Myford wiring

Hi folks.

I have a Myford super 7 with a Brook,Crompton,Parkinson 550w single phase motor. I wired this in to a Dewhurst reversing switch as per the wiring diagram in the Myford manual, but when I tried to start the motor the RCD in the house tripped.

Upon firther inverstigation of the motor internal wiring, i see two fixed links between terminal AZ-Z and A-T. So, my question is are these links meant to be there? Or are they here because the previous owner had a 3 pin plug wired directly into the motor and the only way of starting it was by switching the wall socket on? I have attached a pic of the terminals for clarity.

Scott

Edited By Scottmk1 on 13/03/2013 15:31:35

My Myford book shows Crompton as having. A and AZ as the running windings, and Z and T as the starting windings.

Your pic. does not look like that at all.

I venture that the motor is wired 3phase, someone will be along soon to correct the problem.

Clive

Hi Clive, thanks for your reply.

I'm not sure about it being wired for 3-phase. If I connect a single phase supply to the motor (Neutral to terminal A & Live to terminal AZ) the motor runs.

From memory,and hope I've have got it correct. Remove both links.

Connect Live to terminal 1 on the Dewhurst switch Neutral to terminal 3. Connect terminal A on the motor to 5, AZ to 7, the other two terminals on the motor to 2 & 6 either way round. The motor might run opposite direction to that shown on the switch, if so exchange 2 & 6. By the way Dewhurst switches a notoriuos for bad arcing contacts,could that be the trouble, they are not designed to be used as ON/OFF switches inspite of them being fitted to Myford lathe.Better get a proper motor starter with Green/ Red push buttons and no volt release. Used the starter as ON/Off and the Dewhurst for direction only. Best of luck and if you need any more help call out. Ted

From memory,and hope I've have got it correct. Remove both links.

Connect Live to terminal 1 on the Dewhurst switch Neutral to terminal 3. Connect terminal A on the motor to 5, AZ to 7, the other two terminals on the motor to 2 & 6 either way round. The motor might run opposite direction to that shown on the switch, if so exchange 2 & 6. By the way Dewhurst switches a notoriuos for bad arcing contacts,could that be the trouble, they are not designed to be used as ON/OFF switches inspite of them being fitted to Myford lathe.Better get a proper motor starter with Green/ Red push buttons and no volt release. Used the starter as ON/Off and the Dewhurst for direction only. Best of luck and if you need any more help call out. Ted

From memory,and hope I've have got it correct. Remove both links.

Connect Live to terminal 1 on the Dewhurst switch Neutral to terminal 3. Connect terminal A on the motor to 5, AZ to 7, the other two terminals on the motor to 2 & 6 either way round. The motor might run opposite direction to that shown on the switch, if so exchange 2 & 6. By the way Dewhurst switches a notoriuos for bad arcing contacts,could that be the trouble, they are not designed to be used as ON/OFF switches inspite of them being fitted to Myford lathe.Better get a proper motor starter with Green/ Red push buttons and no volt release. Used the starter as ON/Off and the Dewhurst for direction only. Best of luck and if you need any more help call out. Ted

Hi, thanks for your input.

Your memory seems to serve you correct and its just the links that are causing me trouble. i will remove them and try again.

Scott

I agree with Teds wiring of the Dewhurst switch. My pic. shows no links attached.

Is there no diagram under the cap over the connection box?

Clive

Hi Scott, I have some PDF dos of the wiring diagram from the Myford handbook if you message me with your email I will send them to you.

John

Ted has got it right. Simply all you need to do is remove the links, they are there for direct one-way connection. and then wire to the Dewhurst in accordance with the diagram and Ted's instructions.

Also, do as Ted says and fit a decent on/off switch such as a Crabtree on-line (DOL) or an NVR switch between the Dewhurst and the power supply.

Phil

Clive, there is no wiring diagram under the cover of the motor, so I will just remover the links and see how it goes.

John, I have the original Myford book, but a PDF copy would be great for reference, will message you my email address.

Thanks to everyone else for their input/help. I will get hold of a dol most likely and use that. The Dewhurst switch I have is new and unused so it ould be a shame to ruin it.

If you go for a DOL, you will find it is built for 3-phase use, with 3 connectors, 3sets of coils etc. where the inputs are L1, L2, L3 and the outputs are A, B, C. It will still be fine with single phase and just needs a link from say input L2 to output A. Then connect your input to L1 (line) and L3 (neutral) and take the outputs from B (line) and C (neutral).

If you already know this, apologies, just thought it might be worth noting in advance. The above is the scheme recommended by Tubal Cain in his "Model Engineer's Handbook", and is what I have used several times.

Phil

Hi Phil, thanks for the advice, no it wasnt something I was fully aware of already so your advice is welcome.

Scott

Just as an update, wiring the motor/switch combo as per the instructions worked once the two links were removed. Now I just need to get the on/off starter as advised.