Testing 3PH motor ??

Chief Mcgee

unread,

Mar 30, 2010, 4:45:27 PM3/30/10

to

I have a 20HP, 3ph motor on my lathe. The label says it is a 220/440, but
there are only 3 wires coming out of it. I assume it was rewired straight
some time in the past. Motor appears to be 1940's model. Is there a way
to test the motor to tell if it is wired for strsight 220 or 440 ? The
controls have 440 stickers on them. So I assume the motor has been rewired
for 440. But is there a way to test for sure? thanks, McGee

Robert Swinney

unread,

Mar 30, 2010, 5:09:37 PM3/30/10

to

Are you sure the motor doesn't have a junction box where the 3 wires come out?

Bob Swinney
"Chief Mcgee" <McGe...@mchsi.com> wrote in message
news:eYudnWyPkeN0_y_W...@mchsi.com...

Ignoramus28422

unread,

Mar 30, 2010, 5:41:30 PM3/30/10

to

out of where exactly do three wires come out?

I would look into the control box, see what is the control transformer
doing and what is the voltage of the contactor, that should be proof
enough of the motor voltage.

i

Existential Angst

unread,

Mar 30, 2010, 6:04:08 PM3/30/10

to

"Chief Mcgee" <McGe...@mchsi.com> wrote in message
news:eYudnWyPkeN0_y_W...@mchsi.com...

Well, if you can't find more wires, I would just put 220-240 on it, see how
it sounds.
If the contactor just buzzes on 240, then it proly is 440.
--
EA

Wes

unread,

Mar 30, 2010, 7:17:54 PM3/30/10

to

"Robert Swinney" <jud...@tx.rr.com> wrote:

>Are you sure the motor doesn't have a junction box where the 3 wires come out?

My Clausing 6903 had the wires to change from 480v to 240v buried inside the liquidtite
flex. I was worried for a while. I sure didn't want to buy a 3-5 KVA 3 phase transformer.

http://wess.freeshell.org/Clausing_6903_motor_leads.jpg

You can see how the wires tapered from the splices. Piss poor wiring practice. GM
Saginaw electrician did the deed according to the property tags.

Currently running happily on 240v from my rotophase.

Wes

Gunner Asch

unread,

Mar 30, 2010, 8:16:37 PM3/30/10

to

On Tue, 30 Mar 2010 15:45:27 -0500, "Chief Mcgee" <McGe...@mchsi.com>
wrote:

Check the voltage rating on your contactors and/or what voltage
position the control transformer input is set at.

Gunner

"First Law of Leftist Debate
The more you present a leftist with factual evidence
that is counter to his preconceived world view and the
more difficult it becomes for him to refute it without
losing face the chance of him calling you a racist, bigot,
homophobe approaches infinity.

This is despite the thread you are in having not mentioned
race or sexual preference in any way that is relevant to
the subject." Grey Ghost

Jon Elson

unread,

Mar 31, 2010, 12:20:45 AM3/31/10

to

** 20 ** Hp? If you connect a 20 Hp 220 V motor
to your home mains, you may well need a truck from
the power company to get the lights back on at
your house.
The run current of such a motor, even at no load,
would be around 66 Amps on 3-phase mains. Trying
to run it off single phase (not sure that's what
you are trying to do, so this message may be way
off the mark) the line current would be HUGE, and
the starting draw would be a couple hundred amps.

If you do have 3-phase 240 V power there, and the
motor is set for 440, and assuming the contactors
will pull in, you would get a slow start that
should be pretty obvious. It would take maybe
5-10 seconds for the motor to accelerate even with
the lathe gears in neutral. With the right
voltage, the motor should accelerate to full speed
well within one second.

Jon