Determining Bus Rating for Electrical Panel

[Benihana]

Hi guys

Was curious about how other people may determine the bus rating needed for an electrical panel when designing. The way I've been taught is to determine the total amperage based off the total connected load and voltage (i..e. if 10,000 VA was connected to a 120/208V panel, the total amperage would be 27 amps (10000 / (208*1.732) ). With that total amperage, I'd multiple that by 1.25 and select the next standard size up.

Is there a better/more accurate way to do this?

 

[charlie b]

That process will work. But it might not give you the best design choice. In your example, you might have chosen a 60 amp panel, and that might not suffice for the client's needs. You need to make sure the panel has enough breaker positions and can accommodate the breaker ratings that will be used. Sometimes that will force you to select a panel with a rating well above what is needed for the calculated load.

Let me ask your reasoning for the 125%. If you are thinking you need that to account for continuous loads, my response would be that that factor is part of how you first calculated the load to be 10KVA. Some (many !) clients require the load calculation to include an allowance and for future growth, and 25% is a common amount.

 

[charlie b]

Hi guys

Guys and gals, perhaps?

 

[Benihana]

I should clarify that I'm asking about determining the required bus size specifically, not so much the spaces, etc.

 

[ggunn]

Guys and gals, perhaps?

"Guys" is pretty much taken as gender neutral these days.