Switch wiring help needed

[Char]

My better half has asked if I could post this request for help, hoping that one of you loverly electrical wizards will be able to help.

I apologise for bothering you, but I hope that you may be able to assist with a small query that I have.
My log saw motor switch recently packed-up. It is a switch with an electro-magnetic function (?). The motor is brushless.
I have purchased what was claimed to be a direct replacement for mine (said to be identical).
However, my switch has four wires going to the motor, but the replacement only three.
I have attached a photo of my switch and a scan of the wiring for the new one.
The live wire from mine joins to a fat red wire and also a thin black wire at the motor.
The neutral wire connects to another fat red wire.
In addition to the earth wire, there is a black wire from the switch that attaches to a second thin black wire from the motor.
I hope that this is clear.
I need to know what I have to do to enable me to attach the black wire from the motor to the switch.
I have contacted the vendor (German, I should add) who is useless.
Thank you in advance for any assistance that you may be able to give,
Mr.Char

Old Switch

IMG_20231011_100049.jpg

New Switch

IMG_20231011_100145.jpg

[hughnique]

what are the connection notes on the new switch paperwork, normally that would give you a clue

[hughnique]

From what I can see on the old switch wiring it looks as though the black and the grey are both neutrals

[niemeyjt]

Just to assist a little

https://www.kedu.cn/products_cont.php?id=397 (registration required - so PM me if you want the PDF file I have already downloaded)

https://sys2sell.de/Schalter-Stecker-Ko ... KEDU-KOA2Y

From the former, option F2 matches. U< - I am wondering if this is an NVR safety switch?

switch.png

My thinking - maybe you have the wrong part - order the correct one from Alibaba using my link above.

[RobertArthur]

Char, a very quick answer, busy in the garden.

In the first KOA7 diagram the alimentation of the motor arrives of course as L and N. Current output to the motor Brown and to my surprise Grey where you would expect blue. Extra is the undervoltage relay (U<) directly connected to N and its other end going to the motor with a black wire. So far 3 connection points, all switched. Never switch the PE /yellow/green wiring, so that one goes to contact point 4, a direct connection. The undervoltage function dtects abnormalities, voltage dropping down to about 70% and then it trips the breaker.
Safety feature, saw trying to sink its teeth in steel...a piece of tree trunk with shrapnel.

In the second diagram the PE wiring goes directly fom PE arrival to the motor, not using any contact point on the switch itself. Not unusual. Okay, three left. The L and N nothing special. Contactpoint 3: in the second diagram the internal relay is already connected to neutral, when the switch has been pushed manually to "on". It should get its power from somewhere else, in this case the L arrival. Where in the original switch it is connected to the motor assembly using a thin black wire from the switch to let a tiny current flow in the relay coil to activate the switch function, everything off.

Only first thoughts, back to the garden, i stand to be corrected and will ask a friend of mine, electric motor expert, for further advice.

[Polarengineer]

It would appear the new switch that you have does not allow the connection of the motor thermal overload protection, here is a diagram of a three phase connection for thermal protection just ignore L1 and L2 is connected to N and you have the single phase like yours.

F9300F72-1736-4EF5-9FBC-B6B131F35679.png

If you disconnect the relay U< b from 4 in your new switch and connect the black wire from your motor to b then you should restore all functions.
If I’m wrong, nothing comes to harm as the motor will not start and stay running.
Try it and I would be pleased to hear the result.

[Polarengineer]

SAFETY WARNING.. to add to my previous post. The small wire from b to 4 should really be removed completely. Terminal 4 is a neutral line and as such possibly harmless, however one never knows with wiring and one does not want any loose ends flapping around where electricity is concerned. There are enough live wires on this forum without adding to them.

[RobertArthur]

@ Polatengineer, thx for the missing link, the thermal switch inside the electric motor. It is a simple series connection with the undervotage switch/relay U<. If one should want to keep this thermal cut-out function, there might also be the possibilty to change the wiring inside the new switch assembly a little bit. Depends on the internal configuration of this switch: everything on a printed circuit board or still some "hard" wiring. One could disconnect the internal connection to Live and replace it with the thin black wire going to the thermal switch inside the motor, also connected to Live.

[Polarengineer]

RA. I have a similar saw and this switch is good old fashioned hard wire I’m sure. Apply the kiss technique.

[RobertArthur]

So far we've been looking at the switch and en passant I was again surprised by the many national electrical wiring color codes. After reading the comments made by a friend of mine the following remark: perhaps we should also have a closer look at the specifications of the motor, a photo of the name shield would be helpful. As a reminder: single-phase AC motors need a little help at the starting line and also to keep them running.

The trial and error method as suggested by Polarengineer is of course a practical shortcut.