Form A, Form C contacts 3

slavag · Aug 24, 2009

Dear ANSI EE.
Could you please give short explanation, what is a different between Form A and Form C contact.
What need use for the trip and close commands,

Additional, what is a From A with current control contact.
Sorry for Q, Im never work with ANSI relay.
Thanks in advance.
Best Regards.
Slava

rbulsara · Aug 24, 2009

Form A is single normally open contact.

Form C is one normally open contact and one normally closed contact with a "common" terminal between them. Form C contact assembly has three terminals. NO-Comm-NC.

They can be part of any type of a relay or auxiliary switch.

Normally open contacts are commonly used to trip and closing commands,but really it depends on the control circuit.

Rafiq Bulsara

http://www.srengineersct.com

davidbeach · Aug 24, 2009

Form A - Contact open in the rest/deenergized/shelf state of the device.

Form B - Contact closed in the rest/deenergized/shelf state of the device.

Form C - Two contacts, one A and one B, with a single common.

Code:

   |            |           __|__
   |            |           |    |
  ---          ---         ---  ---
                /                /
  ---          ---         ---  ---
   |            |           |    |
   |            |           |    |
   A            B              C

jghrist · Aug 24, 2009

See the attachment, scanned from an old Siemens document How to Read German Schematic Diagrams of Industrial Equipment. The "change-over contact" is Form C.

slavag · Aug 24, 2009

Thanks a lot.
It's more simple, that I think

.
NO, NC, CO in the IEC world.

Best Regards.
Slava

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Form A, Form C contacts 3

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