How to reconnect motor from 480 volts back to original 230 volts ?

This on SCMI tablesaw, made in Italy. Usually there is a diagram in the connection box, but not this time. Any idea how to rearrange the wires in there for 230 volts ? I have a call into SCMI on this, but won't surprise me if they never call back. Any motor manufacturer that doesn't have voltage wire arrangements printed on a rivetted metal plate ought to be shot at dawn.

This appears to be a 12-wire motor. There are provisions for wiring as Y for both 230 and 460 volts. There are also provisions for wiring as ∆ for both 398 (really, 400) and 796 (really, 800) volts.

We can ignore the ∆ options as those are generally not encountered in North America.

On such a motor, being wired as a 480 volt Y, there is a "star point" at T10, T11 and T12, where these are connected together, and connections between T4 and T7, T5 and T8 and T6 and T9.

As usual, the line is T1, T2 and T3.

To rewire such a motor for 240 volts, there is a second "star point" at T4, T5 and T6 and, additionally, there are connections between T1 and T7, T2 and T8 and T3 and T9.

Also as usual, the line is T1, T2 and T3.

The challenge, then, is to determine which of the twelve threaded studs are T1, ..., T12.

The nameplate states the motor is presently wired for 480 volts, and tracing the wiring should identify most of those terminals, with T1, ..., T3 obviously being the line.

The three copper or brass bars appear to be there for the purpose of connecting T4 to T7, T5 to T8 and T6 to T9, for 480 volts.

It would appear that the additional jumpers are there for the purpose of making a "star point".

Only testing, using a DMM in continuity checking mode, can say for sure.

That J-Box is typical of european motor suppliers - here are a few diagrams that may be of some help.

peterh5322 said:

The challenge, then, is to determine which of the twelve threaded studs are T1, ..., T12.

The nameplate states the motor is presently wired for 480 volts

Click to expand...

Yeah, and the salt in the wound is this is probably the most difficult to get to motor connection box I've ever encountered. I took the photo of the open box by poking my iPhone in there and guessing at the "aim"....took 4 tries to get that photo !

Aside from difficult location, it looks pretty easy. It LOOKS like you take the nuts off the brass bars and reinstall them vertically connecting the 3 posts on the right center 4,5,6. Then move the left end of the black jumper wires from 10,11,12 to the left center posts where the bars were 7,8,9, and making sure the 1 jumper now goes to 7, 2 to 8, 3to9. The left posts 10,11,12 would also be tied together, maybe the brass bars are doubled up now and that would give you enough bars to do that?

From the pic I'd say posts are, from right to left,
bottom row 1-4-7-10
middle row 2-5-8-11
top row. 3-6-9-12

Your diagram seems to be page 2 of Guru's attachments, top right, delta. That figures out right, as that is "460V", the lower of the upper range voltages..

So you want the parallel variety of that, which is the "double delta" wiring shown on the same page. at top left.

JST said:

Your diagram seems to be page 2 of Guru's attachments, top right, delta. That figures out right, as that is "460V", the lower of the upper range voltages..

So you want the parallel variety of that, which is the "double delta" wiring shown on the same page. at top left.

Click to expand...

Yep....it occured to me later that I had another saw with the same make of motor...larger HP but same manufacturer and style. That one still had the wiring diagram attached, and sure enough, it was as simple as moving the brass connectors as shown in the double delta drawing (luckily, there were still 6 connectors available via double stacking in 460V mode)

Simple, but the hard part was actually getting to it...I had to lift the machine six feet in the air with forklift and risk certain death (if it fell) by doing the changeover standing underneath the machine. Otherwise it would have been many contortions and cussing with a mirror.