MICRO SWITCH ON A MACHINE DOOR

[WELLSIANA]

I have to fit a micro switch to a very old machine door so it cuts the power off if the door is openend...i can easily divert the stop button circuit to activate but was not sure as its a 16 amp 3 phase machine do i need that type of micro switch as the best i can find is 15amp 380v...or because its just breaking the control circuit can it be a different spec micro switch and voltage...it will simply act as another stop button by diverting the exisiting through it ...thanks

 

[Spark123]

I take it that the machine is run via contactors? If so then the switch will only need to handle control current, not the full current of the machine.
I take it you are buying a proper limit switch for the job?
What is the control voltage - does it have a transformer in the machine? What voltage contactors?

 

[RF Lighting]

Is this machine in a workplace or in your house?

 

[333rocky333]

some machines use 240 volt control circuits
some use 415 volt control circuits
there are even ones using lower voltages

If the stop buttons operate a contactor which you would hear clonk in and out, you would need to assertain the coil voltage of that, usually on the coil itself, a rating plate or safely measured.

If it is operating a contactor then its usually only the coil current passing through the control circuit switches rather than the machine load.
If so a 5 amp rated switch is likely large enough, but its important it can switch the control circuit/coil voltage

 

[WELLSIANA]

It has a contactor but not easy too get too...the machine itself is on a red 16 amp 3 phase plug and the 3 phase is via a generator...limit switch?...i just want a micro switch to do the same job as the stop part of the stop start button if the door is openend ...there is no transformer as i know its a simple saw that cuts metal sheet but very old on a flex red plug...

 

[333rocky333]

You dont mention a neutral, if so then the control circuit may be 415 volt, are you competent to work on that voltage

 

[Spark123]

A limit switch is basically the same thing, something nice and beefy like this: http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=170571&MER=baynote-170571-pr

 

[ricicle]

Once you start altering the control/safety system of machine you become responsible. A thorough risk assessment of the machine needs to be carried out and the category of safety assessed.
It might not be a simple microswitch, it might be a keyed type such as Guardmaster or even Castell interlock system.
Make sure you are clear what is required.

 

[bhm1712]

A simple micro switch on machine fixed guarding which drops out the main contactor is not enough to comply with the machine safety directive. It doesnt matter if the machine was not originally fitted with a guard switch - you are now altering the safety protection of the machine. This machine must be fitted with an independant safety circuit which when open, must prevent the machine from being able to start without the circuit being closed (by closing the door) and then being manually reset by the operator. The saftey switch and circuit components must comply with the current machine safety directive.

 

[bhm1712]

some machines use 240 volt control circuits
some use 415 volt control circuits

In my short 10 years in the pharma manufacturing and packing industry, followed by my recent move into another high speed manufacturing industry i have never come across a machine which uses a 415v or 240v control circuit. Even on some of the oldest machines from the 60's that i have worked on and upgraded control wise were 110/92v control before i ripped it all out and put a shiny new AB Compact Logix in.

The norm these days is 24v AC or DC.

 

[Spark123]

415/400v is common in simple motor control circuits such as DOL and Star/Delta starters. Have come across it a lot!

 

[bhm1712]

So have i,

however i wouldnt really class a DOL starter as having a control circuit as such in the form which we are talking about, with DOL you apply full line voltage to the motor terminals by switching single phase onto the contactor coil etc etc.....

Usually on a machine you have the power circuit which deals with the actual supply to motors, actuators, servos and so on, and then the control circuit which deals with energising/de-energising the relays, contactors, supplying sensors, switches and operator interface lighting etc.

As im sure you know. Not trying to teach ya mam to suck eggs

 

[bernardgreen]

It would not be sensible to take 415 ( or even 230 ) volts to a switch mounted on a machinery door.

Also the switch should not be a micro-switch but be a switch in which the contacts are mechanically forced apart and separated by an insulator when the door opens. This prevents the possibility of welded contacts not opening when the door is opened, a failure which woud mean the machine could still run even though the door was open.

 

[WELLSIANA]

i dont know if we are looking at this too deep , i only asked as i was given a switch to try to fit and it was a simple 1 amp 230v door contact switch.
The machine has a stop start old metal type beside the door so to try it i diverted the stop wires through the switch....it worked fine but was the wrong way round, you had to have the door open to work the machine....the green start had to be pressed manually to restart the machine , so if it basically did the job although its hard to get to the contactor it can not be too much a load..and all connections are covered...

 

[RF Lighting]

No we aren't looking at this too deeply, it's you who isn't understanding all the implications of motor control and the risk you could pose with a botched E-stop system.