Thread: Knob & Tube in cold air return

Is it acceptable to leave live knob and tube wiring in a cold air return duct?

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Originally Posted by Jon mackay

Is it acceptable to leave live knob and tube wiring in a cold air return duct?

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No.
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I didn't think so.
Does anyone have verbiage of the rule?

I would like to pass it on to the electrician that said it is acceptable.

Have the sellers ask their insurance company

I don't even bother with the code issues as everywhere I inspect K&GT is now virtually uninsurable - the last time a client checked the best any agent could do was a ninety day policy for around $1500 - contingent on the removal of all active and inactive K&T within that time frame.

Originally Posted by A.D. Miller

394.12 Uses Not Permitted.
Concealed knob-and-tube wiring shall not be used in the following:
(1) Commercial garages
(2) Theaters and similar locations
(3) Motion picture studios
(4) Hazardous (classified) locations
(5) Hollow spaces of walls, ceilings, and attics where such spaces are insulated by loose, rolled, or foamed-in-place insulating material that envelops the conductors.

Concealed knob-and-tube wiring is designed for use in hollow spaces of walls, ceilings, and attics and utilizes the free air in such spaces for heat dissipation. Weatherization of hollow spaces by blown-in, foamed-in, or rolled insulation prevents the dissipation of heat into the free air space, resulting in higher conductor temperature, which could cause insulation breakdown and possible ignition of the insulation.

Ok, so duct work is not labeled as a place not to use Knob & Tube? This means that it is ok?

Originally Posted by A.D. Miller

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Unless the self-anointed electrical gurus of this forum deem otherwise, I would think that is what the code is indicating.

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No Guru Here ( or elsewhere )
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But NEC. 300.22 ( B) does seem to Prohibit.
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Hello Jon,

If you are looking to "quote the code" then you should be looking at the code that was in effect when the wiring was installed and not the most recent NEC. Also, any local ammendments in effect when it was installed should be taken into consideration. That can be quite the research project.

If you are looking to give your clients good advice, then tell them what you think and don't worry about what the electrician says. These situations will always end up in a he-said / she-said agrument. For every electrician who says it is ok, I'll give you two that will say it's not ok.

This really applies to everything we do, not just this issue.

Sincerely,

Corey

Originally Posted by Corey Friedman

Hello Jon,

If you are looking to "quote the code" then you should be looking at the code that was in effect when the wiring was installed and not the most recent NEC. Also, any local ammendments in effect when it was installed should be taken into consideration. That can be quite the research project.

If you are looking to give your clients good advice, then tell them what you think and don't worry about what the electrician says. These situations will always end up in a he-said / she-said agrument. For every electrician who says it is ok, I'll give you two that will say it's not ok.

This really applies to everything we do, not just this issue.

Sincerely,

Corey

Good sound advice Corey, thank you..

Originally Posted by Jon mackay

Is it acceptable to leave live knob and tube wiring in a cold air return duct?

Originally Posted by Corey Friedman

Hello Jon,

If you are looking to "quote the code" then you should be looking at the code that was in effect when the wiring was installed and not the most recent NEC. Also, any local ammendments in effect when it was installed should be taken into consideration. That can be quite the research project.

If you are looking to give your clients good advice, then tell them what you think and don't worry about what the electrician says. These situations will always end up in a he-said / she-said agrument. For every electrician who says it is ok, I'll give you two that will say it's not ok.

This really applies to everything we do, not just this issue.

Sincerely,

Corey

Originally Posted by Jon mackay

Good sound advice Corey, thank you..

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Just When Did They Install Knob & Tube and Central Air and Heat Together ?
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Knob and tube is not plenum rated, therefore (regardless when the knob and tube was installed) the knob and tube is not allowed to be run in the plenum (which is what your description is describing to me).

The section you are referencing, 300.22(C), is applicable only to conductors which 'pass through' (versus 'run in') those stud spaces. I.e., the cables 'pass through' perpendicular to the studs, not run in the stud space parallel with the stud space (which is what I think you are describing).

Nonetheless, though, 300.22(C) states, in the exception: "Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces."

Which means that, for conductors 'passing through' the stud space and which are perpendicular to the stud space, section 300.22(C) does not apply. So you can ignore 300.2(C), which includes (1) and (2).

Also, being as you are describing a stud space being used as a duct, 300.22(C) does not apply anyway:
- (C) Other Space Used for Environmental Air. This section applies to space used for environmental air-handling purposes other than ducts and plenums as specified in 300.22(A) and (B). It does not include habitable rooms or areas of buildings, the prime purpose of which is not air handling.
- - FPN: The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies.
- - Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces.

That means that you would go back to 300.22(B).

Note that the above is from the 2008 NEC, and the correct code to use would be the one in effect when the stud space was made into a duct for environmental air.

Yes, I do find there to be a conflict in those sections of the NEC, and people much smarter than I wrote it, but one would think that with them being that smart that they would not have written that conflict into those sections.

