3 phase question.

[strmtrpr73]

In my time doing electrical work, I have mostly dealt with 120/ 240 single phase systems, so my 3 phase knowledge is next to nothing. I have a little situation, 120/240 3 phase system. 120v to neutral on all legs, and 240 between any two phases. Correct? I have a hood fan system name plate 460V 3 phase is all I could see from where I was. I haven't gotten into the unit yet.
when I saw this I freaked. I told the Owner months ago that he had a 3 phase system, but it was 120/240. Now I think I know the answer, Is it possible that it can be changed over? I am sorry I do not have anymore specs. any help would be great.

Thank you

 

[infinity]

First, if you have 120 volts between all three phases and the neutral you do not have a 120/240 volt system. You would have a 208Y/120 volt system. If you need 460 volts for a piece of equipment it would be possible if you installed a three phase 208-460 volt step up transformer.

 

[eric stromberg]

Hopefully, the motor is dual-voltage rated and can be connected to either 240V or 480V. The nameplate would indicate either 230V or 460V. If this is the case, connect the motor in the 230V configuration and connect it to the 240V system. You'll have to 'bump' the motor and see which direction it rotates. If it is rotating the wrong way, swap two of the motor phases.

If the motor is not dual-voltage, it would be easier and most-likely cheaper to buy a 230 Volt motor. If you stick with a 460 Volt motor, you would have to install a transformer to get you from 240 to 480. Trouble is, unless you special order a transformer, you would be connecting up the 240 Volt Wye side as the primary and the 480 Volt Delta side as the secondary. You would then either have to corner ground the 480 Volt system or you would have to buy an additional transformer to use as a grounding transformer. No matter how you do it, it would become a mess.

Eric

 

[eric stromberg]

Trevor,
Nice catch. I saw that the first time, but it didn't register. As soon as i read 240 between the phases, my mind switched over to a high-leg system.

I still think the best solution would be to investigate buying a motor of the correct voltage. For this system, it would be a 200 Volt motor.

Eric

 

[infinity]

Another thing that caught my eye was that he said it is a "hood fan system". Reading that I envisioned that it may be setup from the manufacturer with a starter or controls that utilize a 460 volt supply voltage and may have an integral control transformer. In that scenario I think that he might have to figure out a way to supply it with 460 volts. Trying to convert it to a different supply voltage could become a large undertaking if we're not simply talking about a dual voltage motor.

 

[strmtrpr73]

Thank you very much much for your quick replies, I just don't have that much experience with 3 phase. To know the ins and outs, If anyone has a chance could you explain the different voltages of 3 phase systems. Trevor stated that I am dealing with a 208/120v system, where does the 208 come into play? Is there such a thing as 120/240v 3phase system. Sorry for the stupid questions.

Thank you again for your quick replies.

 

[infinity]

Trevor stated that I am dealing with a 208/120v system, where does the 208 come into play? Is there such a thing as 120/240v 3phase system.

]

There are a few different 3 phase systems. One being a 120/208 Wye system, a 120/240, 4 wire Delta system and a 240, 3 wire Delta system. The major difference between the three is the voltage.

>A 120/208 volt Wye system will have 120 volts from each phase conductor to the grounded (neutral) conductor and a voltage of 208 volts between the phases.

>A 120/240 volt, 4 wire, Delta system will have 120 volts between two of the phases and the grounded conductor and 208 volts between the other phase and the grounded conductor. And 240 volts between all three phases.

>A 240 volt 3 wire Delta will have 240 volts between each of the three phases.

There are other 3 phase systems but I think that the information provided should answer your question. When looking at a panel for the first time, if it isn't properly labeled, a digital multimeter should be used to determine which three phase system is in place. Otherwise you may simply be guessing.

 

[strmtrpr73]

Thank you very much, For some reason when I measured The voltage a month ago, I swear I saw 240 on each leg, But it is 208(actually 215).
But thank everyone, for their posts. THe hoodfan control box is all that is installed right now, which requires 460V. Anyway thanks again.