Contactor wiring, break ring circuit through a stop button

[Sparkyy57]

Hi guys , I have to break a ring circuit through a contactor with an emergency stop button .. just want to double check my wiring in the diagram is correct .. haven’t done much of this sort of work so any feedback is appreciated.

 

[mainline]

The instructor will be the “trained” individual and will know that all machines are off or unplugged before turning on the circuit.

We don't know what the instructor is trained in, he may be only good at sticking soles on shoes.

 

[DPG]

I'd just go for an isolator switch. Nice and simple and does what is required.

 

[Sparkyy57]

So it’s not an emergency stop?

Just an isolator?
Simple on/off switch to control the contactor would be fine.

The instructor will be the “trained” individual and will know that all machines are off or unplugged before turning on the circuit.

They have asked for the stop button that needs key to renegage

 

[mainline]

They have asked for the stop button that needs key to renegage

The contactor would be a N/O with a N/C stop switch.
You don't need a 4 pole contactor, a double would be fine or as said even a single depending on the earthing system.

 

[davesparks]

I should add, The scenario for this wiring is in a classroom situation , for the instructor to kill the power when leaving the room. There won’t be any power tools used in this scenario so there shouldn’t be any reason for issues with anything starting up when engaging the stop button again .
Having said this , will the wiring be ok ?

So not an emergency stop at all then!

You just need a normal switch operating a contactor

 

[DPG]

So not an emergency stop at all then!

You just need a normal switch operating a contactor

Indeed. But why not just use an isolator switch? No need for the contactor.

 

[davesparks]

They have asked for the stop button that needs key to renegage

So it's to prevent unauthorised switching on?
You'd be better off with a key switch than an e-stop button

 

[davesparks]

Indeed. But why not just use an isolator switch? No need for the contactor.

Assuming this is an existing circuit it may be much easier to install a contactor next to the DB and just run a switch cable rather than re-routing the circuit to the location of the switch.

 

[DPG]

Assuming this is an existing circuit it may be much easier to install a contactor next to the DB and just run a switch cable rather than re-routing the circuit to the location of the switch.

Fair point.

 

[westward10]

Used to see these in schools all the time but not so much anymore. Mostly a 6.0 to a cooker switch then the ring final from there.

 

[SparkySy]

I was going to say ^^^^^
At school we had an isolator in a store cupboard in each classroom, some of us used to find it amusing to switch the ones in the IT rooms off until they started locking the door!

 

[Simon47]

How far away from the RCBO is the contactor going to be? You'd be better off having a single 4mm conductor from the RCBO to the contactor.
If the contactor is far away from the OCPD then somebody could mistakenly add sockets to the ring before the contactor.

My first thought was that as drawn it's introduced the potential for a contact to fail and because everything still works it won't be noticed. As you say, better to have a single larger cable to the contactor and then split out the RFC after it as a lollypop circuit.

Used to see these in schools all the time but not so much anymore. Mostly a 6.0 to a cooker switch then the ring final from there.

I remember back in school a woodwork teacher starting to give me a (gentle) ticking off when he came back into the workshop and saw me leaning on an e-stop. He stopped when I pointed out that it was to stop my classmates from maiming themselves or each other playing with the machinery while he had left a bunch of mischievous teenagers unsupervised in a woodwork room.

I also remember that in one of the metalwork shops, the contactor had developed a fault, so each time it got turned off, a teacher had to climb a ladder and push it in with the wooden handle of a hammer - with the cover having been left off so that the armature was suitably exposed for the purpose.