Socket outlets supplied via an emergency trip button

[stever37]

I was wondering if any one has installed anything like what I have been asked to do.

It is in a training enviroment and they would like approx 5 sockets installed allong a wall that can have the power switched off via an emergency trip button by the teacher if required.

I was thinking a radial circuit fed via a contactor which opens when the emergency trip sw is hit. Not that experienced with contactors to be honest. If the contactor is N/O therfore requires a supply to keep it closed (which will be the normal state) will this not eventually burn out the energising coil ? Or does a contactor `latch in`. Was thinking of the control circuit via the emergency trip sw with N/C contacts hence when operated de-energises the operating coil of the contactor thus de-energising the radial circuit. (But concerned about burning out the operating coil)

I am on the right track here ?

 

[telectrix]

you need a DOL starter. wire the EM stop in series with the stop button. when you press the start button, the coil energises and pulls the contactor in, which latches through the slave contacts.

 

[Engineer54]

you need a DOL starter. wire the EM stop in series with the stop button. when you press the start button, the coil energises and pulls the contactor in, which latches through the slave contacts.

Maintained Tel, ...latched is performed by mechanical means,. ...lol!!

 

[tigerpaul]

Make sure it is wired so that the em stop button breaks the circuit, not makes the circuit. Otherwise it will not be fail safe.

 

[telectrix]

Maintained Tel, ...latched is performed by mechanical means,. ...lol!!

i stand corrected, as usual. LOL.

 

[Engineer54]

Make sure it is wired so that the em stop button breaks the circuit, not makes the circuit. Otherwise it will not be fail safe.

It'll also mean the sockets will never energise until the stop button is depressed!! lol!!!

 

[telectrix]

i think he means breaks the circuit when pressed.

 

[ackbarthestar]

I've seen latching EM stops wired in series where local unlatching causes a restart, not what I call safe
Either use a DOL motor starter or a contactor with a key switch with an auxilliary contact

 

[Engineer54]

I know, but his second statement would mean the the control wiring was wired thru the EM stop buttons NO contacts, which when pressed would close the contactor energising the sockets...

 

[Engineer54]

I've seen latching EM stops wired in series where local unlatching causes a restart, not what I call safe
Either use a DOL motor starter or a contactor with a key switch with an auxilliary contact

Most EM stops are latching, that need to be released to re-energise. So those EM stops must have been wired wrongly in the first place...

Depends how the coil has been wired to energise, You need to use the correct accessories to suit the application

 

[netblindpaul]

As has been said generally a DOL starter type system.
Remember Emergency Stops are just that red, mushroom headed, latching and on a yellow background as defined in statute law.
There is also a code of practice, not an ACoP, but a CoP for such systems that must be followed to comply again with statute law.
BS4163 the title starts Schools, but it covers a wider scope than this.

 

[High Tower]

Use Em stop buttons with keys, permanent supply with a NC stop buttons wired in series......simples!! hit a stop button and it drops the contactor out

 

[stever37]

Guys

Thanks for info and I am enjoying the `banter`. I get how to install now, but can you ease my concern. If I use a DOL and the sockets are left permanantly energised , will the contactor coil burn out sooner rather than later or am I missing something ? As I said before not that familiar with contactors.(i.e are the operating coils designed to be permanantly energised ?)

 

[netblindpaul]

HighTower,
You cannot allow the circuit to re-energise on release of the stop button, this is against PUWER98 requirements, and is not in compliance with the CoP.
It is also down right dangerous.
However, you are IMHO spot on with the keyed s-stops it is what I use and once the reason is explained to the customer they normally agree, in this situation, not on general industrial machines mind!
However, I did fit one today to a machine, but it is a bit of a special environment where the users of the machines are very limited.
Can't take any photos as cameras are not allowed either!

 

[netblindpaul]

stever37,
Yes contactor coils are designed to stay energised, if you study the specs, you will find a pull in current and a holding current, the coils are so designed to be current limiting once the armature has shifted.