Installation of Solenoids in Hazardous Locations

[DM2-Inc]

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:

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.
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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:
  
  1. The maximum pressure effects of the gas mixture.
  2. 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.

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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?

 

[rbalex]

Your fundamental assumption is in error; a Division 2 mark doesn't imply NEMA 7. See 500.8(C)(2).

 

[DM2-Inc]

I took another look at my original post, and I'm not seeing where I make the assumption that Division 2 mark implies NEMA 7. I do make the assumption NEMA 7 implies suitability for hazardous locations, but not the specifics (i.e. Div 1, Div 2, Groups...what ever).

I understand that a label indicating the devices is suited for Class I, Div 1 or 2, Group X, is not an indication of the enclosure type. The enclosure type would be indicated separately on the manufacturers label. I understand that attention must also be focused on the T rating if it's indicated on the label as well.

The solenoids I'm talking about indicate:
- Hazardous location rating (i.e. Class I, Div 1 Groups C and D, etc.)
- Enclosure Type (i.e. NEMA 3, 4, 4X, 7 and 9, etc.)

For the longest time, I thought you still needed a seal at the enclosure for the solenoid coil, which is rated for hazardous locations. However I've seen so many installations with out it, I began to wonder. So I had a read through chapter 5 to try and understand when the seal is required and came to the conclusions in my first post.

In summary, I've come to the conclusions that seals aren't required on solenoids labeled for Class I, Div X, Groups X, locations, based on the following:
1. Section 501.115(B)(1) only requires seals at enclosures that are required to be explosion proof.
2. NEMA 250, Annex B.2.1.1, states that a NEMA 7 enclosure, while being suitable for hazardous locations, doesn't mean that the enclosure has to be designed to withstand an internal explosion if the equipment inside of the enclosure doesn't have the ability to generate an explosion.
3. Section 501.120(B)(2) allows solenoids to be installed in general purpose enclosures.

My question is, is this correct, or have I missed something in the NEC?

 

[rbalex]

I apologize; I misread the intent of your third paragraph: "If the label on the solenoid housing indicates a NEMA rating of 7 ..." Since you started the discussion with "...solenoids, rated for Class I, Div 2 locations,..." I thought you meant it was marked "Div 2" and that indicated NEMA 7.

As I understand you now, the solenoid is marked NEMA 7. In that case, it is also probably marked, Class I, Group X with no reference to Division at all. Referring to the same Section 500.8(C)(2), we see it is suitable for either Div 1 or 2. Section 501.120(B)(2) tells us we can use general purpose enclosures for solenoids in Division 2. So, while the NEMA 7 enclosure may also be suitable for Division 1, it isn’t required to be; therefore there is no condition in Section 501.15 (B)(1) that requires it to be sealed in Division 2.