I inherited a 1972 Unisaw 3hp 3Phase motor. I have a 30 amp breaker going to my detached garage with a sub panel of 4 15amp breakers. The VFD to run the saw has an input of 230V single phase 28.5amps (I am not sure if this is the correct amount of amps, seems kind of high) and an output of 230V 3phase 10A. The saw motor is a 230/460V 7.4/3.7A wired to 230. My house box is 200amps. What do I need for a breaker and wire gauge to run the saw and still have power to spare? Can I do it combining 2 of the 15's in the garage and making a dedicated circuit or do I need to switch the 30amp from the house panel to a 40amp and switching the 15's to 20's (2 20amps and one 40 amp)?? Just trying to get some answers before dumping money into this adventure. Thank you all.

Me again. This is the exact VFD that I have.

3HP 230V GE 1PHASE VARIABLE FREQUENCY DRIVE NEW D5815 - eBay (item 360209423814 end time Apr-18-10 04:53:23 PDT)

I or you should find the manual.

There is a 1.73 (sqrt(3)) factor on the 3 phase side and there are 3 converters that are probably around 85% efficient, so that's likely where the discrepancy comes from as well as the power factor of the connected motor.

Tk is going to have to deal with this one.

Anticipating the following questions to be asked:

How far away is the garage?
4 wire feed?
What's the current wire gauge?
Ground rod for garage panel?
Easy to change wire size to garage?

I think your hung up on the fact that breakers need to be less than or total the feed breaker. Loose that notion. The main breaker can act as a disconnect in the garage and can be higher than the feeder. e.g. you can have a 125 A panel with a 125 A main breaker in the garage fed from a 60 A breaker. The wire would be sized for 60 A, 240. The 125 A breaker can act as the required disconnect since the garage is detached. Ground rods are typically required for detached structures with a 4 wire feed. Neutrals and grounds are separated at the sub-panel and a ground bar kit may be required for the panel to do so.

Just a little heads up, for now.

<moved from Electrical Engineering>

Based on the details given, and I can find by reviewing the datasheet for the GE Model # D5815, see attached, the VFD alone would need a 40 Amp feeder.

The datasheet does not give the input max amps of 28.5 amps mbranum provides, but sounds correct. Odd that GE does not provide any input amp data, since NEC 2008 Section 455.4 states the nameplate of a phase converter needs to state input single phase input amps. Perhaps because this is a phase converter bundled in a VFD is how they were able to not need to provide this data. Somehow Mbraunum does provide the input amps.

The feeder for this VFD and motor needs to be sized by the 28.5 input amps, therefore the 40 amp feeder is required.

To have one feeder for the motor and the existing outlets, a min 60 amp feeder is needed.

A 60 amp feeder using conduit and pulled wire, can be 3- #6 THHN/THWN copper wire with one #10 green THHN/THWN as an equipment ground, assuming 100 feet or less.

A panel in a detached garage will need a main breaker or no more than 6 branch circuit breakers to act as a disconnect, and at least one ground rod grounding the equipment ground bar in the panel. The neutral bar shall not be bonded to the equipment ground bar or the panel box.

The panel in the garage would then need the 40 amp breaker for the VFD/motor feeder.