Update & follow up question!

[grumpyjohn01]

Just bumping a thread I started back along to get some views!!

Thread 'Motor configuration'

Apr 26, 2025

Hi all,
I have a customer who has bought at great expense a machine directly from a Chinese supplier for a specialist mushroom cultivation task and he has asked me to install.
I have identified immediately some pretty serious safety issues that need to be addressed but skipping over those for now, my main interest atm is the way the main, pretty huge single phase motor has been configured.
I have attached a drawing of the way I would expect a single phase motor with start and run capacitors to be set up and the way this one has been supplied.
Motors are not my field of expertise but I...

• grumpyjohn01
• Replies: 17
• Forum: UK Electrical Forum

and reposting below the text from my recent update, and a question.. Thanks!!

 

[grumpyjohn01]

Just bumping a thread I started back along to get some views!!

Thread 'Motor configuration'

Apr 26, 2025

Hi all,
I have a customer who has bought at great expense a machine directly from a Chinese supplier for a specialist mushroom cultivation task and he has asked me to install.
I have identified immediately some pretty serious safety issues that need to be addressed but skipping over those for now, my main interest atm is the way the main, pretty huge single phase motor has been configured.
I have attached a drawing of the way I would expect a single phase motor with start and run capacitors to be set up and the way this one has been supplied.
Motors are not my field of expertise but I...

• grumpyjohn01
• Replies: 17
• Forum: UK Electrical Forum

and reposting below the text from my recent update, and a question.. Thanks!!

Hi again all, Thanks for all the contributions to this thread, just thought I'd post an update and another question!

I have not been able to give much attention to this but finally managed to visit the site and carry out some testing which revealed a straightforward solution - the nomenclature on the terminal box on the motor was simply incorrect, U, V & Z mixed up, when rearranged it was wired as a 'standard' setup. Good.

Now I am on to solving all the other issues and have ordered parts as the reversing contactors supplied had no interlock (mechanical or electrical) and no overload.
I have now sourced a reversing contactor arrangement that has all of those features, however I have realised that with the 4 wire setup to the single phase motor, 1 wire will bypass the contactors and be permanently connected (this could be L or N I guess as 2 of the 4 wires are permanently L & N respectively whereas the other 2 switch polarity depending on desired motor direction.) therefore also bypassing the overloads.
Question is , for a single phase motor such as this, do both L & N need to pass through the overload or just (for arguments sake and most likely) just L? . If both I guess I need to find a 4 pole overload as a standalone (not hanging off T1-T3) or put a 3 pole standalone upstream of the contactors? If only L needs to pass through I can stick with the arrangement I have.
Thoughts anyone?
Thanks!

 

[brianmoooore]

It's conventional to wire 3 pole overload relays used on single phase so that the full motor current passes through each pole of the relay. This is usually done by passing the neural current through one pole of the contactor and relay, passing the live through another pair and then 'looping back' to the third pair. Whether it actually has any effect on the tripping characteristics, I have no idea.
On single phase, the live current is the same as the neutral, so there's no reason that I can see why looping back twice so that just the live goes through all three relay poles should be a problem. The only reason the neutral is fed through one pole of the relay on single phase is to get the DP switching from the associated contactor.
Someone at some time in the past produced a stand alone mounting and terminal block for a 'modern' type overload relay. I'm sure of this because I obtained and used one on a job once. Quite possibly Klockner-Mueller, since I used their contactors for years.

 

[grumpyjohn01]

Tha

It's conventional to wire 3 pole overload relays used on single phase so that the full motor current passes through each pole of the relay. This is usually done by passing the neural current through one pole of the contactor and relay, passing the live through another pair and then 'looping back' to the third pair. Whether it actually has any effect on the tripping characteristics, I have no idea.
On single phase, the live current is the same as the neutral, so there's no reason that I can see why looping back twice so that just the live goes through all three relay poles should be a problem. The only reason the neutral is fed through one pole of the relay on single phase is to get the DP switching from the associated contactor.
Someone at some time in the past produced a stand alone mounting and terminal block for a 'modern' type overload relay. I'm sure of this because I obtained and used one on a job once. Quite possibly Klockner-Mueller, since I used their contactors for years.

Thanks for this. I am aware of the 'looping back' practice and have also used a standalone overload relay before however in this case I'm not sure it would help unless I put it upstream of the contactors. I'll explain.
The new contactor arrangement is shown in the photo and the diagram shows the 4 wire setup to the motor as supplied from the factory.
wire 1 is L bypassing contactors going to start winding
wires 2 & 3 are switched polarity for main winding
wire 4 is always N going to centrifugal switch
capacitors are permanently connected to switch and start winding.

The new contactor arrangement has overload relays fitted to outgoing terminals as per pic so if I wired it the same as the diagram the full motor current would pass through 1 or other of them depending on motor direction via the neutral conductor so they should work but of course wire 1 is permanently live to the motor and would remain so in all states unless isolated at upfront isolator I plan on fitting. I feel this is sub optimal. I could of course change the wiring to the permanent neutral (currently wire 4) being the conductor that always remains 'live' at the motor and switch all the L's through the contactors but not sure that is really that much better.
The contactors I have sourced are very cheap compared to other brands which is to satisfy budget remaining on this project and those thermal relays were the only type I could find in Chint's catalogue, also I can't seem to find a 4 pole standalone of any make to put all 4 wires through.
Can you suggest a better solution? I need to get this done now and I'm running out of ideas!!

 

[Brother Blue]

Whether it actually has any effect on the tripping characteristics, I have no idea.

It has a big effect in so far as it will trip after a short period of operation if current does not pass through all 3 poles if the overload. I learned this as an apprentice when I connected a single phase motor through just 2 poles of the 3 pole overload.

The overload relay also trips on imbalance of current through the poles.

 

[grumpyjohn01]

It has a big effect in so far as it will trip after a short period of operation if current does not pass through all 3 poles if the overload. I learned this as an apprentice when I connected a single phase motor through just 2 poles of the 3 pole overload.

The overload relay also trips on imbalance of current through the poles.

so my arrangement with the 1 L wire not passing through the overload(s) won't work you reckon?

 

[grumpyjohn01]

Can anyone link a diagram of single phase reversing contactor arrangement with overload, I can't find one anywhere and as you can see am struggling to work it out!

 

[Brother Blue]

so my arrangement with the 1 L wire not passing through the overload(s) won't work you reckon?

I wouldn't have thought so as the current through the overload won't be in balance.

I don't know how it's normally done with reversing an SP motor but I'd be inclined to put an MPCB before the reversing contractors rather than use a thermal overload on the output.

Or just buy a complete reversing starter and use that

 

[grumpyjohn01]

I don't know how it's normally done with reversing an SP motor but I'd be inclined to put an MPCB before the reversing contractors rather than use a thermal overload on the output.

this sounds like a reasonable idea , must admit I have never used one before so I'll look into it, Thanks

Or just buy a complete reversing starter and use that

couldn't find a suitable one or I would have done, anyway too late now have bought the quality Chint gear!