Important - check AC Wiring/Voltage Safety every time you work on your solar system

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  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: Important - check this every time you work on your solar system
    DanS26 wrote: »
    IMHO you have not found or fixed the underlying problem in that RV.

    Here is a post from Jim when he was asked about this on my forum.

    First of all, while you might think there needs to be an internal hot-to-ground fault to produce the voltage in the first place, that's not entirely true. ANY appliance plugged into a power plug can have some current leakage that will produce a voltage of some level. But the AMOUNT of fault current is limited by UL Labs to less than 0.75 mA for an "ungrounded appliance" such as your iPhone charger, or less than 3.5 mA for a "grounded appliance" for something like your microwave oven. Generally, anything plugged into an electrical outlet and NOT malfunctioning will have its chassis migrate to around 1/2 of line voltage. So it's perfectly normal (but somewhat scary) to measure 60 volts AC on the body of your iPhone while plugged into its wall-wart charger. But because the maximum leakage current is supposed to be under 0.75 mA, that's right below the current threshold that most people will notice a shock.

    On the other hand, a microwave oven (or any other grounded appliance) can leak up to 3.5 mA of fault current and still be considered "safe" by UL standards. This will generally produce the same 60 volts on the chassis if left ungrounded, but that 3.5 mA of current at 60 volts will produce a very noticeable, but not dangerous shock. And all these leakage currents are additive, so if your RV has a broken ground wire (EGC - Equipment Grounding Conductor) then everything plugged into your RV can leak more current to the chassis, and it's entirely possible to have 20 or 30 mA of leakage fault current available even if nothing is really "wrong". I call this a low-current (high impedance) fault, which can be painful but generally not deadly. Now, if your EGC is in place, then that 20 or 30 mA of current will be drained harmlessly to the grounding point of your service panel. However, if there's no ground path in your power cord and you touch anything metal on your RV while standing on damp ground or grass, then you can feel a very big shock. Now remember that 10 mA is a pretty good shock, and 20 mA will cause your hand to clamp down on a wire or ladder rung and not be able to let go, and 30 mA through your chest cavity for a few seconds almost guarantees heart fibrillation and death in minutes if CPR isn't immediately begun, so even these "low current" leakage voltages can get dangerous.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    mtdoc wrote: »
    OK. Please explain how a fault in a home PV system - will cause my PV panels, PV wire run, charge controller, or any DC wiring or enclosure to become energized with AC.
    PV frame, panel mounts, DC negative connected to ground. So is AC Neutral. If ground is faulty then PV frame, panel mounts, and DC negative are all connected to one side of the AC.

    Bingo. All of your equipment is already all connected together. You just need to add an equipment fault and bad ground and all of that equipment is now energized. That is why I started this thread.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • mtdocmtdoc Solar Expert Posts: 600
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    PV frame, panel mounts, DC negative connected to ground. So is AC Neutral. If ground is faulty then PV frame, panel mounts, and DC negative are all connected to one side of the AC.

    But if you loose your main earth connection then the whole system is now floating, correct? There could be some leakage current making a potential difference between neutral and earth but that would likely be minimal. I don't think a NCV detector would be of any use in this situation, would it?

    Also wouldn't the loss of my home's ground mean that any metal enclosed appliance, outlet boxes, etc would now also be floating at the same potential as the PV equipment? Should I be checking them every day before I use them? This could happen in any home with or without a PV system. Is everyone at risk from this?

    What would all the home's GFCI's do in that scenario?

    What about all those metal roofs with PV array's on them. All we all in danger anytime we touch a metal roof with solar panels on it?

    Has there ever been a case of someone being electrocuted in the above scenario?




    I can think of lots of p
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

    Look at it another way: if the NCVD held in your hand detects a current potential through your body to Earth ground then there is a problem, regardless of the Voltage or current involved. The NCVD acts as an isolator for that potential current path through you. If it were not there then whatever current potential there is goes through you.

