IS barriers

[kspifldorf]

Where does it state you have to use IS barriers on thermocouple wire, when the controller is outside the classified area. Of course we know the signal is generated inside the C2D1 Garea monitoring bearing temp.

 

[rbalex]

There is no direct statement. It may be the indirect requirement of the Control Drawing. Thermocouples are usually classified as ?non-incendive? rather than ?intrinsically safe;? but a Control Drawing is required in either case. See 501.10(B)(3) and 504.10(A).

 

[weressl]

There is no direct statement. It may be the indirect requirement of the Control Drawing. Thermocouples are usually classified as ?non-incendive? rather than ?intrinsically safe;? but a Control Drawing is required in either case. See 501.10(B)(3) and 504.10(A).

Thermocouples could be installed in and as an IS circuit. They MAY be listed as non-incendive when used with appropriately labeled interface. (Ex. Some DCS I/O's are listed as non-incendive.)

Non-incendive would not meet Div. 1 requirements unless it is specifically approved for Cl.II, Div. 1.

 

[rbalex]

You don?t need to go back too many Code cycles to see that Intrinsically Safe and Nonincendive have only received formal definition fairly recently. More importantly, the underlying definitions are outside the NFPA altogether. The ?official? descriptors of both systems are ANSI/ISA 12.12.01 and ANSI/ISA RP 12.06.01.

In the early years, as these wiring systems were developing, they were almost treated interchangeably. Ultimately, the ISA took control of these wiring systems.

As I said earlier, both systems require a Control Drawing. If you want to treat thermocouples as Intrinsically Safe, you will need a manufacturer?s support to do so.