35k aic vs 65k aic

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Joed384

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I need to install a 200 amp breaker in this switchboard to feed a 480v panel.
The existing 400 amp breaker is a 65k AIC and it feeds (2) 480v panels.
The other breakers are 20 and 30 amp breakers at 35k AIC which feed AC units.

Does anyone know if the breaker I need to install should be 65k or can it be 35k?
 

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Joed384 said:
Does anyone know if the breaker I need to install should be 65k or can it be 35k?
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No one on this forum can answer that with the info given.

You either have to calculate the fault current (I can't do that)

Or use at least a 65K breaker and even that is assuming someone before you did the calculations correctly.
 
Because there are existing 35kAIC breakers, that makes the panel rated at 35kAIC.

Without calculating, there is no way to know if 35kAIC is the proper rating or if someone accidentally put 35kAIC's in there and it should have been 65kAIC.

Unfortunately, common practice is to match existing, which would be 35kAIC. That doesn't make it right though
 
iwire said:
No one on this forum can answer that with the info given.

You either have to calculate the fault current (I can't do that)

Or use at least a 65K breaker and even that is assuming someone before you did the calculations correctly.
Click to expand...

Im not sure how to figure out the calculations.
Do you think a safe bet would be stick with a 65k?
 
Joed384 said:
Ok I think I will match with a 65K.
I forgot to mention that this particular switchboard is also fed with an 800 amp 65k.

Thanks
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If it is fed from another breaker of the same manufacturer, chances are pretty good you could use a series rating for the downstream breaker. With a little googling you should be able to find the tested series rating combination list from the manufacturer.
 
electrofelon said:
If it is fed from another breaker of the same manufacturer, chances are pretty good you could use a series rating for the downstream breaker. With a little googling you should be able to find the tested series rating combination list from the manufacturer.
Click to expand...

Great suggestion. :cool:
 
Joed384 said:
Ok I think I will match with a 65K.
I forgot to mention that this particular switchboard is also fed with an 800 amp 65k.

Thanks
Click to expand...

It is best for you to recalculate your system as additions would mean more fault contributions especially if motor loads are added. Can you post a single-line diagram here?
 
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