[RE-wrenches] dial-down breakers and buss rating

[Hans Frederickson]

Kirk,
Well, the NEC just refers to the sum of the "ampere ratings" of the
overcurrent devices, which doesn't leave much wiggle room for adjusting an
800A "rated" breaker downward. I would check with your inspector ahead of
time if you want to try this approach.

-Hans



From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kirk
Herander
Sent: Friday, March 30, 2012 12:44 PM
To: RE-wrenches
Subject: [RE-wrenches] dial-down breakers and buss rating

Hello,
Here's one I haven't come across before. I am about to start a 110kw system.
This is a 480/277 three phase ac output. The calcs tell me I need a 200 amp
breaker(after rounding up from the actual breaker calc of 180.5 amps)
feeding a 800 amp panelboard which is also fed by a 800 amp utility main
breaker. Following the 120% rule no more than 960 amps can be put on the
buss. But the source input will be 1000 amps from grid and pv combined.
However, the 800 amp breaker can be current-limited down lower (in this case
at least to 760 amps) by a manual dial with calibration markings on its
face. So I would think a reasonable AHJ would accept this as code-compliant.
The only other alternative is to replace the main with a 700 amp (no
fixed-amperage breaker is made between 700 and 800 amps), which for load
reasons the owner doesn't want to do. Thanks for your comments.

A pesky inspector might say "what's to prevent some yahoo from turning the
breaker back up to 800 amps once I leave", for instance.


Kirk Herander
VT Solar, LLC
dba Vermont Solar Engineering
NABCEPTM Certified installer Charter Member
NYSERDA-eligible Installer
VT RE Incentive Program Partner
802.863.1202