An odd trouble call...

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Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
Occupation
E
got a call from a friend of mine, who has a neighbor....
you know how these things go....

house was remodeled three years ago, 200A. service upgrade,
room additions, second story, etc.

living room plugs were fine last night, this morning, nothing.
homeowner pulls plugs out of wall, and starts fiddling... just
measuring voltages and such. i end up getting a call after he
goes to my buddy, drags him away from the football game,
and he can't figure it out, and calls me, and drags me away
from learning how to fly my next door neighbors brand new
second drone....

anyway, i get there, and the receptacles all have the same
thing going on with them.

hot > ground = 125 volts
neutral > ground = 90 volts
hot > neutral = 0 volts

breaker does not trip.

i've not investigated further, as the football game was running,
the neighbor was getting his drone batteries recharged, and i
didn't want to get into this and spend my sunday there, to be
honest. suggested he leave the breaker off, get an extension cord
for the TV, and this battle will get fought another day.

in any event, i figured i'd see what the peanut gallery thinks of
this one. there are seven receptacles on this circuit, and nothing
was plugged into any of them at the time measurements were
taken. the voltages were the same at each device.
 
Fulthrotl said:
got a call from a friend of mine, who has a neighbor....
you know how these things go....

house was remodeled three years ago, 200A. service upgrade,
room additions, second story, etc.

living room plugs were fine last night, this morning, nothing.
homeowner pulls plugs out of wall, and starts fiddling... just
measuring voltages and such. i end up getting a call after he
goes to my buddy, drags him away from the football game,
and he can't figure it out, and calls me, and drags me away
from learning how to fly my next door neighbors brand new
second drone....

anyway, i get there, and the receptacles all have the same
thing going on with them.

hot > ground = 125 volts
neutral > ground = 90 volts
hot > neutral = 0 volts

breaker does not trip.

i've not investigated further, as the football game was running,
the neighbor was getting his drone batteries recharged, and i
didn't want to get into this and spend my sunday there, to be
honest. suggested he leave the breaker off, get an extension cord
for the TV, and this battle will get fought another day.

in any event, i figured i'd see what the peanut gallery thinks of
this one. there are seven receptacles on this circuit, and nothing
was plugged into any of them at the time measurements were
taken. the voltages were the same at each device.
Click to expand...
Loose neutral, trace it back
 
ptonsparky said:
I agree with open neutral but MWBC has nothing to do with it. Had the H-N been anything greater than 0 You could throw that into the mix but with the info given, just a bad neutral.
Click to expand...

single wire circuit. 12-3 Romex, in and out of each box.
no devices connected to any of the outlets. an open neutral
getting backfed thru a MWBC, or a device connected to the
circuit was my first thought, but the situation doesn't support
those theories.

the 90 volts floating on the neutral without tripping the
breaker sounds like a floating neutral, except that when i
measured the voltage, it was with a fluke 12, which has a
2K ohm shunt across the meter leads, which kinda cancels
out transients and noise that shows up on DMM's with
really high ohm/volt ratios. it tends to show you what working
voltage you really have, which is why it's my favorite meter,
even tho discontinued by fluke.

and the voltages read the same across every outlet. one
thing that did pop into my mind is a staple across the home
run, that was pinched and finally shorted across hot to neutral,
and in doing so, zorched the netural, opening it in a wall somewhere,
while making a poor connection to the downstream portion of the
neutral.

it would explain the partial voltage under a 2k ohm load, while
the homeowners DMM showed a full 120 volts on the neutral.
and if the neutral had burned away, and the hot staple couldn't
make a good path to ground..... but that is a stretch, i'll admit.

oh, and the splices were pigtailed to the device, not using the
device as a termination.
 
