Gas Detection in C1D1/D2 locations

[Tbowman]

Hello ALL,
I have an outdoor area that is mostly D2 but there are "bubbles" of D1 locations around (within 20'). For all the gas detectors previously we have used MCHL cable to make it fool proof on which detectors needed what. The customer has brought in a large skid with 4 gas detectors, they are rated for C1D1, and some of them are in the bubble (using MCHL) and some of them not (using TC-ER). I believe that all of them need to be MCHL due to the possibility of an accidental gas release.

They are not connected to any barrier in the purged panel, so straight off the fuse (24VDC) and straight to the Allen-Bradley PLC. I think this keeps the wiring from being nonincendive and its not a simple apparatus. Please let me know your thoughts.

 

[gadfly56]

You're proposing to wire everything D1 "just in case." An accidental release is exactly what D2 is all about, and you don't need to follow the D1 requirements in that area for that reason. If it's your money, you can do as you like, but I wouldn't be trying to convince a customer on this.

 

[rbalex]

I'm citing the 2023 NEC.:

• The installation, as described, is noncompliant with Section 500.7(K)(1)(e) in the first place and has been since gas detection has been recognized as a protection technique.
• All gas detectors must be rated for Class I, Division 1 anyway. [Section 500.7(K)(1)(a)] and sealed per Sections 501.15(A)(1) or (B)(1).
• As long as the cables are an otherwise recognized wiring method under Section 501.10 and sealed at the termination as required by Section 501.15(D) or (E), the skid is fine.