transformer clearances

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ggonza

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I'm not sure if this is a dumb question or not. Is drywall considered a combustible material? Specifically when it comes to transformer clearances?
 
cowboyjwc

cowboyjwc

Moderator
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Location
Simi Valley, CA
I usually just go by the sticker on the front, it was six inches for the longest time and I've seen a few lately that say three inches. What I the sticker says is for ventilation that six inches of clearance are required, I'm not sure that it mentions combustible.
 
Howard Burger

Howard Burger

Senior Member
Location
N of Anchrage, AK
not a dumb question

not a dumb question

Not a dumb question at all, esp. when boxes set back in sheetrock more that 1/4 in. need an extension ring (314.20) which I haven't figured out, since sheetrock won't burn. But the paper covering could burn.

As to transformers, the manufacturer sets out requirements for distances from walls for air circulation room; last time I checked, I couldn't find anything in the NEC about such distances, and was told to look at the mfg. information for stand-off distances. I'm talking 75kVA dry type xf.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Howard Burger said:
Not a dumb question at all, esp. when boxes set back in sheetrock more that 1/4 in. need an extension ring (314.20) which I haven't figured out, since sheetrock won't burn. But the paper covering could burn.

As to transformers, the manufacturer sets out requirements for distances from walls for air circulation room; last time I checked, I couldn't find anything in the NEC about such distances, and was told to look at the mfg. information for stand-off distances. I'm talking 75kVA dry type xf.
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infinity said:
IMO no given the setback allowance for Sheetrock that Howard mentioned.
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314.20 In Wall or Ceiling.
In walls or ceilings with a surface of
concrete, tile, gypsum, plaster, or other noncombustible
material, boxes employing a flush-type cover or faceplate shall be
installed so that the front edge of the box, plaster ring, extension ring, or
listed extender will not be set back of the finished surface more than 6 mm (?
in.).
In walls and ceilings constructed of wood or other combustible surface
material, boxes, plaster rings, extension rings, or listed extenders shall be
flush with the finished surface or project therefrom.
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1/4 inch setback is allowed for all non combustible surfaces. Drywall happens to be one of them. If drywall were combustible material boxes would have to be flush.
 
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