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Monday, April 17, 2023
Question:
Hello CQD. We inherited a piece of equipment originally designed for Class I, Div 2, Group B with a purge system on the main control cabinet (2 door NEMA 4X cabinet). At some point before we inherited it, the purge system was abandoned and a gas detector was installed inside the cabinet, tied to an externally located shunt trip breaker that isolates the control cabinet in the vein of NEC 500.7 (K)(4) allowing the use of GP devices inside the cabinet that is located within a Class I, Div 2 location.
While they tried to adhere to this protection method allowed in 500.7(K)(4) by interpreting the "Enclosed Space" term as the electrical enclosure, we don't believe this term refers to a control cabinet, but more to a closet or room located within a Class I, Div 2 bubble. I would be interested to hear your take on this interpretation of the 500.7(K)(4). Thank you in advance. George M.
A
Answer:
Hello George, thank you for the detailed information/question. To start, the 2020 NEC® restricts the application of Section 500.7(K) to industrial establishments with restricted public access, and where the condition of maintenance and supervision ensure only qualified persons service the installation. Once that is established then in order to use gas detection as a protection method, ALL five (5) of the criteria listed in Section 500.7(K)(1)(a)-(e) must be met.
Section 500.7(K)(1)(e) then limits the application of gas detection as a protection technique to those listed in Section 500.7(K)(2), (3), or (4).
Section 500.7(K)(4) specifically applies to the interior of a control panel, and the protection and wiring located therein. This Section would not apply to wiring or protection outside of the control panel.