What is a potential free contact

[Rick F]

Reading a brochure..    Trying to understand what a potential free contact is .  

It sounds like a mag starter ..     

but It seems like they wouldn't need to advertise that ..  lol .. 

Is it better than a mag starter ?

[JGrout]

quote some guy on the innernet  " Potential free contacts are also sometimes called volt free or "dry" contacts, and simply refer to relay contacts, or switch or sensor contacts, which haven't been wetted with voltage by the machine or device in which they exist. It doesn't refer to some characteristic of the contacts themselves.

So if you were interfacing to a machine with dry contact outputs for interlocks, you would have to provide the circuit voltage source as well as 
the relay coil or PLC input or other means of accepting and utilizing the information represented by the contact.
Steve Myres, PE
Automation Solutions

[Rick F]

Joe.   

I gotta admit..   I read an online explanation almost exactly the same as that ..  and then I asked here..    lol 

It may as well have been written in Portuguese...

[JGrout]

well it most definitely is a European definition I also tried to find a more conventional or Americanized version and failed

[Souperchicken]

Just think of it as two pieces of metal that are either touching or not depending on the state of something, usually the position of a switch. Neither piece of metal is connected to any voltage or ground, they are electrically floating. The pieces of metal are hooked to wires that you can hook to something else that would like to know the state of that switch. One example would be an extra set of contacts on a machine switch, you could use those to activate a relay which would start your dust collector, or turn on a light.

[Just_Dave]

Interesting terminology. 
I would call it an auxiliary set of dry contacts.  There is an extra set of contacts with no power or anything attached.  As was pointed out you could use those contacts to do what ever you wanted simply by applying your own power source to the common terminal.

[Rick F]

So ..  you could use them to turn on a dust collector .. or a light  ..  or whatever..

[EricU]

turning on a DC was my first thought.

[TDKPE]

Without seeing the unit in question, you'd probably need to use a motor-rated relay to operate the DC, using the dry contacts for control. They're usually very light-duty, used for logic, control and indication, not for any real power. Be sure the coil inrush is less than the dry contact rating.

'Dry contacts' are commonly used for the latching function of motor controls, where pushing the 'stop' button breaks continuity to the coil that's holding the starter closed, and pushing the 'start' button closes the loop around the dry contacts, energizing the coil. The dry contacts are mechanically connected to the starter mechanism, and often many can be stacked.

You can make them un-dry by putting line voltage to one side, like with line-voltage motor controls (like the typical Chinese woodworking machine control), or leave them separate and run 24V control voltage, like the typical low-voltage (LV) control (like the vintage Delta controls, in the big pancake box).

[EricU]

good point, use the dry contact to drive the winding of a contactor for the dust collector.  Although I like to have my DC on and running after the cuts, and my cutting machines shut down asap after the cut.