IS loop and Shield connection


Thread Starter

Rashid Iqbal

In one of a skid package i have a few IS loops.

Since in the IS loop i am using Active barrier, which means i do not need the dedicated IS Ground. But if the IS cable is shielded, do i need to terminate the IS cable? If yes, then will i terminate the Shield to the normal Instrument earth, or I need to have the dedicated Intrinsic Earth?

Bruce Durdle

According to IEC60079.14:

"If an earthed intrinsically safe circuit is run in a screened cable, the screen circuit shall be earthed at the same point as the intrinsically safe circuit which it is screening.

If an intrinsically safe circuit or sub-circuit which is isolated from earth is run in a screened cable, the screen shall be connected to the equipotential bonding system at one point."

So for an isolated circuit, the screen does not go to the instrument earth but to the general plant bonding system.