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

[Kirk Herander]

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

 

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