# ID wires on a 3Phase motor.



## trg-s338 (Apr 26, 2011)

I have a 9 wire three phase motor to be used as an idler for an RPC. There are no labels on the wires, lost or cut off when decomissioned. I have looked extensively on the net how to figure it all out. Seems complicated and confusing. Does anyone have a suggestion for a do it yourselfer? Is there a simple way to figure it?  If not, I guess I'll have to take it to a motor shop and pay $80.00. Can I save the money?


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## Tony Wells (Apr 26, 2011)

I'm not aware of a method of identifying the leads. It may be worth the bucks not to burn up a good motor.


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## pdentrem (Apr 26, 2011)

Take it to the motor shop. They may have the equipment to figure it out. The question was asked on the Leeson site and that was the answer the tech gave as it is impossible to determine the sequence of the coils.


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## trg-s338 (Apr 27, 2011)

Motor shop it is! Thanks.


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## trg-s338 (Apr 30, 2011)

Thanks guys.


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## trg-s338 (May 3, 2011)

Well, just got the motor back from the motor shop. It cost $65.00 to get the wires relabeled but I got to see it run, wired for 240 V 3Phase.


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## Tony Wells (May 3, 2011)

Money well spent. Now you know what you have. Is it quiet, are the bearings OK?


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## trg-s338 (May 4, 2011)

I'm not sure if the guy at the shop was trying to drum up extra business but he wanted to replace the bearings. While running, however, the motor was smooth and quiet so I'll "let it ride" for a while until it gets loud before I do the bearings.


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## pdentrem (May 4, 2011)

Bronze bushings or bearings? May see a difference once there is loading on the motor but as you say lets see what happens.


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## hermetic (May 14, 2011)

Bit late I know, but for future reference, this is how you do it (see attached) if you are using a normal three phase supply, and after you have identified the three coils, you connect the motor and one of the coils is the wrong way round, the motor will hum and run slowly. However if you are using a VFD or other form of Electronic artificial three phase system it may be damaged. If you are using a rotary phase converter, or a system using capacitors and a slave motor, that will be ok too. To use a three phase motor on 240v three phase from a VFD it must be connected in Delta. As has been said above, unless you are sure, it's cheaper and safer to consult an expert!!
PHIL.


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## trg-s338 (May 16, 2011)

Just curious, what book is that out of? Thanks for your reply.


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## hermetic (May 16, 2011)

It is from "installation and maintenance of electric motors" published by Brook Motors of Huddersfield UK. it is a pocket book distributed free to the electrical trade (or it was, Mine is fifteenth reprint 1971) and it is a mine of usefull info. Known in the trade as the "Brooks book" I don't think they publish them any more, but you could email and ask 	csc@brookcrompton.com
Try ABE booksearch or car boots etc. Really worth having, and has spent all it's life in my AVO 8 case!
Phil


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## Ulma Doctor (Feb 24, 2013)

trg-s338 said:


> I'm not sure if the guy at the shop was trying to drum up extra business but he wanted to replace the bearings. While running, however, the motor was smooth and quiet so I'll "let it ride" for a while until it gets loud before I do the bearings.



just an fyi, you can easily replace your own motor bearings. three phase motors are simple in design , the bearings are easily available on ebay or from local bearing houses. Part of my business is rebuilding 3 phase motors and constructing RPC units.
If you need assistance when the time comes, i'd be happy to assist. i probably have the bearings in stock.
good luck!
mike )


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## arvidj (Feb 24, 2013)

Not sure if this is legitimate post here but I'll give it a try and Tony can delete it if it violates a rule.

Google '9 wire 3 phase motor wiring' and look at the results, There is a thread on another machinist site with a title that matches the Google search criteria exactly. Look at post #10 on that thread.

They did not have a diagram in that thread so here is one that may help.

Based on the description, I suspect this is one of those cases where an analog volt meter would be much preferred over a digital volt meter to see the 'kick' as the voltage is induced in the coils. Note that the 'kick' is created when the coil is initially connected to the battery. Current flows thru the coil and generates an expanding magnetic field which induces current flow in some of the other coils. Once the current flow from the batter stabilizes in the powered coil the magnetic field stabilizes and the induced current flow in the other coils drops to zero. Hence the 'kick' in the analog meter as it quickly goes from zero to some value and then drops back to zero again. It might be difficult to see the 'kick' on a digital meter as it is a relatively short pulse.

When the battery connection is opened the stable magnetic field collapses and generates another induced 'kick' in the other coils ... just like the ignition coil on a gas engine when the points open.

Arvid


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