30 amp breaker issues

[steamboat]

Just purchased a Wilton 3" X 79" belt sander. Motor is 4HP, 220 volt, 3 phase at 3456 RPM, 15.2 amps. I had a static phase converter 4 to 8 HP and attached it to the machine. I'm running 10/3 wire with a 30 amp breaker. The belt sander will start up without any issues and run strong for 30 seconds or so and then trip the breaker. Not sure if I need to run heavier wire and increase the breaker to a 40 or 50 amps. I didn't think the start up on the machine would be double the 15.2 amps and trip the 30 amp breaker. Is there any alternative to running the larger wire and breaker.

 

[Norcal]

Motor rules are different then "normal" branch circuits, & it may be fine to use a larger breaker then would be normal, but if NM cable (Romex) is used it has to be used at the 60 degree C ampacity, another thing is your static converter just starts the motor, after that it single phases, a rotary phase converter would be a better choice & then the 1/3 of the HP loss that happens w/ a static converter is not a problem.

 

[Alchymist]

Clamp on ammeter on the input to the inverter and see what it's drawing. Go from there.

 

[steamboat]

I had a rotary phase converter and sold it with another machine. I see now that was foolish. But I am running romex 10/3 wire and is dedicated to that 220 plug in. Nothing else draws on that line except what I plug in. Can I get away with putting on a 40 amp breaker and see if the motor will run without tripping the large breaker. I don't have a Clamp on ammeter to test the converter. If I have to run heavier wire I will, but not looking forward to it.

 

[steamboat]

Should of mentioned the phase converter can be changed from a 4 HP setting to a setting that allows up to 8 HP. The manual states if the motor will run not on the 4 HP setting, change it to the up to 8 HP setting. Never tried the 4 HP setting the converter can prewired on the up to 8 HP setting. Not sure if a change to the 4 HP if that would make any difference at this point.

 

[wyliesdiesels]

I had a rotary phase converter and sold it with another machine. I see now that was foolish. But I am running romex 10/3 wire and is dedicated to that 220 plug in. Nothing else draws on that line except what I plug in. Can I get away with putting on a 40 amp breaker and see if the motor will run without tripping the large breaker. I don't have a Clamp on ammeter to test the converter. If I have to run heavier wire I will, but not looking forward to it.

As Norcal already pointed out, a breaker feeding NM wire is sized on the 60c deg column so no u cant put a larger breaker on that 10/3. Also, breakers for motors are sized at 300% of FLC, which u would have to look up as i dont have my code book in front of me!

 

[steamboat]

Sorry for not picking up on that right away. Looks like a 50 amp breaker is going in. I could have used a larger breaker on numerous other occasions. Any suggestions on romex or another type.

 

[steamboat]

Pic of the Wilton belt sander

 

[wyliesdiesels]

Sorry for not picking up on that right away. Looks like a 50 amp breaker is going in. I could have used a larger breaker on numerous other occasions. Any suggestions on romex or another type.

Yes, wire is sized at 125% of FLC and unfortunately, my books are at work so i cant size the wire for u. But i know pattenp or another sparky on here will be able to.

 

[lametec]

3 phase amps are not the same as single phase amps.

If the motor draws 15.2A on 3 phase, it will draw 26.3A from the single phase supply. This is an "ideal" conversion, though, and the fact that you're using a static converter probably skews the numbers a bit.

Not that it should draw anywhere near 15.2A idling.

 

[theoldwizard1]

I didn't think the start up on the machine would be double the 15.2 amps and trip the 30 amp breaker. Is there any alternative to running the larger wire and breaker.

A rough rule of thumb is that a 3 phase motor running through a phase converter will draw about 3 time the amount of current. If it is a rotary phase converter, figure 4 times.

 

[steamboat]

Thanks to all for the information. It really helped to figure out the issue. Not sure if I want to go with romex type of wire or another option.

 

[wyliesdiesels]

Thanks to all for the information. It really helped to figure out the issue. Not sure if I want to go with romex type of wire or another option.

So based on what theoldwizard said, u need a wire rated for 57a. 15.2*3=45.6*125%= 57a. You could use either #4 NM or #6 thhn individual wire in conduit!

 

[steamboat]

Again thanks for spelling it out for me and taking the time on this... steve