690.47 (was Enphase) [RE-wrenches]

Ray Walters walters at taosnet.com
Sat Jun 14 07:59:53 PDT 2008


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>
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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