Requirements for instrument cable protection

[bradenbash]

I have a customer who uses an armored marine shipboard rated cable (IEEE 45) to connect instruments on a natural gas compression package that is sometimes installed in Class I div 2 areas. Most of these instruments are simply providing contact closures in certain situations, i.e., pressure rise, level change, etc. They have asked me if it is permissible to apply the armored cable in classified areas without using conduit and poured seals. Does anyone have any insight into proper practices according to NEC?

 

[rbalex]

The odds are a natural gas compression package creates a Class I, Division 2 location as a minimum.

Depending on the construction of the armored cable and the instruments, you may be able to omit some seals. A nonincendive or intrinsically safe wiring method may also permit deleting some seals. Read all of Section 501.15 (E).

 

[stickelec]

I would question the thinking that the Armor cable you speak of could somehow change the requirement for a seal.

However, I?ve seen this wiring method many times on Natural Gas Compressors. Seals are installed where required and the Armor cable enters the seal via a CGB - as it does when it enters any enclosure.

The real problem I have is the armor is never grounded. It is cut-off just as it passes through the CGB and remains isolated. The cable is then routed over Fiberglass Channel, it too remains isolated.

A Compressor Skid with 80 I/O is a lot of cable with the Armor floating.

 

[bobgorno]

Armored cable should be installed with a fitting that provides ground continuity to the armor on both ends. If the wiring methods are not non-incendive or IS, then using a type TMCX fitting on MC-HL cable will achieve both needs. Conduit is not required, however supports for the MC-HL cable are required every 6 feet and within 12" of the terminations.

 

[weressl]

I would question the thinking that the Armor cable you speak of could somehow change the requirement for a seal.

However, I?ve seen this wiring method many times on Natural Gas Compressors. Seals are installed where required and the Armor cable enters the seal via a CGB - as it does when it enters any enclosure.

The real problem I have is the armor is never grounded. It is cut-off just as it passes through the CGB and remains isolated. The cable is then routed over Fiberglass Channel, it too remains isolated.

A Compressor Skid with 80 I/O is a lot of cable with the Armor floating.

CGB is not designed for connecting armored cable. There are other approved fittings that are designed to terminate armored, metallic jacketed or other type cables. (Right tool for the job.)
In case of instrument cable the issue of shielding requirement comes up. If you use armored cable and ground it at both ends, you may create a ground loop that will randomly mess up your signal.