    I, for one, do not want this to happen.
  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    mtdoc wrote: »
    But if you loose your main earth connection then the whole system is now floating, correct? There could be some leakage current making a potential difference between neutral and earth but that would likely be minimal. I don't think a NCV detector would be of any use in this situation, would it?

    This is exactly the situation where the NCVT will detect a problem. Since the rest of the utility's system is grounded, when you touch that equipment you now complete the circuit.
    Also wouldn't the loss of my home's ground mean that any metal enclosed appliance, outlet boxes, etc would now also be floating at the same potential as the PV equipment? Should I be checking them every day before I use them? This could happen in any home with or without a PV system. Is everyone at risk from this?

    Yes this is possible. Same as I've said before, equipment fault, bad ground, and your microwave's case is now dangerous.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • mtdocmtdoc Solar Expert Posts: 600
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    Look at it another way: if the NCVD held in your hand detects a current potential through your body to Earth ground then there is a problem, regardless of the Voltage or current involved. The NCVD acts as an isolator for that potential current path through you. If it were not there then whatever current potential there is goes through you.

    Agreed. But this whole idea that because a home's connection to earth can possibly be severed or disconnected means that we should be using NCVDs before touching anything that might be connected to neutral is just alarmist IMHO. If that was a real risk no one would be safe in any home. I'm all for electrical safety but sometimes you can lose the forest for the trees and end up in more danger because you're focused on the wrong risks.
    I, for one, do not want this to happen.
    Nor do I!
  • DanS26DanS26 Solar Expert Posts: 219 ✭✭✭
    Re: Important - check this every time you work on your solar system
    Voltage overcomes resistance, not current.

    He said he recorded no more than 60 volts
    18.2kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED System monitoring with PVOutput.org
  • mtdocmtdoc Solar Expert Posts: 600
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    techntrek wrote: »
    This is exactly the situation where the NCVT will detect a problem. Since the rest of the utility's system is grounded, when you touch that equipment you now complete the circuit.

    I understand how NCVDs work. The point is that in that scenario - a lighting up of the NCVD light indicates a wiring problem but the potential difference between neutral and earth and the associated leakage current are not likely to be high enough to be dangerous. It would light up around any metal connected to neutral and would no longer be distinguishing between live and "not live" conductors.
  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    mtdoc wrote: »
    It would light up around any metal connected to neutral and would no longer be distinguishing between live and "not live" conductors.

    It doesn't. Stick yours in an outlet in the neutral position (bottom-right if the ground is at top) and it won't light up. Move it to the hot leg (bottom-left) and it will.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • mtdocmtdoc Solar Expert Posts: 600
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    techntrek wrote: »
    It doesn't. Stick yours in an outlet in the neutral position (bottom-right if the ground is at top) and it won't light up. Move it to the hot leg (bottom-left) and it will.

    Well of course! But that is because the neutral is bonded to earth!

    In the scenario you propose the neutral is now "energized" because the earth connection has been lost. And the NCVD has lost its utility in distinguishing a dangerous live wire from a not so dangerous "not live" (not neutral anymore but not energized enough to be dangerous) wire.

    All this is assuming that the threshold for activating a NCVD is low enough to be activated by the leakage current present(i'm not sure if that is true) If not then it goes back to being of no utility because it does not tell you anything is wrong. And if you had the scenario that you lost your earth and you had a short between lvie and neutral - well now the neutral would be dangerously energized - but of course breakers would be then tripped!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Important - check this every time you work on your solar system
    DanS26 wrote: »
    He said he recorded no more than 60 volts

    Which does not change the fact that Voltage overcomes resistance, not current.

    Here's a coincidence: he reported 60 Volts, exactly 1/2 120 Volts and what would be expected from current leakage - and also what the NEC considers to be the low end of "high Voltage".

