[RE-wrenches] DC positive and negative in same conduit, other inspection issues

[August Goers]

Dave,

Do you have any photos? -August

________________________________________
From: re-wrenches-bounces at lists.re-wrenches.org [re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Dave Click [daveclick at fsec.ucf.edu]
Sent: Wednesday, August 19, 2009 2:41 PM
To: RE-wrenches
Subject: [RE-wrenches] DC positive and negative in same conduit,        other inspection issues

All,

Couldn't find this anywhere in the archives; sorry if it's a repeat. I
just went out to inspect a ground-mount system that had 3 source
circuits feeding a metal DC combiner/disconnect. Wiring was free air
until it got near the disconnect, then the positive wires entered an
open 3' section of FNMC (no strain relief or box at the other end of the
FNMC). The negative wires ran through a *separate* 3' section of FNMC.
The array had N-S-run support rails, and along the top of each rail was
run a #6 bare continuous through Wiley lugs that ran to a ground rod on
the west end. This #6 bare used split bolts to connect #6 bare taps to
the disconnect switches, with the #6 bare entering a separate knockout
from the positive and negative wiring conduits, with strain relief
provided by... a romex cable clamp. This was then repeated on the rest
of the 75kW array.

So I found the following corrections:

1. Running the positive and negative wires through separate conduit
violates 300.3, and could cause eddy currents in the combiner/disc boxes.
2. Running the equipment ground separately from the +/- wiring is also
not code compliant
3. Using romex cable clamps for something other than Romex is also less
than correct, and I imagine that has some effect on the UL listing or
warranty of the NEMA 3R box (at least the clamp is in a bottom knockout,
but still)
4. When entering the open conduit with USE-2 home runs, you need to have
some kind of strain relief; I usually recommend liquid-tight cord grips,
against the wishes of 98% of the installers that I speak with.

For the grounding electrode wiring, it seems that it's fine to me since
they ran the continuous #6 to each rail and then to the rod, qualifying
as the 690.47(D) supplemental electrode. But the split bolts tapping
that GEC to "ground the disconnect," these are required to be
irreversible connections to the ground bus in that disconnect, right?

Did I miss anything? Thanks for reading this far and for the backup.

Thanks,
DKC
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