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Code Ref. - Bonding jumpers on HVAC needed


Kyle Kubs
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In a recent inspection I commented about the lack of by-pass jumpers on the vibration dampers of metal ducting for the HVAC system. I just got a call from the HVAC contractor saying there is no such requirement and that he even put in a call to someone in State Gov. that say's there is none. I'm nowhere near my books and my normal computer that has this stuff is down. Anyone have the specific NEC referance for this?

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Originally posted by Speedy Petey

First off, what is a "by-pass jumper"?

There is NO requirement to bond ducting, it is only suggested 250.104(B) FPN.

Excuse my imperfection... Bonding Jumper.

Actually the FPN in 250-104 "Bonding all piping and metal air ducts within the premises will provide additional safety." is only part of it.

250-110

Equipment fastened in place or connected by permanent wiring methods.

Exposed noncurrent-carrying metal parts of fixed equipment likely to become energized shall be grounded under any of the following conditions:

1)Where within 8ft vertically or 5 ft horizontally of ground or grounded metal objects and subject to contact by persons.

2) Where located in a wet or damp location and not isolated

There are six conditions in all but these two apply to most situations.

Neal, Thanks for the offer of help. If you want to e-mail me the # I guess it couldn't hurt to have around.

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Originally posted by Kyle Kubs

Anyone have the specific NEC referance for this?

Obviously you do. [:P]

I don't know about you, but I do NOT consider duct work "likely to become energized".

Possible? Sure.

Likely? Not so much.

No more than ANY other metal object in a home or commercial establishment.

If bonding of duct work were considered mandatory there would be NO reason for 250.104(B) FPN.

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I have been shocked two time by ductwork. The first time I was helping to install the ductwork in a old house . and some one fastened the support angle to the flooring and hit an wire. The power was off to that wire at the time. The next day we can back to finish installing the ductwork I got shocked when I touched the ductwork

The second time I was under a house and I was sliding around the end of the ductwork and a bare wire fell on it and bit me. That ended the inspection at that time.

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In this area ductwork likes to live in crawlspaces and attics, the same place wiring and rodents like to live. When I don't have 50 other things distracting me I will take my tester and use a good known ground source, (water pipe, conduit...), and check for current from other things like ducting, gas pipes, water pipes, I have found them all live and at high potential many times.

Why would ducting be any less likely to be energized then water or gas piping?

As phillip said, ducting seems to be a great place to lay down the wire you just disconnected, no caps, still live, and just leave it there. I see this constantly.

Maybe it is a little over zealous. Maybe the electrical department is a good place to be a little over zealous...

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  • 1 month later...

I once saw an office addition with a hung ceiling. One of the wires holding up the metal ceiling framework was screwed into a metal ductwork hanger...

Then the fluorescent light fixtures were grounded and electrically contacting the metal ceiling framework.

All the grounding for the office addition was connected together.

BUT... All the wiring for this addition went to an old fuse box and was not grounded there!

So basically you had all the grounds in the entire office addition electrically connected to the ductwork without any ground connection at the main panel. Had anything plugged in, light fixtures, etc. malfunctioned and shorted to ground, all that ceiling framework and ductwork would have become energized.

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I got one better than that.

I was zapped by a door knob on a new build about 15 years ago. The painters had removed the cover on the gas fireplace in the master bedroom and the hot lead for the blower switch was touching the fireplace frame, thus making the fire place, the double wall pipe and strapping, the steel cap on the chase, the foil face building wrap, the aluminum clad windows, and the steel entry doors all live. It had rained the night before, and it was mid-afternoon before the ground had dried up enough that you could touch any of the doors without getting a pretty good jolt.

Tom

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Originally posted by Speedy Petey

. . . If bonding of duct work were considered mandatory there would be NO reason for 250.104(B) FPN.

There's a flaw in that logic. That fine print note refers to both piping and ductwork yet, clearly, the bonding of piping is mandatory.

That logic aside, I agree with Speedy. There's a lot of wiggle room in 250.110. A conservative interpretation might include metal roofing, gutters, the metal webs of trusses and structural steel. What about metal cabinets? Metal fences? Aluminum siding?

In my area the AHJs, uniformly, don't require bonding of those items -- or of heating ducts beyond the isolation damper. (Of course, the ducts that are actually attached to furnaces are grounded via the furnace's electrical wiring.) I tend to respect the AHJs in this instance. I try not to be more royal than the king.

- Jim Katen, Oregon

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Originally posted by Jim Katen

That logic aside, I agree with Speedy. There's a lot of wiggle room in 250.110. A conservative interpretation might include metal roofing, gutters, the metal webs of trusses and structural steel. What about metal cabinets? Metal fences? Aluminum siding?

- Jim Katen, Oregon

I alway recommend the aluminum siding be grounded; doesn't everyone?

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Actually so far as grounding metal fencing, this is REALLY needed sometimes! This is if you live under one of those very high "zillion volt" electrical transmission lines.

Mostly for farmers who move metal irrigation pipes, etc. around, but also for fencing and anything metal, they have specific guidelines as anything metal can become energized and give you a good zap.

FYI - Here is more on this...

http://www.bpa.gov/corporate/pubs/Publi ... orking.pdf

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Originally posted by msteger

I don't think I've ever seen gas piping (black iron or CSST) bonded in any homes I've inspected in the past 6 or so years. Maybe they don't require this in PA or at least in my area.

It's absolutely required by the NEC and by the CSST manufacturers.

- Jim Katen, Oregon

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That logic aside, I agree with Speedy. There's a lot of wiggle room in 250.110. A conservative interpretation might include metal roofing, gutters, the metal webs of trusses and structural steel. What about metal cabinets? Metal fences? Aluminum siding?

The historic home I am working on in Portland ended up with an energized gutter system. A gardener bumped into a downspout, and it started arcing. It tok 2 electricians 2 days to track down the cause. The roofer's flashing conacted some exterior wall knob and tube wiring, which energized the flashing and gutter systems. Luckily, nobody completed the circuit while working on the roof/ gutters, etc.

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Originally posted by Jim Katen

Originally posted by msteger

I don't think I've ever seen gas piping (black iron or CSST) bonded in any homes I've inspected in the past 6 or so years. Maybe they don't require this in PA or at least in my area.

It's absolutely required by the NEC and by the CSST manufacturers.

- Jim Katen, Oregon

True, but it is rare, if ever, that an additional external bond must be run.

The circuit ground of the appliance the gas piping is feeding is what is bonding the pipe.

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