501.15(D) Cable Seals, Class I, Division 1.
Code Change Summary: Requirements for cable seals in Class I Division 1 locations have been expanded.
The most common wiring methods used in locations classified as hazardous are rigid metal conduit and intermediate metal conduit but there are also many cable types listed for use in hazardous locations such as MC-HL (metal-clad hazardous location), TC-ER-HL (tray cable exposed run hazardous location), ITC-HL (instrumentation tray cable hazardous location) and MI cable (mineral insulated).
Proper sealing of wiring methods in classified locations is critical. A correctly installed seal-off fitting keeps any sparks occurring in a junction box from igniting flammable materials that may be present in the specific hazardous location. They also work to prevent explosions from spreading throughout the conduit systems and limit flammable vapors from passing between classified and nonclassified locations.
In the 2017 NEC®, the rule for sealing cables in a Class I Division 1 location now requires the seal-off fitting to be within 18 inches of the enclosure where the cable terminates or as required by markings on the enclosure. This is generally not an issue since most cable seals are accomplished by using a listed connector that threads directly into the explosionproof junction box (see image).
Another change now mentions all of the items that are permitted between the sealing fitting and the enclosure. “Only explosionproof unions, couplings, reducers, elbows, and capped elbows that are not larger than the trade size of the enclosure entry shall be permitted between the sealing fitting and the enclosure”. This aligns with similar language for conduit seals located in 501.15(A)(1).
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC® edition of NFPA 70.
2014 Code Language:
(D) Cable Seals, Class I, Division 1. In Division 1 locations, cable seals shall be located according to 501.15(D)(1) through (D)(3).
(1) At Terminations. Cables shall be sealed with sealing fittings that comply with 501.15(C) at all terminations. Type MC-HL cables with a gas/vaportight continuous corrugated metallic sheath and an overall jacket of suitable polymeric material shall be sealed with a listed fitting after the jacket and any other covering have been removed so that the sealing compound can surround each individual insulated conductor in such a manner as to minimize the passage of gases and vapors.
See actual NEC® text for exception.
2017 Code Language:
(D) Cable Seals, Class I, Division 1. In Division 1 locations, cable seals shall be located according to 501.15(D)(1) through (D)(3).
(1) At Terminations. Cables shall be sealed with sealing fittings that comply with 501.15(C) at all terminations. Type MC-HL cables with a gas/vaportight continuous corrugated metallic sheath and an overall jacket of suitable polymeric material shall be sealed with a listed fitting after the jacket and any other covering have been removed so that the sealing compound can surround each individual insulated conductor in such a manner as to minimize the passage of gases and vapors.
Seals for cables entering enclosures shall be installed within 450 mm (18 in.) of the enclosure or as required by the enclosure marking. Only explosionproof unions, couplings, reducers, elbows, and capped elbows that are not larger than the trade size of the enclosure entry shall be permitted between the sealing fitting and the enclosure.
See actual NEC® text for exception.