Potential Free contacts????

Potential free" or "dry contacts" are used when the device being controlled has its own power supply. For example, most VFDs have a 24 VDC power source in the drive that is used to control starting the drive. The external contact used to start the drive is a dry contact, and it switches the voltage supplied by the VFD to let it know it should begin running. Closing the dry contact connects the drive input to the VFD's 24 VDC and powers the drive input. The internal devices sense the voltage, start the drive, and the current and voltage is returned to the VFDs own power supply "-" through internal circuitry.

The term "potential free" is only in reference to the control contact when it is not connected to an external device. Obvioulsy, during operation, there must be potential or voltage passing through the contact or nothing can happen.

This term is meant to differentiate between a dry contact, powered extenally, and a contact that is connected to a voltage source inside the control system that is sent to an external device. An example of this would be a PLC output that uses the PLC's own 24 VDC power, and when the contact closes this voltage is connected to an external "unpowered" load such as a relay coil.

The above defintion is from a Mr. Tom Jenkins in the US and is a good defintion of what a potetnial free contact is.

Hi Guest, here is another asnwer to your question,

[Edit]

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.

Also known as voltage free contacts. They are insulated from the device controlling it so that it may be connected to another circuit without the control circuitry interfering with the that circuit, and vise-versa. Usually used to indicate some sort of condition status, such as "alarm activated" condition in safety monitoring equipment. Also for safety. Two independent systems could, for instance, be at different voltage potentials (e.g., one is earthed, the other at 110V). Connecting them electrically could have catastrophic consequenses for both equipment and operator. Problem solved with potential-free contacts.

Regards.

Contacts not used to pass current but only Potential, used as Signal contacts.

These are normally mercury-wetted to aviod sulfation or oxidation as no current passes thru. If Dry contacts are used [Not wetted with murcury become unreliable.

Hope of some information

Regards

It is more descriptive.

Hi Prashanth.

I made an example to understand better what the other guys have already told you.

This example shows an "external alarm circuitry". A relay is used for the desirable voltage isolation between the system (Vc and gnd) and the external circuit (e.g. a lamp connected to an external -a.c. or d.c.- voltage source). In this way, the system alarm (i.e. Vc=5V) will close the relay's contact and make the external lamp to be turned on, showing us the alarm condition of the system.

(Of course, instead of a relay we could use e.g. an optocoupler, taking advantage of the voltage isolation between its 'led' and its 'output transistor'.)

Perfect, George !!! High Five !!!

Dear Mr. G.K

Thank you for a detailed reply and taking time out to post it

Regards

Prashanth