@Jim Murphy Having read the other posts, let me suggest one other possibility which I've personally uncovered in the past five decades.
TLDR warning FIRMLY in place:
In one case this was 44 stories up in a brand new executive board room supplied by three
phase 120 / 208 volts.
The other instance was in the basement of someone's two story dwelling supplied by single
phase 120 / 240 volts.
In both situations, the root cause of the problem was identical in the following way:
Inadvertently the hot conductors of two circuits had been mistakenly connected [Marretted] together such that either / both circuits effectively powered all of the related lamps in parallel. No "short circuits". No sparks or overheating of any kind. No symptoms of any problems other than you could turn off each and every
breaker one at a time and the related lamps NEVER went out.
In the first situation back in 1967, the homeowner had purchased his home used and lived in it for several years before wanting to remove the correct
fuse and replace his basement ceiling lights as part of a basement recreation room upgrade. He removed every
fuse one at a time and neither of his two basement lights ever went out. He solicited many opinions and chased down many red herrings but, in spite of investing much time and money, the mystery was never solved.
One day a friend of a friend related the tale to me and the mystery nagged at me for several months. Finally, I just had to see this bizarre phenomenon for myself.
Let me move this along.
This was in the days when original contractors routinely roughed in lighting in unfinished basements as one ceiling mounted
porcelain lamp
socket at either end operated by a pull-chain / string hanging from each
socket.
You descended the stairs to your basement and pulled the first string, the light came on and you were happy.
If you needed to go to the far end of the basement, you walked over there and pulled the second string. The second light came on and again you were happy. You reversed the procedure upon departing often cursing yourself upon ascending the stairs and realizing you'd left one of the lights on. That's when you'd come home from hockey practice and Dad would say "Go downstairs and turn the light off for me."
I've digressed. My
point was / is everything was working normally. The original home buyer hadn't paid for the deluxe upgrade that would have provided a
switch at the top of the basement stairs for the basement lights. Only the wealthy paid for such frivolous upgrades in those days. Along came TV in the fifties and the early adopters had their sets in their living rooms. The crowd who just had to have the latest new gadget of the year, installed their new sets in the living room and moved their old set to the basement for Dad and his buddies to watch the ball game while Mom and the wives took over the parlor.
By the time the home's present owners purchased the home, many renovations had taken place with wall mounted duplex receptacles having been extended from the existing ceiling lights' back-boxes. As each light was switched by its own pull chain, everything functioned normally. Wall receptacles were always live regardless of whether or not lights were on. Along came the present owners wanting to exchange the original
porcelain socketed / bare
incandescent lamps for the then new and modern cool white fluorescents and were totally bewildered to learn they could remove every
fuse from their panel and their basement lights NEVER went off.
Let's move this along a little faster:
Showed up armed with flashlight.
Homeowner removed each
fuse one at a time demonstrating neither of the two lights went out.
Single family dwelling.
No neighbors on opposite sides of walls powered from alternate services.
No emergency lights.
No battery back-ups.
No generators.
No extension cords from the neighbor's exterior
receptacle.
Service entrance was a fused
disconnect.
Lit flashlight and pulled the main
switch.
Lights went off.
Homeowner was surprised.
Clearly lights were being powered from his immediately adjacent
fuse panel as it was the only
fuse panel supplied from his main
disconnect.
Pulled all fuses to remove the load and re-closed the main
switch.
With my flashlight still on, replaced the fuses one at a time while the homeowner and his family hollered from room to room and floor to floor dutifully noting what worked vs what did NOT work on each
fuse.
Imagine everyone's total awe when we discovered two fuses each supplying exactly the same items.
Returned all of the fuses to their starting points and Dad gathered the family to collate and compare notes.
Bid them au revoir and left them to compare notes.
They offered money. I graciously refused, I was having just far too much fun debunking all of the various scenarios that had been suggested. At the time, I was still a lowly construction and maintenance electrical apprentice. It's not like I was a journeyman yet let alone a licensed electrical contractor used to showing up with my
hand out. Nah! For me this was all just too much fun and great conversation for coffee and lunch breaks during my days on job sites.
