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

[robert ellison]

Kirk,
This is out of my normal realm but i would expect the inspector to
take the breaker at it's max setting for the calculations. You could
turn it lower without a problem but i doubt he would allow a lower
setting due to it being turned up after he left.
I bet they don't give that breaker away!

Later,
Bob

On 3/30/12, Kirk Herander <kirk at vtsolar.com> wrote:
> 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
>
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>
> 802.863.1202
>
>
>
>