Intrinsically Safe wiring can be an excellent alternative to hard-piping electrical instruments in explosion proof areas.
Traditional methods for wiring instruments in explosion proof areas involve running hard pipe conduit and sealing the ends (packing). This is costly, time consuming for installation on site. Intrinsically Safe (IS) wiring has a lot of advantages over hard-piping/packing for electrical wiring in explosion proof applications. Some of the advantages are;
- Lower Cost
- Easy Site Installation
- Unfamiliarity with IS systems and how they meet codes
- Lack of experience with IS systems
- Perceived higher cost compared to hard-pipe conduit
IS wiring involves keeping the amperage and voltage low enough that it cannot produce a spark with enough energy to initiate an explosion. Barriers are used to shut down a circuit if a high current is sensed. This allows flexible wire which has been pre-packed and wired with receptacles for easy installation. Junction Boxes can also be used as shown below to combine up to eight instrument wires to one main cable.
Figure 1 IS Junction Box with 8 Ports
This allows much easier installation, for example, a skid with 24 instruments can be prewired need only three (3) main cables to be connected in the field. This particular system uses hand tightened connectors. Each instrument is wired with an IS Receptacle to be connected by a 4-wire IS cable. The instruments need to be rated for the appropriate area classification and for IS operation.
Figure 2 Flow Rate Transmitter with IS Cable
Figure 3 Pressure Transmitter with IS Cable
The flexibility became evident when during final build, some instruments were changed and some were added to the skid. The Junction boxes had enough extra ports to accommodate the added instruments and all that was need was to update the electrical drawing with the new port information.
Figure 4 XP Skid (on its side) ready for shipment with all prewired IS instruments