FW: Grounding screw requirement [RE-wrenches]

[Sky Sims]

Personally I prefer to use bolts with star washers for the grounding
points. Our rack is secured at four points with bolts and star washers
to each panel. The rack becomes the ground wire. This eliminates the
need for ground wire between panels. You don't need to worry about the
bolts stripping out either. 

This method won't work with every type of rack but it should be
acceptable with most.

Sky Sims
Ecological Systems
www.ecologicalsystems.biz
220 County Road 522
Manalapan, NJ 07726
732-462-3858   fax)732-462-3962

-----Original Message-----
From: Brian Wiley [mailto:btw at we-llc.com] 
Sent: Wednesday, February 20, 2008 3:01 PM
To: RE-wrenches at topica.com
Subject: RE: FW: Grounding screw requirement [RE-wrenches]


Hi Aaron,

I do not think there is any such specification for electrical 
connections.  The 3 thread rule of thumb is for mechanical engineering 
and relates to mechanical strength, not current carrying capacity.

This is why UL requires the manufacturer to provide a specific screw 
with their product.

Tests in my laboratory have established that a 10-32 stainless steel 
screw with 3 threads (as is commonly used on PV modules) is capable of 
carrying enough current to be used with a 10 AWG wire maximum.

Brian Wiley
Wiley Electronics LLC



Aaron Wellendorf wrote:
> 
> Fellow wrenches,
> 
> I am resending this as it did not seem to post.
> 
> I am trying to come up with documentation regarding the requirements
for
> ground screws, such as those used to mount a mechanical lug inside of
a
> disconnect switch or a junction box. I have seen installations with a
> Tek screw holding ground lugs to electrical boxes. I have always
> used/required the typical 10-32 ground screw that is self tapping, or
a
> properly sized pre-threaded hole to put in the 10-32 screw. I was
taught
> that proper thread engagement was 3 threads touching the metal to
ensure
> long term contact and continuity. I am searching for the requirement
for
> the 3 threads or any other specification relevant. I have searched my
> electronic copy of the NEC and can't find a reference to this. Can
> anyone tell me where a written specification can be found?
> 
> Square D tech support says that to maintain their UL listings, their
> safety switches require the use of their grounding kit, part #GTK0610,
> which has a 12-24 hex head self-tapping screw 0.62" long with a
washer.
> The screw must be installed in the location marked with the ground
> symbol. 
> 
> 	"Aaron,   All of our  safety switches have a UL label inside the
> switch that lists the UL listed accessories that can be used.  The
> ground kits for these switches are listed on this label.
> These UL listed kits are the only accessories that should be used in
> these switches to retain the UL listing, and warranty.  Using anything
> not listed on this label will not be UL listed as an accessory, and
void
> any warranty.
> 	Tim Milbert  Product Support Specialist"
> 
> Thank you,
> 
> Aaron Wellendorf


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