override switch

[DTSFA]

if one is using an override switch (overides control/safety switch) , and a standard calls for that override switch to have 'positive separation' for such a switch, and currently the switched used to override part of the circuit is normally open, how would one achieve the 'positive separation' , this surely applies to a normally closed switch ?

 

[VEBill]

Disclaimer - this isn't exactly my area, so standby for others to confirm or refute.

A safety switch would normally OPEN a circuit. To override the open, one would have a NORMALLY OPEN override switch wired in parallel with the safety switch.

It makes sense that override switch, when flicking it back to the normally open position after using it, the switch should be designed internally to force the contacts open.

It would be a nightmare if the override switch contacts failed to open, perhaps being welded closed (might be more likely than you might think given that it's already an abnormal operation circumstance with safety switches opening, etc.).

I think that this requirement precludes many push buttons where the contacts are separated only by spring pressure. That's a bit counter-intuitive. Interesting...

Stand by for others with some actual expertise in this area.

 

[makesparks]

What do you need to override? For instance, Banner makes an enabling switch used for things like hold-to-run applications and manual machine control. Basically, if you let go, or get hit and your hand tightens up in a convulsion, the machine will stop if the switch is wired in properly to the safety circuits. I would review machine safety devices and information from various vendors to get some more insight.

 

[DTSFA]

thanks for replies so far,

the safety circuit is using normally closed devices, the overrride is currently normally open, (is required because at certain point of operation, the safety circuits has to be overriden for the machine to continue to operate)

It makes sense that override switch, when flicking it back to the normally open position after using it, the switch should be designed internally to force the contacts open.

think this is good, think the wording positive separation does not necessarily apply to N/C switch only. Is interpretation of standards, as usual.

I will contact our switch manufacturer as you say, and see what they say.