One pair of wires for each device

Group Equipment Category

Locations Corresponds

to Comments

Gases Dusts

I M1 Mines

n/a Capable of functioning safely in the presence of an explosive atmosphere

I M2 Mines

n/a Must be de-energised when an explosive atmosphere is present

II 1G 1D Other

Zone 0 Protection assured in the event of two independent failures

II 2G 2D Other

Zone 1 Protection assured in the event of foreseeable failures

II 3G 3D Other

Zone 2 Protection assured during normal operation

Source : Wikipedia

Isolation Barrier

All this wiring could be replaced by a Single Twisted-Pair

Fieldbus-based

PROFINET

*

* Above 31.25kb/s