Cable size calcs for motor

[flyingsparks]

I need to put a supply in for a 22A FLC 3ph motor (fan unit). Cable length is about 100m.
I am not sure on the motor connections as inside the terminal box there is just the 3 line conductors, and no options to fit star/delta links.
What would be the maximum permissible volt drop on start up without it causing problems, I believe 15% is OK?
Based on this, 3.8mV/A/m 10mm cable will give me a 40V drop (approx.) at 100m and with a start up current of 120A.
Thoughts?

 

[ericmark]

It is as much down to what it drives as the motor its self. Using a resistor start is a valid method of starting a motor, I have seen where contactors have failed causing the resistor to stay in circuit, and of course resistor gets very hot, but it did not affect the motor. However with refrigeration volt drop is a real problem. So if only driving a fan then you could ignore to some extent the start amps, at least as far as volt drop goes, as it does not matter how fast it gets to speed.

How is it being started? and where is the starter? If the starter is local to motor then there will be a volt drop on the starter, if remote then no volt drop, at those amps not really a good plan for direct on line, as well as the electrical shock there is also the mechanical shock to the system, many options today, electronic soft start or inverter, or a resistor start or even an auto transformer although the latter rather expensive for a fan. I have seen fluid coupling to reduce the mechanical strain but most large fans I have worked with were resistor start. Maybe showing my age?

 

[flameport]

I believe 15% is OK?

Perhaps, depends on the motor.
Also consider cost of large cable compared to much smaller cable & a soft starter.

inside the terminal box there is just the 3 line conductors,

Of the style where you bang the power on and hope it gets up to speed before flames appear.

 

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