    I don't think anyone is suggesting checking your wiring before you turn on the TV each time. But when you are about to work on it or a known change has occurred it is a good idea to test and make sure all is as it should be. Switching to/from 'shore power' at camp sites is a known change, especially as some have a notoriety for poor quality electric service.
  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    mtdoc wrote: »
    Well of course! But that is because the neutral is bonded to earth!

    In the scenario you propose the neutral is now "energized" because the earth connection has been lost. And the NCVD has lost its utility in distinguishing a dangerous live wire from a not so dangerous "not live" (not neutral anymore but not energized enough to be dangerous) wire.

    All this is assuming that the threshold for activating a NCVD is low enough to be activated by the leakage current present(i'm not sure if that is true) If not then it goes back to being of no utility because it does not tell you anything is wrong. And if you had the scenario that you lost your earth and you had a short between lvie and neutral - well now the neutral would be dangerously energized - but of course breakers would be then tripped!

    They are both dangerous if the neutral has lost its bond to earth.

    Current isn't the trigger. It is voltage. You can walk under a 750 kv power line with your NCVT and it will light up, but the current between you and ground is in the milliamp range.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    mtdoc wrote: »
    All this is assuming that the threshold for activating a NCVD is low enough to be activated by the leakage current present(i'm not sure if that is true) If not then it goes back to being of no utility because it does not tell you anything is wrong. And if you had the scenario that you lost your earth and you had a short between lvie and neutral - well now the neutral would be dangerously energized - but of course breakers would be then tripped!

    It isn't activated by leakage current per se, it is activated by a Voltage potential between the probe end and Earth ground.

    Without that Earth ground 'neutral' is just as hot as 'hot'. Breakers only trip if the current flowing through them exceeds their rating. You don't need 15 Amps to kill someone; you pointed that out yourself.

    It's not an "all or nothing" scenario. There are plenty of variations in between 'off' and 'on' which may not trip OCP but still can give you a shock.

    If you don't believe it, that's your problem. If it kills you don't come crying to me saying you weren't warned.
  • mtdocmtdoc Solar Expert Posts: 600
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

    Without that Earth ground 'neutral' is just as hot as 'hot'.
    I disagree. It's only as hot if there is a short - in which case the breakers trip

    Yes - of course the potential difference it required to light up the NCVD. The leakage current creates that potential difference but does not carry enough energy to be dangerous.
    Breakers only trip if the current flowing through them exceeds their rating. You don't need 15 Amps to kill someone; you pointed that out yourself.

    Yes, but without a short between hot and neutral you would never get the neutral energized enough to produce a lethal current!
    It's not an "all or nothing" scenario. There are plenty of variations in between 'off' and 'on' which may not trip OCP but still can give you a shock.

    Agreed. But getting a shock is not the same as being electrocuted. If it was we'd all be dead.
  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

    You didn't read my last post. You also seem to have a basic misunderstanding of how AC power and AC wiring works.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • mtdocmtdoc Solar Expert Posts: 600
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    techntrek wrote: »
    You didn't read my last post. You also seem to have a basic misunderstanding of how AC power and AC wiring works.

    Yes - I read your last post. Please elaborate on my misunderstanding.
  • BB.BB. Super Moderators Posts: 26,872 admin
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

    I would rather we not continue down the road of "what ifs" and "it could happen"...

    There are an unlimited ways that something as complex as an off grid power system can fail and the symptoms it could have with each different failure.

    It is probably not worth trying to examine each of these possible failures in detail. Just understand that things happen. A good set of tools with a bit of debugging, and usually the fault(s) can be isolated and fixed.

    AC and DC are similar in many ways. However our tools (the NCVD, and even a "simple" DMM) can react in ways that are not always easy to understand--For example, many less expensive DMMs when connected to a hot DC circuit will read zero volts when set to AC scale. And a True RMS reading DMM will read the DC voltage. Similar issues with AC line power and a meter set to read DC voltage.

