<html><body><span style="font-family:Verdana; color:#000000; font-size:10pt;"><div>Eric-</div><div>Sounds like you have a ranch panel. One 200 amp breaker will go to 200 amp busbars; the other does not have busbars at all but lugs for another subpanel. Generally these panels are sold with a main breaker that match the busbar rating. <br></div><div>The 120% rating is on the busbars, not the breakers per se. The busbars allow .12 x 200 = 240 amps total as the sum of grid current coming in through the main breaker plus solar backfed current.<br></div><div>One way to get more solar is to downsize the 200 amp main breaker to maybe 150 amps. Now you have an extra 50 amps allowance on top of the 40 amps allowed by the 120% rule, for a total of 90 amps solar current. </div><div><br></div><div>We just did something like this with a new 600 amp subpanel. With a 600 amp main breaker it would allow .12 x 600 = 720 amps total, so only 720-600=120 amps solar allowed. But with a 400 amp main breaker then 720-400=320 amps is allowed for solar current to accommodate this 55 kW system at 208 VAC. <br></div><div><br></div><div><br></div>
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From: <a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a><br>
[<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] On Behalf Of Chris Mason<br>
Sent: Thursday, December 19, 2013 2:41 PM<br>
To: RE-wrenches<br>
Subject: Re: [RE-wrenches] Busbar rating with multiple main breakers<br>
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The 120% rule refers to source breakers, not load breakers. <br>
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On Thu, Dec 19, 2013 at 3:16 PM, SunHarvest <<a href="mailto:eric@harvesthesun.com">eric@harvesthesun.com</a>> wrote:<br>
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Hi guys -<br>
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Concerning the 120% rule: I've encountered several circumstances recently<br>
where a 400A nameplate-rated (listed on inside label) main panel has two<br>
200A main breakers. One of the breakers will be feeding the busbar in the<br>
main and the other will feed a subpanel. I had previously thought the main<br>
busbar is rated at the nameplate rating (400A in this case) regardless of<br>
quantity of main breakers. My lead electrician says the main busbar in these<br>
types of panels is derated to 200A because of the split. However, I have two<br>
other reliable electrician friends who disagree with my lead electrician.<br>
One of my C10 buddies says it depends on whether or not the busbar in the<br>
main is broken up into 2 sections (200A) or it is continuous (400A). Can<br>
anyone clear up, beyond doubt, our disagreement?<br>
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Thanks!<br>
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Eric Stikes<br>
SunHarvest<br>
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