I have an electric water heater that uses 220ac volts. The BX cable from the panel to the heater has a red and black wire inside. I am adding a timer but the wire I have for that has the white, black and copper ground wire. I would like to know what color (red, black on the BX) should connect to the black and white wire for the timer
Thanks

What voltage is the timer? Both the black and the red of the heater wiring are hot legs. There is no neutral in 240V wiring. Sounds like timer is 120V.