[RE-wrenches] down-sizing main breaker

[Matt Lafferty]

Hi Bruce,
 
Unless you are leaving something meaningful out of your description, the AHJ
is wrong. Your description is fine as far as the code goes. I recommend
installing a 100A main in the new 200A panel for local disconnect @ house. 
 
Leave 100A main & feeder as-is (assuming safe, properly sized feeders,
suitable grounding, etc.). There is nothing in the code that says you have
to use identical size breaker to the buss rating. 
 
Try explaining it to the AHJ this way: Take the solar away from the
question. The 100A main breaker determines the MINIMUM rating of the feeders
and busbars. The busbars and feeders determine the MAXIMUM rating of
overcurrent devices. For example, using the AHJ logic, you would be
prohibited from using a #2 for feeder conductors between the 100A main and
the house because they are rated for up to 130A. Doesn't make any sense,
huh?
 
The extra ampacity in the bussing is permitted and provides additional
safety.
 
Best of luck!
 
Matt Lafferty

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Mendocino
Solar Service
Sent: Friday, July 31, 2009 9:57 AM
To: RE-wrenches
Subject: [RE-wrenches] down-sizing main breaker


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
Mendocino Solar Service
PO Box 1252
Mendocino, CA 95460
707-937-1701



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