u/BlkCdr

I’m an electrician who does a good bit of control work. Most of our projects are fresh and wastewater treatment. I come across intrinsically safe relays quite a bit, but I don’t really understand how they work.

For example, at a site I was at earlier this month, all of the level switches hit IS relays. The relays have 120vac supply and two sets of contacts. The wiring from the field lands on terminals that are jumped to two other terminals through resistors. What is electrically happening inside the relay? I’ve asked google, but he doesn’t seem to be able to give me the answer I’m looking for. I’ve asked a couple engineers that I work with, but they frankly don’t really seem to know either.