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Old 05-13-2013, 12:43 PM   #1
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Wire a single phase motor into a three phase circuit


My boss asked me to wire a single phase motor into a three phase circuit at our building. There are no single phase circuits nearby. He wants me to use one of the three phases for hot, and the ground for neutral. I asked him what we were going to replace the ground with, and he said the aluminum BX spiral sheath would suffice. I'm not an electrician, and not feeling good about this. It sounds like it would be against the code, and unsafe. I've been able to delay doing the job for another reason. But I have to do something soon.

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Old 05-13-2013, 01:14 PM   #2
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Wire a single phase motor into a three phase circuit


It is certainly against code to use the ground as a current carrying conductor.

People get hurt doing stupid stuff like your boss is asking you to do
.

Hire an electrician to do the work correctly.

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Old 05-13-2013, 01:34 PM   #3
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Wire a single phase motor into a three phase circuit


No, you cannot do that. You are right that it is unsafe and against code. It is rather concerning that your boss is asking you to do stuff like this. What is the voltage of the motor, and what is the voltage of the 3-phase service? If it is a 240V motor and a 240V delta service, you would just wire the motor between two of the phases. If that's not the arrangement, then it may be a bit more complicated.
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Old 05-13-2013, 07:24 PM   #4
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Wire a single phase motor into a three phase circuit


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No, you cannot do that. You are right that it is unsafe and against code. It is rather concerning that your boss is asking you to do stuff like this. What is the voltage of the motor, and what is the voltage of the 3-phase service? If it is a 240V motor and a 240V delta service, you would just wire the motor between two of the phases. If that's not the arrangement, then it may be a bit more complicated.
That'll certainly work, and even if the service voltage is 120/208, the vast majority of 230 volt motors will run just fine on 208.
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Old 05-14-2013, 06:27 AM   #5
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Wire a single phase motor into a three phase circuit


An unlicensed person doing commercial electrical work? Probably not a good idea (and probably illegal). You are right to be hesitant.
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Old 05-14-2013, 08:44 AM   #6
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Wire a single phase motor into a three phase circuit


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No, you cannot do that. You are right that it is unsafe and against code. It is rather concerning that your boss is asking you to do stuff like this. What is the voltage of the motor, and what is the voltage of the 3-phase service? If it is a 240V motor and a 240V delta service, you would just wire the motor between two of the phases. If that's not the arrangement, then it may be a bit more complicated.
The OP stated it was a single phase motor that needs a neutral. I don't think whether the system is wye or delta has anything to do with needing a neutral for the motor. If it's a 240V motor, it would run on 240V delta or wye.
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Old 05-14-2013, 01:30 PM   #7
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Wire a single phase motor into a three phase circuit


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The OP stated it was a single phase motor that needs a neutral. I don't think whether the system is wye or delta has anything to do with needing a neutral for the motor. If it's a 240V motor, it would run on 240V delta or wye.
He didn't actually say it needed a neutral. He said his idiot boss told him to use ground for neutral. That's why I asked what voltage the motor is. If it is a 120V motor, it can probably be rewired for 240 - and should be.
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Old 05-14-2013, 10:03 PM   #8
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Wire a single phase motor into a three phase circuit


Excuse me for being away so long. I lost the link to the posting. Thanks for the replies.

This stuff is really confusing to me. Guess I have lived too long and the old brain is scrambled.... Please forgive me for being so slow on the uptake.

The new motor is a 120Vac single phase unit, and there are no markings indicating it can be jumpered for 240 V operation.

I've read that Wye systems only supply two voltages - 208V and 120V. (I don't know why.) Since those are the only two voltages I have encountered in our building, I suppose we have a Wye system.

I'm not clear on how our three phase outlets are wired. It is a four conductor twist lock. I haven't had one apart recently, but I think they are wired with 4 conductor cable. So does that mean the neutral is brought from the panel to the socket, or is the earth ground brought to the socket? Does a 3 phase motor need a neutral wire to operate?
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Old 05-14-2013, 11:38 PM   #9
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Wire a single phase motor into a three phase circuit


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Excuse me for being away so long. I lost the link to the posting. Thanks for the replies.

This stuff is really confusing to me. Guess I have lived too long and the old brain is scrambled.... Please forgive me for being so slow on the uptake.

The new motor is a 120Vac single phase unit, and there are no markings indicating it can be jumpered for 240 V operation.

Sometime you look at the moteur nameplate and verify the word " Volts " it will say X number of voltage like 120 or 120-240 etc.

I've read that Wye systems only supply two voltages - 208V and 120V. (I don't know why.) Since those are the only two voltages I have encountered in our building, I suppose we have a Wye system.

That is most common commercal and some resdentail power supply format on triphase useage Just double check all the lines to make sure you are not reading 240 volts if so then you got delta system.

I'm not clear on how our three phase outlets are wired. It is a four conductor twist lock. I haven't had one apart recently, but I think they are wired with 4 conductor cable. So does that mean the neutral is brought from the panel to the socket, or is the earth ground brought to the socket? Does a 3 phase motor need a neutral wire to operate?
For the 4 conductor twistlock for true three phase source you will have three line and ground or earth connection that it.

For the triphase moteur almost never use the netural at all so it will not be needed at all.

But as I did read in the details If this is commercal building then you will have no choice but get a electrician to come out and assit you on them.

Merci,
Marc
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Old 05-15-2013, 08:48 AM   #10
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Wire a single phase motor into a three phase circuit


Thanks. The production boss has interceded, and is going to hire an electrician to run a 120Vac drop. The motor is not rated over a range of voltages. Just 120V.

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