Type 3 Latching state devices
|
3. Latching state devices Where the state of the operating device can be latched in either state and therefore the normal state is not clearly defined a different style of contact definitions may be used. 3.1 Form A contact A Form A contact is closed when the operating device main contact or mechanism is closed or latched. Its function is logically equal to the device it resides on. 3.2 Form B contact A Form B contact is a contact that is closed when the operating device main contacts or mechanism is open or latched open. Its function is logically inverted to the device it resides on. 3.3 Form C contact A small relay using a Form C contact. A Form C contact is a combination contact composed of a normally closed and a normally open contact operated by the same device, with a common electrical connection resulting in only three connection terminals. These are usually labeled as normally open, common, normally closed (NO-C-NC). These contacts are quite frequently found in electrical switches and relays as the common contact element provides a mechanically economical method of providing a higher contact count. KYZ contacts used on energy meter outputs are an example of Form C contacts where each contact reversal or contact state change represents a measured amount of energy (Kp, Ki or Ke). |
Previous:Type 2 Normally open contact next:Type 4 Contact wipe