AC output / hot vs. neutral

So, there is this off-grid vacation house in Mexico. One of the batteries was dead (interesting story in and of itself -- it had the cover on backwards and had been installed with reverse polarity for 2+ years) and the house was rented out but had no power. The owner decided to "borrow" grid power for the week it was rented out. The electrician disconnected the AC output cables from the inverter and spliced in cables from the grid. When the renters left, he disconnected the cables running from some other cables that are in a more long-term borrowing arrangement with the nearest transformer, but he did not reconnect the cables to the inverter. I replaced the bad battery and went to reconnect the AC output cables to the inverter, but there are 3 cables: 1 black, 1 red and 1 green that had previously been connected to the inverter. The green cable is not ground, as the grounding is all in place. It appears that the original installer had used 2 hots and a shared neutral. Since color coding of the cables was not followed and the cables all go direct into conduit running under the foundation of the house to the control panel, and since I cannot be certain that the color of the cable entering the conduit on one side is the same color on the other side, is there some way I can figure out which of these cables are the hots and which is the negative?


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: AC output / hot vs. neutral

    Ohm meter/continuity tester and a really long extension on one lead.

    You sure you're not dealing with 240 Volt wiring? That would make sense so - probably not. :roll:
    Don't you just love hack-job wiring? :grr
  • jagecjagec Solar Expert Posts: 157 ✭✭
    Re: AC output / hot vs. neutral
    Ohm meter/continuity tester and a really long extension on one lead.

    You sure you're not dealing with 240 Volt wiring? That would make sense so - probably not. :roll:
    Don't you just love hack-job wiring? :grr

    You already have an of the other wires. Disconnect the cables at BOTH sides, and hook two of them up to a 12V battery. Then stick a voltmeter on the other end to identify positive, negative, and "ground" (disconnected). Now that the wires have been properly identified, you should be able to fix the horrible wiring job. Put a dash of paint on each wire to "fix" the color coding, and maybe even put a note in there for the next guy who has to deal with it.
  • animattanimatt Solar Expert Posts: 295 ✭✭✭
    Re: AC output / hot vs. neutral


    We are building our off grid house somewhat close to cancun. (petempiche specifically)

    Where is the property located. By your name I am guessing Tulum.
    What is your relation to the property?

    Anyway a few points for you that you already probably know. and for anyone else.

    Do not trust color coding unless you have good reason to do so. Especially in areas with very loose to non existent inspection process. More often than not down here I would say it is incorrectly color coded.

    I have seen wiring jobs down here where I take down a ceiling fan and see about 15 blue 14gauge cables and about 5 red. It was a pain to straighten that up.(without clamp meter)

    There literally may have been a sale on blue cable or it "feel off a truck" somewhere. While it is horrible to do that at least color code it with a good helping of electrical tape anywhere it can be accessed.

    Now on our house down here I have been physically on site watching in almost 6 days a week for several months now. It was actually 7 days this week. While it is a pain I like to see all the detail work done the way I want it. It is a bit hard done here as once things are done almost all of it ends up in concrete walls.

    I had to explain to the electrician that ground never carries electricity. The people down here have very little fear of jumping in and trying to do something. They do get alot of hands on learn, which definitely help in things mechanically, but electricity is another story which leads to many very poor wired buildings.

    People down here love to interchange neutral and ground all the time. At least from my experience. I have seen many occasions where ground cable was used as neutral to actually power something.

    I would use colored electrical tape to fix the identification problem. I put several individual strips around the each end of the wire. Also anywhere that it maybe seen mid trip. Paint could do the trick as well, I just like the look of the tape.

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: AC output / hot vs. neutral

    This "borrowing" of electricity from the nearest transformer sounds very interesting indeed. Reminds me of when I was a kid and someone suspended lights over an outdoor skating rink, ran some wires and "borrowed" the power to light them from a nearby power line. All worked well till one of the sockets shorted out, and lit up the night with bright flashes and roars. Some parents found out and put an end to the night skating.
  • TulumtamTulumtam Solar Expert Posts: 37 ✭✭
    Re: AC output / hot vs. neutral

    Thanks Jagec, for a logical solution! Everything is reconnected and taped with the appropriate colors now. No telling what happens in that conduit in between....

    I mainly put in solar for new constructions, so I work with the electrician doing the main electrical installation and if he is not color coding, I follow him around with tape to mark everything. I have opened up some boxes and pulled out single-colored masses of spaghetti. Sometimes there are wires in there not even connected to anything. Borrowing from the nearest transformer is pretty common practice, especially when the pace of development is far faster than the expansion of the grid. Then you get people borrowing from the cables that are borrowing and voltage goes all over the place. Some friends blew out their fridge being down a borrowed line from a corn mill. None of the electricians I have met here have any fear of working in a hot box, either. And there are some solar installers whose systems I refuse to work on.... So far I have only seen one system down here that has any indications that the designer and installer knew what he was doing. There are pluses and minuses to having no inspections....

    Hi Matthew, I am 9 kilometers out of Tulum, towards Coba. I have built two off-grid houses down here, sold one, living happily in the other. As I said, I mainly do new constructions and include, where possible, low voltage LEDs, refrigerators, pumps. My house is my experimentation lab....

    Thanks again to everyone. There is always a solution on this forum!
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