Gridtie, breaking grounded conductor [RE-wrenches]

[Jason Fisher]

Bob,

You can break the grounded conductor only if you simultaneously break
all un-grounded conductors so he's not off-code on that one but this is
a pretty silly reason to "require" this! My question (and for future
situations!) is did anyone whip out a voltage tester and show that there
is no potential from negative to ground? He probably just got bit from
capacitance build up in the insulation; isn't it always raining there in
Oregon?

A question I would ask with regards to the roof-mounted disconnect is
why? There is no code requirement for this. If they say they want the
disconnect for safety during maintenance then say "sure" and show them
how a mechanic can pull apart an MC connector to isolate certain parts
of the array. If they say these are not load-break then point out how
the DC disconnect at the inverter IS and is lockable and discuss how
proper OSHA procedures require lockout and tagging of disconnects. I
hope they would understand why it actually makes sense to have the DC
disconnect near the inverter, since this is where someone working on the
inverter would want to isolate all sources of power (without climbing on
the roof to do it!). In my experience, the desire for a disconnect
"readily accessible" at the array comes from a fear of the unknown and
not an understanding of real hazards. Explain how this is not a motor
that could grab your shirt while you're working on it, thus demanding an
immediate disconnect. If you are feeling bold, point out how
disconnecting the array from the inverter does absolutely nothing to
reduce the potential of shocks from an array in the sun (but watch out
with this one as this may open a whole new can of worms!).

My advice, gather some good materials, study all the hot button code
references (look to Wiles), go try to setup a casual meeting with your
inspectors (including the chief), buy donuts (as I believe Matt once
wisely suggested!), hand out selected materials, and talk things over as
a group without having to do it in the field. Many times other
inspectors will say things to their fellow inspectors that you would
only dream of saying (i.e. "you idiot, it doesn't work that way!"). From
there do exceptionally clean work and ALWAYS meet the inspector, no
matter how much of a pain this is. The only job that I didn't get passed
on the first shot was when I wasn't there to meet the guy. I think they
take offense at this!

Best,

Jason Fisher
Aurora Energy 
Annapolis, MD

-----Original Message-----
From: Bob Maynard, Energy Outfitters [mailto:bob at energyoutfitters.com] 
Sent: Tuesday, February 24, 2004 2:01 PM
To: RE-wrenches at topica.com
Subject: [SPAM] - Gridtie, breaking grounded conductor [RE-wrenches] -
Email found in subject

Wrenches,

Now that Oregon has a gridtie rebate program (severely under funded), we
are starting to feel many of the inspector related issues that have been
discussed before.  Oregon's program in addition to inspection by the
AHJ, must pass inspection by the rebate program's own inspectors.  The
contractors in certain Oregon jurisdictions are being told by the AHJ's
inspector that a  dc disconnect is required at the array on roof mounted
arrays, any advice is appreciated on the best way to address this.

More importantly is a recent issue brought up by a program inspector.
What could be happening?

The inspector said that he received an electrical shock from the
negative conductor within the dc disconnect of a standard residential,
battery less, PV system. At first, this seemed very odd to me since the
unbroken conductor should be bonded to ground and thus possesses the
same potential as ground. Upon further discussion with him,  he is
convinced the system is ungrounded since the grounding bond occurs on
the ac side and the GFI prevents the proper dc grounding. He contends
that the bond needs to occur at the source; the PV array. I am still
puzzled about this. Since the grounded bond occurs within the inverter,
does this not properly perform the bond required between the negative dc
conductor and ground. Could there possibly be a capacitive charge build
up. If so, how is it possible with a bonded connection to ground?  His
recommendation now is that the dc disconnect must break the array
positive AND negative.

We've got some real pro's on this list and I look forward to their
input.

Regards,
Bob Maynard
Energy Outfitters

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