[RE-wrenches] down-sizing main breaker

[William Miller]

Dick:

I disagree with your plan.  To qualify as a supply side tap, the tap needs 
to be on the supply side of the main disconnecting means,  If I understand 
your plan correctly, your suggestion does not achieve this.

Bruce:

Your inspector is correct -- not in his interpretation of the code -- but 
in the reality of implementing your plan.  I wrote in this forum recently 
(6/25/2009) of the difficulties we had in down-sizing a main breaker 
because no manufacturer has made provision for this in meter/main/combo 
(m/m/c) panels.

In the situation cited, we had the capability of back feeding 75 amps into 
a 100 amp m/m/c.  There was not enough PV to allow this, but the three 
Xantrex XW6048 inverters had a combined sell capability of 75 amps.  In 
reality, for a short time after a utility outage, these inverters could 
battery-sell up to the 75 amp capability.  Our best solution would be to 
install a 200 amp meter panel with a 100 amp breaker.  The application is 
an agricultural based residence, so based on how one interpreted this, the 
back feed allowance would be either 100 amps or 120 amps, enough to cover 
our back feed.

We were told by a supplier that we could purchase a 200 amp m/m/c and field 
retrofit a 100 amp breaker into it.  We requested the supplier contact the 
manufacturer (GE) and obtain confirmation of this claim.  We were assured 
that this was possible.

Based on the assurances, we bid the job and won the contract.  When we 
purchased the equipment we found that the 100 amp breaker could not 
physically fit into the 200 amp m/m/c.  We spent a full day calling GE and 
then other manufacturers only to find out that no one builds a 200 amp 
m/m/c that can fit a 100 amp main.  All of the panels we looked at were 
cleverly configured to not allow the smaller breaker to be held in place.

Has anyone out there found a 200 amp m/m/c that can fit a 100 amp main?  If 
so, I want to know.

We ended up jury rigging a 100 amp main into a Square D Home-line "ranch" 
panel, against manufacturer's recommendations.  The retrofit was solid, but 
we essentially violated the listing.  I did not like doing this, but we 
were in a corner.

In my earlier post I point out the fact that electrical equipment 
manufacturer's are behind the times in implementing equipment that can 
adapt to the new requirements for solar electric systems.  Now that 
Schneider, owners of Square D, now own Xantrex, maybe there can be some 
"cross-pollination" of ideas so that Square D can build meter panels that 
allow installation of down-sized main breakers.  I can see no reason why it 
would be unsafe or unfeasible to allow this to happen.  I am cc'ing Mark 
Edmunds of Xantrex with this e-mail in hopes it will draw his attention.  A 
memo from him on Xantrex letter head may have enough credibility to get the 
attention of Square D engineers.

Sincerely,

William Miller





At 04:11 AM 8/1/2009, you wrote:
>Bruce,
>
>This sounds like a good situation for a line side tap,
>rather than going to all the work of replacing the panel.
>
>Turn off main breaker at the pedestal, no need to touch the meter.
>At the house, pull the feeder out of the panel.
>Put it into a proper new junction box. Splice
>one set of new conductors to refeed the panel and another
>new set of conductors to feed a new small panel for the solar.
>
>Dick Ratico
>Solarwind Electric
>
>
>--- You wrote:
>Hi Folks,
>
>Can anyone provide code reference or advice on this question?
>Our customer has 100 amp service at the meter pedestal, 100 amp main
>breaker feeding 200 foot underground run to a 100 amp panel at the
>house. We need to land a 40 amp breaker, so are proposing to replace
>main panel at house with 200 amp panel. The AHJ says we need a 200
>amp main breaker in this panel, which will work, but says this
>requires upsizing the feeder, main breaker at meter, and therefore
>utility service to 200 amps.
>
>I've read on this list and elsewhere about downsizing the main
>breaker in a panel to create capacity to make the 120% rule. This AHJ
>says you can't put in a breaker smaller than the panel size, and
>furthermore, everything upstream would have to be upsized. Is this
>from the code?
>
>Bruce Erickson
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20090801/f75cfe29/attachment-0003.html>