Mike Dolt Enterprises
Mike Dolt Enterprises
User: session88, Location: USA
Asked on: Monday, March 21, 2011 at 7:21 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:04 am EDT
Question: We are having a contractor install an HMI touch screen in our coal fired power plant. It will be installed near some coal conveyors. My understanding is that this area is a Class II, Division 1 location because even with our dust collector system running coal dust accumulates everywhere on that deck. As far as we know an area clasification study has not bin done here. Some people here are saying it is ok to buy a NEMA 4 enclosure, cutt a hole into the cover for the HMI and seal it to the enclosure door and presurize the enclosure with plant air. This home made enclosure dosen't seen right to me. I beleve the enclosure needs to be manufactured for this area. Any thoughts or an old thread someone can direct me to that might help me end up with the proper installation?
NEC Requirements for Class II, Division 1 Locations
According to the National Electrical Code (NEC), Class II, Division 1 locations are areas where flammable materials are present in the form of gases or vapors and are likely to be released or dispersed under normal operating conditions.In these locations, the NEC requires enclosures for electrical equipment to meet the following criteria: Type "N" Enclosure
Designed to prevent the ingress of dust and water.
Explosion-Proof Enclosure
Designed to withstand an internal explosion without releasing flames or sparks.
Purged and Pressurized Enclosure
Maintained under positive pressure with clean air or an inert gas to prevent the entry of flammable gases or vapors.
Suitability of Homemade Enclosure
The proposed homemade enclosure, consisting of a NEMA 4 enclosure with a hole cut into the cover and sealed to the door, does not meet the NEC requirements for Class II, Division 1 locations. Ingress of Dust
The homemade enclosure is not designed to prevent the ingress of dust, which is a flammable material in this location.
Positive Pressure
The enclosure is not maintained under positive pressure, which could allow flammable gases or vapors to enter.
Proper Installation
The proper approach is to install an HMI touch screen in a Type "N" or explosion-proof enclosure that is specifically manufactured for use in Class II, Division 1 locations. These enclosures are designed and tested to meet the NEC requirements and provide adequate protection for electrical equipment in hazardous environments.
Old Thread for Reference[NEC Class II Division 1 Enclosure](https://www.control.com/thread/1065950003)Additional Considerations Ensure that the HMI touch screen is suitable for use in the specific Class II, Division 1 environment. Consider the potential for electrostatic discharge (ESD) in the area and take appropriate steps to mitigate it. Regularly inspect and maintain the enclosure to maintain its integrity. Flag for review