3 phase motor wiring...

[REVCAM_Bob]

Hi I have a big 3 phase electric motor. I am reinstalling it as it needed to be removed for transporting the press it was on. In checking the motor conections I am seeing that the wires in the electrical box are not grouped together as the tag says they should be. On the motor is a tag that shows both the proper set up for 240 volt 3 phase and the proper set up for 480 volt 3 phase. It matches neither. So I am wondering if anyone might be able to tell me if there is any way to check the setup with an ohm meter or in any way test the set up to see if it is connected correctly or not. I would think that if it was not correct it would burn up the motor or be shorted out or something? I don't know...... ugh.

Thanks for any help

[Al_The_Man]

If the motor was functioning OK with the present wiring and it will be re-installed using the same voltage, then maybe the prudent way may be to write down the present hook-up and reconnect the same way?
Do you have a diagram or list of the present connections #'s?
Al.

[WCIS]

Al is right, if the supply voltage is the same at the machine's destination wire it back up the way it was - assuming of course it IS running correctly at it's present location.

I have seen a few 3 phase delta wound motors straight from the factory with incorrect lead markings. These are relatively easy to read with an ohmmeter and correct. If you make a mistake and wire it incorrectly the motor won't live long at all. I use three analog current meters clamped around each phase feeding the motor and monitor the current when energizing for the first time to be sure it is balanced after the initial inrush. This also is best done at the lowest voltage the motor is rated for to avoid over current within one winding and killing it. At the higher voltage the current will be double it's rating and won't take but a second or two to burn out.

If you must re-tap for a different voltage I would say the safest bet would be to find yourself a competent rewind shop and ask them to have a look at the internals. They should be able to remove an end bell and identify the taps. I have also had motors re-wound that were 12 lead motors before the rewind and 9 lead after. Again, I've sent in 9 lead motors and got back 3 lead motors. When the latter happens the motor isn't dual voltage capable anymore. This may be the reason you see something different.

[REVCAM_Bob]

Thanks guys, the motor was running, however I had the press inspected and the guy who checked it out put an amp meter on the motor and said it had somewhat excessive draw upon start up. It was hooked to 240 3 phase, and I have 480 in my shop so I sort of need to re tap it.... is there any way to tell without tearing the motor apart? i.e. with an ohm meter or something? If there are some documents or schematics on the internet showing how it all works, is it possbile to figure out? Taking it into a shop is not a good option for me as it weighs about 3 or 4 thousand pounds I am guessing (ugh) and is currently mounted about 15 feet in the air on the press......

[REVCAM_Bob]

I have both the plate on the motor that shows how it should be connected, and the wires are well marked how they are linked together. I could post both if you think it might help....

[Al_The_Man]

It may help to see how they actually have it right now.
The excessive draw may be normal, an induction motor is essentially a dead short at actual switch on, it is needed is to bring it up to speed or normal load as soon as possible, motors that are already hooked to a load at switch on, exhibit high current due to a longer power up.
This is why motors that have a high load initially have star-delta starting, or other methods to overcome this.
Imagine a 3 phase transformer with a shorted secondary, this is what the supply see's at switch on.
Al.

[WCIS]

Again, Al is correct.

Try to write down how it is connected now and post. Also, post the data plate information along with connection diagrams. If the horsepower rating of the motor is 100+ there may be a soft start circuit involved which will make the actual connection differ from the diagram. Most large motors, as Al eluded to, usually have a two stage start to lower the initial inrush current AND reduce the time the motor windings are in this overcurrent state. There are various ways to accomplish this. Without the data plate and diagram information it's just a shot in the dark on my end.

Do you know if there are magnetic starters that switch power to this motor? Be sure you change the overload heaters or adjust after you get the motor taps changed. Going to the higher voltage and not doing so will leave the motor unprotected. This could save you having to remove the motor after it burns out.

Another question could be is there an electronic soft start and bypass contactors? If so, you must be sure the soft start can handle the higher voltage. In most cases they cannot. OL heaters/settings apply here as well.

As a good practice be sure the motor starters are rated for the higher voltage. There have been only a couple times I've seen foreign equipment utilize motor starters that were rated for 380 (not 480) and they didn't live long at the higher voltage.

Try calling your local rewind shop and ask those guys. You will still need the above information. A pair of trained eyes on the situation is sometimes the best. Fewer mistakes are usually made. You may also find what you need on the manufacturer's website if the motor isn't ancient.

[rmcguire]

what about control ckts they maybe wired 230 also, check control xformer and starter ratings as 230 will be large in amp capacity. is mtr old nema or newer mtr. manafacturer"s web site may offer info.

[Al_The_Man]

Originally Posted by rmcguire .....and starter ratings as 230 will be large in amp capacity. is mtr old nema or newer mtr. manafacturer"s web site may offer info.

He mentions going from 240v to 480v so the current draw will be less.
The overloads should be changed though, as mentioned earlier.
Al.

[cflas]

going from 240 to 480 the windings on the motor need to change from parallel to series. if they are number it is a more simple process but make sure you verify as i have not done this in a very long time. Example you have a delta or wye configuration. more than likely if is 240 is delta wye would be 208. think of a triangle. wires would connect t1 -4-7-10-2-5-8-11-3-6-9-12 -back to 0ne were 1,2 and 3 would be your line voltage. Three phase motors are reverse by changing one line make sure the motor is running in the right directionif not exchange one line with any of the others. Hope this will help and look for delta wiring on the internet. The electrician should know how this is done. think safety first and take no risk.

[cflas]

Originally Posted by cflas going from 240 to 480 the windings on the motor need to change from parallel to series. if they are number it is a more simple process but make sure you verify as i have not done this in a very long time. Example you have a delta or wye configuration. more than likely if is 240 is delta wye would be 208. think of a triangle. wires would connect t1 -4-7-10-2-5-8-11-3-6-9-12 -back to 0ne were 1,2 and 3 would be your line voltage. Three phase motors are reverse by changing one line make sure the motor is running in the right directionif not exchange one line with any of the others. Hope this will help and look for delta wiring on the internet. The electrician should know how this is done. think safety first and take no risk.

found this on the internet probably makes more sense:
The connections are:
LV: L1 to 1, 6 & 7; L2 to 2, 4, &8; L3 to 3, 5 &9
HV: Li to 1, L2 to 2, L3 to 3, Join 4 & 7, 5 & 8, 6 & 9

[Al_The_Man]

I usually use this US Motors reference.
Just about all combinations here.
Connections
Al.