Wiring interlock switches into machine controls to inch only when doors open

[GaryM]

One potential job that needs looking at (not been to site yet) is to fit 3 interlocks to doors on a Webster & Bennett vertical borer.
The way they want it wiring is so that the table can only be inched when any of the doors are open.
I'm not sure if there's an inch button though assume yes as that's what's been mentioned.

Any brief ideas of where to interface the N/C contacts of the guard circuit?

 

[Jonesy83]

can they be wired in series with the hold open contact

 

[GaryM]

That's what I considered but so used to wiring into stop circuits and not start circuits.
I was just wondering if I was missing something.

 

[Knobhead]

I’m sorry but you need to find / give a lot more information. We can’t 2[SUP]nd[/SUP] guess how it may be wired.

 

[GaryM]

No apology needed though I was talking more 'in principle' than wire for wire. No worries though.

 

[Knobhead]

The borer will most likely have 3 position control XYZ so don’t be surprised if you have to break in to several circuits.
It sounds a good project to get involved with. But don’t forget to keep in mind your responsibility regarding safety. Engineering shops are fantastic at coming up with shortcuts around safety gear.

 

[GaryM]

Engineering shops are fantastic at coming up with shortcuts around safety gear.

They certainly are Tony, past experience tells us that. Madness really.

 

[netblindpaul]

So they want to bypass the safety systems with the guards open and allow machine movements in inch?

You will need NO & NC contacts on the switches and a couple of relays, all will have to be safety rated.

Probably a full blown safety relay TBH as well.

 

[GaryM]

So they want to bypass the safety systems with the guards open and allow machine movements in inch?

That's basically the script, yes.
It'll be the company who write up a new risk assessment after the modifications so as long as they're comfortable with the arrangement....

 

[netblindpaul]

OK, as long as you get that IN WRITING!!!

You will need to wire the NC contacts of the door limits into the e-stop circuit.

You will need to wire the NO contacts of the door limits into the Inch circuit.

You will now need to find a way of enabling the e-stop circuit again when the doors are open!

You may need a 2 hand device, or look at having 2 levels of e-stop circuit!

The basic e-stop circuit from the stops which activates at all times.

Then a 2nd level which can be bypassed for the doors open.

Please remember if you are designing this, then no matter what, you could still be held liable.

You will need suitable and sufficient PI insurance to cover the design, else if things go wrong you could be left carrying the can personally.

 

[vaughant]

Just picking up on something Paul put about hand control.
We use a system in work where there's actually a 2 stage hand control pendant,you can push it down slightly to let it move in inch but if you push it right the way it cuts out.
I think the fact it goes off when fully depressed is so it's even more difficult to overcome illegally,particularly by production i.e tiewrapping the hand switch shut so 2 hands can be put in the machine.
It's quite common practice to use an enable pendant in the places where I've worked,most came directly from the manufacturers,but as Paul is more heavily involved in the licensing/insurance side than I am,it's worth listening to what he says.