Insulation and Knob & Tube

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Re: Insulation and Knob & Tube

How many homes burned over the non ic recess cans ? I know of 3 personally.I pointed the non ic cans out to one customer doing a remodel and they elected to pay me to replace them.
All we can do is warn the customer of any serious violations.To cover my butt i would indicate the warning on the bill.Should a house burn you know they are looking at the last electrician.
 
Re: Insulation and Knob & Tube

Educating insulation contractors
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Isn't that an oxymoron ???

To expand on what Charlie was saying, K & T was OK for its intended use. Over the years when people started buying these older homes they often dumped every $$$ they had into buying the house and couldn't afford to gut the entire house and rewire it. So, as years went by, they started renovating room by room. Now you come along as the electrical contractor who is wiring for the renovation, you take out a permit to do the work and get it inspected. Then the new homeowners notice that they didn't have enough insulation and along comes "Joe Insulation Contractor" who doesn't need a license to do his work, doesn't have to keep up on the NEC and in most states doesn't have to take out a permit to inject his poodle hair insulation. So there's no inspection of his work. Suddenly and mysteriously there's a fire and it's determined that it is electrical in nature. Whether it was your fault or not you're on the hook and you'll have to defend yourself.

I don't mean to sway your decision one way or another. You'll have to make a judgement at the time of your installation as to whether the
K & T is in good condition or not and talk to your customer about insulating around it. If not, you'll have to make it know "up front" to your customer and in writing. If they won't sign it and agree, walk away from the job.

Just my opinion !!!
 
Re: Insulation and Knob & Tube

Sounds like a great idea to me.Let it state conditions it is in when you leave and the warning of insulation and need to finish the job.I have rewired many while customer still lived there and it is not that costly.I figure 1 item an hour for me and a good helper.
 
Re: Insulation and Knob & Tube

How is knob and tube with the correct OCPD any more of a hazard than NM when installed in insulation?
Don
 
Re: Insulation and Knob & Tube

Don:
One answer could be that the K&T splices seamed to be where ever it was convenient, and not in boxes.

[ January 01, 2005, 09:48 PM: Message edited by: russ ]
 
Re: Insulation and Knob & Tube

Don, if I am not mistaken, the ampacity of the wire was taken from the single conductors in free air and you didn't have the limits of #14 @ 15 amperes and #12 @ 20 amperes. I never installed any K & T and do not know for sure but am going from memory from what I was told a long time ago. :D
 
Re: Insulation and Knob & Tube

One answer could be that the K&T splices seamed to be where ever it was convenient, and not in boxes.
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Russ, the K & T splices were made mechanically sound first and then soldered & taped. In my opinion, they were better than anything we normally do today. :D
 
Re: Insulation and Knob & Tube

I understand through a thread on another board that insurance companies are refusing to insure structures with K&T wiring. This leaves the owner or potential owner no choice but to rewire.

-Hal
 
Re: Insulation and Knob & Tube

Originally posted by jimwalker:
All we can do is warn the customer of any serious violations.To cover my butt i would indicate the warning on the bill.Should a house burn you know they are looking at the last electrician. [/QB]
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Reminds me, I was at a neighbors house putting in a phone jack, and while I was there they asked me to look at this recep./switch that didn't seem to be working, I decided to look inside the panel, only to discover that the last electrician they hired to do a remodel a couple of months ago had installed nothing but #14 wire on 20A breakers, with the exception of the range circuit and the dryer circuit, both 40A wired with #8, this included the kitchen circuits and the dishwasher. I told them of the danger of this, and to call the electrician who did the work to come back.

[Edited for spelling :eek: ]

[ January 01, 2005, 10:10 PM: Message edited by: bensonelectric ]
 
Re: Insulation and Knob & Tube

charlie:
I agree when done by most electricians, the splices were soldered, and sound. I have run into ones that were never soldered. Who knows who put those kind of splices together. Many times the wire was skind in the middle and a tap wire rapped around the skined part.
I can't think of any other reason for why K&T and insulation is any more taboo than NM and insulation like Don said.
 
Re: Insulation and Knob & Tube

Don,

I have four thoughts in response to your question. </font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">1. The K&T installed between porcelain posts in the attic floor tends to be deflected when I've uncovered it. On occasion I've found the conductors (no loom) in contact with the metal pipe of an early 1900s dwelling plumbing or heating systems. The worst cases have been where newspaper and cardboard were jammed against the conductors (WWII).</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">2. Additional protection of K&T (adding loom) is rarely done with piping system alterations that result in contact with conductors.</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">3. Light fixture replacement will have occured without adding a box and the "modern" fixture will overheat the insulation. The worst of these installations are the edge pullchains that wiggle the assembly.</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">4. BX extensions laying over the unprotected K&T conductor that is eventually grounded elsewhere because of late 20th century needs.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">Even with correct OCPDevices, the thermal energy released in a low level fault is enough.

Edit typo - Al

[ January 01, 2005, 11:00 PM: Message edited by: al hildenbrand ]
 
Re: Insulation and Knob & Tube

Is anybody here olde enough or have a Code book olde enough to respond to my previous post (misspelling intentional)? I am not sure of my "facts" and don't want to be a purveyor of untruths. :D
 
Re: Insulation and Knob & Tube

Great question, Charlie.

The 1933 NEC Chapter 5 Table 1 Allowable Carrying Capacity of Wires makes no distiction for rubber insulation. 600 Volt Type R (rubber covered conductor), in Column A, is simply #14 = 15A, #12 = 20A, etc. That's It! No free air, no cable or raceway 3 or less, no ambient temperature adjustments.

As an aside, there is an interesting paragraph in the Abbot Handbook, 2nd edition, that I will post later. Back in a bit. :)
 
Re: Insulation and Knob & Tube

Thanks Al, it looks like I was all wet. Now the question that Don made begs an answer (just before my incorrect response). :D
 
Re: Insulation and Knob & Tube

In the National Electrical Code Handbook, 2nd Edition, by Arthur L. Abbott, based on the 1933 NEC, the following explanatory material is found. The quoted text is referring to Table 1 - Allowable Carrying Capacity of Wires.
The allowable current-carrying capacities given in the following table for the various sizes of wires and cables are the currents which may safely be carried continuously. For rubber-covered wire, these values are approximately 60 per cent of the currents which would produce a temperature rise of 75?F above the surrounding air. With a room temperature of 75?F., a rise of 75?F. would mean that the wire or cable would reach a temperature of 150?F., and above this temperature rubber begins to deteriorate rapidly. The figure of 60 per cent has been adopted as allowing a reasonable margin of safety to provide for either an overload on the conductor, or a room temperature somewhat higher than 75?F.

The Code specifies that rubber-covered wire shall not be used where the temperature exceeds 120?F. If it is assumed that the temperature rise of a conductor is proportional to the heat generated in the conductor, the rise at the allowable carrying capacity would be 27?F. and, with a room temperature of 120?F., this would mean that the conductor would reach a temperature of 147?F., which is close to the allowable limit of 150?F.

. . .

Under loads not exceeding two or three times the safe carrying capacity, quite an appreciable length of time is required for a large wire or cable to reach its final temperature. In general, the larger the conductor the longer the time required. An insulated conductor may therefore carry considerable overload for a short time without becoming hot enough to injure the insulation.
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Other wire insulations talked about are </font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Varnished-cambric</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">slow burning</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">asbestos</font>
<font size="2" face="Verdana, Helvetica, sans-serif">
 
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