Reset the keying mechanism on a CHARM Terminal Block

The keying mechanism on most CHARM terminal blocks is in a neutral position when shipped from the factory. In most cases, installing a LS CHARM sets the keying mechanism. For most LS CHARMs you can reset the keying mechanism if you need to remove the LS CHARM from the terminal block and install a LS CHARM of a different type. Some terminal blocks have fixed keying and cannot be reset: CHARM Thermocouple / mV, LS DVC (simplex and redundant), LS Redundant DTA and ETA Relay.

Figure: Terminal block latch and release button


  1. Insert a small screwdriver into the release button to the left of the terminal block's latch, depress the release button, and remove the terminal block from the baseplate.
  2. Flip the terminal block 180° and notice the two small keying posts protruding from the bottom of the terminal block.
  3. Push the two keying posts completely in to return the posts to the neutral position.
    You will hear a click when the posts are completely pushed in.
  4. Verify that the keying posts are in the neutral position.
    In the neutral position, the ends of the posts sit slightly inside the bottom face of the terminal block. That is, the keying posts are sub flush to the bottom face of the terminal block. If the keying posts are flush with the bottom face of the terminal block, the keying posts are not yet in the neutral position. In this case, use your fingers to push the keying posts to the neutral position.
  5. Snap the terminal block back into the slot on the baseplate.
    You can now install a LS CHARM of a different type into the terminal block.