E-Stop Wiring - Best Practices (Sub Machines)

It seems as if some people are getting hung up on the term "risk assessment". Does it have to have an engineering stamp on it? (That would give it more clout than say, the floor sweeper signing off on it.) I don't think so: rules may be different all over. What it requires is a thorough examination by all involved. Google the term. A concientious look from multiple viewpoints (supervisors, operators, maintenance personnel) using a standard risk check - basically a probability of injury and severity are the concerns. I don't pretend to know the law. What I do know is that in the eyes of the Ministry of Labour in Ontario, if there is no paperwork for the R.A. it didn't happen. If your not sure where you or your company stands, call a lawyer before the accident happens.

When it comes to sub-machine wiring, the 'Best practice' in my experience is for each machine to provide it's own E-stop condition AND:

1. The ability to tie another system into the E-stop condition (ie - extra terminals with jumpers in addition to the E-stop on a safety relay for example)

2. The ability to send the status of the machine's E-stop to another system. (ie - a spare set of contacts on the safety relay or signal from both aux safety relay contacts)

At that point, a proper risk assessment will determine what each machine's E-stop should do - shut the line down or stop just it's own machine.

Either way, a main station should be able to monitor if the machine is in an e-stop condition and alert the other machines or operators appropriately. This could vary wildly depending on the intended process.

Rson said:

When it comes to sub-machine wiring, the 'Best practice' in my experience is for each machine to provide it's own E-stop condition AND:

1. The ability to tie another system into the E-stop condition (ie - extra terminals with jumpers in addition to the E-stop on a safety relay for example)

2. The ability to send the status of the machine's E-stop to another system. (ie - a spare set of contacts on the safety relay or signal from both aux safety relay contacts)

At that point, a proper risk assessment will determine what each machine's E-stop should do - shut the line down or stop just it's own machine.

Either way, a main station should be able to monitor if the machine is in an e-stop condition and alert the other machines or operators appropriately. This could vary wildly depending on the intended process.

Click to expand...

+1
This is a very important point, often ignored.

A practical tip:
When you tie in external safety contacts to your safety relay, and provide contacts from your safety relay for an external system to use, you must think about who/how the safety relay is reset. If the external system is not just one or a few E-stop buttons, but is actually a safety system with safety relay(s), then there is the risk of a catch-22 situation. Your safety relay is deactivated because the external contacts are deactivated, which deactivates the external seafety relay, which deactivates its contacts, .....etc.
What we do is to have at least one safety relay dedicated for external safety system. This safety relay auto-resets in our system. When an external safety stop is activated, the resetting must happen in the external system.
Conversely, we inform in our documentation that our contacts must be reset in our system, and the external safety system should auto-reset.