Need electrical advice on RAS

[Rick Potter]

Today, I looked at a 16" DeWalt radial arm saw. The motor is clearly marked single phase, 3HP.

The owner said he had it rewired and checked over 8 years ago and it has sat in his shop ever since. The shop is a commercial building.

As I said, the motor is clearly marked single phase, but there is a newly added (8 years ago) electrical box under the saw. It also says something about single phase on it, but I could not make it out. The plug however is a four prong twist lock and clearly states it is 240/460 Volt, 3 phase.

All I can guess is that the shop is three phase, and that the electrician somehow wired the three phase plug into the new box which magically turns it into single phase at the switch or motor.

I have wired my desert cabin from scratch, and done remodels, but I have no clue about three phase wiring. Is this something that could have been done?

The saw runs fine at his shop.

Thanks in advance,
Rick

Jousting at windmills again.

[Matt Day]

Simple answer appears to be yes, wire the motor for single phase 240 and wire it with 2 legs of the 3 phase power.

Here's a discussion about it after some simple Google-fu "single phase motor on three phase power"

http://www.practicalmachinist.com/vb/transformers-phase-converters-and-vfd/single-phase-motors-3-phase-power-156954/

[Bradley Gray]

Any single "phase" could have run your motor. I think it is likely if you open up the plug you will find it has unused prongs. substituting a 220v single phase plug should get it running.

[Wade Lippman]

Frequently motors can run on either 240v single phase or 208 3 phase (using 2 of the 3 phases). The new box is probably just an adapter. As Bradley said, one prong probably isn't connected to anything.

[Bill Space]

Frequently motors can run on either 240v single phase or 208 3 phase (using 2 of the 3 phases). The new box is probably just an adapter. As Bradley said, one prong probably isn't connected to anything.

Wade,

Just to clarify, a single phase motor will run off single phase voltage, which is obtained by using any two wires of the three phase source.

It it is not running on three phase power. It is running on single phase derived from the three phase source.

The way you stated it could confuse those less familiar, so I thought I would add this clarification just in case.

Bill

[Rich Riddle]

My thought is he simply used a three phase plug and wired it with single phase motor. Many old timers simply use the plug on hand. Is it the correct way? No. Do they still do it? Yes. The bad part would only happen if someone attached the tool wired with the wrong plug into a three-phase service.

[Rich Riddle]

Wade,

Just to clarify, a single phase motor will run off single phase voltage, which is obtained by using any two wires of the three phase source.

It it is not running on three phase power. It is running on single phase derived from the three phase source.

The way you stated it could confuse those less familiar, so I thought I would add this clarification just in case.

BillI never considered some folks would do this, but it's possible. Three phase is set at 120 degree intervals vs 180 degree intervals for single (split-phase) 220 VAC. That would cause some minor potential issues many years down the line much like a rotary phase converter that has 90-90-180 intervals isn't the same as true three phase at 120-120-120 intervals. Of course the answer there for true three phase is a Variable Frequency Drive. I don't know of anything that coverts three phase 120-120-120 degree intervals back to 180-180 split phase intervals.

[Wade Lippman]

I never considered some folks would do this, but it's possible. Three phase is set at 120 degree intervals vs 180 degree intervals for single (split-phase) 220 VAC. That would cause some minor potential issues many years down the line much like a rotary phase converter that has 90-90-180 intervals isn't the same as true three phase at 120-120-120 intervals. .

You never considered this? The top manual on my pile is the 3hp SS. It says to use 208v - 240v. Are they recommending something that will cause issues?

[Rick Potter]

Thanks, guys,

Uncertainty and advancing old age have made me decide to pass on this one. I just don't need another possible project right now.

If anyone is interested, it is a nice saw. The owner is a nice guy who needs to clear out a building it is in, and is asking $600 for it. You can find it in the Inland Valley Craigs List (CA).

Thanks again for the advice,
Rick

[Bill Orbine]

Thanks, guys,

Uncertainty and advancing old age have made me decide to pass on this one. I just don't need another possible project right now.

If anyone is interested, it is a nice saw. The owner is a nice guy who needs to clear out a building it is in, and is asking $600 for it. You can find it in the Inland Valley Craigs List (CA).

Thanks again for the advice,
Rick

Advancing old age?????? A lot of stuff made back in the day are made better than what you can get today. That much is CERTAIN.:D

[Rick Potter]

Ahhhh Bill?

I was referring to MY advancing old age. 74 in about a month. :eek:

[Matt Day]

Ha, got a chuckle from that one.

[Bill ThompsonNM]

Ahhhh Bill? I was referring to MY advancing old age. 74 in about a month. :eek:
But that means you need a birthday present! Remember you're only old as you think you are!
?