[RE-wrenches] Fuse sizing in battery circuits

Wed Apr 17 09:06:03 PDT 2013

A "metal underground water pipe" is still a "pipe" in all cases, so I 
think I'm missing your inspector's logic.  A water main is always going 
to be made out of pipe, so I think the exception to 250.166 (C) should 
always apply. (unless some places make them square?;-) ) The difference 
in pipe between 250.52A1 and A5 is that one is a pipe set in the ground 
by an electrician with the sole purpose of being a grounding electrode, 
while the other is used for water and is set by the plumber.  The reason 
I heard that water lines into the house had to have supplementary 
grounding is that they often transition to PVC and so aren't always 
continuous metal.  They also might be cut and changed later by a 
plumber.  That also was a change from earlier code, that used to allow 
the water main to be used as the sole grounding electrode.  EIther way, 
250.166 does not make a distinction, it just says "Pipe" and would cover 
all GEC connections.

The 4/0 GEC horror stories probably are from earlier editions of the 
code.  BIll Brooks can tell us when that changed.  My guess is that it 
was a pre 2002 code requirement, as I saw that on 90s PV systems.
Your final suggested install should be code compliant with all the 
various NEC sections (IMHO); just use a lay in lug type pipe grounding 
clamp, to keep the GEC continuous to the rod.
Some of this code stuff makes you wonder whether we should have studied 
law to be a Wrench.....(ugh)

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

On 4/17/2013 7:44 AM, Garrison Riegel wrote:
> 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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