Intrinsic safety standards require — for instruments in hazardous locations — that certain points of the system be grounded, and others be isolated from ground.
Grounding intrinsically safe circuits reduces the probability of generating excessive energy levels. Isolation from ground prevents the possibility of having two grounded points with different potentials, and the possible circulation of a high current.
IS standards also require that only one point be grounded, and the rest of the circuit isolated from ground (500 VAC min.). This is done with a conductor connected to the reference ground system and isolated from any other plant grounds.
The grounding requirement, maintenance, and testing can be considerably reduced by using isolated barriers — that don’t require a maintained IS ground.
The circuits are floating ground systems, and are usually equipped with three transformers (on input, output, and power). Below, you can see a comparison of wiring methods using isolated barriers.
|Conventional Passive IS Zener Barriers||Active (Powered) IS Isolation Barriers|