Answer Posted / abdelrahman

Potential free contacts (also called "dry contacts") are
simply contacts which are physically operated with the main
device, but not electrically connected to it. For example a
motor contactor often has auxiliary contacts that are
operated by the main coil and open and close at the same
time as the main contacts but are not used for control of
the motor starter. If they are connected to an outside
circuit to indicate the status of the starter without being
powered by the motor supply they would be considered
potential free contacts.
These type also called Signal-Contacts.

In case of relays and switches if the common/pole is
connected internally to a given potential like a 110V phase
etc., the contact is not POTENTIAL FREE but if both the
common and the normall open (and at time also the normally
closed) contacts are presented to the user for connecting
in his system as he pleases,the contact is said to
be "potential-free".

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