Dewhurst reversing switch

Hi everybody,

I have a Harrison L5 which I would like to reverse for single point threading purposes. Now I have been looking around on the internet how to do this or better still get my head around what is happening in the motor and the reversing switch, however my electronics skills are not all there. The motor I have is a single phase P.C.M 2.8 HP.

anyway my question if you have not guessed already is how would I go about connecting this. Most diagrams I have seen are for our standard Brooke Crompton model of motor, the terminals on my motor are marked differently U, V and W tags. (See photos) any help will be appreciated.

I will attach images next.

Edited By Mani Matharu on 17/12/2019 15:42:18

Hello Mani, first of all take a photo of the motor terminal block as it is now( in motor working mode). Hopefully you have a multi meter or a plain Ohmmeter, better still can you see making on the wires such as U1 & U2 which are the run winding wires. Also Z2, CA4, CA2, SW and CA1 & CA3. Having now got the picture or sketch of the original terminal layout remove the both links and locate U1 & U2. I think the two blue wires are connected to terminal which is CA1 & CA3. A blue wire to each capacitor. John

U1 to Dewhurst terminal 5,

U2 to Dewhirst terminal 7

Z2 to DH terminal 2

CA1& CA3 to DH terminal 6

. 240 volt supply to 1 & 3. Locating U1 & U2 the run winding is important.

Hi john many thanks for your reply. The supply live was connected to 1u and the neutral supply to 1v. Sorry John but I do not understand what you mean by the above especially the new markings you have introduced me to fro z2 to ca3. The wires are unmarked coming from windings and caps. Correct me if I am wrong but there seems to be 3 of them (capacitors)? I will upload another picture showing which caps these wires are terminating at. I do have a multimeter

the wires below the terminal block going to the windings are also unmarked. Just got colours brown and black total of 6 wires 2 black and 4 brown.

Back again Mani. I see your motor is different to the one my friend has,it had just two capacitators and yours has three. All the marking I mentioned came from my friends motor and was attached to each wire.

Leaving all that to one side and looking at the latest picture from you, I think all you have do is move the copper links from the vertical positions to the horizontal positions. I notice both copper links have proper machined slots in them to facilitate easy repositioning. The electric supply still goes to 1u and 1v as before.John

So John, I have moved the copper plates to the horizontal position, please do not mind the connections they are not permenant for this exercise. The motor reverses. I have had help from a cousin also which has boosted my confidence in doing this. I need to just work out how to get the reversing switch to do the switching.

see pics below, I have also come across an instruction regarding the Dewhurst switch. Just for convenience of others.

Mani, before you finalise the connections best to get a cable gland to fit the threaded entry, supports the cable and will prevent damage on the threads.

Emgee