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AC Motor 4 wire


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VC11/02/2018 14:49:14
40 forum posts
9 photos

Hi to all the "Sparkies"

Have fitted a ZP Mottori Elettrici 1/4 hp motor to my Quorn .

Need the beastie to run forward and reverse.

Has four wires coming out two green and two blue and a capacitor.

Motor runs in both directions but needs to be hand spun to start and the "fun" part is if I touch anything metal in the shed eg steel bench I get a shock

So help please with a wiring diagram

Thanks in advance

John Rudd11/02/2018 14:54:24
1161 forum posts
55 photos

My advice, fwiw.....scrap the motor and buy a new one.....its dangerous if you are receiving shocks from it.

You could get it tested/repaired by a local motor rewinders, but is it worth it?

Risk management......

Billy Bean11/02/2018 15:00:59
174 forum posts
1 photos

WIth regard to the shocks I would call in a qualified sparky to check out your shed wiring, and in particular your earthing and bonding system.

Billy Bean11/02/2018 15:44:04
174 forum posts
1 photos

I have just looked at your shed photo in the picture album.

That is the first time I have ever seen an extension lead with SEVEN items plugged into it.

Seriously, as a qualified sparky, I would advise getting a qualified electrician in there asap.

Brian Wood11/02/2018 18:27:08
1608 forum posts
35 photos

I would first put a meter across all 4 wires in turn and the motor case to see if there was leakage before doing anything else, then decide on the way ahead


peak411/02/2018 18:48:50
544 forum posts
41 photos
Posted by Billy Bean on 11/02/2018 15:44:04:

I have just looked at your shed photo in the picture album.

That is the first time I have ever seen an extension lead with SEVEN items plugged into it.

Seriously, as a qualified sparky, I would advise getting a qualified electrician in there asap.

Notwithstanding the issue about getting a belt off the motor, what's wrong with having 7 items plugged into an 8 way extension board, provided that it is fused at 13A, and is itself plugged into a suitable socket.

OK I certainly wouldn't recommend running a welder and a compressor off one, but if the total current draw of the devices is less than the rating for the board, I'm not sure there's an issue, or is there??

Olson boards are much used in certain fields, often with up to 10 sockets.

Robbo11/02/2018 19:09:57
1449 forum posts
126 photos


Have a look at page 3 on the pdf file in this link, should help, you can see which are the start and run windings and take it from there. **LINK**

Edited By Robbo on 11/02/2018 19:11:19

VC11/02/2018 19:17:00
40 forum posts
9 photos

Thanks for the reply's

Top of my head nice and brown and not smelling that great.

Have had a look at my photos and there are none of the inside of my shed or the seven sockets

plus extension lead.

Not saying that I don't have multi plug sockets but only run one thing at a time.Seemed a good way

to save time ???

So unless Google Earth has taken the time and trouble to "stalk" me and my shed

Must just be MAGIC.

No help with the wiring yet

Billy Bean11/02/2018 19:28:30
174 forum posts
1 photos


Edited By Billy Bean on 11/02/2018 19:28:48

Billy Bean11/02/2018 19:30:42
174 forum posts
1 photos

Have had a look at my photos and there are none of the inside of my shed or the seven sockets

Just had a look and found the one above ?

This looks like an eight way block with 7 plugs in it unless I have made a mistake .

Edited By Billy Bean on 11/02/2018 19:38:25

Billy Bean11/02/2018 19:52:18
174 forum posts
1 photos


You may feel I am being a pain in the arse and giving you a hard time on the electrical safety / good practice side of your post.

As an apprentice electrician I saw my mentor electrocuted - metal benches , earthing , bonding all questionable?

I am trying to offer you good advice - touching metals benches and getting a belt - the word FUN sticks in my throat.

I hasten to add that some forty years later the image is still crystal clear in my mind.

Please accept my comments in the spirit in which they are offered.

Enough said - I will not post on this matter any more.


Edited By Billy Bean on 11/02/2018 19:53:05

SillyOldDuffer12/02/2018 09:58:22
3126 forum posts
628 photos


Can anyone help with an answer to Vic's original question? I don't know enough to suggest more than:

  • The two BLUE wires are the RUN winding, and the two GREEN the START winding, OR
  • The two GREEN wires are the RUN winding, and the two BLUE the START winding
  • Asking on the forum how the motor might be wired to start in forward or reverse, which you've already done!

