We are using SD32 Surge protectors for our field devices and are connected to Yokogawa DCS/Invesys Triconex PLC and other third party interfaces.

one of the interface is between MCC to DCS via SD32 Surge protector. We are exchanging digital signals like Start (Pulse), Stop, Run, Local/Remote, Fault signals from MCC to DCS. These signals are transferred through Allen-Bradly relay to/From DCS. The coiled resistance of Allen-Bradly relay is 58 Ohms. We are using Continuous - 1(on) signal from DCS to MCC via Surge protector(SD32) and AB relay for STOP command.

Problem:

For certain Motors ,when we start the motor,STOP surge protector Fuse Gets blown. Also these surge protector are abnormally Hot unlike others.

Query:

What could be the reasons for surge protector getting hot?

Why Fuse gets blown when Motor starts?

Are theses surge protector are under rated for Allen-Bradly Relay coil resistance of 58 Ohms?

 

Surge protectors get hot when they are absorbing energy. Check that all the signals are staying in range and there aren't drive harmonics, etc. being picked up on the lines. This is a case where an oscilloscope is almost a must. I'd bet on a signal voltage out of range triggering the SP or some sort of ground loop/loss. High signal voltage _at the SP terminals_ would cause all the things you mention.

Regards
cww