Here is the situation I am trying to understand:
An 50 year old house (late knob and tube wiring). No distributed
grounds to electrical outlets or junction boxes. Everything works fine
electrically for a long time.
When doing some electrical work, a wire was cut. If you want the
details, it was supposed to be a wire to an electrical outlet that
work was to be done on. Turns out this was not the wire to that
outlet. The breaker was switched off for the outlet, but the wire was
hot. Only other info is that this was a white wire running parallel
with a red wire.
What happened was that when the wire was cut, the 110 recessed lights
in the room near by (the kitchen) went to double brightness.
Everythign was shut down, the wire was reconnected and the kitchen
lights were back to normal brightness. How is this possible??
Presumedly the house circuits are divided between the 2 phases of a
220 feed into the house. And somehow cutting that one wire put 220
across the kitchen lights, since that is the only way I can understand
the double brightness (and measuring with a voltmeter betweent the 2
cut ends, about 210V was measured). But I can't visualize how the
house wiring would be such that a 110 light circuit works fine
normally, but cutting one wire only somehow puts 220 to that circuit.
You disconnected the neutral conductor of a shared-neutral circuit (aka Edison
circuit). That changes the two hot legs of the circuit from two 120V circuits
to one 240V circuit -- and that's why the lights got extra-bright: you were
pushing 240V through 120V light bulbs.
Following is a simplified diagram of the connections in a shared-neutral
circuit. (View in a fixed-space font such as Courier)
HOT1 ---------------- LIGHT1
There's 240V between HOT1 and HOT2, and 120V between each of them and NEUTRAL.
When the neutral conductor is intact, current from HOT1 and HOT2 each flows
through the neutral conductor back to earth ground, and LIGHT1 and LIGHT2 each
Cut the neutral, though, and you have the following 240V circuit:
HOT1 ---------------- LIGHT1
Hope that makes it clear...
Doug Miller (alphageek at milmac dot com)
On Feb 19, 2:08?pm, firstname.lastname@example.org wrote:
You have a REAL SAFETY HAZARD!
Open neutral, which allowed near 240 volts on that circuit!
How old is your main panel? Fuses.
I suggest for safety insurance and resale value you replace your knob
and tube COMPLETELY! A total rewire!
That wiring is likely a 100 years old, how many things do YOU own that
last that long? New wiring gets you all grounded outlets with GFCIs
and AFCIs, adding greatly to safety and resale value.
Its likely you cant sell your home because homeowners doesnt want K&T
and neither do mortage companies......
You have 2 issues, a op[en neutral which MUST be fixed IMMEDIATELY!
and K&T more of a long term issue........
When he cut it, yes, it was open. See Doug's response on Edison
circuit (shared neutral).
Well, since it was given that the house is only approximately 50 years
old, it's highly unlikely the wiring is 100...
He did fix it and it wasn't open until it was (inadvertently) cut.
It would certainly be nice if you didn't knee-jerk react to every
mention of K&T you see, haller... :(
There's absolutely nothing in OP's post that indicates any reason
whatsoever that the k&t in his house is of any concern whatsoever.
The dual bogeymen of sale value and insurance don't hunt in many
jurisdictions as we've already gone 'round with and there's not even a
hint here that either has any bearing on the question or work
you ignore the complete lack of safety grounds, GFCI, AFCI, and the
lkely overloading of such circuits and excess use of extension cords
since K&T had few outlets very far apart.......
Obviously you havent walked thru whats left of a home after a fire,
and seen the devastation both physical and menta such a event can
It AMAZES me people will think NOTHING of spending 15 grand and up for
a new vehicle but refuse to invest a fraction of that on a critical
yeah whatever,,, I think the biggest protesters are those who have K&T
and are trying to justify THEIR decision to ignore the issue.
I don't know that there's any justification for a blanket assertion of
All OP really said was there aren't grounds on the lighting and
receptacle circuits. Doesn't address whether there are grounded
appliance circuit(s) or even, possibly, GFCI outlets, etc. elsewhere.
Maybe, maybe not -- but that wasn't the question raised and there's
insufficient data to confirm/deny. Same goes for extension cords,
etc., -- maybe, maybe not. I've seen k&t houses wired quite
adequately for numbers of outlets and others not so much. Again, it's
simply a leap to assert what the situation is for any given house
You also have no idea of how many house fires I have seen nor who I
know directly or indirectly that have been involved. I'll only say
the number is greater than zero and of that number the number is zero
wherein k&t wiring was to blame.
We had this discussion only a short time ago and as I noted there, I
have been involved in old housing retrofits for quite some time and
have found cases where deemed it mandatory to replace it where it was
in bad enough condition and others where it just wasn't the most cost-
effective thing to do with limited funds.
Again, my real problem is the universal "one size fits all" advice on
the basis of no firm data other than a preconceived notion of "k&t
bad, must go".
-- That wiring is likely a 100 years old, ...
- Well, since it was given that the house is only approximately 50
- old, it's highly unlikely the wiring is 100...
Unless the electricians worked really, really slow when the house was
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