690.47 (was enphase) [RE-wrenches]

[Dick Ratico]

Mark & Ray,

The first paragraph of 690.43 refers us to 250.134 where we find Exception No.
2:

"For dc circuits, the equipment grounding conductor shall be permitted to be run
separately from the circuit conductors."

The third paragraph of 690.43 then contradicts that by saying to run it with the
circuit conductors (possibly allowing us to locate it in a trench, direct buried
next to the circuit conductors). In the 2008 Code Handbook, following this, the
extra explanatory text says, "To maintain the shortest electrical time constant
in each dc circuit, the equipment grounding conductor should be routed as close
as possible to the circuit conductors. This routing facilitates the operation of
overcurrent devices."

I don't think this is true. This time constant business refers to ac circuits
not dc circuits. Additionally, the, this time helpful, Fine Print Note following
690.45(B)says, "The short-circuit current of photovoltaic modules is just
slightly above the full-load normal output rating. In ground-fault conditions
these sources are not able to supply the high levels of short-circuit or
ground-fault currents necessary to quickly activate overcurrent devices as in
typical ac systems. Protection for equipment grounding conductors in
photovoltaic systems that are not provided with ground fault protection is
related to size and withstand capability of the equipment grounding conductor,
rather than overcurrent device operation."

Dick Ratico
Solarwind Electric




Mark wrote:

Ray,

NEC 2008 690.43, "...Equipment grounding conductors for the PV array and
structure....shall be contained within the same raceway or cable, or
otherwise run with the PV array circuit conductors when those circuit
conductors leave the vicinity of the PV array."

Mark Frye
Berkeley Solar Electric Systems
271 Vistamont Dr
Grass Valley CA 95945
(530) 401-8024
www.berkeleysolar.com 

-----Original Message-----
From: Dick Ratico [mailto:Richard.- at VALLEY.NET] 
Sent: Sunday, June 15, 2008 11:39 AM
To: RE-wre- at topica.com
Subject: Re: 690.47 (was enphase) [RE-wrenches]


Ray & Mark,

This may prove controversial, but according to 2005 and 2008 NEC Article
250.134(B) Exception No. 2: 

"For dc circuits, the equipment grounding conductor shall be permitted to be
run separately from the circuit conductors."

Accordingly it would seem acceptable to bond the array GE and any and all
other GEs available, with the appropriate size of direct buried bare copper.
This bonding system would also serve as the dc equipment grounding
conductor, if one is not run with the circuit conductors. Doing this
eliminates the inductive grounding loop (but note that metal raceway, if
used, enclosing the dc cicuit conductors could also contribute to a loop),
and puts a lot of CU in the ground to help dissipate any surges. This also
reduces the likelihood of potential voltage differences between GEs, which
cause surges to travel over EGCs run with circuit conductors.

Regards,

Dick
Solarwind Electric
Bradford, VT


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