Grounding Paint Booths

[ssommers]

I'm in a bit of a quandry about how to improve our paint booth grounding. I have a tube mill with 2 movable paint booths on wheels. Each one has a different color paint and only 1 is used at a time. They look like a 55 gallon drum with a box on top that has a trough. The paint is pumped up from the drum using a pneumatic pump and then flow coats the tube as it runs thru the trough and excess paint returns to the drum. There is a good ventillation system hooked up to the top of the box which scrubs out the VOCs before venting to the outside. My problem is that the operators sometimes forget to hook up the grounding alligator clip to the paint booth when they change from one color to the next. I can't make the connection permanent because they sometimes take the 2nd booth to another tube mill or to another area if it needs to be cleaned out. A manager asked if I could find a way to make the ground connection part of the paint booth track. NFPA 70 & 79 are kinda vague on this subject other than it needs to be grounded. Could I have a permanently mounted plug either under or at the front of the paint drum that would automatically make the connection when the booth is in the right place? Are there any other codes to I need to check? Has anyone else done this? Thanks, Susan

[TimWilborne]

I don't know if it is code or convenience but I have always seen this done with alligator clips What I am thinking is could it be change to a 3 prong plug. One for the ground and jumper the other two. Connect the other two to an intrinsically safe relay to signal that it is connected.

[ssommers]

I definitely think the alligator clip comes from convenience & the fact that the codes only say that it has to be grounded with no specifics on how or where. The 3-prong plug + safety relay idea sounds kinda neat. Add 1 safety relay contact to the paint pump output & monitor another contact thru the PLC to flash a light at the operator panel if it's not hooked up. Now to figure out where to put it on the paint booth to keep the plug from getting paint all over it during refills & cleanouts. Thanks TW!

[TimWilborne]

How about water tight plugs that have spring loaded hinges over the terminals? I have never had a need for them is small plug applications but I bet they make something. A rep dropped a book off a few weeks ago with them in it. I will try to remember to look Monday

[IO_Rack]

Do you mean like these? Lapp USA There are many manufacturers of this style connector, these I've found to be the most inexpensive.

[TimWilborne]

Yes that is what I was thinking

[TimWilborne]

Susan, just curious, did you make a decision on how you are going to do this?

[ssommers]

After talking with the supervisors, doing some heavy NFPA code reading (NEC, NFPA 34) & talking with the paint manufacturer, alligator clips are still the best thing to put on the paint booth since the teeth dig through any paint buildup. The supervisors wanted the ground spot to be underneath the rolling booth so it wouldn't interfere with operations. I had to explain that anything that would clip or plug in automatically beneath the booth increases the spark potential. Therefore it would have to be put outside the fume area meaning that it would have to be plugged into a place higher than the booth or away from the booth by X feet. My personal opinion is that a new set of ground straps & clips and thorough operator training is all that's needed at this point. Thanks, Susan with a new found appreciation for why grounding & bonding is needed around flammable vapors & liquids.

[TimWilborne]

I think they have a good point about the teeth digging into the paint