Voltage differences in household lines

Discussion in 'General Electronics Chat' started by alsek, Jul 10, 2016.

  1. alsek

    Thread Starter New Member

    Jul 10, 2016
    7
    4
    My background is not electrical so bear with me as I describe the problem.

    When a load is added to the system in my house (standard voltage) I see a difference between L1 and L2 voltages that is as high as 20 V. Sometimes it levels out quickly but other times it will maintain the difference (e.g. 112 V and 132 V) for 10+ minutes. Other times an added load will throw both lines to ~126-132 V and then they both go back to ~120 quickly. Problem is not caused by one specific appliance or circuit. To make matters worse, every time a line goes over 130 V the photovoltaic system shuts down and reboots.

    I'm not sure what to test to narrow down the issue. Any help or advice is appreciated. Thanks!
     
  2. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
    204
    "Standard Voltage" doesn't mean anything in an International forum. So, you have a 120-0-120 system. (10% fluctuation (citation needed) I believe is considered normal. Now, I believe you have a grid-tie inverter, so it's possible the inverter could be causing the upsets?

    That you have to figure out.
     
    Last edited: Jul 10, 2016
  3. alsek

    Thread Starter New Member

    Jul 10, 2016
    7
    4
    Yes, 120-0-120 system. The inverters were disconnected and we saw the same issue. We've seen one of the lines go up to 150 V.
     
  4. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
    204
    I might be inclined to think of a poor ground on the primary side of the transformer.

    Bad connection on the secondary generally point to significant drops in voltage.

    The utility regulation is taking place on the primary and your center-tapped secondary has little to do with that.

    Voltages ACROSS the legs of the main breaker (should be in the mV range) and the voltage between Neutral and the ground rod for the most part take care of your end.

    A transformer breaking down somewhere or a LOT OF FRIED SQUIRRILS, tree branches close to the uninsulated primary could cause a short and then a spike to recover.

    I'd give the problem to the power company.
     
  5. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,036
    1,662
    Sounds like a bad common line 0 in the 120 - 0 - 120 configuration.

    Someplace in your electrical system you have a bad wire and or bad connection which is allowing for the large voltage differentials between the two lines that need immediate attention.

    Where is the over voltage being read from? If it's at the end of certain circuits then that where you need to start looking for the bad connection and or undersized wire issues. If it's at your main breaker/fuse panel right of the main feed lines (ahead of primary breakers/fuse set) it's something your utility company needs to know about immediately.
     
  6. #12

    Expert

    Nov 30, 2010
    16,298
    6,810
    I agree. This smells like a bad neutral wire. The symptom which points to this is one side of the power line voltage rising in voltage instead of declining when a load is attached.
     
    MaxHeadRoom likes this.
  7. alsek

    Thread Starter New Member

    Jul 10, 2016
    7
    4
    Thanks all for the responses. The reading is from the main lines into the house before the breakers and also seen from the connection at the edge of the property. This morning's reading was 103 and 141. We're trying to get the utility company to come out but right now they don't believe the issue is on their side. It's been frustrating. Should I be worried about appliances and electronics frying?
     
  8. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,036
    1,662
    Yes! You should!:eek:
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    I would agree it could be a possible neutral problem, I have seen some damage caused by a loose neutral.
    I would ensure all neutral connections in the service panel are secure, including the service entry.
    Max.
     
  10. alsek

    Thread Starter New Member

    Jul 10, 2016
    7
    4
    Thanks Max. All neutral connections were checked and tightened all the way to the edge of property.

    Anyone have experience with Maui Electric?
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    My extension cord does not reach that far!:p
    Max.
     
  12. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
    204
    Those measurements (103+141)/2 = 122 does suggest a neutral/ground problem.

    Generally the neutral and the ground in your main panel are tied together. How, exactly depends on how/when the house was built.
    Ours uses a burried cold water pipe which isn't strictly legal now. Someone adds a plastic meter and by bye bond, Not in out case, though.

    In any sub-panels in non-detached structures, the ground and neutrals will remain separate,

    A breaker can be bad, hence measuring ACROSS the breaker (hard to do) and it should be a low voltage. Measuring across ground and neutrals is another.

    Some tests like ground resistance, you will have a hard time doing.

    A commn place for problems on overhead lines is the splice connections overhead.
     
  13. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
    204
    Where is the neutral/ground bond?
     
  14. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,036
    1,662
    It should be in your main panel and all of your outlet grounds and common line should show continuity and a near zero voltage differential regardless of the overall load on the home systems.
     
  15. #12

    Expert

    Nov 30, 2010
    16,298
    6,810
    Ah, yes. It's been a very long time since I thought about that one, but the plastic bootie melted off my connection at the weather head, obviously because of a high resistance connection. Some years later, I found an illegal splice in the neutral between the meter and the breaker box. That was when appliances started blowing up.:eek:
     
  16. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
    204
  17. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
    204
    Here: http://www.familyhandyman.com/elect...-safety-how-to-connect-a-new-circuit/view-all isn't a bad main breaker panel. There are some subtleies. Note the two points A points and the points to the right an left of C point. This is where you can test the volatge drop across the main breaker and the main breaker connections. It should be zero.

    Even though a wire is touching, it does not have to be connected so lug to wire is also a way to check for connections, Autoranging meters are better for this job.

    Neutral comes in near a green screw. That screw bonds neutral to the case ground. It would be removed if this was a sub-panel.

    There is a horizontal black wire bridging the neutral and what's likely an isolated bar.

    There is a ground coming from the main entrance cable and I wish I could see more of it. So, this is where the single point ground is made in this case. That ground SHOULD be coming from a ground rod.
     
  18. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Overhead or underground?
     
  19. alsek

    Thread Starter New Member

    Jul 10, 2016
    7
    4
    Underground.

    I was simplifying the problem a bit in my description. Two houses each have lines from the utility connection. The issue is seen in both main panels, even when each house is isolated from the other.
     
  20. #12

    Expert

    Nov 30, 2010
    16,298
    6,810
    That helps define where the problem is...outside the houses.
     
    JWHassler likes this.
Loading...