Contactor wiring, break ring circuit through a stop button

[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