hazardous area valve limit/position switches

K

Thread Starter

kjg

I have an application where the area is class 1 div 2 group C and D. I will be using type Z purge on the main controller. I have to wire from the main contoller out to valve position/limit switches and then back to the PLC input in the main controller. The switches on the valves are rated for the area.

Is it better/safer to use 24Vdc or 24 vac or 120 Vac or doesn't it matter? Thanks.
 
B

Bob Peterson

Better and safer are pretty subjective terms.

There are several ways to skin this cat. What kind of switches do you have?
 
S

SUSHANTA SAHA

Reply: Standard paractice is to use 24 VDC with Active isolators (MTL or P&F). However, if the distance between controller and Limit switches is greater than 300 metres, then 120 Vac may be used through interposing Relay provided the Limit switch housing is Ex-proof/Flameproof type suitable for the Hazardous Area. 24 vac is a non-standard voltage level and generally not used.
 
The switch housing is rated for the area. The switches will small microswitches SPDT mechanical style. Thanks.
 
B

Bob Peterson

What possible reason could you have for putting an inperosing relay in the circuit?

BTW, 24VAC is not all that uncommon.
 
Top