Output Wiring

If a Controller or expander loses power for any reason, all relays will return to their unpowered state. When designing a system it is a good idea to consider what would happen in failed condition to any devices you may be controlling with these relays.

Output terminals are labeled in their un-powered state. Where a terminal is labeled NC or Normally Closed this set of contacts will be closed when the output is off.

If your system was specified to control some lighting, it would be a good idea to use the NC or Normally Closed terminals to do this. If for some unexpected reason, the module fails and the output turns off, then the lights being controlled would be turned on. Ultimately, in a failed state it would be better for the lights to be stuck on than stuck off.

This can however lead to programming confusion, but as long as smart naming conventions are used, this can be avoided.

For instance, the above example could be labeled Lighting Control (ON to de-energize).