DM2-Inc
Senior Member
- Location
- Houston, Texas
I often see solenoids, rated for Class I, Div 2 locations, installed using liquid tight flex but without a seal at the solenoid housing/enclosure. I'm trying to understand when, if at all, Solenoids that are rated for hazardous locations, are permitted to be installed in such a way.
I'm using the 2008 edition of NFPA 70, and I read in 501.115(B)(1) that seals are only required at enclosures that are required to be explosion proof. Section 501.120(B)(2) tells me that solenoids are permitted in general purpose enclosures. When I look at the label of the Solenoid, it reads that it is acceptable for use in Class I, Division 2 locations, Group [what ever].
If the label on the solenoid housing indicates a NEMA rating of 7 most references on the Internet simply state (and I'm sumerizing here), "...shall be capable of withstanding the pressures resulting from an internal explosion..." as does NEMA in there White Paper "NEMA Enclosure Types", page 5. NEMA 250, Annex B.2.1.1 however states:
Because B.2.1.1.a states "...or from operation of internal equipment." I'm assuming that the enclosure for the solenoid coil doesn't need a seal at the conduit connection to the housing. I'm also guessing that the "...internal hydrostatic...test..." referenced in "d" above, would not have been conducted, considering that the coil wouldn't have generated the explosion needed to get "...the maximum internal pressure obtained during explosion tests..."
Is this a correct assumption?
Did I miss anything?
I'm using the 2008 edition of NFPA 70, and I read in 501.115(B)(1) that seals are only required at enclosures that are required to be explosion proof. Section 501.120(B)(2) tells me that solenoids are permitted in general purpose enclosures. When I look at the label of the Solenoid, it reads that it is acceptable for use in Class I, Division 2 locations, Group [what ever].
If the label on the solenoid housing indicates a NEMA rating of 7 most references on the Internet simply state (and I'm sumerizing here), "...shall be capable of withstanding the pressures resulting from an internal explosion..." as does NEMA in there White Paper "NEMA Enclosure Types", page 5. NEMA 250, Annex B.2.1.1 however states:
Type 7 enclosures shall be capable of withstanding the pressures resulting from an internal explosion of specified gases, and contain such an explosion sufficient that an explosive gas-air mixture existing in the atmosphere surrounding the enclosure will not be ignited. Enclosed heat generating devices shall not cause external surfaces to reach temperatures capable of igniting explosive gas-air mixtures in the surrounding atmosphere. Enclosures shall meet explosion, hydrostatic, and temperature design tests.
When completely and properly installed, Type 7 enclosures:
- Provide a degree of protection to a hazardous gas environment from an internal explosion or from operation of internal equipment.
- Do not develop surface temperatures that exceed prescribed limits for the specific gas corresponding to the atmospheres for which the enclosure is intended, when internal equipment is operated at rated load.
- Withstand a series of internal explosion design tests that determine:
- The maximum pressure effects of the gas mixture.
- Propagation effects of the gas mixtures.
- Withstand, without rupture or permanent distortion, an internal hydrostatic design test based on the maximum internal pressure obtained during explosion tests and a specified safety factor.
Because B.2.1.1.a states "...or from operation of internal equipment." I'm assuming that the enclosure for the solenoid coil doesn't need a seal at the conduit connection to the housing. I'm also guessing that the "...internal hydrostatic...test..." referenced in "d" above, would not have been conducted, considering that the coil wouldn't have generated the explosion needed to get "...the maximum internal pressure obtained during explosion tests..."
Is this a correct assumption?
Did I miss anything?