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charlie b

charlie b

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Quick check please. A 225 amp breaker in a distribution panel feeds an overhead plug-in busway in a new lab building. The busway is rated 225 amps. None of the equipment to be eventually plugged in has been selected yet. So I calculated the KVA equivalent of three phase, 225 amps, divided it by 3, and put that value on each phase of the panel schedule as the busway load. The client is now telling me that I should have multiplied this value by 80%, because of the 80% rating of the breaker. My view is that the total load (all 225 amps) represents 100% of the non-continuous load plus 125% of the continuous load, and that I can therefore show (on the panel schedule) a load of 100% of the breaker's rating.

What say ye?

(I will probably do what the client wants anyway, but I prefer knowing that I was right-if indeed I was right.)
 
I agree with you on this.

If for example, you actually knew the loads to be connected and you performed the load calculation taking into account the continuous and non-continuous loads and came up with 225 amps it would be permissible to feed these loads from a 225 amp rated breaker that, in and of itself, would not have to be 100% rated.

All of this is, of course, just my humble opinion.

Pete
 
charlie b said:
...What say ye? ...
Click to expand...
I like it.

Just curious:
Is there trouble with the up-stream feeder rating to the distribution panel with the number you used?

Is this for one of the university's and their EE department is reviewing?

charlie b said:
... (I will probably do what the client wants anyway, ...[/quote]
Yes, I like that one too

charlie b said:
... but I prefer knowing that I was right-if indeed I was right.) ...[/quote]
Yes, that too

cf
Click to expand...
Click to expand...
 
Thanks, Pete and CF. This is for a university, but not a local one. I'll give you a hint. The number I showed for each of the three phase loads was 50 KVA. We are working under an architectural and engineering company, and my client is their head of electrical engineering services.
 
charlie b said:
Quick check please. A 225 amp breaker in a distribution panel feeds an overhead plug-in busway in a new lab building. The busway is rated 225 amps. None of the equipment to be eventually plugged in has been selected yet. So I calculated the KVA equivalent of three phase, 225 amps, divided it by 3, and put that value on each phase of the panel schedule as the busway load. The client is now telling me that I should have multiplied this value by 80%, because of the 80% rating of the breaker. My view is that the total load (all 225 amps) represents 100% of the non-continuous load plus 125% of the continuous load, and that I can therefore show (on the panel schedule) a load of 100% of the breaker's rating.

What say ye?

(I will probably do what the client wants anyway, but I prefer knowing that I was right-if indeed I was right.)
Click to expand...

Agreed, given that you seem experienced enough to make a good engineering judgment. If I had ABSOLUTELY no idea what the load was I might consider 30-50% of it as continuous & use the 1.25 multiplier (assuming 80% rated OCPD). Since it sounds like you've worked on similar projects before and probably assumed, likely with good reason, that the entirety of the load is non-continuous I think your logic is fine. BTW, I pretty much did the same thing (assume all non-continuous) for plug-in busways for the boeing co. in one of their testing rooms. It passed the city plan check + boeing eng. review just fine. Finally I agree that you should just do what they ask - since you don't really know what the load is it really makes no difference and you'll keep the client happy.
 
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