TS wiring: 220 to 115

[Tim Allaire]

Is it possible to rewire a 3hp phase 1 220v tablesaw to 115v plug if it is on a 20a circuit? Other than power loss on ripping will it work? What harness do you need to accomplish this (if possible)?

[Art Mann]

No. :( The rest of this message is to meet the odd requirement for a minimum of 10 characters.

[Ken Garlock]

I think the answer is NO.:) Somewhere on the saw motor or the saw cabinet, you should be able to find the full load amperage, FLA. On my 3hp cabinet saw, the rating is 13 amp at 240 volts. When you rewire for 120v, you automatically double the current load. So now you are looking at, say, 26 amp FLA. Plus you need to have a safety factor built in, say 20%, so add another 4 amps an you are talking a 30 amp circuit. That in turn requires at least 10 ga wire.

Your best bet is to get a 240v circuit installed.

[Rob Russell]

You might be able to rewire the motor to 115, if the motor allows it. The real question is how much current the motor would draw at startup and whether that would trip the breaker. Once the motor's running, you could probably take it easy and keep the amperage draw below 20 amps.

I do agree that running a 240v circuit would be best, although I realize that might not be an option. Rewiring the motor and pushing the circuit's limits would be my last resort.

[Tim Allaire]

Thanks. I think I am just going to have to put a 220v circuit in to accomodate the saw. More time and headache, but it is the only way.

[Greg Mann]

Thanks. I think I am just going to have to put a 220v circuit in to accomodate the saw. More time and headache, but it is the only way.

If the motor is three phase as you originally stated you will need three phase 220. Residential 220 is single phase. If you have access to three phase and are comfortable about springing for the cost of hooking up it will give you lots of options on other used equipment. Machines with three phase motors are usually a lot less money because fewer folks can hook them up. Three phase 220 is great if you can get it.

[Thom Sturgill]

What Ken said. If you increase the breaker size and do not have heavy enough wiring in the wall, you risk having the wiring let its smoke out. That can be very bad in a room full of dry wood.

[Chris Friesen]

If the motor is three phase as you originally stated...

I think you misread the original post. I read it as 3HP, 1 phase.

[David Gunn]

It will not result in less power, but the amps on a 3hp motor will exceed 20 amps. The only way to run it on 120 volt would be to put in a 30 amp breaker, which would include running #10 wire also.

[Chris Padilla]

It will not result in less power, but the amps on a 3hp motor will exceed 20 amps. The only way to run it on 120 volt would be to put in a 30 amp breaker, which would include running #10 wire also.

120V/30A is pretty rare to see...that is a NEMA 5-30 plug/receptacle. Better to go 240V/30A and use a NEMA 6-30 or 6-20 for 240V/20A would work just fine, too.

You need #10 for 240V/30A or #12 for 240V/20A. You might as well go with the #10 even if you decide to put in a 240V/20A outlet because if you need to plug in something that needs higher current in the future, all you have to do is change the plug and the breaker.

[douglas hyde]

no no you can not you can not go over 1/1/2 hp on 110v

[Chris Padilla]

no no you can not you can not go over 1/1/2 hp on 110v

1.5 hp = 1120 W

1120 W / 110 V = 10 A

Now start-up current might be an issue but running 1.5 hp over 120V line is fine near as I can tell.

[Wade Lippman]

1.5 hp = 1120 W

1120 W / 110 V = 10 A

Now start-up current might be an issue but running 1.5 hp over 120V line is fine near as I can tell.

Typically 1.5hp is 14a to 18a. There are certainly more efficient motors, but none are as low as 10a.

OP, it depends on your motor. The Grizzly 3hp is 18a/240v. No way that will ever run on 120v. The Steel City is 13a/240. That could run on a 30a circuit (if it can be changed to 120v of course); but if you have to put a circuit in, you might as well put in a 240v circuit.

[Chris Padilla]

Typically 1.5hp is 14a to 18a. There are certainly more efficient motors, but none are as low as 10a.

So 1.5 HP is AFTER the efficiency is figured in? You lose 4-8 A in the wiring as heat or what?

[Mark Engel]

no no you can not you can not go over 1/1/2 hp on 110v

My HF dust collector is rated at 2hp. It runs on 110 volts at 20 amps.

[Jason Beam]

My HF dust collector is rated at 2hp. It runs on 110 volts at 20 amps.

Precisely the reason HP is horrible for discussing circuit size. :)

[judson davis]

So 1.5 HP is AFTER the efficiency is figured in? You lose 4-8 A in the wiring as heat or what?

1.5 HP is the power produced on the mechanical side of the motor. Since no motor can convert electrical energy to mechanical energy with 100% efficiency, you will always have more energy going into the motor than coming out of it. The same would hold true of a generator. You would have to put more mechanical energy (from the gas engine) into the generator than the electrical energy you would receive out of it.

[Wade Lippman]

So 1.5 HP is AFTER the efficiency is figured in? You lose 4-8 A in the wiring as heat or what?

Some European tools show both the input HP and the output HP. Your figure might work for the input.

There are losses due to resistance, impedance, mechanical resistance, and probably a few other things I don't understand.

[Rick Christopherson]

1.5 hp = 1120 W

1120 W / 110 V = 10 AThe problem is that your equations are incomplete. It is true that 1.5 hp = 1120 watts, but your conversion from watts to amps is not correct because it overlooks the inductive reactance of the motor, plus the efficiency. The proper equation for this is:
A = W / (V * pf *eff) = 1120 / (120 * 0.8 * 0.8) = 14.5 amps (based on typical values)

It is possible to have up to 2 hp on a standard 120 volt circuit, but this requires a 20 amp circuit. Going above this is still feasible, but it is not common.
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To the original poster's question, this is all a rather moot point, because you are very unlikely to find a 3 hp motor that is dual voltage for 120 volts. Even though it is feasible to have a dual voltage, 3 hp motor, you are not going to find one on a standard piece of woodworking equipment.

Even in the rare event that you did have a dual voltage motor, it would require a 30 amp circuit, which would mean running a new circuit any way. Your only option is to run a 240 volt circuit.

[Mike Henderson]

Rick is correct. Let me point out one other interesting thing about power factor.

When you have an induction motor running without load, the motor looks like an inductor to the power line. Because of that, the current is way out of phase with the voltage. But when you measure "power (or watts)" the only thing that counts is the voltage and current that are "in phase"

Anyway what all this means is that an induction motor running without load is drawing a lot more current than you would think it would just based on the HP being produced. As the motor is loaded, and starts producing more HP, the current moves more in phase with the voltage but doesn't increase that much. At full load the power factor is about 0.8 as Rick indicated but at no load the power factor could be 0.2 or even less.

When you run an induction motor at a light load, you're only paying for the power (KWh) you're actually using, but the power company has to provide you with the extra current caused by the "inductance" and your wires have to carry that current.

But maybe this is only "interesting" to engineers:)

Mike

[judson davis]

Mike,

Thanks for the info, I did find it interesting.