501.105 Meters, Instruments, and Relays
Exception: General-purpose enclosures shall be permitted if current-interrupting contacts comply with one of the following:
- Are immersed in oil
- Are enclosed within a chamber that is hermetically sealed against the entrance of gases or vapors
- Are in nonincendive circuits
- Are listed for Division 2
Exception: General-purpose-type enclosures shall be permitted if such equipment is without, make-and-break or sliding contacts [other than as provided in 501.105(B)(2)] and if the marked maximum operating temperature of any exposed surface will not exceed 80 percent of the autoignition temperature in degrees Celsius of the gas or vapor involved or has been tested and found incapable of igniting the gas or vapor. This exception shall not apply to thermionic tubes.
- The attachment plug and receptacle are listed for use in Class I, Division 2 locations and listed for use with flexible cords.
Exception No. 1: A Class I, Division 2 listing is not required if the circuit involves only nonincendive field wiring.
Exception No. 2: In industrial establishments where the conditions of maintenance and supervision ensure that only qualified individuals service the installation, the Class I, Division 2 listing is not required when the requirements of 501.105(B)(6)(2), (B)(6)(3), and (B)(6)(4) are satisfied and the receptacle carries a label warning against plugging or unplugging when energized.
- The flexible cord does not exceed 900 mm (3 ft), is of a type listed for extra-hard usage, or if listed for hard usage is protected by location.
- Only necessary receptacles are provided.
- Unless the attachment plug and receptacle are interlocked mechanically or electrically, or otherwise designed so that they cannot be separated when the contacts are energized and the contacts cannot be energized when the plug and socket outlet are separated, a switch complying with 501.105(B)(2) shall be provided so that the attachment plug or receptacle is not depended on to interrupt current.
Exception: The switch shall not be required if the circuit is nonincendive field wiring.