
	circuit. (Section continues).

>
>It sure would be nice to just ground the rack and mast, although I
>wouldn't rely on the concrete surrounding a mast to provide a good
>ground path, especially with the paint on the mast.
>

How about coiling up 20 feet of 4 AWG bare copper?  As long as each turn is
encased in 2" of concrete, should be OK:

	250.52 (3) Concrete-Encased Electrode. An electrode 
	encased by at least 50 mm (2 in.) of concrete, located 
	within and near the bottom of a concrete foundation or 
	footing that is in direct contact with the earth, consisting 
	of at least 6.0 m (20 ft) of one or more bare or zinc 
	galvanized or other electrically conductive coated steel 
	reinforcing bars or rods of not less than 13 mm (½ in.) in 
	diameter, or consisting of at least 6.0 m (20 ft) of bare 
	copper conductor not smaller than 4 AWG. 
	Reinforcing bars shall be permitted to be bonded 
	together by the usual steel tie wires or other effective means.


>
>When I make the ground connections to the individual panels, I separate
>the strands of the ground wire and shoot a self-drilling, self-taping
>screw between the strands and into the module frame with a S.S. washer
>on the screw.  I have heard these screws don't meet code, but it seems
>more like grounding overkill to me. 

As long as your screw is not classified as a sheet metal screw, it should
be OK:

	250.8 Connection of Grounding and Bonding Equipment.
	Grounding conductors and bonding jumpers shall be connected 
	by exothermic welding, listed pressure connectors, listed 	
	clamps, or other listed means. Connection devices or fittings 
	that depend solely on solder shall not be used. Sheet metal 
	screws shall not be used to connect grounding conductors to enclosures.


Self tapping machine screws are generally hard to find.  One easy to find
self tapping machine screw listed for this use is a green grounding screw,
found at your local wholesaler!  I find these to be much more robust than
the screw provided with the Shell modules.

End







__________________________________________________________________
William Miller
Miller Power and Communications
PO Box 50, Santa Margarita, CA 93453
Voice :805-438-5600		Fax: 805-438-4607	VMail: 805-546-4875
email: wrmiller at slonet.org
http://millerpowerandcomm.com
License No. C-10-773985
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