Break Horsepower vs Nameplate for Service Calculation

[buddy91082]

Hi there.

We are trying to right size our electrical service. We asked the mechanical engineer if there was any "fluff" in their pump and motor sizing. They said yes. For example, the calculated BHP on one pump is 23 bhp. They selected a 30hp motor (a 23% increase). We ere thinking we could use the BHP selections for our service calculations but for individual motor and pump wire and overcurrent protection we would use the nameplate ratings per the National Electrical code.

Any reason not to use the BHP in our service sizing calculations?

Thanks.
b

 

[davidbeach]

Other than the NEC requirements, no there's no reason not to use the BHP...

Geez, do it right.

Oh, and by the way it would be Brake Horsepower.

 

[Parchie]

Choosing an oversized motor may allow your motor to be able to carry the actual load if and when the actual process head was wrongly computed (actual head is higher than the hydraulic calculations of your designer). BTW, 30/23 mean a 30% oversizing. This value is what I usually see on most of the pump installations that I saw. If the 30 HP motor is still too small, your options are to throttle the discharge valve of your pump or ask the mechanical people to trim the impeller a bit so your motor doesn't overload.

 

[waross]

By all means use calculated BHP for a reality check for serious mistakes when the service is sized right according to the NEC.
But don't try to "Right Size" the service.
"Size it Right" according to the NEC.

Bill
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"Why not the best?"
Jimmy Carter