Armed with their new-found findings, the homeowners went back to two or three of their previous contractors and paid money to have them assess their now neatly detailed notes.
The tales that came back down the 'friend of a friend' grapevine just kept getting sillier and sillier / less and less plausible / easier and easier to refute.
Cutting to the
chase:
In those days it was common practice to run a
circuit to an octagon box at one end of your unfinished basement.
From that box, you'd run
Romex up to a living room duplex and on up within the wall to feed a bedroom's overhead light and receptacles.
You'd repeat this with two or three runs emanating from this same box /
fuse and extending up to various points on the
ground level and upper floor.
At the opposite end of the unfinished basement's ceiling, you'd do exactly the same thing servicing the opposite end of the dwelling.
Two fuses. Two circuits, covering the bulk of the dwelling's ceiling lights and wall receptacles.
Range hoods were pretty much unheard of in working class neighborhoods.
Washroom ventilating fans were luxury items beyond the aspirations of working class stiffs.
The home's original purchaser MAY have gone 'hog-wild' and sprung for a separate
circuit for his kitchen counter with a toaster and trendy new
electric frying pan in mind.
You may have a couple of 30 amp cartridge fuses for your hard-wired clothes dryer.
Perhaps a couple of 40 amp cartridges for your hard-wired
electric stove.
Maybe you had a separate
fuse for an outside
receptacle for your car's
block heater or battery charger but that was pretty much it. Thus it wasn't at all uncommon to find your entire home powered by basically two fuses.
Neither the great explosion of electrical appliances; microwaves, home stereos, room air conditioners, ceiling fans, et al nor
electric heating had occurred yet. Telephones had rotary dials and were hard-wired to the wall with 6' cords.
Times were radically different and total electrical loads per dwelling far, far less.
My grandmother's two story home was originally supplied by a single
phase, two
wire, 30 amp main service: One hot. One
neutral. Overhead from the street, through a simple weather-head, through a hard-wired / non-socketed single
phase single
leg meter and directly on to an open
porcelain block holding two [Count 'em 2] 15 amp twist in fuses.
Times were definitely different.
Getting back to the home owner with the mysteriously powered lights:
Over the years, through the course of several previous owners, the two circuits [The circuit for one end of the home and the circuit for the opposite end] had become connected together within the dwelling. As luck would have it, both the circuits in question were sourced from the same side /
leg of his single
phase 120 / 240 volt panel thus no "shorts", no sparks, no flames, no apparent problems.
True, you now had 14
gauge / 15 amp
wire fed by effectively 30 amps but everything appeared to be normal and functional until they inadvertently tripped over the fact that they appeared to be in possession of mysteriously powered lights.
Fast forward roughly four decades to a 44th floor executive board room in the heart of downtown Toronto.
Include a fabulously huge board room table seating 24.
Add fancy A/V, HUGE 3 X
Barco PJ's, four
PTZ cameras that descended from the ceiling and automatically tracked the various executives as they were recognized by the 'chair'. Indirect and direct
CFL and
incandescent lights, dimmers, computer controlled, motion sensed and IR controlled up the wazoo.
Basically a bigger client with deeper pockets being taken advantage of by an even greater number of higher class contractors.
Root of the their problem:
EXACTLY THE SAME with the ONLY difference being a 3
phase 120 / 208 volt service this time coupled with the errant connection being within a
junction box above a very fancily finished ceiling.
The client was armed with documented data from the room control systems computer logs when they brought in their lawyers and cheerfully paid my boss's invoice.
I won't go into the myriad of red herrings postulated and presented to either the original home owner or the bank in downtown Toronto but I'll cheerfully entertain and refute all comers.
I'm not suggesting this is
@Jim Murphy 's problem, just throwing it out there as one more plausible possibility to consider.
I did provide a TLDR warning.
It's lunch time here.
Toodleoo!
Ron Hebbard.