pump power rating versus electricity consumption

[semenzato]

Greetings,

My pool circulation pump has a 3/4 HP motor. My electric utility (PG&E)
recently replaced my mechanical meter with a digital one and I can
see now that running the motor uses up 1.2 kW. Is this normal?
3/4 HP is about 560 Watt. Even with a 0.8 power factor and another
10% of losses I should still be under 1 kW. Or perhaps the 3/4 HP
rating doesn't really mean 3/4 HP?

Thanks!
Luigi

[mas985]

It depends on your service factor as well. Most high efficiency pumps have fairly high service factor of 1.6 or greater which makes the braking HP (true HP) higher. For a 3/4 HP pump, that is about 1.2 braking HP with a service factor of 1.6. BHP to energy use is about 75%-85% efficiency:

Kw = BHP * .746 / .75 = 1.2 kw

So what you are reading is reasonable.

[CJDahl]

I'm not familiar with the term "service factor". What does this represent and how is it calculated? thanks for any info!!

[mas985]

Service factor is determined by the motor manufacture and is usually stamped on the motor label along with the horse power. The "labeled" HP is virtually meaningless without taking into account the service factor. The true horse power of a pump (i.e. braking horse power) is the labeled HP times the service factor.

[semenzato]

It depends on your service factor as well. Most high efficiency pumps have fairly high service factor of 1.6 or greater which makes the braking HP (true HP) higher. For a 3/4 HP pump, that is about 1.2 braking HP with a service factor of 1.6. BHP to energy use is about 75%-85% efficiency:

Kw = BHP * .746 / .75 = 1.2 kw

So what you are reading is reasonable.

You are indeed correct. The service factor on my pump is 1.67.