circuit sizing help

[rvieceli]

I'm going to be running a 2 hp three phase motor off a vfd in my shop. The motor plate says 5.4 amps at 220. It's for a table saw so the vfd not doing anything fancy.

My question is what size should the 240 circuit feeding the vfd be? It is wired with #10 romex.

Thanks in advance.

Ron

 

[matt_i]

I go about it like this.

2hp * 750 W/hp = 1500W

1500W x factor of 2 for inrush = 3000W

3000W / 240vac = 12.5 A

I would breaker at 15A. You can always leave the #10awg in place.

The VFD should have its own overcurrent protection for the motor built in.

(I realize its 745W/hp but the above is conservative when sizing)

 

[sberry]

Yes, 15 most likely.

 

[Bert_]

Given the same amperage, 3 phase carries 1.73 times the power of single phase.

So since your motor at full load draws 5.4 amps on a three phase line, it will require ~9.5A from a single phase line.
Your wire should be sized to 125% of this value, #14 would be enough.
The breaker can be sized 250%, but with a VFD there really isn't a need to go that large as the startup surge should be minimal. A 15A breaker would be fine in my opinion.

 

[rvieceli]

Thanks