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.

 

[littlespark]

I would simplify things and place the socket RCBO in its own garage consumer unit, and the contactor on the supply to this CU.

What is the ring circuit used for? Power tools in a workshop?

 

[snowhead]

Who has decided the Circuit needs an E.M stop and what is the reason for this decision?
Has whoever made the decision thought of the consequences of the EM stop being reset and whatever is plugged in suddenly starting up?
As it would be on 13amp sockets, anything in the future could be plugged in and subject to uncontrolled restart.

Normally anything under Em Stop control would have individual no volt release protection to stop the above happening.

 

[Spoon]

Don't call it an Emergency Stop..... Just a Stop Button.
Next fit a Shunt Trip for the 32A RCBO.

 

[mainline]

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.View attachment 108600

Why not use a latch off-key reset stop switch. ?

Emergency Stop Key Release Pushbutton Station IP65

Compact dimensions

www.cef.co.uk

 

[Sparkyy57]

Who has decided the Circuit needs an E.M stop and what is the reason for this decision?
Has whoever made the decision thought of the consequences of the EM stop being reset and whatever is plugged in suddenly starting up?
As it would be on 13amp sockets, anything in the future could be plugged in and subject to uncontrolled restart.

Normally anything under Em Stop control would have individual no volt release protection to stop the above happening.

It is a stop button that needs a key to disengage it again

 

[timhoward]

It is a stop button that needs a key to disengage it again

It’s more that when it’s disengaged it turns on again anything plugged in e.g an angle grinder could unexpectedly start up. There is stuff in regs about avoiding rotating machines starting without warning.
A possible solution might be to also change the sockets to non-latching RCD sockets so restoration of power requires each socket to be individually reset.
I still don’t hugely like this though as by adding a facility to stop everything it’s introducing multiple scenarios of a button unexpectedly starting things.

 

[davesparks]

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.View attachment 108600

No, to the best of my knowledge that is non-compliant as the contactor will re-energize immediately when the stop button is reset.

There should be a minimum of a seperate reset button.

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.

 

[davesparks]

Why not use a latch off-key reset stop switch. ?

Emergency Stop Key Release Pushbutton Station IP65

Compact dimensions

www.cef.co.uk

That would still need a seperate reset control.

There's a big issue with the key reset type of E-stop in that human nature is to leave the key in it so that you don't loose it. This means the button can't be as easily operated as it should be.

 

[mainline]

That would still need a seperate reset control.

Why ?

There's a big issue with the key reset type of E-stop in that human nature is to leave the key in it so that you don't loose it. This means the button can't be as easily operated as it should be.

If someone is silly enough to leave the key in after going to all the trouble of fitting a key to reset stop.

The same could be said for a tripped RCD or MCB do we need a separate reset for them as well ?

 

[davesparks]

Why ?

Because, to the best of my knowledge it is one of the minimum requirements for emergency stops of any type, this isngiverned by legislation and not bs7671. I'm far from an expert on the relevant legislation though so yes I may be wrong.

If someone is silly enough to leave the key in after going to all the trouble of fitting a key to reset stop.

But you can't design a safety system based on whether it would be silly for someone to do something, these systems need to be designed failsafe and if one possible failure is a key being left in an e-stop then it should be designed out of the system.

The same could be said for a tripped RCD or MCB do we need a separate reset for them as well ?

The same cannot be said for those things, they are completely different and governed by completely different rules!

An MCB or RCD will automatically trip again if the fault still exists, an E-stop will not automatically press itself if reset in error.

If the E-stop fails to latch in the off position for any reason then having it electrically latched and requiring a second deliberate action to reset it will prevent a dangerous situation.

 

[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.View attachment 108600

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 ?

 

[mainline]

Because, to the best of my knowledge it is one of the minimum requirements for emergency stops of any type, this isngiverned by legislation and not bs7671. I'm far from an expert on the relevant legislation though so yes I may be wrong.

Emergency switching: 537.4​

Emergency switching should be provided for any part of an installation where it is necessary to isolate the supply quickly to remove unexpected danger.

In installations with rotating machinery, this is usually done by using ‘stop’ buttons. Care should be taken to ensure that the stop buttons are…

• Near to the machine / equipment
• Should not be capable of being reset remotely, unless with a key switch.
• If remote resetting is possible, then the activated stop button must remain activated at the point of the danger until being reset once the danger is removed.
• In areas where there are untrained people, the stop buttons should lock when operated.

There is a difference between an emergency stop, generally used on moving machinery, and emergency switching off to turn off a few sockets, which is what the OP is intending.

An MCB or RCD will automatically trip again if the fault still exists, an E-stop will not automatically press itself if reset in error.

That's only if a fault is still present, it could be that the fault is intermittent, such as a partially cut cable.

If the E-stop fails to latch in the off position for any reason then having it electrically latched and requiring a second deliberate action to reset it will prevent a dangerous situation.

Emergency stop is an emergency operation intended to stop a process, system, machine, or a movement that has become hazardous.


Emergency switch off triggers an operation of switching off the supply of electrical energy and aims to reduce risk of an electric shock or other hazard.

 

[littlespark]

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 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.

 

[mainline]

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 ?

The wiring is fine.
You probably don't need to disconnect the Neutral, depending on the earthing system.
In fact, you don't even need a contactor.

 

[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.