690.47 (was Enphase) [RE-wrenches]

Drake Chamberlin Drake.Chamberlin at redwoodalliance.org
Sun Jun 15 19:48:44 PDT 2008


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Hi Ray,

Thank you for your post.  This is an issue that I've been thumping on 
for years.  I had thought that we got rid of the mandatory ground 
loop with the 2008 Code, but you are right that Exhibit 690.8 shows a 
ground loop.  I hope this was left in by mistake.  690.47 (c) has 
certainly been rewritten, and this requirement doesn't seem to me to 
be in there.

After many rereads of the 690.47 (c), I finally see how we get by 
with a conductor smaller than #8 between the AC neutral bar and the 
inverter ground connection.  The wire is considered a jumper on the 
load side of the service, rather than a grounding electrode conductor.

"690.47 (c)(3)
A conductor that serves as both an equipment grounding conductor and 
as part of the bond between ac and dc systems for an inverter 
incorporating dc ground-fault protection shall meet the requirements 
for equipment bonding jumpers in accordance with 250.102 "

This seems like an appropriate rule to me. I believe that a wire 
sized in accordance with Table 250.122,  as allowed for equipment 
bonding jumpers on the load side of the service, is certainly 
adequate for grounding.  It seems totally in line with the 
protections required in the rest of the Code.

Drake


At 08:59 AM 6/14/2008, you wrote:


>I'm all for better grounding, but if we're not careful with the
>interpretation here, we're going to start creating ground loops.
>If you bond the array directly to the GE, and tie the array to the
>premise's grounding through the EGC;
>you will create an inductive loop if you make any other connections
>to the array's GE (say a bare #6 back to the premise's ground rod, or
>even back to the inverter's ground bar)
>An inductive loop will be subject to lightning induced surges.
>Article 690.47 D) though intended to help with lightning, actually
>could cause more trouble than it cures if not carefully applied.
>Even the pictures in the 2008 NEC Handbook (Exhibit 690.6) shows the
>supplemental array GE but it is labeled "optional".
>This picture also clearly shows a ground loop created by bonding the
>AC & DC electrodes, while all their EGCs are connected as well.
>Considering the AC & DC ground systems are already bonded through the
>EGCs, I would NOT further bond them directly.
>Exhibit 690.4 shows 2 loops and an interesting AC load center that is
>grounded through the Inverter chassis.
>  I always thought you had to have a GEC from the AC load center
>(picture seems to contradict 690.47C(6))
>and what? Now there's no supplementary ground off the array  (what
>happened to 690.47(D)?
>I paid extra for the Handbook, so I could understand this better.
>The more I study the pictures and read the new text in article 690,
>the more inconsistencies IMHO.
>I can date a system by what weird requirements for grounding were in
>place at the time of installation. (remember 4/0 cable as the GEC?)
>  It seems we'll soon have vintage 08 systems to redo later.....
>Why do I think we're going to have more ground connections required
>by AHJs that will quietly have to be removed after inspection to
>actually insure some lighting protection?
>
>Ray
>
>
>
>
>
>
>>In any case, you have to run an additional GEC (separate from the
>>DC system
>>GEC/EGC run as a single conductor from the inverter) from the array
>>to this
>>new GE.
>>
>>Mark Frye
>
>
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