COMMENTARY TABLE 501.1

National Electric Code 501

[” Article 501 ● Class I Locations 501.15
COMMENTARY TABLE 501.1

Conduit and Cable Sealing Requirements
Classification Application Location of Seal
Conduit Seals
Class I, Division 1

Switch enclosure
Circuit breaker enclosure Fuse enclosure
Relay enclosure Resistor enclosure
Arcing or sparking apparatus High-temperature apparatus
Explosionproof enclosure containing arcing or sparking contacts that are hermetically sealed against gas or vapor entry
Explosionproof enclosure containing arcing or sparking contacts that are immersed in oil, in accordance with 501.115(B)(1)(2)
Enclosure containing terminals, splices, or taps; fitting containing terminals, splices, or taps

Two explosionproof enclosures with a conduit run between them of 36 in. or less

Two explosionproof enclosures with a conduit run between them greater than 36 in.

In conduit run within 18 in. of enclosure.

 

NEMA 7 Explosion Proof Enclosure

NEMA 7 Explosionproof

In conduit runs smaller than trade size 2, no seal is required. If conduit is trade size 2 or larger, in conduit run within 18 in. of enclosure.

 

In conduit runs smaller than trade size 2, no seal is required. If conduit is trade size 2 or larger, in conduit run within 18 in. of enclosure.
In conduit run within 18 in. of each enclosure. Permitted to use a single seal in each run as long as the seal is within 18 in. of each enclosure.
In conduit run within 18 in. of each enclosure.

Conduit run leaving Division 1 location Within 10 ft of either side of boundary. No unions,
couplings, boxes, or fittings (other than explosionproof reducers) permitted between the seal fitting and
the point where the conduit leaves the Division 1 location.
Metal conduit containing no unions, couplings, boxes, or fittings that passes completely through a Class I, Division 1 location, with no fittings less than 12 in. beyond each boundary
Not required to be sealed if the termination points of the unbroken conduit are in unclassified locations.

Class I, Division 2 Enclosure required to be explosionproof Seal as required for similar equipment in Division 1
location.

Conduit run leaving Division 2 location Within 10 ft of either side of boundary. No unions,
couplings, boxes, or fittings (other than explosionproof reducers) permitted between the seal fitting and the point where the conduit leaves the Division 2 location. Not required to be explosionproof seal.
Metal conduit containing no unions, couplings, boxes, or fittings that passes completely through a Division 2 location with no fittings less than 12 in. beyond each boundary
Conduit systems terminating at an unclassified location where a wiring method transition is made to cable tray, cablebus, ventilated busway, Type MI cable, or open wiring
Conduit leaving a purged enclosure or room that is unclassified due to pressurization and entering a Division 2 location
Not required to be sealed if the termination points of the unbroken conduit are in unclassified locations.
Not required to be sealed if passing from the Class I, Division 2 location into an outdoor unclassified location or an indoor location if the conduit system is all in one room. The conduits do not terminate at an enclosure containing an ignition source in normal operation.
Not required to be sealed at the boundary.

 

National Electrical Code Handbook 2014 587
501.15 Article 501 ● Class I Locations
COMMENTARY TABLE 501.1 Continued
Classification Application Location of Seal
Cable Seals
Enclosure with integral seal Conduit seal fitting not required.
Class I, Division 1
Multiconductor Type MC-HL cables with a gastight/ vaportight continuous corrugated metallic sheath and an overall jacket of suitable polymeric material
Cables in conduit with a gastight/vaportight continuous sheath capable of transmitting gases or vapors through the cable core

Multiconductor cables with a gastight/vaportight continuous sheath capable of transmitting gases or vapors through the cable core
Seal at all terminations with a listed fitting after removing the jacket and any other covering, so that the sealing compound surrounds each individual insulated conductor.
Seal in the Division 1 location after removing the jacket and any other coverings, so that the sealing compound surrounds each individual insulated conductor and the outer jacket.
Permitted to be considered a single conductor by sealing the cable in the conduit within 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 Removal of the shielding material or separation of the
twisted pair is not required. Sealing the cable in the conduit 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.
Each multiconductor cable in conduit if the cable is incapable of transmitting gases or vapors through the cable core
Class I, Division 2 Cables entering enclosures that are required to be
explosionproof for Class I locations

Multiconductor cables with a gastight/vaportight continuous sheath capable of transmitting gases or vapors through the cable core
Considered a single conductor. These cables are sealed in accordance with 501.15(A).

Sealed at the point of entrance. These cables are sealed in accordance with the requirements of Division 1 locations.
Sealed in a listed fitting in the Division 2 location after removing the jacket and any other coverings, so that the sealing compound surrounds each individual insulated conductor.

Multiconductor cables in conduit Sealed in accordance with the requirements for Division 1 locations.
Cables with a gastight/vaportight continuous sheath that will not transmit gases or vapors through the cable core in excess of the quantity permitted for seal fittings. The minimum length of such cable run is not less than that length that limits gas or vapor flow through the cable core to the rate permitted for seal fittings (0.007 ft3 per hour of air at a pressure of 6 in. of water).
Cables with a gastight/vaportight continuous sheath capable of transmitting gases or vapors through the cable core

Cables  gastight/vaportight continuous sheath

gastight/vaportight Cables

Cables with an unbroken gastight/vaportight continuous sheath that pass through a Class I, Division 2 location

Cables that do not have a gastight/vaportight continuous sheath
Not required to be sealed unless entering an enclosure that is required to be explosionproof.

Not required to be sealed unless entering an enclosure that is required to be explosionproof or unless the cable is attached to process equipment or devices that may cause a pressure in excess of 6 in. of water to be exerted at a cable end, in which case a seal, barrier, or other means is provided to prevent migration of flammables into an unclassified area.

No seal required.
Sealed at the boundary of the Division 2 and unclassified location in such a manner as to minimize the passage of gases or vapors into an unclassified location. ” ]
588 2014 National Electrical Code Handbook