knob and tube wire and romex

[bulldog195169]

new scenerio. older house wired originally with knob and tube. over the years new wiring has been spiced in, knob and tube in attic has been covered with insulation, and a short in the attic has brought the electical inspector to the home. the questions is... does the knob and tube portion have to be removed now that it has been altered and covered or since it is preexisting do you have only the damaged area replaced. knob and tube in basement has been spliced into (no junction boxes. the service panel has been upgraded from 60 amp buss fuses to 100 amp breakers. does the nec regs provide guidelines for requirements when two different wiring methods have been mingled together?

 

[pierre]

Re: knob and tube wire and romex

"394.10 Uses Permitted. Concealed knob-and-tube wiring shall be permitted to be installed in the hollow spaces of walls and ceilings or in unfinished attics and roof spaces as provided in 394.23 only as follows:
(1) For extensions of existing installations
(2) Elsewhere by special permission 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-inplace insulating material that envelops the conductors"


"300.15 Boxes, Conduit Bodies, or Fittings ? Where Required.
A box shall be installed at each outlet and
switch point for concealed knob-and-tube wiring.
Fittings and connectors shall be used only with the specific wiring methods for which they are designed and listed."

 

[al hildenbrand]

Re: knob and tube wire and romex

And don't forget:

300.16 Raceway or Cable to Open or Concealed Wiring

(A) Box or Fitting A box or terminal fitting having a separately bushed hole for each conductor shall be used wherever a change is made from conduit, electrical metallic tubing, electrical nonmetallic tubing, nonmetallic-sheathed cable, Type AC cable, Type MC cable, or mineral-insulated, metal-sheathed cable and surface raceway wiring to open wiring or to concealed knob-and-tube wiring. A fitting used for this purpose shall contain no taps or splices and shall not be used at luminaire (fixture) outlets.

(B) Bushing A bushing shall be permitted in lieu of a box or terminal where the conductors emerge from a raceway and enter or terminate at equipment, such as open switchboards, unenclosed control equipment, or similar equipment. The bushing shall be of the insulating type for other than lead-sheathed conductors.

The bold italics that I added in 300.16(A) above show that open splices, with out a box, are permitted where K&T is connected to by another wiring method, say NM or AC or EMT or others. The "fitting" is like the weatherhead on the end of a conduit service mast where the conductors in the conduit come out and connect to the open wiring of the service drop. The "fitting" cannot have splices in it, which means, the splice takes place in open air.

394.56 Splices and Taps

Splices shall be soldered unless approved splicing devices are used. In-line or strain splices shall not be used.

394.56 "approved splicing devices" means wire nuts, split bolts, crimps, etc. which would be in open air when used with a "fitting".

And here is, arguably, the most difficult part for the job you describe in the opening post:

The prohibition of installing K&T in insulation was introduced into the NEC with the 1987 NEC.

Note that that is installing K&T. I doubt you will be installing new K&T in the work at this job.

And if it looks like any new K&T was installed since 1987 that is in insulation, then that should be addressed as a nonCode installation. The the K&T installed before the 1987 NEC went into effect is grandfathered in. The exception to this statement is if there is local ordinance that was in effect before 1987 that said what the NEC started saying about K&T insulation contact in 1987.

 

[tshea]

Re: knob and tube wire and romex

Check with your AHJ on local regs. Typically on an upgrade to a residence, all the attic K&T goes out. This is for two reasons-
1. Safety.
2. Insulation.
K&T is replaced with a grounded wiring method--NM.
The HO can now insulate their attic.

I would bid the job to remove the K&T and replace.

 

[bulldog195169]

Re: knob and tube wire and romex

i really thought this would be discussed more than it has as it is a common occurance found in rural areas. my thought is know and tube was not intended to be intergrated with other wire types, it wasnt intended to be covered with insulation and it wasnt intended to be used in a wet basement where it was within common reach.
thats all im saying.

 

[peter d]

Re: knob and tube wire and romex

Originally posted by bulldog195169:
i really thought this would be discussed more than it has as it is a common occurance found in rural areas.

FYI, mosts subjects only receive 2-10 responses unless they are very controversial or confusing. Knob and tube is not a hot topic but it does get discussed on occasion. When you ask a question here, most of the time the answer will be a code article with a little bit of commentary. What more are you expecting?

[ October 14, 2005, 04:39 PM: Message edited by: peter d ]

 

[jwelectric]

Re: knob and tube wire and romex

Originally posted by bulldog195169:
i really thought this would be discussed more than it has as it is a common occurance found in rural areas.

If you want to have this subject discussed then add a little more to it like K&T installed on the small appliance circuit or I want to replace a two wire receptacle wired with K&T with a three wire receptacle.

Open the door to a 300 post debate where K&T will be lost in the back ground. Shucks, if you will debate it one way I will go in the other direction.

 

[iwire]

Re: knob and tube wire and romex

Originally posted by bulldog195169:
my thought is know and tube was not intended to be intergrated with other wire types,

As Al pointed out there are code compliant ways to do that.

Originally posted by bulldog195169:
it wasn't intended to be covered with insulation

Again as Al pointed out that was not an issue when K&T was installed and is not an issue now if the insulation comes later.

Originally posted by bulldog195169:
and it wasn't intended to be used in a wet basement where it was within common reach.

I have never heard of any code issue with this.

In general any installation that was code compliant at the time of installation is still compliant today.

Of course some areas may have local rules that go beyond the NEC.

