Are three-phase contactors rated per pole or in total? For example, have a look at this datasheet for a random three-phase contactor: datasheet
In the datasheet it says that for AC-3 loads (1) the rated operational current [Ie] is 32 A, and (2) the motor power rating is 7.5 kW at 220..230 V. These numbers match, since 32 A * 230 V = 7360 W.
On the Technical FAQ pages of this manufacturer it says:
"Contactor current ratings are per pole. For example a contactor rated 40 amps AC3 could switch upto 40 amps AC3 on just one pole or on all the other poles." (see source)
What I'm confused about is that motor power rating is usually not declared per pole, but in total. So if I use 10 kW contactor for a 10 kW motor, my contactor if oversized by a factor of 3. Is this correct, or I'm missing something?
Best Answer
I think the calculation is not that easy because:
I think the powers that are given in the datasheet you write about is the one you can find for standard motors. For example, here is a list of AC 3 phase motors from Emerson/Leroy-Somer:
For example, a 4kW motor at 415V (voltage difference between two phases) 50Hz has a rated current of 8.2A and a power factor of 0.81. We could calculate its efficiency:
$$ \eta = \frac{4000} {\sqrt{3} \times 415 \times 8.2 \times 0.81} = 0.84$$
Now, if we take the datasheet for contactors from Schneider (TeSys Green) (I think this is approximately the same products you gave the datasheet):
We can see that for a 4kW/415V motor, we have a 9A current. This is just above the 8.2A of the aforementioned motor.
Also, when you read motor datasheets, you will see that standard output powers are the same given in your document: 7.5kW 15kW 18.5kW...