part of the protection system. Conduit seals shall be installed within 450 mm (18 in.) from the pressurized enclosure.
FPN No. 1: Installing the seal as close as possible to the enclosure reduces problems with purging the dead airspace in the pressurized conduit.
FPN No. 2: For further information, see NFPA 496-2003, Standard for Purged and Pressurized Enclosures for Elec- trical Equipment.
(4) Class I, Zone 1 Boundary. Conduit seals shall be pro vided in each conduit run leaving a Class I, Zone 1 loca tion. The sealing fitting shall be permitted on either side of the boundary of such location within 3.05 m (10 ft) of the boundary and shall be designed and installed so as to minimize the amount of gas or vapor within the Zone
1 portion of the conduit from being communicated to
the conduit beyond the seal. Except for listed
explosionproof reducers at the conduit seal, there shall
be no union, coupling, box, or fitting between the
conduit seal and the point at which the conduit leaves
the Zone 1 location.
Exception: Metal conduit containing no unions, couplings, boxes, or fittings and passing completely through a Class I, Zone 1 location with no fittings less than 300 mm (12 in.) beyond each boundary shall not require a conduit seal if the termination points of the unbroken conduit are in unclassified locations.
(5) Cables Capable of Transmitting Gases or Vapors.
Conduits containing cables with a gas/vaportight continuous sheath capable of transmitting gases or vapors through the cable core shall be sealed in the Zone 1 location after removing the jacket and any other coverings so that the sealing compound surrounds each individual insulated conductor and the outer jacket.
Exception: Multiconductor cables with a gas/vaportight continuous sheath capable of transmitting gases or vapors through the cable core shall be permitted to be considered as a single conductor by sealing the cable in the conduit within 450 mm (18 in.) of the enclosure and the cable end within the enclosure by an approved means to minimize the entrance of gases or vapors and prevent the propagation of flame into the cable core, or by other approved methods. For shielded cables and twisted pair cables, it shall not be required to remove the shielding material or separate the twisted pair.
(6) Cables Incapable of Transmitting Gases or Vapors.
Each multiconductor cable in conduit shall be considered as a single conductor if the cable is incapable of transmitting gases or vapors through the cable core. These cables shall be sealed in accordance with 505.16(D).
(7) Cables Entering Enclosures. Cable seals shall be provided for each cable entering flameproof or explosionproof enclosures. The seal shall comply with
505.16(D).
(8) Class I, Zone 1 Boundary. Cables shall be sealed at the point at which they leave the Zone 1 location.
Exception: Where cable is sealed at the termination point.
(C) Zone 2. In Class I, Zone 2 locations, seals shall be located in accordance with 505.16(C)(1) and (C)(2).