Multi conductior, shielded, and twisted pair cables in C

[jamieschmidt]

Multiconductor cables with a gas/vapor-tight continuous sheath are required to be sealed by removing the outer jacket and any other coverings so that the sealing compound will surround the individual insulated conductor and outer jacket, minimizing the gases and vapors that are passed.

An exception to 501.15(D)(2) and 501.15(E)(1) Exception No. 2, permits shielded cables and twisted pair cables to be treated like a single conductor so that it is not necessary to separate the individual conductors of the twisted pair, or remove a shield.

Is it ok to not remove the outer jacket of the shielded cables and twisted pair cables when sealing them in a Class I area? My concern is that removing the outer jacket has the potential for damaging the shielding of the cables and that this may cause more problems than minimize gases.

 

[rbalex]

Re: Multi conductior, shielded, and twisted pair cables in C

You're concern is one of the primary purposes of the exceptions. The purpose of sealing cable ends is to reduce the conductors themselves as being paths for ignitable vapors and gases through a seal (See 501.5 FPN No. 1&2)

There are two issues here; one, for medium voltage conductors, and, at the other extreme, for power limited conductors.

For shielded medium voltage cables, commonly used "stress cones" terminations are generally considered an "...approved means to minimize the entrance of gases or vapors and prevent propagation of flame into the cable core."

For, power limited cables there is a different concern. "Regular" sealing compounds are conductive and exposing the shields to the compound creates a likely potential for "common mode" noise. These constructions are permitted to go completely through a seal without alteration as long as they have an "...approved means to minimize the entrance of gases or vapors and prevent propagation of flame into the cable core.? Small shrink kits with mastic or even simply dipping them is wax is suitable. Note 501.15(E)(1) applies only to conductors entering explosion proof equipment.