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Bonding Ductwork?? #205432 02/20/12 11:12 PM
Joined: Apr 2002
Posts: 7,233
HotLine1 Offline OP
Member
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
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Re: Bonding Ductwork?? [Re: HotLine1] #205436 02/21/12 01:33 AM
Joined: Jul 2004
Posts: 9,569
G
gfretwell Offline
Member
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
Re: Bonding Ductwork?? [Re: HotLine1] #205437 02/21/12 10:15 AM
Joined: Apr 2002
Posts: 7,233
HotLine1 Offline OP
Member
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
Re: Bonding Ductwork?? [Re: HotLine1] #205439 02/21/12 11:24 AM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
Cat Servant
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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.

Re: Bonding Ductwork?? [Re: HotLine1] #205440 02/21/12 02:39 PM
Joined: Apr 2002
Posts: 7,233
HotLine1 Offline OP
Member
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
Re: Bonding Ductwork?? [Re: HotLine1] #205441 02/21/12 03:06 PM
Joined: Jul 2004
Posts: 9,569
G
gfretwell Offline
Member
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
Re: Bonding Ductwork?? [Re: HotLine1] #205600 03/12/12 08:52 AM
Joined: Feb 2002
Posts: 2,233
H
harold endean Offline
Member
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.

Re: Bonding Ductwork?? [Re: HotLine1] #205601 03/12/12 01:55 PM
Joined: Apr 2002
Posts: 7,233
HotLine1 Offline OP
Member
Harold:
Thanks for that. At the moment, the job seems to be in limbo for some reason.



John
Re: Bonding Ductwork?? [Re: harold endean] #205602 03/12/12 02:14 PM
Joined: Nov 2007
Posts: 763
K
KJay Offline
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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.

Re: Bonding Ductwork?? [Re: HotLine1] #205603 03/12/12 02:18 PM
Joined: Jul 2004
Posts: 9,569
G
gfretwell Offline
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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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