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Help needed wiring a three phase motor


Doc
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Any electricians that might be able to help me?

 

I have just bought via a local auction a brand new Brook Crompton 3 phase dual voltage 550w motor for a bargain price The idea is to join this up to a single to three phase inverter and connect this to my milling machine. I haven't bought the inverter yet.

 

Below is a photo of the terminals as it is now and I think it's connected in star configration and to connect it to delta configuration I need to undo the black, brown and white leads connected to "N" terminal and do the following:

 

A : Connect Brown to Red

B: Connect White to Yellow

C: Connect Black to Blue

 

Leaving "N" vacant.

 

Is this correct do far?

 

What I really need to know is the four core cable that I connect from the Inverter to the motor, which wires go to ABC. Does it matter which wires go to which phase. The earth goes to the body of the motor of course but where do the rest go. 

 

IMG_20161205_102358.jpg

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Hi Mick, just need a bit more info...from the photo it looks like it is connected in star... i.e wired for 415vac. You are correct, Most single phase to three phase inverters are 230vac single phase in and 230v three phase ac out, so the wires do need to be connected in Delta.

 

You state the following;

A : Connect Brown to Red

B: Connect White to Yellow

C: Connect Black to Blue

Where did you get this info, have you done a continuity test through the windings? Or is it written somewhere on the motor?

Cheers

steve

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It will not matter initially which way you connect your 3 phases from the inverter to the motor terminals a, b, c, if the motor goes the wrong way, then you can swap over any two wires on the feed cable or tell the inverter to reverse etc.

 

Your 4 core cable will ideally need to be SY (screened cable, with the screen grounded at both ends) to prevent high induction currents circulating and Electromagnetic interference (EMI), 

Cheers

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That's all good news Mick, I was half hoping it had a nameplate and info under the terminal chamber. Just connect the wiring as directed.

Get an inverter that matches the nameplate details. 

Stand well back when you try it! :D

 

How long will the feed cable be?

Do you have a bit of SY cable etc? The inverter info will probably say you need screened cable...

cheers

To reverse, it says swap over any two line wires, this means any two of the feed cable wires, you can do it at the inverter end if necessary, it might be easier, but first allow the inverter to discharge fully, this can take a minute or so...

cheers

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Thanks Steve.

 

It all looks pretty simple. The motor is 550 watt so that is about 3/4hp so when I do buy an inverter I need one at least 3/4hp. But will it be OK if I find one at say 2hp, will it make any difference?

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27 minutes ago, Doc said:

Thanks Steve.

 

It all looks pretty simple. The motor is 550 watt so that is about 3/4hp so when I do buy an inverter I need one at least 3/4hp. But will it be OK if I find one at say 2hp, will it make any difference?

 

It can be a problem with some inverters, they monitor the motor and deduce how much current they should be taking... the inverter could assume a fault lies with the motor. You are better matching them up, or getting it as close as possible, e.g. in your case a 0.75kw inverter though too big, would work fine although the inverter is 1hp rated ( 1hp is 746watts). also get one with a knob on the front to regulate the speed if possible...

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