3 Phase Motor Wiring

Right Angle · Mar 11, 2013

I recently acquired a metal lathe from my uncle. It's an early 80's Jet. It sat unused in his garage for 20+ years. It currently has a 3 phase motor that was wired in the low voltage wye configuration.

I have 3 phase power, but after hooking it up, it turns really slowly. Unfortunately, the plate is completely worn off except for the stamped values. I am wondering if this is not a dual voltage motor and is only set up for 460. Is there any way to determine if this is a 230/460 motor?

Thanks in advance for any help.

Gooch · Mar 11, 2013

Right Angle said:
I recently acquired a metal lathe from my uncle. It's an early 80's Jet. It sat unused in his garage for 20+ years. It currently has a 3 phase motor that was wired in the low voltage wye configuration.

I have 3 phase power, but after hooking it up, it turns really slowly. Unfortunately, the plate is completely worn off except for the stamped values. I am wondering if this is not a dual voltage motor and is only set up for 460. Is there any way to determine if this is a 230/460 motor?

Thanks in advance for any help.

how many leads are in the peckerhead? 3=single voltage, 9=dual voltage.

930dreamer · Mar 11, 2013

It looks like there's two amp figures on the right side, so dual voltage.

Stuart in MN · Mar 11, 2013

930dreamer said:
It looks like there's two amp figures on the right side, so dual voltage.

Yup, where it says 2.8/1.4.

wyliesdiesels · Mar 11, 2013

Right Angle said:
I recently acquired a metal lathe from my uncle. It's an early 80's Jet. It sat unused in his garage for 20+ years. It currently has a 3 phase motor that was wired in the low voltage wye configuration.

I have 3 phase power, but after hooking it up, it turns really slowly. Unfortunately, the plate is completely worn off except for the stamped values. I am wondering if this is not a dual voltage motor and is only set up for 460. Is there any way to determine if this is a 230/460 motor?

Thanks in advance for any help.

What type of 3-phase service do u have- wye(208v) or delta(240v)?

Right Angle · Mar 12, 2013

Gooch said:
how many leads are in the peckerhead? 3=single voltage, 9=dual voltage.

There are 9.

930dreamer said:
It looks like there's two amp figures on the right side, so dual voltage.

Stuart in MN said:
Yup, where it says 2.8/1.4.

That's kind of what I was thinking.

wyliesdiesels said:
What type of 3-phase service do u have- wye(208v) or delta(240v)?

I believe it is a high leg delta.

If it is a dual voltage motor, any ideas on why it's running so slow?

Norcal · Mar 12, 2013

Check the leads if it's wired for 460V, that is very likely the problem, & it's better then being supplied w/ 480V & wired for 230V.

Right Angle · Mar 12, 2013

Norcal said:
Check the leads if it's wired for 460V, that is very likely the problem, & it's better then being supplied w/ 480V & wired for 230V.

I'm almost positive it's wired for low voltage. Currently it's: L1=1&7, L2=2&8, L3=3&9, and 4,5, and 6 are wired together.

sparky36000 · Mar 12, 2013

Right Angle said:
I'm almost positive it's wired for low voltage. Currently it's: L1=1&7, L2=2&8, L3=3&9, and 4,5, and 6 are wired together.

Yeah, that's the low voltage connection..........how does it sound when it's running? Loud growling and low torque? Can you put a clamp ammeter on the leads and see if it''s close to the 2.8amp rating? Curious to see what you find out.

Right Angle · Mar 13, 2013

sparky36000 said:
Yeah, that's the low voltage connection..........how does it sound when it's running? Loud growling and low torque? Can you put a clamp ammeter on the leads and see if it''s close to the 2.8amp rating? Curious to see what you find out.

I didn't let it run for more than a couple of seconds. It sounds similar to a motor that's starting up, a low constant hum.

I was thinking about using an ammeter after I reconnected everything.

OccupantRJ · Mar 13, 2013

Check the bearings and motor shaft. i have seen shafts wear inside bearings, and worn bearings that would let a rotor get off center a tiny amount, which can cause drag. Replacing the bearings or repairing the shaft took care of things.

Right Angle · Mar 17, 2013

After deciding that everything looked proper, I wired the motor back up to test the leads with an ammeter. A funny thing happened, the motor seemed to spin at the proper speed.

I'm not sure if I was just mistaken originally when I thought the motor was spinning slowly, or if something changed. I'm thinking it was the former.

As an aside, each of the three feeds showed roughly 1.6 amps while running. I'm assuming these don't simply sum for total draw. What's the correct math to determine the draw?

Thanks for everyone who chimed in to help.

sparky36000 · Mar 17, 2013

The amp on the nameplate is per leg you don't add them together. The 2.8amps is also full load amps, with no load on the machine it will be less. Sounds like your good to go.

wyliesdiesels · Mar 17, 2013

sparky36000 said:
The amp on the nameplate is per leg you don't add them together. The 2.8amps is also full load amps, with no load on the machine it will be less. Sounds like your good to go.

Exactly! Its a balanced 3-phase load!

Right Angle · Mar 18, 2013

sparky36000 said:
The amp on the nameplate is per leg you don't add them together. The 2.8amps is also full load amps, with no load on the machine it will be less. Sounds like your good to go.

wyliesdiesels said:
Exactly! Its a balanced 3-phase load!

Oh man, of course! Now I feel a bit silly for not thinking about this for a couple of seconds. Thanks again.

wyliesdiesels · Mar 18, 2013

Right Angle said:
Oh man, of course! Now I feel a bit silly for not thinking about this for a couple of seconds. Thanks again.

Dont worry! Even seasoned sparkies forget things theyve known for years from time to time!

kevin47 · Mar 19, 2013

Whoa...Hold on there..You didn't tell us what size lathe, etc....

Right Angle · Mar 22, 2013

kevin47 said:
Whoa...Hold on there..You didn't tell us what size lathe, etc....

It's a Jet from 1981. It has a 10" swing with roughly 20" between centers. It's been a little hard to find info on it.

StayThirsty · Mar 23, 2013

any chance you bumped the speed knob between having it on and off? I was going to say it sounded like you lost a leg and was "single phasing" if you had a fused disc. Sounds like you got it figured out though. Watch out for the ol ******* leg!

wyliesdiesels · Mar 24, 2013

StayThirsty said:
any chance you bumped the speed knob between having it on and off? I was going to say it sounded like you lost a leg and was "single phasing" if you had a fused disc. Sounds like you got it figured out though. Watch out for the ol ******* leg!

The high/stinger leg, aka what ur calling the ******* leg, is only of concern with single phase 120v loads!

StayThirsty · Mar 24, 2013

wyliesdiesels said:
The high/stinger leg, aka what ur calling the ******* leg, is only of concern with single phase 120v loads!

correct you are!

3 Phase Motor Wiring

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