Fulthrotl said:
single wire circuit. 12-3 Romex, in and out of each box......
Click to expand...
12-3 homerun or 12-2 homerun and switched outlets?
the 90 volts floating on the neutral without tripping the
breaker sounds like a floating neutral, except that when i
measured the voltage, it was with a fluke 12, which has a
2K ohm shunt across the meter leads, which kinda cancels
out transients and noise that shows up on DMM's with
really high ohm/volt ratios. it tends to show you what working
voltage you really have, which is why it's my favorite meter,
even tho discontinued by fluke.
Click to expand...
I love my Fluke 12 too. Hopped on ebay one day and found a batch of them for sale. Someone must have been retiring a fleet of them so I bought three.
and the voltages read the same across every outlet. one
thing that did pop into my mind is a staple across the home
run, that was pinched and finally shorted across hot to neutral,
and in doing so, zorched the netural, opening it in a wall somewhere,
while making a poor connection to the downstream portion of the
neutral.

it would explain the partial voltage under a 2k ohm load, while
the homeowners DMM showed a full 120 volts on the neutral.
and if the neutral had burned away, and the hot staple couldn't
make a good path to ground..... but that is a stretch, i'll admit.

oh, and the splices were pigtailed to the device, not using the
device as a termination.
Click to expand...
Even with the low z function if I poked around and did not find a bad splice or problem in the panel I would put a load on the circuit, 100W bulb in a rubber socket is one of my favourites.
 
electrofelon said:
What, was your neighbor looking to buy a third :lol:
Click to expand...

hey, this was his second one this week....
the first one might best be described as "tuition".

the first one was a phantom 3 standard...
this one was the phantom 3 advanced...

it seems there is a joystick movement you can do with the controller
that will turn off the controller. he did that with the thing about 150'
up in the air... it came down on the roof of a tilt up building a couple
miles from the house... he was flying it there last sunday.

they aren't very crashworthy, it seems... but some of the residual parts
he can use on this one, if it becomes necessary. we put it in learning
mode, which limits the elevation and range to 30 meters, and i flew it
around a bit... 20 some odd years ago, i had a RC helicopter, so i've
had a bit of experience with breaking things... this one survived my ten
minute thrill ride.

this could be fun, however. it's interesting the ipad records the flight,
and you can adjust it to make flight plans, hopefully missing the palm
tree in the back yard.
 
you had 35 volts drop across a bad neutral connection, maybe on the neutral bus in panel or in an outlet upstream of ones you checked, or even supply side connection of one you did check. You also have a connected load somewhere in the circuit causing the "hot" to feed thru that load and onto the neutral.
 
kwired said:
you had 35 volts drop across a bad neutral connection, maybe on the neutral bus in panel or in an outlet upstream of ones you checked, or even supply side connection of one you did check. You also have a connected load somewhere in the circuit causing the "hot" to feed thru that load and onto the neutral.
Click to expand...

This. Open neutral with no loads of any kind on the circuit would generally produce 0V N->G, not 90V.
 
169125-0907 EST

Fulthrotl:

A 2k impedance at 60 Hz is about 1.6 ufd of capacitance, or about 5 Henrys of inductance with little power dissipation. 1.6 ufd could be a reasonable weight, a 5 H inductor would not be. At 120 V and 2k resistance power dissipation is 14,400/2000 = 7.2 W a lot of heat to dissipate in a small meter. What is actually in your meter?

If the meter and short from hot to an open neutral are resistances, then the short is about 670 ohms based upon this one point measurement. I would change to a high impedance meter. Assuming the short is a 670 resistance, then a high impedance meter should read 120 V. Load neutral to ground with a 25 W incandescent (at 120 V about 0.21 A, R is about 570 ohms; at 90 V about 0.18 A, R is about 500 ohms).

If the hot to neutral short is a constant 670 ohm resistance, then said 25 W bulb will have about a 42 V drop across the bulb and a current of about 0.12 A. Measured with 660 ohms series resistance.

You can do your own measurements on a 100 W bulb.

Using multiple different loads on the circuit under test can provide useful information. If the short is not a constant resistance, then determininng what is the short is more dufficult.

From your limited measurements it does look like a short from hot to neutral and an open neutral before the shorting point.

.
 
JFletcher said:
This. Open neutral with no loads of any kind on the circuit would generally produce 0V N->G, not 90V.
Click to expand...
kwired said:
Also neutral is not completely open or you would see full 125 volts instead of 90, there is a 35 volt drop across the problem area.
Click to expand...
I agree with Kwired that you don't always get a fully open neutral. If the circuit was shorted the breaker should trip. and if the neutral were open the would be 0 volts to ground on the neutral unless there is something connected. If you know which circuit you are dealing with it's better to go to the panel and take the neutral and hot loose and see how much resistance there is between them. If you are sure there is nothing else on the circuit you could even meg the cable (home run). Around here I would think of an over driven staple or even a flying splice in a wall or ceiling.
 
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