Calender Roll Pull Cord Safety - Type


Thread Starter

Bob Welker

Are there any specific requirements by OSHA or other groups as to whether cable pull stop switches must be maintained (requiring an intentional reset operation) or are momentary limit switches (with an MCR circuit) acceptable?

I've looked at OSHA 1910.216, and it doesn't address this particular question. From what I have found so far, it appears it's up to the builder/user.

We're adding a couple of pull safety switches on an older line using momemtary limit switches, and I'm looking for justifications for my desire to use a modern, maintained cable pull safety switch.

Guess I need to print out the pages and read them *before* pronouncing that I can't find something!

Sometimes I miss phrases and entire paragraphs when reading from the computer screen, but it was right there ... the specific cite is in
1910.216(e). "Trip and emergency switches. All trip and emergency switches shall not be of the automatically resetting type, but shall
require manual resetting."

It is OK to use a momentary contact switch as long as that switch drops out a manually resetable safety relay circuit. Three safety relays are required wired in a "voted" contact configuration, or you can buy a integrated safety
relay unit. The safety relays have the advantage that they can be set up to detect welded contacts in either the relay or the safety switches.

david mertens

Maintained switches are required in europe because that is the only guarantee that you have to check the area where the stop cord was pulled before being able to restart the machine. Deadly accidents are bound to happen if someone pulls the safety cord and anyone else can just restart the machine.

James Bouchard

Limit switches are not designed for safety applications. The require a bit of engineering to arrange the equipment to keep the tension on the pull cord. If it is a slack cord type there is a problem as the cord could be cut and then it would be impossible to actuate the switch. Since this is a safety application I would go for the pull cord safety switch that is designed for a taut cord application. It is safer and a broken or removed cord will stop the machine. All of the ones I have seen are a maintained action that requires a local reset at the switch which is a good safety practice. You don't want the switch being reset without at least a check being made.

Our internal policies also require a safety relay ( like an MCR ) In Europe it would be required but it probably depends on the degree of risk and how far you want to go.

James Bouchard
I want to thank everybody for their insight on this question. Several of the replies exposed facets of this issue I had not considered, but which, after their discussion, make quite a bit of sense.