ONLINE TOOLBOX
 Reference Book
Software Downloads
Links To Related Sites
Industry News
Training Opportunities
Glossary Of Terms
Online Calculators
Technical Information
EPAct
Rebate Information
Factory Cross Reference |
 |
HOW CAN I WIRE IT? HAZARDOUS LOCATION WIRING METHODS SIMPLIFIED
- Published in Southwire's Power Cable Update newsletter in February 1998
- Reprint permission granted
Here's help in tracing usability of wiring methods across NEC hazardous location texts.
"I'm running rigid metal conduit through an area with combustible dust. Can I also run it through the room next door where there's flammable cleaning solvent?" Probably not.
When multiple environments are classified as hazardous locations, you may find yourself picking your way through Chapter 5 of the National Electrical Code (NEC) to see what wiring methods are allowable in all of them.
Sections 501, 502 and 503 of the NEC describe acceptable wiring methods and requirements for the three NEC hazard classes: Class I for flammable vapors and liquids, Class II for combustible dusts, and Class III for ignitable fibers. Within each class, Division 1 means hazard is present in normal operations and Division 2 means it's only present if something goes wrong.
The wiring methods you can use depend on the Class and Division. (But they don't depend on the group, which defines the hazardous substance itself) Because the NEC sections are organized by Class and Division, it can be tricky — or at least tedious — to track down all the areas where a specific wiring method is — or is not — allowed.
To simplify the task, IEEE Standard 141-1993 contains a table that helps you trace the usability of a specific wiring method through the NEC hazard classes. We're presenting it here, along with an update for type MC cable from the 1996 NEC. Be sure to check the details of your specific installation with the appropriate NEC sections.
Wiring Methods for Hazardous Locations |
Wiring Methods |
Class I, Division 1 |
Class I, Division 2 |
Class II, Division 1 |
Class II, Division 2 |
Class II, Division 1 or 2 |
Threaded rigid metal conduit |
X |
X |
X |
X |
X |
Threaded steel intermediate metal conduit |
X |
X |
X |
X |
X |
Rigid metal conduit |
|
|
|
X |
X |
Intermediate metal conduit |
|
|
|
X |
X |
Electrical metallic tubing |
|
|
|
X |
X |
Rigid non-metallic conduit |
|
|
|
|
X |
Type MI mineral, insulated cable |
X |
X |
X |
X |
X |
Type MC metal-clad cable |
* |
X |
* |
X |
X |
Type SNM shielded non-metallic cable |
|
X |
|
X |
X |
Type MV medium-voltage cable |
|
X |
|
|
|
Type TC power and control tray cable |
|
X |
|
|
|
Type PLTC power-limited tray cable |
|
X |
|
|
|
Enclosed, gasketed busways or wireways |
|
X |
|
|
|
Dust-tight wireways |
|
|
|
X |
X |
*Allowed in certain industrial environments. See 1996 NEC Section 501-4(a) and 502-2(a). |
Sources: IEEE Std. 141-1993, 1996NEC |
|