Vic: photos of the motor would help and also wiring diagrams of what you tried if you can put them up.

The shock is worrying: either the motor is faulty or your test wiring was defective. (Everyone makes mistakes!)

I initially read Billy's comment as a rather unwise rebuke alleging misuse of an extension lead. Re-reading his posts carefully, I think his actual concern was with " if I touch anything metal in the shed eg steel bench I get a shock". If you have a workshop with metal fixtures it's well worth earthing them. A normally safe metal bench can become lethal if an electrical fault or wiring mistake somehow makes it Live. If it's earthed, which is easy to do, the fault will blow a fuse or pop an RCD rather than zap bystanders.



Edited By SillyOldDuffer on 12/02/2018 09:59:37

Brian Wood12/02/2018 10:31:40
1608 forum posts
35 photos


I would add to that above by observing that it is not at all clear if the live bench has come about after wiring the motor or was a pre-existing condition.

If the latter I would definitely share the concern to that expressed so eloquently by Billy Bean that it needs sorting out in a hurry before the coroner needs to be informed The practice of multiple plugs into an eight way socket isn't good practice in a case like this, it would be fine serving a bunch of computer equipment for example which can be conveniently grouped together at the back of a cabinet.

Regards Brian

Edited By Brian Wood on 12/02/2018 10:37:11

Emgee12/02/2018 10:58:52
820 forum posts
173 photos

Vic, look at this topic **LINK**

John has done a sketch showing 2 sets of windings, one end has both windings joined together and is the neutral connection, a capacitor is connected across the other windings ends, live is fed into one end of the capacitor for fwd, changing power in to the other side of the capacitor reverses the motor.

This is as used for the Parvalux range of FHP motors, here is a link to Parvalux site

Best head the advice given by others in relation to getting shocks from metal benches or other equipment.

Make your installation safer by adding a 30ma operating current RCCB (Residual Current Circuit Breaker) to the incoming supply.


Edited By Emgee on 12/02/2018 11:01:17

Martin 10012/02/2018 13:02:21
235 forum posts
6 photos

There is nothing wrong with 8 (or even 10 sockets as I have on an extension lead under my desk) IF the thing is properly fused.

It might not even be a motor fault, you might be in a situation where there is no effective earth provision, nor adequate cable protection, nor adequate protection from electric shock.

Wiring to outbuildings is never just a case of extending the cabling. Without a proper understanding of the existing installation, from the incoming cable to the consumer unit, to the type of earthing in the main property then you cannot even start to know how to effectively and safely wire and earth the outbuilding.

There is some guidance here (to the 16th edition of the wiring regs, but we are almost to the point of using the 18th edition) It is not extensive nor does it cover all situations.

I've seen a similar 'shock' problem in a kitchen of a relative many years ago, the cooker earth had fractured in the consumer unit due to bad stripping of the sheath, one change of ownership later and a couple of years later the cooker oven element had failed (the issue I was called to) but the element had burst and shorted to 'earth' but as an effective earth was not present the entire cooker was raised to live potential, the fuse also having not failed due to zero fault current. The floor was wood, quite dry and thus reasonably insulated, but a potentially fatal shock was less than one outstretched arm away with a very well earthed metal sink. Rather than just fix the cooker and the failed earth, a full wiring test was performed followed up with the installation of a new consumer unit with an RCD.

not done it yet12/02/2018 16:03:24
1961 forum posts
11 photos
Posted by Martin 100 on 12/02/2018 13:02:21:

There is nothing wrong with 8 (or even 10 sockets as I have on an extension lead under my desk) IF the thing is properly fused.


They would not make the things unless the sockets were expected to be used. Certainly more aimed at computer installations than a workshop, perhaps?

A far worse installation could be an extension lead with only two cores....

Edited By not done it yet on 12/02/2018 16:03:49

Mike Poole12/02/2018 16:25:28
1406 forum posts
41 photos

A band playing in our village hall kept tripping the sound level monitor which seemed to be set ridiculously low. Only the stage area sockets are via the limiter so the bright idea to run the stage from an extension cable was soon put into play, somebody turned up with a garden machinery extension which only had two cores and a 13A plug and socket on each end. I insisted they did not use that one, lucky I was there I think. There must be accidents that happen due to extension leads with no earth. I must say I am not a fan of double insulated equipment I always feel that it would be safer with metal parts earthed anyway. I think orange should have been reserved for two core cable but you never know at the moment unless you check.


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