# Tension Release Limit Switch



## BBQ (Nov 16, 2010)

I think any quality switch would be fine.


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## nolabama (Oct 3, 2007)

Big John said:


> Is there a name or a style of limit switch where the operator is designed to be under constant tension for extended periods of time (weeks, months)?
> 
> I'm worried that using a normal limit switch in this application will tend to fatigue the spring, so when it finally gets tripped, it won't operate.
> 
> ...


We are in the process of installing a go switch on a contraption with stainless piano wire to be under tension. It slides along a cradle and makes contact with the switch. Contraption is about as big as a shoebox. Travel indicates its overall length. This is prolly of little use to you.


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## varmit (Apr 19, 2009)

The cable type e-stop switches might work for your application. Some are designed for slack cable use. Others are designed for the cable to be in tension constantly.


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## Big John (May 23, 2010)

varmit said:


> The cable type e-stop switches might work for your application...


 That would actually be perfect. That's the direction I've been heading, but all our usual suppliers carry is the slack-cable version.

You know who might make a constant-tension version?

I could probably make this work with a regular limit switch, but it's a redundant limit where if it fails there's a lot of money and possibly someone's safety on the line, so I'm gun-shy about using generic parts.

-John


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## JRaef (Mar 23, 2009)

A "Slack" cable switch means it IS under tension all the time and if it goes slack, the contacts change. Essentially the difference is that a "rope pull" safety switch has NC contacts and if you pull the rope, they open and drop out the control circuit. A Slack switch has NO contacts that are held closed by the tension and if the cable goes slack, they open and break the control circuit.

Rees makes them, I've used them on aggregate plants because they have one that operates if you pull the cable OR the cable is broken (released), but they also have ones that are just "Slack" switches.

http://catalog.reesinc.com/category/cable-rope-operated-switches


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## Big John (May 23, 2010)

That should do it. Apparently the hard part of all this was figuring out what the hell I was trying to describe. Thanks for the help guys.

-John


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