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#205432 02/21/12 12:12 AM
Joined: Apr 2002
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Scenario: Sheetmetal ductwork for a dust collector system in a woodshop.

(5 HP, 3 phase, 208 volt motor)

Does the ductwork require any bonding? How about static?

Any code references appreciated.


John
Joined: Jul 2004
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I would assume the duct work gets bonded via the EGC to the dust collector motor and enclosure. This is similar to a duct heater.
Static is a whole 'nother thing, particularly if this is a plastic duct. In some of the woodworking BBs they have discussions about this. The fear is "lightning" in the duct could cause an explosion. I would think simply bonding a metal duct would bleed off the static charge.

I do not know of any article that deals with this unless you can call it "pipe" 250.104(B)


Greg Fretwell
Joined: Apr 2002
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Greg:
I'm looking for any requirement, other than 'spec' for this.

The two woodshops I installed dust collector systems in years back both had duct bonding on the 'specs'.



John
Joined: Jan 2005
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I believe the bonding requirements are in the Mechanical code, and are dependent on the CFM of the unit. That is, your typical home workshop collector isn't big enough to require it.

Ironically, the problem is with plastic ducts, rather than metal ones.

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Reno:
Thanks for the input. I searched the mech code to no avail, it sends ya to NFPA codes, and that is vague also.

I dumped this back to the design pro to see what kind of response I get from him/them.



John
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Maybe this gets back doored in by the manufacturer's installation instructions.

Other than that I can't find anything either.

It is probably like steel studs and the NFPA is waiting for a body or two.


Greg Fretwell
Joined: Feb 2002
Posts: 2,233
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John,

I had computer issues the past month so I wasn't on line.

I have seen the plastic dust collectors have a bonding wire run along side of them to discharge the static when sucking up the dust, but I haven't seen too many metal duct collector systems. My guess is that the metal will bleed off any static as it starts to build up as long as the metal duct is attached to a grounded piece of equipment.

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Harold:
Thanks for that. At the moment, the job seems to be in limbo for some reason.



John
Joined: Nov 2007
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From what I can find on the subject, the general consensus seems to be that with that type of installation the bare wire should be run inside the plastic duct to actually be effective. Placing it outside supposedly does nothing to dissipate any static build up inside the duct, which apparently is where the dust ignition problems occur.

Joined: Jul 2004
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They do make this stuff (conductive duct) but it ain't cheap.

http://www.globalindustrial.com/p/h...-duct-black-12-inch-dia-15-ft-long-strap


Greg Fretwell

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