Classifying a Location

[jtester]

I am trying to get a better idea of if and how to classify a woodworking shop. Previously, posts indicated that a typical woodworking shop might not be classified at all.

I've read NEC Article 503, and the explanatory notes in the Handbook after 503.5 say "Sawmills and other woodworking plants, where sawdust, wood shavings, and combustible fibers or flyings are present, may also become hazardous."

Would Bob or some of the other hazardous location experts please share some insight into when a shop ought to be classified? Maybe something as simple as a dust collection system would declassify an area, but it would seem that a system would change an area from a Div 1 to a Div 2.

Thanks

Jim T

 

[bphgravity]

An AHJ has to make that determination. This could be an insurance agent, fire marshall, or perhaps the building official. In most cases this is first determined by the design professional before plans are submitted or work is started.

 

[petersonra]

I have seen a fair amount of woodworking equipment and never seen any of it made to meet any hazardous area classification.

I think the key is house keeping.

TEFC motors are a good idea in any case for other reasons.

 

[jtester]

Thanks Bryan and Bob. I am a design professional often called upon to design electrical for wood shops. Thru my ignorance, I usually specified those spaces to be Class III. The local inspectors and I have a very good relationship, and we would be able to agree on classification or not. They have enforced the classification in the past, because it was on my plans.

From the posts here, I've learned that I am probably wrong. I'd like to relook at the classification issue, and on future projects be correct. If I change my design philosophy and don't classify my next woodshop, I will surely get to explain my reasoning to the inspectors.

Thanks for your help.

Jim T

 

[rbalex]

Sorry, I've been internet deprived these last few days.

In general, the concern in Class II and III is the build-up of ignitible materials in relatively small areas rather than their overall migration to other locations. Basically, Groups E&F are conductive dusts (metallic and carbon based) and Group G dusts are usually insulating but may become conductive under the right conditions.

In both cases, with sufficient build-up, they may be ignitable but not explosive. This is important to remember because you still have a fire hazard ? even if you use ?explosionproof? equipment. Good housekeeping is always essential.

Conversely, with good housekeeping, electrical area classification may not be necessary at all. Where it is necessary is when the process creates particulate dusts in suspension in air.

NFPA 497 defines Combustible Dust as, ?Any finely divided solid material 420 microns or less in diameter (i.e., material passing through a U.S. No. 40 Standard Sieve) that presents a fire or explosion hazard when dispersed.?

It takes a great deal of fine wood sanding to create this ? and it must be kept in suspension to be explosive although it may ignite if it builds up. Neither ?Dust tight? nor ?Explosionproof? equipment would prevent a ?build-up? fire.

Side note: There is virtually no difference between Division 1 and Division 2 for Class III.