Knob-and-tube wire guages

[inspector_guy]

in the era of knob-and-tube wiring, there were very few items one could buy that used electricity. Most of these items were low wattage(in comparison to todays electrical gadgets). Back in June of this year, I inspected a house that was built in 1911. The house had been remodeled and the service upgraded. In the attic, i found that most of the original knob-and-tube wiring was disconnected and replaced with modern Romex. I examined one of the discarded pieces and noticed that the guage of the wire was exremely small. Maybe 14 ga. or smaller. I'm sure that many of you out there have far greater knowledege of the 'original' branch circuit wiring. If this old wire is connected to a 20 amp or larger breaker, would this not create a fire hazard?

 

[lazorko]

Re: Knob-and-tube wire guages

The 14AWG wire was, I hope, protected by a 15A fuse (or breaker), just as 14AWG is protected in a modern installation.

I've worked on old homes for years; some of the worst wiring I've seen wasn't knob and tube, but the early "romex" cable with rubber and cloth insulation (used in 30's - 40's?). The insulation is often so dry-rotted, we call it "crumble wire".

 

[iceman2610]

Re: Knob-and-tube wire guages

I too have rewired many houses with this "crumble wire" I feel it is far worse than knob & tube. Knob & Tube wiring is actually much safer than early romex, because of its ability to disapate heat quickly. Much of the knob & Tube wiring I have replaces (though scary by today's standards) has actually been in very good shape.

 

[don_resqcapt19]

Re: Knob-and-tube wire guages

The original knob and tube wiring was "open wiring in free air" and the OCPD was often 25 amps for #14.
don

 

[al hildenbrand]

Re: Knob-and-tube wire guages

inspector_guy,

The concealed knob and tube installed in one and two story dwellings in the first quarter of the 20th century was 99% 14 guage and, because it was concealed for some or all of its length, was fused at 15 amps.

I work with a lot of old dwellings and have removed, maintained and even altered many a knob & tube installation and I have only stumbled upon two original 12 guage circuits to date.

 

[stamcon]

Re: Knob-and-tube wire guages

Al, it's something how varying the installations are in different parts of the country. I'm in the San Francisco Bay Area and all K&T work I come across is a mixture of 14 gauge and 12 gauge.

 

[al hildenbrand]

Re: Knob-and-tube wire guages

Stamcom,

That is interesting. The most common configuration I find will have two original 120 volt, 15 amp branch circuits. One circuit will supply the lighting of the dwelling, and the other will go to a three gang box in the kitchen that houses a snap switch, on-indicator light and single receptacle. If the building is somewhat larger than the average modest dwelling, another 15 A lighting circuit will have been installed. All of this is knob & tube, or, infrequently, black rigid conduit.

Over the decades following the original installation, extensions are added, most commonly to the lighting circuit(s), and most commonly using BX (old style armoured cable). Once that is overloaded, the second circuit is gotten to and extended.

Sometime along the way, the coal furnace gets upgraded to oil or natural gas, and a new 15 A 120 V circuit gets shoe horned into the original fuse center, and as a rule, this circuit gets no extensions added to it. (People up here seem to intuitively understand the value of protecting the heat source from nuisance trips ).

20A 120 V branch circuits start showing up when the original 30 A service is upgraded to 60 A (1930s thru 1950s work, required locally to be "all metal" - BX, EMT, flex, etc.) and predominantly go to the kitchen, but may have the laundry tacked on as well. (It wasn't until later that adding a seperate laundry circuit to an existing electrical system became a local requirement).

In your experience, what loads are the 20 A knob & tube circuits in your area supplying?

 

[jackmcg]

Re: Knob-and-tube wire guages

Interesting history of wiring.... back in "75" I worked for a small company in Reading PA whose owner was 75 years old at the time... his first job as an electrician, when he was 16, was to drive a horse drawn wagon outside the city to the farms and try to get 10 different homeowners to agree to change over from gas light to electric light... the power company required at least 10 homes so that it was economically feasible to run a pole line out to the area.... once he had at least 10 homes under agreement, he would install knob and tube wiring and a 120v 30 amp service to each home...it was for lighting only... in "75" he still owned a drilling tool that could hold 6 separate drill bits (brace and bit style) all mounted on a "T" bar on top of a vertical arm that could be adjusted for height, the whole thing was mounted on a wheeled base.... it had a big crank on it to turn all 6 bits at once.... it was used in the cellar to drill consistant holes for inserting the tubes .... one guy would apply pressure from behind while the other would turn the crank... he also told me that orginally in the city, the electric meters were coin operated... you would go outside the home and drop in a nickel and get several hours of power... I'm a bit off topic but the talk of knob and tube brought back the memories..

 

[luke warmwater]

Re: Knob-and-tube wire guages

I wonder who got to calibrate the timer on the 'coin op.' meters

 

[karl riley]

Re: Knob-and-tube wire guages

Jack, that's great historical info. I never thought about how those holes were drilled. I am sure there are other users of this forum who have info or memories like that. They should be encouraged to let us in on it.

Karl

 

[maniacwhiz]

Re: Knob-and-tube wire guages

Knob-and-tube wiring came in 12 and 14 AWG. I guess 14 were used for lights, 12 for switches/receptacles. I have a few knobs from a friend's house that got rewired.

On the nail head of the knobs, two knobs says 12, others say 14. I guess the AWG is stamped on the nail head? I am not sure, but the only thing I could come up with.

I also have scanned a picture of the joist boring machine for drilling tubes in the joists to run knob-and-tube wiring, but do not have a place to post. Any help?

[ August 27, 2003, 10:33 PM: Message edited by: maniacwhiz ]