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#97003 - 01/16/06 04:02 PM Spray Booths  
Paul O'Connell  Offline
Joined: Jul 2005
Posts: 56
Allen Park, Mi. USA
Article 516 references NFPA 33. NFPA 33 requires bonding and grounding of all metal parts of a spray booth be bonded or grounded for static electricity. NFPA 33 does not reference the size of this conductor nor does it reference using Tables 250.62 or 250.122. NFPA 77 on Static Electricity tells us that regarding this conductor the size does not matter but that it should be stranded or braided for flexability. Does anyone know of any other NFPA publication that can direct me to the proper sizing of this conductor?

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#97004 - 01/16/06 04:58 PM Re: Spray Booths  
earlydean  Offline
Joined: Dec 2003
Posts: 751
Griswold, CT, USA
Here is what the NEC handbook says about static in spray booths:
"To prevent sparks from the accumulation of static electricity, all electrically conductive objects, including metal parts of spray booths, exhaust ducts, piping systems conveying flammable or combustible liquids or paint, solvent tanks, and canisters, should be properly grounded. See Section 4-5 of NFPA 33 and Section 9.3 of NFPA 77, Recommended Practice on Static Electricity. "

Section 4-5 of NFPA 33 requires bonding and grounding, and Section 9.3 of NFPA 77 warns of the danger of static discharge. But the Appendix A 4-5 references NFPA 77 in its entirety. of NFPA 77:
"Where wire conductors are used, the minimum size of the bonding or grounding wire is dictated by mechanical strength, not by its current-carrying capacity. Stranded or braided wires should be used for bonding wires that will be connected and disconnected frequently."

The NEC, (NFPA 70), Section 516.16 requires the bonding jumper to be sized according to 250.122 and no smaller than #14 AWG.

But, you already know all this.

I would bond the metal parts of the electrical installation using table 250.122, and let the user worry about bonding the portable stuff.

If the customer has hired you to do the jumpers then: Appendix C of NFPA 77 has several pictures on how this is done in spray booth applications. They recommend 1/4-3/8 inch flexible bronze or 1/8 inch stainless jumpers and clamps, among other sizes and methods. Pick and choose a method that works for your situation.


#97005 - 02/17/06 06:36 PM Re: Spray Booths  
Paul O'Connell  Offline
Joined: Jul 2005
Posts: 56
Allen Park, Mi. USA
Earlydean: What do you think of the requirement for grounds smaller than #6 to be in conduit? Since some of this requires some type of portable clamping device.

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