TMC verses TMCX on Explosion proof enclosures.

[l_zabel]

We recently had some construction work done on some well heads in which the contractor installed TMC connectors on some explosion proof transmitters. This is a Class 1 Zone 1 area. The transmitter is explosion proof, factory sealed, conduit seal not required. We are using Type MC-HL cable with Crouse-Hinds TMC Terminator fittings. Article 505.16(B)(7) states that a seal off be used no exceptions. Article 505.16(B)(2) addresses the exception of conduit seals when using factory sealed equipment, but does not address type MC-HL cable in the exception. This was approved by the contractors Administrator and engineer. I was wondering if anyone knew how they came to this conclusion? The way I interpret this is we should be using TMCX fittings rather than the TMC's.

Any help is appreciated. Thanks,

 

[rbalex]

From your description so far, 505.16(B)(2) is irrelevant since raceways are not involved. You are correct there are no exceptions under 505.16(B)(7).

In Zone 1, seals provide both flame blocking and gas migration mitigation.

 

[bobgorno]

TMC fittings do not include the epoxy sealing compund that TMCX fittings have. MC-HL cable has a continuous welded armor and is considered a vapor-tight covering. But MC-HL may allow gases to migrate from one end to another. Using a TMCX fitting at the transmitter, even though it is factory sealed is a great place to have your boundary seal. Using a TMC fitting at the transmitter would mean you would still need a boundary seal. It may also be better to stock one type (TMCX) so you can use it on other types of explosion proof enclosures. TMC are not listed by UL for explosion proof enclosures.