Mike Dolt Enterprises
Mike Dolt Enterprises
User: Pat H, Location: Mission Viejo, CA
Asked on: Friday, April 8, 2011 at 10:30 am EDT
Answered on: Tuesday, May 14, 2024 at 3:57 am EDT
Question: I have heard conflicting information about Class II Division II purge requirements for a motor control panel.My interpretation of the NEC 502.115 B is that a control panel needs to be dust tight for CII DII (Groups F&G) and doesn't specifically call for a purge. CI DI does specifically call for a purge unit.The manufacturer of the purge unit tells me that you do need a purge unit for CII DII and the distributor say's you don't really need the purge, but its a good idea because the enclosure seal could wear out.I build control panels and need to know if I am really required to provide a purge system when panel is going to be in CII DII (dust that is not normally present).Can anyone offer any insight to this? Does some electrical code really specifically dictate that a purge unit is necessary in CII DII? If so, can you tell me what code that is? Are they just trying to sell me?Thanks,Pat
According to the NEC, a purge unit is not explicitly required for Class II Division II (CII DII) hazardous locations where the dust is not normally present.
NEC 502.115 B
> Motors, generators, and other rotating electrical machinery having commutators, collectors, brushes, or sliding contacts shall be of the dust-ignitionproof enclosed type unless a special maintenance program is provided in accordance with 502.5(D).
NEC 502.5(D)
> Special maintenance programs shall not be used as a substitute for the requirements of 502.110 through 502.
140. Special maintenance programs shall provide for the following:> (1) Periodic cleaning of dust accumulations from motors, generators, and other rotating electrical machinery and from wiring and other electrical components where dust accumulations could interfere with safe operation or maintenance.> (2) Inspection of motors, generators, and other rotating electrical machinery for signs of overheating or other abnormal conditions.> (3) Prompt correction of any abnormal conditions found during inspection.
Interpretation
NEC 502.115 B requires dust-ignitionproof enclosed motors for CII DII locations. NEC 502.5(D) allows for special maintenance programs in lieu of dust-ignitionproof enclosures.* However, special maintenance programs cannot replace the requirements of NEC 502.110 through 502.140, which do not include a purge unit requirement for CII DII locations.Therefore, while a purge unit may be a good idea for additional protection in CII DII locations where dust is not normally present,
it is not explicitly required by the NEC.
However, it's important to note that local or industry-specific regulations may have additional requirements. Always consult with the local Authority Having Jurisdiction (AHJ) and relevant industry standards for specific guidance. Flag for review