There has been much confusion on how to add a relay to an Ezb. There are three style relays, relay only, relay with a built in transistor circuit, and a relay with an opto-couple circuit. I have the relay with an opto-couple circuit. (817C) ?
This relay requires a 10 K resistor placed in series with the digital output. It is programmed by using a digital output, and "Set Digital". The issue is when the signal sent is "On" the relay is turned off. When the signal is sent "Off" the relay turns on.
This operation needs to be accounted for in your design so relay do not come on during a start up.