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L1 L2 and N running a 3 phase motor? (everyone's confused)

L1 L2 and N running a 3 phase motor? (everyone's confused)

L1 L2 and N running a 3 phase motor? (everyone's confused)

(OP)
We have a Chinese motor with 6 leads coming out of it. It's a squirrel cage induction motor designed for three-phase power. Interestingly, the machine that this motor was found on is only taking L1 and L2, and N from the main board. This motor is intermittently lifting a heavy load up and down (like a 1-meter-tall elevator). The reversing of the motor is achieved by using an auxiliary contactor that reverses the L2 and N wires input to the motor. I wanted to understand how this is possible. There are no capacitors in this system. I have attached the photo of the sticker on the motor. For reference, we are running this in Europe with 220V 50HZ.

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

Hi,
m.ahsaniftikhar,
Attach a nameplate photo and photo of connections in terminal box.
ACW

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

That's a garbage nameplate.

It's a dual 220 Delta/380 V Wye dual voltage motor.

If you have really six terminals, for 220 V Delta, you short terminals A1&B2, B1&C2 and C1&A2 for 3 ph 220 V input supply. For rotation reversal, you swap two supply terminals.

Muthu
www.edison.co.in

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

(OP)
@edison123, Connecting this motor to a 3-phase supply is the obvious choice here. What I am trying to understand is how is it possible for this 3-phase motor to run despite a missing phase. The motor is getting L1 L2 and N wires (I have verified with the multimeter that these are L1 L2 N and I am not simply going by the color coding). The motor is also reversed by switching L2 and N. The motor has no capacitor and it lifts a heavy load of 50kg with a chain and sprocket(120W motor according to the sticker on it). Everywhere I read it says that the motor should not start if all 3 phases are not connected. I even broke open the motor (it burnt up recently) and there is no capacitor in there. But This motor has been lifting the load for the past 3 years. Any clue about how this motor not only runs but also self-starts despite the loaded condition?

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

"it burnt up recently". It was single phasing. Supply 3 phases proper.

120 W only to lift 50 kgs? Post photos of the motor, 6 terminals.

Muthu
www.edison.co.in

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

Looks like a 2 pole winding (very poor workmanship) with single phasing failure. Take it to a good motor repair shop or buy a new one. Hire a professional engineer to wire up the motor to the control panel.

Muthu
www.edison.co.in

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

(OP)
Whoa! how did you determine the number of poles? please show me your ways!

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

6 coil groups = 2 poles x 3 phases.

Muthu
www.edison.co.in

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

(OP)
Is there a reason why all online resources are saying that the motor should not start when single-phasing? The motor obviously started and ran in this single phasing condition.

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

Yes, they won't start on single phase but will run (with much higher current in two phases) if they are given starting kick. Don't know your setup to comment further.

Muthu
www.edison.co.in

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

Google is not omnipotent either.
Something is strange with this wiring diagram.

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

I came across a small fishing boat repair area where all of the welders were connected to two phases and the neutral.
The welders cranked the current setting up until they could weld properly.
The small three phase fans seemed to run OK.
My response when I wanted to reconnect them properly;
"Everything is working OK. Why should we spend any money."
The same yard supplied shore power to boats in the off season.
No three phase refrigeration running, just lights and some portable heaters.
Almost all single phase, 120 Volt loads.
They supplied two phases and a neutral, for 120/208 Volts.
They metered the power with single phase meters.
A single phase, 120/240 Volt meter uses one 240 Volt potential coil and assumes that the voltages, L1 to N and L2 to N are equal.
On 120/208 Volts, the meters read low by a factor of 208V/240V.
"Everything is working OK. Why should we spend any money."

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

@ Mr zlatkodo (Electrical)11 May 23 14:11
" Google is not omnipotent either.
Something is strange with this wiring diagram."


I am a Singaporean Chinese, NOT a machine. I am not omnipotent, but I understand what the drawing shows and try to explain as following:
1) it is a motor having 6 external connection leads, with colour (Black), (Red), (white); (Green), (Brown) and (Blue).
2) a)Power source 3-phase 220V, connect phase A to leads (Black)+(Green), phase B to (Red)+(Brown), and phase C to (White)+(Blue).
b) Power source 3-phase 380V, connect phase A to lead (Black), phase B to (Red), and phase C to (White).
Attention: leads (Green), (Brown) and (Blue) shall be individually terminated on individual terminal blocks, isolated from earth/ground.
3) With phase sequence ABC, leads connection as above 2) a) and b) ; motor operates in CW rotation.
4) In either voltages, only 3-phases (ABC)are used. Attention: Neutral is NOT used. Motor frame shall be earthed/grounded.
5) To reverse the rotation, "usually" interchange power source phase B and C.
Che Kuan Yau (Singapore)

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

Nice job, che. They could have very well put all six leads in that sticker and shown the 220/380 V connections.

Muthu
www.edison.co.in

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

Mr edison123 (Electrical)12 May 23 01:49
".... They could have very well put all six leads in that sticker and shown the 220/380 V connections".
Agreed in full to your learned advice. The drawing should be in greater detail to avoid confusion.
Che Kuan Yau (Singapore)

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

Thanks , Che for your explanation.
可以給我你的聯繫方式嗎? 如果我需要將中文翻譯成英文或有類似的問題,我可以聯繫你嗎? 簡體中文和繁體中文有很大區別嗎?
Contact

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

zlatkodo (Electrical)13 May 23 07:24
"....可以給我你的聯繫方式嗎? 如果我需要將中文翻譯成英文或有類似的問題,我可以聯繫你嗎? 簡體中文和繁體中文有很大區別嗎?"
Yes, no problem, you and all readers are welcome. My email address is che_kuan_yau@yahoo.com.sg
I am a Chinese born Singaporean. Educated in Singapore in electrical engineering. I am able to translate Chinese to English or vice versa, in any Chinese form. It would be pro bono. No advertisement, no commercial.
Che Kuan Yau (Singapore)

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

Sounds like your installer used a neutral instead of a proper third phase. We call this "V phase" where I work. With the two legs 120 degrees from each other, you still have a rotating electrical field and some starting torque. The voltage and phase balance are all wrong for a three phase motor, but it's not exactly single phase either. Probably lucky that it lasted as long as it did.

RE: L1 L2 and N running a 3 phase motor? (everyone's confused)

(OP)
Thanks to all of you. This was quite helpful.

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