Gridtie, breaking grounded conductor [RE-wrenches]

Tue Feb 24 18:16:32 PST 2004

Test to see if a circuit is hot before touching it? Mr. Touchie-Feelie is a
future candidate for a Darwin Award!

----- Original Message ----- 
From: "Jason Fisher" <jfisher at nahbrc.org>
To: <RE-wrenches at topica.com>
Sent: Tuesday, February 24, 2004 2:43 PM
Subject: RE: Gridtie, breaking grounded conductor [RE-wrenches]

> 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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