We are commissioning a steam turbine control panel. It is seen that whenever the final control solenoids (110 VAC) are energised/de-energised, some of the channels in the temp scanner connected to bearing RTD's gives trip contact. It seems that interference from the 110VAC signal is affecting the RTD signal. The solenoid cables & RTD cables from field are terminated in the same JB. The RTD cables are individually shielded and the shield is connected to earth in the JB side. From the JB the RTD cables & solenoid cables are already prewired by the panel vendor and they go to different JB's but through adjacent cable glands.

Any suggestions to solve this issue. What is the minimum distance in air, that has to be kept between these cables?

 

This is a very common problem but usually easily fixed.
Provide a Metal Oxide Varistor across the solenoid wires at the panel end, this prevents the high voltage spike when the coil supply is opened.
I have seen 120 V discrete inputs turn ON when solenoid outputs are turned OFF the Varistor will fix that.

Use a varistor with a voltage rated 5-10% higher than the system voltage.
Roy