Reversing switch

I have recently acquired a 3 phase motor for my horizontal mill, and I’m in the process of wiring it up. It struck me that it would be useful to have a reversing facility, because the mill table has a power feed and it would be nice to let the motor wind the table back to the start rather than doing it by hand.

It happens that I have a reversing switch that I bought once but never got around to installing. So I started wiring it up but then realised that it is a single phase reversing switch.

As I understand it, reversing a 3 phase motor is dead simple. One simply switches any 2 of the 3 wires. I can’t help thinking that this can be done with the switch I have - but when I think about the circuit, my head hurts. Obviously 1 wire goes straight through, but the other 2 need to be split.

Does anybody know how to do this?

It’s probably worth mentioning that I have a NVR switch which will also be on the mail to isolate, the reversing switch and motor entirely.

Steve

Edited By Steve355 on 29/04/2023 19:02:09

Any chance of a picture of the two terminal sides of that switch? Not enough to go on from just one image.
Maybe its the angle but that switch looks to have very little clearance between the contacts and the cover and looks poor quality to me. Does it have a make and or part number?

Robert.

How are you obtaining the three phase to the motor?

If it from a VFD, it is not recommended to use a switch downstream of its own control circuitry.

Could you confirm whether the NVR switch you have is single or three phase.

The best way to understand your reverse switch is to map it out with a continuity meter. Presumably it has three wires going in and three wires going out, and the switch has three positions - forwards, off and reverse.

Diagram (Fig 2 and Fig 3) that might help here:

https://www.industrial-electronics.com/motor_control/3h_Reversing-Motors-Drum-Switch.html

There is another convention with no OFF position.

For this two supply phases would go to 1 and 5 (or 2 and 6) and two motor phases to 3 and 4. The third phase is directly connected.

Robert.

Aha…. There is a circuit diagram on the inside of the lid

The NVR is 3 phase. The reversing switch is no doubt mediocre quality, but the contacts all seem to be substantial, if the case is a little tight.

So I think it’s the style Robert showed in his diagram. He may be correct.

Done it. Once it’s wired up, it’s easy to see how it works. Thanks Robert.

Steve

Hi Steve,

Glad you got it sorted. Please make sure the cover is well earthed. Preferably with a lead rather than relying on the screws. It looks way to close to the terminals. Any distortion, like a knock from bit of stock could cause it to make contact. A bit is insulation inside the cover would not be a bad idea either.

Robert.

Steve , FYI. Following on from Robert's excellent suggestion , thin plastic sheet is available from model shops such as Leeds Model Shop and Nitro Models in Rotherham. In fact just bought an A4 sheet of 0.020" material from NM for only £2.00. No connection with either supplier. Hope you find this of interest.