Class II, Div 2 Transformer

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I have a location rated Class II, Group G, Div 2, where we are installing power transformers, 3ph, 480/240 VAC, 150kvA. These are dry-type transformers. NEC 502.100 (B)(3) states that:

"Dry-type transformers shall be installed in vaults of have their windings and terminal connections enclosed in tight metal housings without ventilating or other openings and shall operate at not over 600 volts, nominal".

We prefer not to install these transformers in vaults, due to space limitations. I've tried to source these transformers but can't find a supplier that has them specifically rated for a Class II, Div 2 location. There are many out there rated for Class I, Div 2 locations, but that is for combustible gases/vapors, not combustible dust.

I'm sure others have run into this issue. Can someone advise of their approach?

Thanks
 

rbalex

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Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I have a location rated Class II, Group G, Div 2, where we are installing power transformers, 3ph, 480/240 VAC, 150kvA. These are dry-type transformers. NEC 502.100 (B)(3) states that:

"Dry-type transformers shall be installed in vaults of have their windings and terminal connections enclosed in tight metal housings without ventilating or other openings and shall operate at not over 600 volts, nominal".

We prefer not to install these transformers in vaults, due to space limitations. I've tried to source these transformers but can't find a supplier that has them specifically rated for a Class II, Div 2 location. There are many out there rated for Class I, Div 2 locations, but that is for combustible gases/vapors, not combustible dust.

I'm sure others have run into this issue. Can someone advise of their approach?

Thanks
Actually, any dusttight metal enclosure will do.

I suspect the real problem is someone over-classified the location in the first place.
 
Location
NC
We don't believe the area is over classified.

A bigger challenge is determining what the NEC means by the term "dusttight". There's a requirement to use "dusttight" enclosures (for Class II, Division 2 locations), as stated in 502.10(B)(4), yet there is no clear definition of which enclosures are acceptable for use in that location, because 110.28, it states that Table 110.28 should not be used to determine which enclosures should be used in Hazardous Locations.

So there's a requirement to use dusttight enclosures in Class II, Div 2 locations, but not a clear definition of what dusttight enclosures are for those locations.
 

rbalex

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Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Both UL 50 and (old) NEMA 250 use(d) the same definitions for dusttight as Table 110.28 and so does CMP14. I suspect CMP 1 was being overly cautious in Section 110.28 since the Table makes no reference to Types 7, 8 or 9.


If you simply must have a hazardous location definition, see Section 500.2 and get a copy of the latest ANSI/ISA-12.12.01, but you won't find any new information.
 

rbalex

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Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Both UL 50 and (old) NEMA 250 use(d) the same definitions for dusttight as Table 110.28 and so does CMP14. I suspect CMP 1 was being overly cautious in Section 110.28 since the Table makes no reference to Types 7, 8 or 9.


If you simply must have a hazardous location definition, see Section 500.2 and get a copy of the latest ANSI/ISA-12.12.01, but you won't find any new information.
I forgot, CMP1 and CMP 14 are constrained to accept the same definition of dusttight as defined in Article 100. That is, dusttight means the same thing in both Article 110 and Articles 500 and 502.
 
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