J Box one end, 3 phase motor on other.
(B) Class I, Division 2.
In Class I, Division 2 locations, motors, generators, and other rotating electrical machinery in which are employed sliding contacts, centrifugal or other types of switching mechanism (including motor overcurrent, overloading, and overtemperature devices), or integral resistance devices, either while starting or while running, shall be identified for Class I, Division 1 locations, unless such sliding contacts, switching mechanisms, and resistance devices are provided with enclosures identified for Class I, Division 2 locations in accordance with 501.105(B). The exposed surface of space heaters used to prevent condensation of moisture during shutdown periods shall not exceed 80 percent of the ignition temperature in degrees Celsius of the gas or vapor involved when operated at rated voltage, and the maximum surface temperature [based on a 40?C (104?F) ambient] shall be permanently marked on a visible nameplate mounted on the motor. Otherwise, space heaters shall be identified for Class I, Division 2 locations. In Class I, Division 2 locations, the installation of open or nonexplosionproof enclosed motors, such as squirrel-cage induction motors without brushes, switching
mechanisms, or similar arc-producing devices that are not identified for use in a Class I, Division 2 location, shall be permitted.
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If your motor is labeled Cl.I, D.1 as per the above highlight, then a seal would be necessary.
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501.10 Wiring Methods.......
(B) Class I, Division 2.......
(4) Boxes and Fittings.
Boxes and fittings shall not be required to be explosionproof except as required by 501.105(B)(1), 501.115(B)(1), and 501.150(B)(1).
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If the junction box is subject to the exceptions then the cable entering into it must be saled.
In both cases you are not sealing the conduit, per se, but rather the XP enclosures to contain the potential explosion internal to those.