Content area
Full Text
In the last issue, we discussed requirements for installing equipment in Class I locations. This month, we're continuing with the NEC's sequence of hazardous location articles to discuss Class II locations. In a nutshell, if the ignitable material is normally present (in sufficient quantities to present a hazard), then it's a Div. 1 location. Less stringent requirements apply for a Div. 2 location, because ignitables are present only in abnormal circumstances.
Like Art. 501, Art. 502 presents many requirements with a Division-based pattern. Where a subsection has an A and a B, the A is for Div. 1, and the B is for Div. 2. It's much easier to keep out dust than gases, so Art. 502 is much shorter than Art. 501. Often, the only requirement is that the equipment be identified for the location.
Article 502 gives you the option of using the Zone system (Art. 506) instead of the Division system [502.6]. However, we'll discuss Art. 506 in a future issue of the magazine.
Wiring methods
In Class II locations, any wiring method allowed for Div. 1 is allowed for Div. 2 [502.10(B)(1)(1)]. For Div. 2, you can use these wiring methods in addition to any used for Div. 1:
- Rigid metal conduit (RMC) or intermediate metal conduit (IMC) whether threaded or not (for Div. 1, these conduits must be threaded).
- Electrical metallic tubing.
- Dusttight wireways.
- Type MC cable with listed termination fittings.
- Type PLTC and Type PLTC-ER cable (installed per Art. 725).
- Type ITC and Type ITC-ER cable (as permitted by Art. 727.4).
- Type MC,MI, or TC cable in cable trays (under specific conditions).
- Schedule 80 conduit and RTRC fittings (under specific conditions).
Sealing requirements
While nearly half of Art. 501 is devoted to sealing requirements, Art. 502 presents those in about a quarter page. They're the same, regardless of Division. Art. 502 sealing requirements exist to keep dust from entering dust-ignition proof enclosures through the raceway. Because dust particles are much larger than gas molecules, Class II requirements are less rigorous than those for Class I (Photo).
Art. 502 provides four ways to keep the dust out [502.15]:
1. A permanent and effective seal (it need not be explosion-proof as with...