What is potential free contacts & how are they different from the normally available relays/contacts?
Potential free contacts are contacts which do not have a voltage potential on them. Ie, if a device must be connected to potential free contacts, then no other circuit or device may be connected to the same contacts.
> plz give a clear example. I m not understanding the concept
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This seems to be a popular European term. Relay contacts (dry mechanical contacts i.e. no active driver circuitry) is what is meant.
Potential free contact as name suggest a contact established without any potential into it. This is also called some times as dry contact. Relays also provide p.f. contact. When the relay is energised, there is no potential in P, NO, or NC. But change over takes place.
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
To me a relay is a potential free contact because the relay terminals are isolated from the electronics of the device. This contrasts e.g. to
transistors and triacs that are not potential free contacts because they are connected to controlling electronics.
It means, the contacts has no potential connected from the device they are in, eg. when you got potential free relay output in PLC, you can connect one connector's side to external supply and the second one to your load (eg. coil).
Potential free contacts are volt free contacts. In selecting a PLC or DCS input module you may ask vendor for potential free contacts. The potential free contacts are used in applications where intrinsically safe electrical classification is required. Potential free contacts are used as a safety in hazardous area where a sparks may ignit the combustible atmosphere.