How does the standard electrical interlock work when installed in a safety switch?


25 July 2022

Product Design Feature

Product Line:
GD, HD and DT Safety Switches 

General Information:

An electrical interlock kit consists of an industrial snap switch that mounts inside the safety switch and works in conjunction with either the switch operating mechanism or the switch blade cross arm and the switch operating handle.
The snap switch will contain either  one 'A' Contact (NO) and one 'B' Contact(NC) OR two 'A' Contacts(NO) and two 'B' Contacts (NC), based on the catalog number of the electrical interlock kit.  
NOTE: NO = Normally Open and NC = Normally Closed.
Kits ending with the number "1" will contain 1NO/1NC contacts and kits ending in with the number "2" will contain 2NO/2NC sets of contacts. 

Standard Operation:
With the interlock kit mounted internal to the safety switch, the 'A' contacts are NC (CLOSED) when the switch is in the 'ON' position and the 'B' contacts are NO (OPEN) when the switch is in the 'ON' position. When the safety switch operating handled is operated from the ON position to the OFF position, the electrical interlock contacts ('A' & 'B') change status BEFORE the main switch blades of the switch break. So, the 'A' contact goes from CLOSED to OPEN and the 'B' contact goes from OPEN to CLOSED. When the switch operating handle is operated back from OFF to ON, the interlock contacts change back to their normal state, BUT the interlock contacts will NOT operate(or change status) before the main switch blades make.

1) The kits can be used to be able to monitor the operating status (ON or OFF) from a remote location via control wiring, or be used to drop out a coil in a motor starter.
2) Some customers install the Electrical Interlock in a Safety Switch with the intent of causing downstream contactor contacts to open before the Safety Switch blades open, and close after the Safety Switch blades close. While this can be done in some circumstances, due to variations in size, operating speed, design, and condition of the contactor, we cannot guarantee this sequencing of the Safety Switch blades relative to the contactor contacts.