Electrical Riddle

Silas Pradetto

Silas Pradetto

Graduate Student
Jan 11, 2011
2,130
1
0
Land of Steady Habits
www.concertsunlimited.com
I have an electrical riddle for everyone, to show how miswiring can cause problems:

What would cause the following in a house:
  • some lights are dim
  • some things don't work
  • main hot legs meter 0 volts across each other
  • both main legs meter about 120 volts to ground and neutral

My dad just recently solved this for a friend.
 
Re: Electrical Riddle

0V across main hots would lead me to believe the service was mis-wired so that both hots were coming from the same leg of the transformer. That would explain why "some things" (240v dryer, hot water heater, oven) don't work. Dunno about the dim lights though.
 
Re: Electrical Riddle

Tom Manchester said:
0V across main hots would lead me to believe the service was mis-wired so that both hots were coming from the same leg of the transformer. That would explain why "some things" (240v dryer, hot water heater, oven) don't work. Dunno about the dim lights though.
Click to expand...

Both hots on the same leg means that the neutral (which would be half the size of the combined hot leg) is carrying all of the current supplied through the double-sized hot leg, rather than carrying only the imbalance between two phases.
 
Re: Electrical Riddle

Milt Hathaway said:
Both hots on the same leg means that the neutral (which would be half the size of the combined hot leg) is carrying all of the current supplied through the double-sized hot leg, rather than carrying only the imbalance between two phases.
Click to expand...

If one hot leg were powering both buses, the neutral would still be sized appropriately (although the panel would be limited to half possible current overall).

That's still not it though.
 
Re: Electrical Riddle

Are you implying that this was solved with a single change - one single problem, or is this a whole house cluster of problems where the above symptoms are spread over? Are your symptoms steady state, meaning that they always measure this way, or does it take a couple scenarios - things plugged in/unplugged, switches flipped to create all the symptoms?
 
Re: Electrical Riddle

TJ Cornish said:
Are you implying that this was solved with a single change - one single problem, or is this a whole house cluster of problems where the above symptoms are spread over? Are your symptoms steady state, meaning that they always measure this way, or does it take a couple scenarios - things plugged in/unplugged, switches flipped to create all the symptoms?
Click to expand...

One change fixed the problem, and the problems are constant.
 
Re: Electrical Riddle

Lost nuetral?

I had my nuetral line (the bare aluminum cable) break and it caused all kinds of bad news. Fluctuating lights, voltage swings from 90-190VAC. Burnt out a LOT of transformer wal-warts, computer power supply, modem and screwed up permanently one old TV and a VCR. All on a Sunday morning, of course ;>)

Boomerweps
 
Re: Electrical Riddle

yup common gotcha is open transformer center tap, but he doesn't report a high voltage on other circuits symptom, to go along with the low voltage leg.

I don't have a guess...

JR
 
Re: Electrical Riddle

Silas Pradetto said:
I got JR stumped? Wow, I feel cool. 8)~:cool:~:cool:
Click to expand...

Take your victories where you can.... I don't claim to know everything...

Your riddle is too difficult for me.

Both main legs measure 120V to ground/neutral but some lights are dim and some things don't work. Not very likely to both be dim "and" measure 120V at the same time, so apparently some inconsistency in the voltage measurement. Perhaps something like a loose wire that introduces series resistance that meters OK with a high impedance meter, but drops voltage when connected to actual load.

Both hots measure 0V across each other... This is also inconsistent with my understanding of typical house wiring. If these measurements are made at the drop into the panel something is seriously wrong. If measured away from the panel could be anything. Both pairs swapped could have 0V on both hots, but wouldn't dim lights. The dryer and stove sure wouldn't work.

nah... Too hard for me,,, you win...

JR
 
Re: Electrical Riddle

John Roberts said:
Both main legs measure 120V to ground/neutral but some lights are dim and some things don't work. Not very likely to both be dim "and" measure 120V at the same time, so apparently some inconsistency in the voltage measurement. Perhaps something like a loose wire that introduces series resistance that meters OK with a high impedance meter, but drops voltage when connected to actual load.
Click to expand...

I have the same question, which was why I asked if the condition was steady state or everything he wrote true at the same time. We'll see if Silas has found the magic Schroedinger's Cat of a voltage both being 120v and not being 120v at the same time, or if there was some creative wording that we collectively aren't lawyer-ey enough to decode.
 
Re: Electrical Riddle

Silas Pradetto said:
I have an electrical riddle for everyone, to show how miswiring can cause problems:

What would cause the following in a house:

  • some lights are dim
  • some things don't work
  • main hot legs meter 0 volts across each other
  • both main legs meter about 120 volts to ground and neutral


My dad just recently solved this for a friend.
Click to expand...
My guess is that a 3-phase breaker panel was installed, so one buss is not getting any power, or that a proper panel was installed, but with one buss disconnected. With one buss floating the low voltage going to some lights are the result of the connected hot going through some 240v device (that isn't working but has resistance across the two hots) and feeding the disconnected buss backwards. This could be verified by turning off the breakers to any 240v devices and the dim lights would go out. Reading 0v between the 2 hots means they are on the same phase, but that's 2 problems and you said it was solved by one fix, so I'm stumped there.
 
Re: Electrical Riddle

Tim McCulloch said:
Uh.. if I get this right, it's really scary.

The hot legs were wired to neutral and ground, and neutral & ground were wired to the hot buses.
Click to expand...

If this were the case, and the neutral and ground lugs were tied together at the service entrance, sparks would have surely flown... Prossibly damaging the transformer, or worse.
 
Re: Electrical Riddle

Andrew Broughton said:
My guess is that a 3-phase breaker panel was installed, so one buss is not getting any power, or that a proper panel was installed, but with one buss disconnected. With one buss floating the low voltage going to some lights are the result of the connected hot going through some 240v device (that isn't working but has resistance across the two hots) and feeding the disconnected buss backwards. This could be verified by turning off the breakers to any 240v devices and the dim lights would go out. Reading 0v between the 2 hots means they are on the same phase, but that's 2 problems and you said it was solved by one fix, so I'm stumped there.
Click to expand...

Sorry for the late response guys. Andrew pretty much got it. The problem was that one of the hot legs had been pulled out of the lug in the meter socket (the feeder was run underground with no slack, and when the ground moved, it pulled it right out). This caused half the panel to lose power, but the water heater was feeding back to the other bus through the element. Once the water heater breaker was turned off, the panel metered correctly (although still minus one bus).

When metered with the house lights off, the buses were both at about 120V, but when lights were turned on, because of the heating element resistance, they were quite dim.

To fix the problem, my dad extended the feeder and reconnected it.

8)~:cool:~:cool:

And to add- this was a service that had been around a LONG time; it was nothing recently installed.
 
Re: Electrical Riddle

I have found water running backwards when doing plumbing, but fortunately never encountered anything like this electrical.

One time I was sent out by the general contractor I worked for to a fraternity house at UMD that had a problem with a bathroom exhaust fan "not working". Everytime they flipped it on, the breaker went. After pulling it out of the ceiling I found the hot return from the wall switch wired directly to ground.
 
Re: Electrical Riddle

TJ Cornish said:
I have the same question, which was why I asked if the condition was steady state or everything he wrote true at the same time. We'll see if Silas has found the magic Schroedinger's Cat of a voltage both being 120v and not being 120v at the same time, or if there was some creative wording that we collectively aren't lawyer-ey enough to decode.
Click to expand...

Perhaps the cat was electrocuted....

JR
 
Top Bottom