NEC 501.105(B)(5) & General Purpose ENclosures

[guggemos]

I have an outdoor Class I, Div 2 area (refinery tank field) with a terminal box which includes a 2A fuse protected 15-pt termial strip. 4 3/4" conduits carry the wiring. Upstream from the box is a Class I, Div 2 rated hermetically sealed switch. NEC 501.105(B)(5) allows a general purpose enclosure for the TB w/o conduit seals.

The issue is the contractor used a Nema 7 rated enclosure for the TB and no conduit seals because of 501.105(B)(5). I think the installation is OK, just overkill with the Nema & box. The inspector wants conduit seals because of the Nema 7 enclosure.

The question: Is the NEC stating "general purpose enclosure" meaning what I'm thinking, that the TB could be any box rated for the outdoor environment like a Nema 4X instead of a Nema 7 and because of the switch upstream it complies with 501.105(B)(1)?

Al

 

[guggemos]

Fuse Allowed

Fuse Allowed

I have an outdoor Class I, Div 2 area (refinery tank field) with a terminal box which includes a 2A fuse protected 15-pt termial strip. 4 3/4" conduits carry the wiring. Upstream from the box is a Class I, Div 2 rated hermetically sealed switch. NEC 501.105(B)(5) allows a general purpose enclosure for the TB w/o conduit seals.

The issue is the contractor used a Nema 7 rated enclosure for the TB and no conduit seals because of 501.105(B)(5). I think the installation is OK, just overkill with the Nema & box. The inspector wants conduit seals because of the Nema 7 enclosure.

The question: Is the NEC stating "general purpose enclosure" meaning what I'm thinking, that the TB could be any box rated for the outdoor environment like a Nema 4X instead of a Nema 7 and because of the switch upstream it complies with 501.105(B)(1)?

Al

Is the fuse even allowed because it is not a low energy circuit. The fuse is 2A on a 1202VAC circuit.

 

[rbalex]

Is the fuse even allowed because it is not a low energy circuit. The fuse is 2A on a 1202VAC circuit.

Low energy is not the question; is it an instrumentaion circuit not subject to overloading in normal use?

Assume it is and 501.105(B)(1) through (B)(4) permits a general purpose enclosure and the fuse is preceded by a switch complying with 501.105(B)(1). The general purpose enclosure only needs to be suitable for an "ordinary location" enviornment. Depending on the edition, see NEC Table 110.20 or 110.28. A NEMA 7 is acceptable too if it also meets the "ordinary location" requirements.

Sealing the NEMA 7 enclosure is subject to Section 501.15 (B)(1). Even though it is NEMA 7, it is not required to be explosionproof. So no seals are required either.

 

[guggemos]

NEC 501 ...

NEC 501 ...

"Table 110.20 shall be used for selecting these enclosures for use in specific locations other than hazardous (classified) locations. "

The TB is located in a hazardous location so this table does not apply. That is why I'm looking for the reasoning behind 501.105 (B)(5).

 

[rbalex]

"Table 110.20 shall be used for selecting these enclosures for use in specific locations other than hazardous (classified) locations. "

The TB is located in a hazardous location so this table does not apply. That is why I'm looking for the reasoning behind 501.105 (B)(5).

The table still applies if the enclosure isn't required to be explosionproof. It still needs to be suitable for the environment; i.e., "indoors", "outdoors" etc. UL 50 and NEMA 250 only identify Type 7 for indoor use.