I have had a few issues recently with an electrical boiler and I have replaced a few electrical parts (relays, time delay switches,...) to keep it running.
Doing so, I noticed that the internal wiring was quite different from the wiring diagram on the panel cover. The diagram includes both a 120 VAC relay and a 24 VAC relay, while the boiler as actually wired runs only with the 24 VAC relay.
The question that came to my mind is: Does the actual wiring include all the safety interlocks required for the safe operation of this 20 kW electrical boiler?
To answer that I started studying the wiring diagram, but there is something I cannot quite understand: the 24 VAC relay is energized when the 120 VAC relay is activated, AND the 120 VAC is energized when the 24 VAC relay is activated.
Take a look at the wiring diagram for this 240 VAC, 4 elements, 20 kW boiler.
I cannot make sense of the operation of both relays. My question is "Why is it like that and how does it work?"
Thank you very much for your insights on this.
Note: I first posted this question on diy.stackexchange.com, but did not get any help.