E-Stop Question

Hello All,
I’ve been reading posts on this site for about a year now and I finally have a question.

At my work, we have a machine that produces “widgets”, controlled by a SLC 5/04. The widgets are feed onto a separate conveyor system controlled by a SLC 5/04. Each system has its own separate E-Stop system. The E-Stop systems are maintained push buttons, pull cords, or magnetic contact switches. Each device has two safety contacts that go to a safety relay that opens a safety contactor that removes all power from the drives, motor starters and solenoids. And a third contact that sends a signal to the PLCs. The PLCs communicate thru DH+.
Our future plans include hard wiring the two systems together, but until we do…

My question is, if the E-Stop on the conveyor system is pressed, may I use the DH+
to send a signal triggering a “machine stop” of the “widget producer”.

My boss told me this was an OSHA violation; because of the appearance that one safety system controlled another.

Thank You,
IndustMech

There many shades of gray in this business, so know what is black, and what is white.

There 2 circumstances in this situation.
Is the system seen as a "Line" or as a "Machine"?
It makes a difference.

In a line circumstance, the Line must be adhered to with a safety controller, via hard-wired devices.

You can certainly pass the contact information via DH+, but the Safety Control MUST BE THROUGH APPROVED SAFETY DEVICES.

Hope that this answers your question.

I'm afraid in your case the answer is "No. Use hard-wired circuits".

Recently there have appeared a number of solutions implementing safety over fieldbus/communication bus. Coming mostly from Europe, they comply with European safety standard EN954 which, in most cases, is acceptable in the US (it is still a good idea to check it with OSHA though). However, I don't think there is a solution designed to work via DH+ network.

If you're simply cycling down the machine because the downstream conveyor system isn't running, I don't see a problem with using your DH+ link to pass the information.

I work mainly with packaging machinery, but it's fairly common to have some type of downstream full/stopped mechanism in place to gracefully shut down or pause a machine. I've seen this done with photocells, hardwired interlocks, communication lines, encoders, etc..

Since you only intend to do this when an e-stop on the conveyor system is pressed, it does give the impression that you are using this as a safety feature though.

IndustMech said:

Hello All,
I’ve been reading posts on this site for about a year now and I finally have a question.

At my work, we have a machine that produces “widgets”, controlled by a SLC 5/04. The widgets are feed onto a separate conveyor system controlled by a SLC 5/04. Each system has its own separate E-Stop system. The E-Stop systems are maintained push buttons, pull cords, or magnetic contact switches. Each device has two safety contacts that go to a safety relay that opens a safety contactor that removes all power from the drives, motor starters and solenoids. And a third contact that sends a signal to the PLCs. The PLCs communicate thru DH+.
Our future plans include hard wiring the two systems together, but until we do…

My question is, if the E-Stop on the conveyor system is pressed, may I use the DH+
to send a signal triggering a “machine stop” of the “widget producer”.

My boss told me this was an OSHA violation; because of the appearance that one safety system controlled another.

Thank You, IndustMech

Click to expand...

I worked in plastic extrusion the extruder, cooling and sizing unit puller and flying cut off saw were all tied together for very good reasons. (stop puller and extruder gobbles up).
HOWEVER it made maintenance and testing a pain.

Re OSHA
1. They do require on "dangerous" machines and E stop. This can include rolls and some conveyers (chipper infeed, etc)
2. Provided the dangerous machine has required E stop then upon initiating E stop you could shut off whole plant (or not) as far as OSHA is concerned. That is NOT a violation.

A full risk / safety evaluation of both machines is a very good idea.

Initiating an E stop on the conveyer and shutting down the widget automatically (I'll call it a "courtesy stop") is not requred but maybe a good idea to keep widgets from overproducing and falling all over the floor.
In this case the courtesy stop would not have to adhere to all safety requirements, would not have to be hard wired and could be done over comms.

IF after a risk safety evaluation it is concluded that E stops are required on each machine AND they must shut down both machines then all of the circuitry must be hard wired and comms would not be acceptible.

Dan Bentler

leitmotif said:

I worked in plastic extrusion the extruder, cooling and sizing unit puller and flying cut off saw were all tied together for very good reasons. (stop puller and extruder gobbles up).
HOWEVER it made maintenance and testing a pain.

Re OSHA
1. They do require on "dangerous" machines and E stop. This can include rolls and some conveyers (chipper infeed, etc)
2. Provided the dangerous machine has required E stop then upon initiating E stop you could shut off whole plant (or not) as far as OSHA is concerned. That is NOT a violation.

A full risk / safety evaluation of both machines is a very good idea.

Initiating an E stop on the conveyer and shutting down the widget automatically (I'll call it a "courtesy stop") is not requred but maybe a good idea to keep widgets from overproducing and falling all over the floor.
In this case the courtesy stop would not have to adhere to all safety requirements, would not have to be hard wired and could be done over comms.

IF after a risk safety evaluation it is concluded that E stops are required on each machine AND they must shut down both machines then all of the circuitry must be hard wired and comms would not be acceptible.

Dan Bentler

Click to expand...

Out of interest does the US/Canada (Not sure who OSHA is ?!) accept the newer estop safety networks ? ie ASi, Pilz, ProfiSAFE etc or does it still have to be hard wired ?

504bloke said:

Not sure who OSHA is ?!

Click to expand...

"If you think that OSHA is a town in Wisconsin, you may be in a big trouble"

Occupational Safety and Health Administration. An agency of the federal government with lots of powers to make one's life quite miserable... For a good reason though.

504bloke said:

Out of interest does the US/Canada (Not sure who OSHA is ?!) accept the newer estop safety networks ? ie ASi, Pilz, ProfiSAFE etc or does it still have to be hard wired ?

Click to expand...

Dave

OSHA is a USA federal regulation "Occupational Safety and Health Act" passed in 1971.

They write very few electrical regulations themselves but rely on others ie NFPA (NEC) and then adopt them. To my knowledge they have not adopted NEC codes addressing worker or machine safety.

I checked on this a year ago here in Seattle with the state equivalent program and they knew nothing and admitted they were quite unqualified to do electrical safety.

So to answer your question I would bet they would not even know what you are talking about.

Individual states have the option to run their own safety program (partial funded by OSHA) or let OSHA do it.

Many if not most run their own program.

Dan Bentler

Thank you all for your prompt and thoughtful responses.


IM