Metal Boxes / EMT on Basement Wall - when is it OK?

[William Deans]

Greetings,

The NEC states that you cannot put metalic boxes onto masonry which may be damp without a 1/4" airspace. Does this mean that you cannot use metal boxes / emt on masonry basement walls? What about metal boxes / emt on masonry basement walls of a row home between the homes?

Thank you for your time and energy, William

PS: This post was previously listed under NEC Clarification Needed which I feel was a poor choice as it did not provide enough information. Since there have not yet been any responses I am reposting it under a different, much improved, heading.

[Hopkins]

My understanding is that you cannot attach boxes directly to masonry, period. But I'm sure someone will come along and provide more and better detail.

[BobK207]

Bill-

Sounds to me like you answered your own question.

The NEC is concerned about corrosion of the metallic box; hence the requirement for the 1/4" airspace. so as not to trap any moisture behind the box,

I'm sure you've seen the surface mounted box in somebody's damp nasty basement that is all rusted out.

Install with the airpace & the box will be fine. Don't use wood or any material that will retain mositure; metal washers would work.

cheers Bob

[William Deans]

Thanks bob -- however, someone on here said that the 1/4" airspace requirement didn't apply to device boxes? Is this true of false?

[Percival P. Cassidy]

I found a Web site some time ago that recommended against using wood between a panel and a concrete wall and said that some jurisdictions even prohibit it. I don't recall whether it said this was because the wood could become a fire hazard or because it could get waterlogged.

The new panel I bought but haven't yet installed has raised sections on the back where the bolts/screws/fasteners go, so that very little of the box would be in contact with the wall to which it is mounted. Does this mean that I could fasten it directly to the concrete basement wall -- and run pieces of wood alongside (but spaced away from the sides of the panel) to which the Romex can be stapled?

Perce

On 05/01/05 01:18 pm BobK207 tossed the following ingredients into the ever-growing pot of cybersoup:

[BobK207]

I don't know for sure about whether the 1/4" space applies to device boxes. Just based on experience, if there is moisture / dampness that can be trapped behind the box you'll enetually have a corrosion problem.

If moisture / dampness is a potential problem, stay away from materials that can absorp it & help corrode the metal.

Metal & wood will last a very long if kept dry. If not, they can be destroyed VERY quickly.

cheers Bob