18kA.
Mike
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| Weakest link circuit breaker? https://brainfiller.com/arcflashforum/viewtopic.php?f=4&t=5420 |
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| Author: | DMB5mil [ Wed Mar 03, 2021 3:03 pm ] |
| Post subject: | Weakest link circuit breaker? |
Say I have a 480V branch panel with a main breaker in a panel that is rated 65kA , and a bunch of branch breakers each also rated 65kA. I also have a few branch breakers that are rated 18kA. Is it 'correct' to consider the panel itself as therefore only rated at 18kA or at the 'weakest link' breaker wise in the panel? If my fault calcs indicated 20kA at the line side of the main breaker, the 18kA breakers are technically threatened since they are within the same enclosure, right? I should swap out those 18's for 65's. Does that sound right? Thanks for your time, Brian |
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| Author: | mpparent [ Wed Mar 03, 2021 3:17 pm ] |
| Post subject: | Re: Weakest link circuit breaker? |
18kA. Mike |
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| Author: | wbd [ Thu Mar 04, 2021 5:36 am ] |
| Post subject: | Re: Weakest link circuit breaker? |
If the main breaker is rated at 65kA, I think the panel would be rated higher than the 18kA breaker as a manufacturer is not going to put a 65kA breaker in a low rated panel. I don't have the info with me but I believe standard panel ratings go something like, 10kA, 22kA, 42kA. Did you see if that 18kA breaker is series rated with the 65kA breaker? |
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| Author: | mpparent [ Thu Mar 04, 2021 2:25 pm ] |
| Post subject: | Re: Weakest link circuit breaker? |
Never know Barry...maybe someone came in after the fact and installed an 18kA breaker (seen it happen all of the time). Good point about series rating... Mike |
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| Author: | wbd [ Fri Mar 05, 2021 6:11 am ] |
| Post subject: | Re: Weakest link circuit breaker? |
Yes, Mike, I had thought of that and that is a reason why on all my labels, I include the short circuit fault current at that location. I hope it will help to stop under-rated breakers from being installed in panels. By code, if it is a series rated system it needs to be labeled as such. |
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| Author: | Leonard [ Mon Mar 15, 2021 6:40 am ] |
| Post subject: | Re: Weakest link circuit breaker? |
Hi All, I agree with Barry, why would an electrical equipment manufacturer install a 65KA breaker in a much lower rated panel. It sounds like someone, perhaps an outside contractor has been installing some breakers in your panel without considering the short circuit ratings. If your fault current calcs indicate 20KA on the line side, then true enough that 18KA breaker could be threatened. Can you consult with the manufacturer or perhaps find out what the actual KA rating is of the panel and then install the correct KA rated breakers accordingly? |
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| Author: | wbd [ Mon Mar 15, 2021 7:21 am ] |
| Post subject: | Re: Weakest link circuit breaker? |
Typically the panel SCCR is located inside the panel on a paper label. Many times I have seen this label non-existent in a panel, usually due to age of panel. |
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| Author: | wilhendrix [ Mon Mar 15, 2021 7:57 am ] |
| Post subject: | Re: Weakest link circuit breaker? |
A couple of options. First, I'd look at both symmetrical and asymmetrical fault current at the panel. It likely the asymmetrical fault current is higher. No matter, you'll be ahead of the game if you install that level AIC rated breaker or more. Most (newer) breakers have a maximum AIC listed on them. Depending on the manufacturer, your cost for a higher AIC rated breaker may not be much more than just getting the minimum rated AIC. You may end up getting something much better for a just little extra cash. Good luck. |
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