 

[al hildenbrand]

Re: knob and tube wire and romex

Bulldog,

There are some here who will argue passionately that Knob & Tube is tangible evidence that Evil exists. . .

But that doesn't enter into the NEC.

I have worked on many K&T installations of varied condition. Examine what is visible to see if it is stable. If a basement has a history of dampness, the humidity will age the K&T insulation. The heat of the attic will also degrade the condition of the insulation. And, of course, overloading the conductors will degrade the insulation.

But just because an attic gets hot and a basement is humid doesn't guarantee that the insulation will be damaged. . .it's likely, yes, but one has to test the insulation. It may still be supple. . .and close examination will likely uncover other issues.

I've worked on K&T installations that have been run within design specs that have been in excellent condition after 90 - 100 years. I fully expect they will survive many more decades, if not another century, if left alone.

When working with old K&T and an existing structure, I will first use the clients money to get new wiring to the heavy loads (kitchen appliances, laundry, furnace, well, etc.) and along the way deal with obvious hazards (exposed and/or damaged wiring, devices, luminaires, appliances). Along the way, bits of the legacy wiring will be retired.

If the client has deep enough pockets, then the K&T is totally replaced.

 

[jimwalker]

Re: knob and tube wire and romex

If all of it was next to new and not covered by insulation i have no problem with the K&T system.Lets get real ,it is atleast 80 years old.All i ever seen was brittle if ever touched.As much as possable should be replaced with nm.Since when did cost change safety ? Only people that would not care are likely landlords that only want $$$$$.You can bet there kids dont sleep in that building.

 

[Leitmotif]

Re: knob and tube wire and romex

I think knob and tube was commonly used in residential until the 50's (??). At least that is what I have observed in Seattle.

The problems with it (and I have seen my share of scorched wood) are that
1. The wiring methods back then (one or two outlets per room or one on each wall if lucky) are insufficient for modern demands and appliances.
2. the wire size is too small for modern residential demands.
3. The old undersized conductor loses more ability to shed heat when insulation is dumped in on top of it. I think this should be outlawed.
4. No ground conductor (green)

I am of the opinion it is actually one of the safer wiring methods if and I mean IF
1 2 3 and 4 above were overcome and of course we now have better insulation.

Free conductors in air have higher ampacity than those in conduit or cable.
The conductors were separated by an air gap of several inches - in romex it is less than 1/2".

Sure would be expensive to install though ESPECIALLY in finished construction.

 

[jimwalker]

Re: knob and tube wire and romex

For all but a few items we no longer need a ground.

 

[Leitmotif]

Re: knob and tube wire and romex

Jim Walker said
For all but a few items we no longer need a ground.

Uhhhhhhh
Jim
why
and
with referance to what do you say that?

 

[peter d]

Re: knob and tube wire and romex

Originally posted by Leitmotif:


Uhhhhhhh
Jim why and with referance to what do you say that?

I think Jim is referring to the fact that only a select few household appliances actually require grounding.

 

[al hildenbrand]

Re: knob and tube wire and romex

I think Jim is pointing at the prevelance of two-wire ungrounded appliances and utilization equipment that abound in the average home.

Arguably, there are only a few things left that require the cord to be three wire grounding. </font>

• <font size="2" face="Verdana, Helvetica, sans-serif">Microwave</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Refrigerator</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Gas Range</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Washer / Gas Dryer</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Window AC</font>

<font size="2" face="Verdana, Helvetica, sans-serif">Double insulated yard and shop tools and laptop computers have done away with another common area of three wire cords. Portable lamps and small electronics have always been two wire.

It begs the question. "Why are the outlets grounded?"

 

[Leitmotif]

Re: knob and tube wire and romex

Al
You asked why are the outlets grounded

Well in light of your point that many appliance tools are only on two prong plug - most interesting question.

So I guess outlets with 3 prong are installed
1. Because we have gotten used to doing it (we alays done it this way ??)
2. People (including me) want em so they can plug something with 3 prong in wherever they want.
3. COnvention ??

SO I agree with all the two prong plugs out there and IF we use non metal boxes we don't need a ground.

Given that another thought occurred
Why do light switches have a ground screw?

[ October 15, 2005, 12:46 PM: Message edited by: Leitmotif ]

 

[macmikeman]

Re: knob and tube wire and romex

For all but a few items we no longer need a ground.

In leu of the fact that I now ground every single switch I install in new construction, and did not necessarily have to every time before the code change, I disagree with the above.

 

[al hildenbrand]

Re: knob and tube wire and romex

Dan,

Yeah, switch grounding. . .but that's a kind of to the side, I think.

Your analysis of K&T included grounding as a deficiency. Some here will argue that adding grounding creates hazard that didn't exist in K&T installations in dwellings that were almost entirely non-conductive, especially given the prevalence of two wire ungrounded utilization equipment likely found in a dwelling.

Back to light switches: 404.9(B)Exception.

 

[Leitmotif]

Re: knob and tube wire and romex

Well my real education in the trade started in the Navy. None of our main distribution (3 phase 440) DC distribution and ligsting was grounded.

It had its points both good and bad I suppose.

Then I became a civilian and learned about neutrals. Education continures.

 

[jimwalker]

Re: knob and tube wire and romex

Looking backwards,just when did grounds become required ? 50's ? Was long before we had gfci.Now with double insulated items and gfci do we really need it ? Any one seen the price of 12-2. $41 at big orange today.