    When you mix AC and DC systems together and have connections (intentional and otherwise)--The results can be quite difficult to understand at first inspection.

    If somebody has a problem, create a thread to discuss that there.

    Techntrek has a real problem that he was able to easily diagnose with a NCVD (bent earth ground pin connected back to the AC mains(?)). Enough energy to cause (at least) a light shock--And if there was another issue (shorted AC Hot to RV ground), the results could have been much worse when wet kids came into the RV--Don't want to see that happen to anyone's family...

    Issues with possible electrocution and shock--Is just one of the many problems that can occur... Hydrogen gas, sulfuric acid, short circuits, large currents in the DC side, higher voltages in the AC side--We have many things that we have to be careful about with these power system.

    Need to always be vigilant.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

    Now that this (unresolved) thread has been promoted to sticky, could it at least tell us what is best practice for RV grounding?
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • BB.BB. Super Moderators Posts: 26,872 admin
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

    Not really for this thread.

    RV grounding is a complex subject ranging from a simple battery+inverter to do wet+dry camping and backup generator (low or high wattage).

    I would start a new thread addressing a specific need.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Alaska ManAlaska Man Solar Expert Posts: 252
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    BB. wrote: »
    I would rather we not continue down the road of "what ifs" and "it could happen"...

    There are an unlimited ways that something as complex as an off grid power system can fail and the symptoms it could have with each different failure.

    It is probably not worth trying to examine each of these possible failures in detail. Just understand that things happen. A good set of tools with a bit of debugging, and usually the fault(s) can be isolated and fixed.

    AC and DC are similar in many ways. However our tools (the NCVD, and even a "simple" DMM) can react in ways that are not always easy to understand--For example, many less expensive DMMs when connected to a hot DC circuit will read zero volts when set to AC scale. And a True RMS reading DMM will read the DC voltage. Similar issues with AC line power and a meter set to read DC voltage.

    When you mix AC and DC systems together and have connections (intentional and otherwise)--The results can be quite difficult to understand at first inspection.

    If somebody has a problem, create a thread to discuss that there.

    Techntrek has a real problem that he was able to easily diagnose with a NCVD (bent earth ground pin connected back to the AC mains(?)). Enough energy to cause (at least) a light shock--And if there was another issue (shorted AC Hot to RV ground), the results could have been much worse when wet kids came into the RV--Don't want to see that happen to anyone's family...

    Issues with possible electrocution and shock--Is just one of the many problems that can occur... Hydrogen gas, sulfuric acid, short circuits, large currents in the DC side, higher voltages in the AC side--We have many things that we have to be careful about with these power system.

    Need to always be vigilant.

    -Bill

    Amen, we lost a boy of 14 years old by electrocution last winter. He lived in a trailer house with his mother, his grandfather rigged a 220V outlet that somehow (I still can't see how) fired up the water pipe behind the clothes dryer. The kid reached behind the dryer for a sock, came in contact with the pipe, it stopped his heart instantly. His mother found him like that. Tragic!!

    There are very good reasons for Building Codes and Certifications. Too many people don't realize just how dangerous this stuff is.
  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

    Sorry to hear that. This is the very reason I created this thread. $30-$40 for a NCVT + plug-in tester is a small price to pay to save a life. We did a 7000 mile trip last month and the 2nd campground we stopped in I found a dozen power poles with no ground... because I tested the one on my site.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • inetdoginetdog Solar Expert Posts: 3,121 ✭✭✭✭
    Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system
    Alaska Man wrote: »
    his grandfather rigged a 220V outlet that somehow (I still can't see how) fired up the water pipe behind the clothes dryer.
    Most likely the dryer/cord/outlet was miswired to put 120V on the case of the dryer and the water pipe just provided the good ground/neutral connection to complete the circuit.
    If the water pipe was really at 120V relative to ground, that would imply a problem with the wiring going into the trailer house in the first place.
    SMA SB 3000, old BP panels.
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