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Need assistance on wiring for my lathe motor

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ron vale 116/07/2020 14:11:36
37 forum posts
5 photos

The preamble

I know NOTHING about elecrics..Sad i know but some people grasp it, other dont, i am one of them, so anything that tells me that this winding is secondary and voltd,amps watts go right over my head pleae do not get techbical it will not help Sorry to be blunt but that is the way my brain is. It jsut cannot get anything electrical in it... even computers i have trouble with, ( but onlt the theory side, using them is ok ,but if it doesn;t work, the i get someone in)

Thats it

Now a few weeks ago my Crompton motor has been making 'noises'

disconnected the wires from the motor from the Dewhurst rotary switch and noted what went where so far so good this, i can deal with

Took it to the local motor repair shop.. new bearings reqd Fixed and brought home yesterday And this is where the problems start. The gremlins that live in the shed have taken the diagram of what went where!!

Not to worry there is a diagram on P19 Fig 25 of the set up to contact it all back. AAARGH the colours are all wrong

jumping forward a bit the terminals on the dewhurst are ion the LH side T1-4 and on the right T5-8 there is an earth connector above T5

Still with me?

The powerto the switch uses T1 Brown and T3 Blue which corresponds to the Fig 25 diagram

Now this is where my brain goes into neutral

Fig 25 shows that connections of the motor , wire colour and termination on the switch as,

A1 black T5

A2 black T7

Z1 red T2

Z2 red T6

However my motor set up has the following

Terminal A brown

A2 brown

T blue

Z blue

Which knackers me what colour is now what?

To make it really confusing is when i did a continuity test i gor the following results ( i call the blue ones B1 and 2 and the Brown as B1 and 2

Thr battery used showed 1.4v ( see i do know a bit!!)

B1 to Z 1.67??????

B1 to T 1.4

B2 to Z 1.4

B2 to T 1.4

Br1 to A 1.4

Br1 to A2 1.4

Br2 to A 1.4

Br2 to A2 1.4

I was hoping to get a 0 on a couple of these readings!!

Now any ideas on what wire i put on what terminal

IIRC the browns went T2 and 6. which equates to the red in fig 25

Blues must go on T5 and 7

If i just connect them up what could go wrong and if the motor runs backwards in the forward position. wI suppose i would have to reverse 2 wires but what ones

In times like this i am glad i turned down that job in Bomb disposal!!!

Any thoughts and explained so a three year old can understand?

Sorry for the length of this Hopefully all the info you need is there

ron vale 116/07/2020 16:20:15
37 forum posts
5 photos

Sorry, left off the bit where i found the diagram. It is Fig 25 on P19 of the Myford S7 manual

Emgee16/07/2020 22:10:40
1545 forum posts
219 photos


Have you details of the information on motor plate ?

How many wires come from the motor and what colours are they ?

A picture or 2 of the motor terminal box may help.


ron vale 117/07/2020 00:20:13
37 forum posts
5 photos


It is now back on the lathe and picture taking is a bit awkward!

The switch is a Dewhurst drum type that has forward and reverse

The Myford S7 manual (i think you get download it) on P19 Fig 25 shows the wiring diagram for such a switch

The motor sows four terminals A1 and A2 and Z1 and Z2

A1 is black and goes to Switch T5

A2 is black and goes to Switch T7

Z1 is red and goes to to switch T2

Z2 is red and goes to switch T6

My motor is a Brook Crompton Parkinson and has four terminals


Z is Blue

AZ is Brown

A is Brown

T is blue

I feel rather aprehensive of doing a 'i will just try this....' just in case i blow up half of Berkshire!

If you could say put this blue from Z on Terminal X and the brown from T on term Y

is really all i need.( plus the other two locations)

The change of terminal nomenclature threw me completely and the change of colour just put the icing on the cake!

Brian Morehen17/07/2020 08:34:09
94 forum posts
11 photos

Motor Blue is now neutral was Black

Brown is now Live was Red I presume this is now the colours of the leads on your repaired motor

If the motor leads were disconnected from your Dewhurst control by you The only difference is in the colurs beingchanged whichis the new format IE Blue was Black Neutral Brown was Red Live

Hope this is the answer to your problem I think it is really the fact that the colouse on your motor have changed.

Regards Bee M

Malc17/07/2020 09:36:37
73 forum posts
5 photos

Hi Ron,

I have an ML7 running on a Crompton motor with a Dewhurst switch. I have a diagram of my set-up (Word document) . If you PM me I will email you a copy if you think it will help.


ron vale 117/07/2020 10:20:18
37 forum posts
5 photos


If your terminals on your Crompton are like mine Z, AZ, A T in the sequence Blue, Brown, brown, Blue that would be great


I have forearms like Popeye cranking the thing around by hand, and no monkey to dance to the music!!

Malc17/07/2020 10:35:24
73 forum posts
5 photos


My motor has the same lettering as yours but I have used my own colours of the cable I used between the motor and the Dewhurst switch. I will try to send you a copy using the “Message member” at the bottom of your post but I don’t usually have much luck on this site.


Malc17/07/2020 10:41:18
73 forum posts
5 photos


Sorry but I don’t think the diagram went with the message. Send me your Email address if you would like it.


ron vale 119/07/2020 14:21:43
37 forum posts
5 photos

Case now Closed, and a VERY BIG public Thankyou to Malcolm, who 'held my hand' and got me there in the end

Thanks again Malcolm..I owe you a few beers


Harry Wilkes19/07/2020 14:53:58
929 forum posts
61 photos

Thanks for letting us know and glad you got it sorted


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