AIC ratings on DC breakers

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AIC ratings on DC breakers

Postby zarmot on Mon Aug 02, 2010 10:35 am

Hello,

Here's an arcane topic -- interrupting capacity ratings for DC breakers, like the OBB-250-125VDC-PNL. Is this breaker rated to 10,000 Amps AIC? And how does that compare to the current surge that can be produced by a large battery bank if it gets shorted? Will there be times when a class T fuse is required in addition to the OBB?

I'm actually teaching a course on advanced battery based PV systems, and this topic has come up as a student question. I'm not having any luck digging up an intelligent answer on the net...

Thanks for any light you can shed!

Mike
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Re: AIC ratings on DC breakers

Postby Kent Osterberg on Tue Aug 03, 2010 5:53 pm

I hoped that someone from Outback would provide a timely reply to this but that hasn't happened so I'll reply based on my memory. The interrupting capacity of the 80 amp and smaller breakers is 5000 amps. The interrupting capacity of the 175 and 250-amp breakers is 20,000 amps. For some large battery banks a class T fuse located near the battery should be used; it is a good idea for all systems.
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Re: AIC ratings on DC breakers

Postby mvrck on Tue Aug 03, 2010 7:12 pm

That little red Outback sticker on the panel mount breakers says 150Vdc, 100 AIC. Normally,the Manufacter side of the breaker has 125Vdc, 10kAIC. I guess that is how they are able to list them at 150V...

Thanks

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Re: AIC ratings on DC breakers

Postby Kent Osterberg on Tue Aug 03, 2010 10:26 pm

The label on the side is certainly more reliable than my memory :wink: The 150 volt 100 AIC rating is adequate on the PV side because PV arrays are current limited. Breakers connected directly to the battery should have a fuse unless the AIC is greater than the short circuit current from the battery bank. The 125 volt 10,000 AIC for the panel mount breakers is sufficient for many (maybe most) battery banks used in RE power systems. For large battery banks a fuse may be needed. A fuse is always a good idea because it provides protection for anyone that doesn't know to disconnect the batteries before working in the dc panel.

Edited:

mvrck,

Just checked a few on my shelf and found quite a range on the labels. Some don't show a spec for AIC. Some show 10,000 ac AIC. And some show 10,000 AIC ac and 5,000 AIC dc. I think the 5,000 AIC dc is correct for all of the small panel mount breakers; that's what Carlingswitch's spec sheet shows. With a 5000 AIC dc rating even more battery banks should be protected with a fuse!
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