ECN Forum Forums General Topics of the Trade General Discussion Area Solid State Relays and electrical isolation

Recently I was asked to replace a solid state relay on a PCB for a Siemens fire alarm system device. The device is a HTRI-R module which controls two sets of fire doors through a solid state relay (on the module's PCB) which are held open with magnetic door holders powered by a 120VAC circuit. I replaced the relay and tested the module with a Siemens DPU which tests the module but cannot verify if the relay is functioning properly. In order to see if the fix worked I placed the module back in the field in the same location it was removed from. The repaired module failed to power the mag door holders. The co-worker who originally replaced the module and requested that I replace the module's relay believes the 120V circuit that powers the mag door holders through the relay somehow damaged it. If that's true and I replaced the relay properly (good solder connections) is it possible there can be greater damage beyond the relay to other components on the module's PCB that the DPU could not detect? Or would a solid state relay generally provide enough electrical isolation from the 120V circuit to prevent further damage? Visually the relay did not show damage (ie burnt, deformed, etc).

BTW, I bench tested the relay that I removed. The relay has 2 coils and one each N/C and N/O terminals. I tested the relay with a proper power supply applied to the coil and it failed to change state of the N/C and N/O. Therefore I assumed it must be damaged.

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