Site wiring fault?

Discussion in 'General Electronics Chat' started by paultwang, May 28, 2006.

  1. paultwang

    Thread Starter Well-Known Member

    Mar 8, 2006
    80
    0
    Is this bad? My whole room in my apartment is like this. Neutral to ground is 36 Vac. I live in USA.

    It might take the management people a while to get this problem addressed. What should I do in the mean time to protect myself, my properties & things.

    FYI:
    my hot to neutral voltage is 123 Vac.
    hot to ground is 85 Vac.
    Most of my UPS (uninterruptable power system) do not like this room's power outlets.

    [​IMG]
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    The NEC says that neutral to ground voltage must not exceed five percent of the neutral to hot voltage. Advise the landlord that they are way out of compliace with code. Advise the landlord that they potentially have a 500 watt heater (in the form of a sloppy or corroded connection) hiding in their walls.

    In the interrum, make darn sure that your smoke detector is working and that your insurance is paid up. Advise your neighbors to do the same.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    My father's apartment was like that. It was built with aluminium wiring. At one time, the breaker panel was almost too hot to touch the cover. Your landlord should be very interested in correcting this problem asap.
     
  4. paultwang

    Thread Starter Well-Known Member

    Mar 8, 2006
    80
    0
    One desktop computer just made a big spark in the process of being plugged into one of the normal outlets. A huge spark (size of a tennis ball) appeared at the PSU vent as the power plug is inserted. I pulled the plug out immediately and went for the fire extinguisher. However, no fire or other sparks was generated.

    The outlet I used was in another room. I tested it before plugging the computer. If there was any serious wiring anomaly, the UPS should have caught it.


    Wall outlet ----> Cheap standby UPS ----> ---> desktop computer

    The following data obtained from UPS outlet, which should be the same as wall outlet when UPS is on standby:

    Hot to neutral: 123 V
    Nominal frequency: 60 Hz
    No transient

    Neutral to ground: 1.3 V max, 0.3 V average
    Nominal frequency: 60 Hz
    High frequency transient between neutral and ground: up to 4.5 kHz


    Is this not good enough for a desktop computer?
     
  5. paultwang

    Thread Starter Well-Known Member

    Mar 8, 2006
    80
    0
    New data:

    Neutral to ground: 49 Vac (was 36 Vac)
    Ground to water pipe: 50 Vac (no previous measurement)
    The neutral to pipe potential is almost zero.

    What could have caused the worse conditions?
     
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,157
    I would go to the store and get an AC outlet tester.

    The indicator lights will probably show an open ground, but the reason to get the outlet tester is to show your landlord there is a problem.
     
  7. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    Use a meter with a Lower Ohms per Volt...
    Most digitals have such a high resistance per volt that they are Notorious for picking up high impedence voltages that might be induced on a run of cable from a neighbouring circuit.
    Otherwise, put a resistance of say 50k to 100kohms in parallel with your probes. That will help determine whether there is a problem, or just a fooled meter.

    Not sure on the system you use over there, but if it's MEN then there should be the same potentual between Phase and Neutral, as between Phase and Earth.... That measurement is a worry.
    If you guys tie your earth to your neutral back at the switchboard, then either that, or a faulty earth stake may be the problem.
     
  8. paultwang

    Thread Starter Well-Known Member

    Mar 8, 2006
    80
    0
    The ground connection in the other rooms are acceptable (up to 1.3 V neutral to ground). The problem is only in my room. I honestly don't know how one wire is corrupted/rusted and not the other wires.
     
  9. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,157
    Paul,

    The age of the building could come into play. At one time the conduit provided the ground and you only had the neutral and hot wires.

    The NEC today requires three wires ... hot, neutral, and ground. The ground and neutral are affixed to the metal distribution box.

    If the age of the building is such that conduit provides the ground path, you would have to physically inspect every time the conduit is affixed to a box, from the outlet to the distribution center.

    The easiest way to verify they are using the metal conduit as the ground, is to remove the cover, remove the plug, and see if there are two wires connected [black {hot} and white {neutral}]. The green {ground} would be missing.
     
  10. paultwang

    Thread Starter Well-Known Member

    Mar 8, 2006
    80
    0
    A repairperson came and reconnected the loose wire. Problem solved.
     
Loading...