dedicated AC disconnects [RE-wrenches]

[Joel Davidson]

Greetings from LADWP (aka Relic-land),

Yesterday, at LADWP's new rebates training session we were told that a utility tech has to specify where the visible, lockable AC disconnect switch is placed and that repair crews sometimes forget to turn PV systems back on so if you notice that your PV system is not producing power because it is still locked out to call LADWP and they will send someone out to unlock your PV system. Once again, LADWP recidivism trumps years of negotiating disconnects 8 feet or within sight of the billing meter and months of a union inspired PV system lockout.

Wearily yours,
Joel Davidson

-----Original Message-----
>From: Geoff Greenfield <Geoff at Third-Sun.Com>
>Sent: Aug 24, 2006 6:41 AM
>To: RE-wrenches at topica.com
>Subject: RE: dedicated AC disconnects [RE-wrenches]
>
>
>Hi Andrew -
>
>This is a relic of an issue and hopefully more and more utilities will be
>going the way of your DC utility (and some west coast and one of the
>utilities in our service area, Duke/Cinergy.)  Most of the utilities we work
>with require a "visible, lockable, exterior disconnect".  We have been
>educating them that this is redundant, never used, and a (most effectively)
>that many utilities are skipping this requirement.  The utility linesman
>still has the ability to pull the meter, but again, it is a non-issue.
>
>This can be a very big expense in a school or large commercial building
>where you could have a short, easy AC home run to the closest sub panel VS a
>long difficult Home Run to an appropriate exterior wall, then back to a
>point of interconnection (and factoring in AC voltage drop and the price of
>copper doubling every six minutes).
>
>Battery based systems with inverters listed for interconnection meet the
>same standard.  You still need a way to isolate the inverter as per NEC -
>often most easily done with the back fed AC breaker if you are next to the
>panel, otherwise a non-fused Air Conditioning Disco is the low cost option.
>While Fronius does have built in AC breaker - this (and their built in DC
>breaker) does not meet a strict interpretation of the code.  The Xantrex GT
>set up does, with the "mothership/docking" top and bottom set up.
>
>Question:  Has anyone successfully argued that an exterior DC disco (pole
>mounted for example) or wind tower mounted AC disco would meet this utility
>requirement?
>
>For a brighter energy future,
>
>Geoff Greenfield
>NABCEP Certified Energy Practitioner
>
>THIRD SUN SOLAR & WIND POWER Ltd.
>340 West State Street
>Athens, OH 45701
>
>www.third-sun.com
>(740) 597-3111
>
>
>Date: Wed, 23 Aug 2006 22:32:47 -0400
>From: "Andrew Truitt" <atruitt at gmail.com>
>Subject: dedicated AC disconnects
>
>
>
>
>When I installed in California UL listed AC disconnects were mandatory
>within 9' of the main meter.  Now I'm installing in DC and no such
>regulation exists. I am wondering if dedicated AC disconnects are really
>necessary for inverters with built in AC discos and automatic shut-off at AC
>signal loss considering a) there are always 2 means of disconnection - the
>breaker and at the inverter and b) the grid will not be backfed as long as
>no signal is present, eliminating the need for the linesman to be able to
>disconnect the system.  2 caveats:
>
>1) Maybe, in the process of testing the lines during an outage, AC signals
>are sent down the lines that could potentially restart the inverter.  Though
>as soon as those signals ceased so would the inverter so I don't see it as a
>problem.
>
>2) I have very limited experience with battery/hybrid systems so if they
>raise special circumstances then please enlighten me.
>
>Andrew Truitt
>Standard Solar
>
>
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>


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