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Grounding Of Hot Air Ductwork ?

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Grounding Of Hot Air Ductwork ? Robert11 08-15-2005
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Posted by Robert11 on August 15, 2005, 12:33 pm


Hello:

Checked the hot air ductwork from a forced hot air furnace, and find that it
is not grounded.

Probably because there is a non-metallic "flex-joint" between the furnace
and the main outgoing duct.

What does the Code say regarding this ?

Should I just run a ground wire between the furnace shell (which is
grounded, probably via the
the AC power ground) and the Duct ?

This should work well, I guess, as most furnaces that don't have a
non-metallic joint are probably being grounded, in effect, in this manner.

What about the electrical Code, though ?

B.




AppliancePartsPros.com, Inc.
Posted by SQLit on August 15, 2005, 11:16 am



> Hello:
>
> Checked the hot air ductwork from a forced hot air furnace, and find that
it
> is not grounded.
>
> Probably because there is a non-metallic "flex-joint" between the furnace
> and the main outgoing duct.
>
> What does the Code say regarding this ?
>
> Should I just run a ground wire between the furnace shell (which is
> grounded, probably via the
> the AC power ground) and the Duct ?
>
> This should work well, I guess, as most furnaces that don't have a
> non-metallic joint are probably being grounded, in effect, in this manner.
>
> What about the electrical Code, though ?
>
> B.

I just took a quick look at the 2002 NEC section 250. and the phrase that I
found over and over was "may become energized"

Practically I have not seen duct work grounded except for a project that I
can not talk about. That not residential and it was more than 10 years ago.
There was not a piece of metal in the whole building that was not grounded
more than once. Door frames were grounded once on the inside and once on the
outside. We installed 250 MCM bare copper on the duct connections near the
air handlers. I protested that the connection would eventually break the
ductwork do to the ductwork moving and the copper would not. I was over
ruled by the EE. He just graduated so consider the source.





Posted by on August 15, 2005, 3:00 pm



>Practically I have not seen duct work grounded except for a project that I
>can not talk about. That not residential and it was more than 10 years ago.
>There was not a piece of metal in the whole building that was not grounded
>more than once. Door frames were grounded once on the inside and once on the
>outside. We installed 250 MCM bare copper on the duct connections near the
>air handlers. I protested that the connection would eventually break the
>ductwork do to the ductwork moving and the copper would not. I was over
>ruled by the EE. He just graduated so consider the source.


I also worked in some places I can't talk about and I agree with you
about the EEs spec on the wire. When we were doing RF shielding we
used very fine stranded cables, not garden variety THHN. "Skin effect"
makes a finely stranded conductor far better than coursely stranded
cable. As a secondary benefit they are a lot more flexible. Just be
sure your terminations are listed for this kind of cable. Regular lugs
are not.


Posted by Carolina Breeze HVAC on August 15, 2005, 12:55 pm



> Hello:
>
> Checked the hot air ductwork from a forced hot air furnace, and find that
> it is not grounded.
>
> Probably because there is a non-metallic "flex-joint" between the furnace
> and the main outgoing duct.
>
> What does the Code say regarding this ?

Our code, states that you dont use ductwork as a ground, ever.
And really, since you would have to bond each joint to be effective, its not
worth the time to.
>
> Should I just run a ground wire between the furnace shell (which is
> grounded, probably via the
> the AC power ground) and the Duct ?

No.
Why do you want to ground the ductwork?

>
> This should work well, I guess, as most furnaces that don't have a
> non-metallic joint are probably being grounded, in effect, in this manner.
>
> What about the electrical Code, though ?
>
> B.
>




Posted by Stretch on August 15, 2005, 10:02 am


If you just need something to fill your time, I bet some local charity
would love to have you volunteer. I know of no reason for you to
ground your ducts.

Stretch



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