[RE-wrenches] Fuse sizing in battery circuits

[Garrison Riegel]

Hi Ray,

Not saying he was right, but it was explained to me by an inspector that the
pipe electrode mentioned in 250.166(C) is different than a water main. The
justification being that 250.52(A)(1) lists requirements for a "metal
underground water pipe" electrode, while 250.52(A)(5) lists "pipe" electrode
separately.  I agree a water main fits the description of a pipe, but I
suppose it could depend on the mood of the inspector.  I've managed to avoid
it myself, but have heard horror stories of 4/0 GECs being required by
inspectors.

Good point about 250.53(D)(2) Supplemental Electrode Required.  Although it
does list a "pipe" again as a possible supplemental electrode to the water
main.  

250.166(C) just seems a little unclear with respect to a water main
electrode.  I have seen a number of sites that do not have a supplemental
electrode in addition to the water main, but I suppose you could simply
install a rod, bond it to the water main, and use #6 copper for the DC GEC.

Thanks,

Garrison



-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Ray Walters
Sent: Tuesday, April 16, 2013 2:22 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Fuse sizing in battery circuits

First, a water main is no longer allowed to be used as the primary grounding
electrode by itself, it needs an additional electrode added to it 25053(D)2.
You still are required to bond to it 250.104(A)1,  but it doesn't count as
the electrode.  Also, 250.166 (C) specifically lists pipe as one of the
exceptions.

R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 4/16/2013 1:06 PM, Garrison Riegel wrote:
> Hi Ray and All,
>
> 250.166 says the GEC must be sized as specified in (A) Not smaller 
> than the neutral conductor, or (B) Not smaller than the largest 
> conductor supplied by the system, except as permitted by (C) through (E).
>
> A water main [as in 250.52(A)(1)] is not listed as an exception in (C) 
> through (E). So if the GE is a water main wouldn't the GEC "need" to 
> be 4/0, if the battery cables were 4/0?  Not saying it makes sense, 
> especially if the water main is 3/4", but this has always made me wonder.
>
> Thoughts?
>
> Garrison Riegel
> Project Manager | Solar Service Inc
> [p] 847-677-0950 | garrison at solarserviceinc.com
>
> NABCEP Certified PV Installation ProfessionalT
>
>
> -----Original Message-----
> From: re-wrenches-bounces at lists.re-wrenches.org
> [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Ray 
> Walters
> Sent: Tuesday, April 16, 2013 12:52 PM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] Fuse sizing in battery circuits
>
> Hi Drake;
>
> Read down a bit more and 250.166(C) and (D) limit the size of the GEC 
> to
> #4 or #6 max., depending on what electrode is used.
> This used to not be the case, and systems in the 90s had 4/0 cable to a
5/8"
> electrode: which just like your 1/2" pipe example was absolutely
ridiculous.
>
> R.Ray Walters
> CTO, Solarray, Inc
> Nabcep Certified PV Installer,
> Licensed Master Electrician
> Solar Design Engineer
> 303 505-8760
>
> On 4/16/2013 9:31 AM, Drake wrote:
>>
>> So, in a standard battery system, with a charge control, ground fault 
>> protection and an array, the DC system will likely need grounding. If 
>> the DC system is grounded, then the battery cables are grounded also.
>> In 250.166 (B) it says the grounding electrode conductor (GEC) shall 
>> not be smaller than the largest conductor supplied by the system.
>>
>> If the battery cables are "supplied by the system" doesn't this imply 
>> that the GEC should be the size of the battery cable?  This is the 
>> logic that has led some inspectors to require a 4/0 copper wire to be 
>> bonded to a 1/2" water pipe. This is, of course, technically absurd.
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