Service panel feeds chiller plus another panel

[m sleem]

Just example, We have a service panel feeds chiller and another panel. The chiller load is 400kva (non-continous load) & the other panel is 100kva (50% continous load). The ocpd of the chiller is 1000a and for the panel is 200a.

The ocpd of service panel will be:
If applies (1.25*continous+1*non continous+0.25*largest motor)/400/1.73
(1.25*50kva+1*450kva+0.25*70kva (largest motor inside the chiller))/400/1.73=766a
the OCPD will be 800a

By comparing chiller ocpd 1000a vs 800a for the service panel, what is the best we can do here?

 

[augie47]

I think it would be more applicable to follow 430.62 which would allow a 1000 amp service breaker.

 

[m sleem]

Just example, We have a service panel feeds chiller and another panel. The chiller load is 400kva (non-continous load) & the other panel is 100kva (50% continous load). The ocpd of the chiller is 1000a and for the panel is 200a.

The ocpd of service panel will be:
If applies (1.25*continous+1*non continous+0.25*largest motor)/400/1.73
(1.25*50kva+1*450kva+0.25*70kva (largest motor inside the chiller))/400/1.73=766a
the OCPD will be 800a

By comparing chiller ocpd 1000a vs 800a for the service panel, what is the best we can do here?

I would think we can apply the formula of (1.25*continous+1*non continous+0.25*largest motor)/400/1.73, as long as the downstream breaker is less than the upstream breaker, but if the downstream breaker larger than the upstream breaker, the upstream breaker would be equal to the next rating of the down stream breaker.

 

[augie47]

You keep using a 1.25 factor which is normally used for conductor sizing and not OCP sizing.
Take a look at 430.62

 

[m sleem]

You keep using a 1.25 factor which is normally used for conductor sizing and not OCP sizing.
Take a look at 430.62

I would think we can use 430.62 for the first feeder, for other feeders we can get the feeder size by the above formula & the ocpd would protect the feeder accordingly.