Am I the only one to have heard "knob and tube" refered to as "ring and pin?" Or did that old electrician make up the term himself. He was wiring houses back in the 1920's.

Oh, man, K&T, hate it no matter where it's ran. As an electrician I know electricians that have been in the biz a lot longer than me that will certify K&T - I WON'T...EVER. I know firsthand that a K&T short will rarely or not trip a circuit breaker. I personally have never seen a K&T short trip a circuit. It will burn & burn & burn. As far as inspecting goes, if you see live K&T running off a circuit breaker, period, note it. An example; a house built in 1900's had partial K&T running to the upstairs. An electrician was hired to inspect the entire system and disconnect ALL service to the upstairs for remodeling purposes. The new owner wanted to gut the lath & plaster & repair structural on account a tree fell on it. Long story short, the owner was knocked on his butt yanking out an old light fixture - it was live. After 3 visits from the electrician they found out the K&T was being back-fed from another circuit, the downstairs dining room. All outlets were dead upstairs. The one fixture in the one upstairs bedroom was the only one live. You'd "think" the electrician would have tested it which was assumed at the time but we know that bad things can happen if even the slightest things are overlooked. Common sense goes a long way.

I've run into the same issue with the Seller's electrician saying K&T is ok for various reasons. Arguing about it is a waste of time.
One of the first things I mention to the client is, 'call your insurance agent'. That phone call usually ends any further BS if the Seller wants the sale to go through.
Beyond that I explain the typical conditions and hazards to the client. In this case I would also mention that they could become electrocuted if the hot wire breaks and rests on the sheetmetal.
As much as I believe in the Code, I don't believe getting into these Code pissing matches with contractors. Most of the time, they don't really know the Code, are working off of construction legend and aren't willing to put anything in writing. My reports are in writing, show me yours Mr. it's Ok.
My responsibility is to educate the client so they can make a good decision, not play macho games with Joe contractor.

Originally Posted by Markus Keller

I've run into the same issue with the Seller's electrician saying K&T is ok for various reasons. Arguing about it is a waste of time.
One of the first things I mention to the client is, 'call your insurance agent'. That phone call usually ends any further BS if the Seller wants the sale to go through.
Beyond that I explain the typical conditions and hazards to the client. In this case I would also mention that they could become electrocuted if the hot wire breaks and rests on the sheetmetal.
As much as I believe in the Code, I don't believe getting into these Code pissing matches with contractors. Most of the time, they don't really know the Code, are working off of construction legend and aren't willing to put anything in writing. My reports are in writing, show me yours Mr. it's Ok.
My responsibility is to educate the client so they can make a good decision, not play macho games with Joe contractor.

AGREED. If they wanted an inspector to inspect by their rules they could have hired one without rules. If they say "Okay, I guess it's YOUR way" I say "No, not MY way, just the RIGHT way". Even my wife knows there's a definite difference between "my" way and the "right" way.

Originally Posted by A.D. Miller

Yes, her way = the right way and your way = your way.

Yet folks still try to argue against that. haha

1953 NEC, section 3020:
"...Where it is necessary to run a wiring system through air-conditioning ducts or plenum chambers, the wiring method shall be rigid conduit, flex steel conduit with lead-covered conductors, or Type ACL armored cable with fittings suitable for the location."

I would be focusing on advising the clients about the old K&T wiring. I mention that it's ungrounded and considered unsafe and obsolete by today's standards. I personally would not be to concerned about it running through a cold air return unless it was near sharp edges of sheet metal. While it's not allowed by today's standards they commonly would install early cloth sheathed Romex in cold air returns that were just sheet-metal attached to floor joists.

This is the natural result of changing times and different trades. I think we need to look at the likely circumstasnces to understand just what likely hapened.

Especially in homes, even today it is fairly common for the HVAC contractor to 'pan' a stud or joist bay so as to form a duct. While this may seem clever and efficient, the same guy making the pan will also tell you that HIS house uses real steel duct - not even flex. It's a design / economy choice. Hop into the 'way back' machine, to the days where air conditioning was still a novelty, and you'll see lots of bays panned to form every manner of duct.

Keep in mind as well that there was no such thing as 'plenum' rated anything until fairly recently. For that matter, 'duct tape' really was once for use on ducts!

These days, a 'work around' is to pierce the bay with a length of pipe, and run the wire through there. The wire is now in the pipe, and not in the plenum.

Keep in mind also - here I drift off on a tangent - that for an air handling space to be a 'plenum' it must also be a part of the HVAC equipment. A vented ceiling or attic is not a plenum, regardless of how much air flows through it. Nor is a crawl space, even if the equipment draws air from the space.

In all probability, the wiring was there first, and the HVAC guy simply panned the bay. It would be beyond his license, and an unreasonable expectation, to ask the guy to re-wire the house as part of the job.

IMO, the various code prohibitions were more intended to address the opposite sequence - where a later sparky finds the ductwork to be a convenient 'chase' for his new wires.

I wouldn't worry about old wires that got panned in; new wires routed through the ductwork is another beast comletely.