knob & tube ampacity

Specific Inspection Topics Electrical Inspections
1

I had a question on a home with a recently updated panel.

All the breakers were 20 amps except for the stove.

All the knob & tube was spliced above the panel in junction boxes.

I took one of the covers off to see if I could see any of the splices.

Could there be some 15 amp wiring in the system?

2

More then likely most of it is .
I recommend Immediate upgrade by qualified personal

3

I found this interesting:

Advantages of Knob-and-Tube Wiring:

  • K&T wiring has a higher ampacity than wiring systems of the same gauge. The reason for this is that the hot and neutral wires are separated from one another, usually by 4 to 6 inches, which allows the wires to readily dissipate heat into free air.

From:

4

True - open-air conductors (K&T) will dissipate heat more effectively and will therefore carry more current.

However, while Larry is correct in theory, the capacity should still be compared to the conductor size. K&T usually represents an aged system and the integrity of the conductors may have diminished over time.

5

I found this knob and tube in a home built in 1915, complete remodel from first appearance, new additions, new main panel etc.
Found this in the attic and my electrical portion of the inspection was pretty well done. "called for complete electrical evaluation and estimate of entire home " . OH YEA, I also found a speaker wire sticking out of the living room ceiling that was HOT! (well, maybe it was a light duty lamp cord, but speaker wire makes the story sound better)

ed

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6

The answer is in those splices. The 12 gauge wires on those 20 amp breakers probably run up to those splices and splice onto 14 gauge wire to the house. I am confident due to the age of the house with the knob and tube. About 15-20 years ago I did a service upgrade in a house and as we are suppose to do match the guage wire to the size breaker,as I did so. The panel had all 12 guage wires, so I matched with 20 amp breakers. There was no major splice boxes to take note of a change over in the size wire. The electrical inspector called me and we both agreed that the living room, bedrooms,halls and like similiar locations are probably 14 guaged wired and he told me to swap out some of the 20’s to 15’s with the breakers. I should of went around the house and opened up a few outlets and switches to check guage before I started. Rick