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  • Meralco's 3-wire service entrace

    Actually this is the continuation of a comment to an article here. My original comment was:

    This is good news if what Meralco provides is a true ground circuit for the user. The 3rd wire could just be a lighting arrestor to protect Meralco's own investment with no real connection to the transformer's neutral. I'll open a topic in the forum ... this is too long.

    Let me continue:

    I'm an electrical engineer though I slept through a lot of my power subjects so I'm looking for answers also. My understanding is that to have a ground wire there actually have to be 4-wires from the secondary of the transformer on the post. Why there are 4 is a long story (3 phase/single phase) but suffice it to say that 3 will need to go to your house, two of which are the normal ones and the third is the ground wire. If someone wants the explanation, ask and I do my best, no as-is-where-is though.

    It is hard to believe that Meralco is providing a true ground wire because not only is the 4th wire an additional expense but also the transformers used would have to be the more expensive Y-transformers. The normal transformer used is the less expensive delta-transformer. While you can get a "ground" with delta transformers, it is not a true ground with an actual physical point ("node" for the geeks) but rather is a "floating" ground. A floating ground is normally established by driving a long copper rod into the earth, you can sometimes see these beside electrical posts with a big wire from it running up the post. While "floating" grounds are ok for lightning protection, I have my doubts about earth leakage current (the stuff that shocks us when an appliance is "grounded").

    So I am wondering if this really a true ground.

  • #2
    Re: Meralco's 3-wire service entrace

    Hi lncc and welcome to the forum.

    I am not an electrical engineer but for two phase service, which is what Meralco and Beneco residential customers have, you don't need 4 wire service.

    To have three phase service, you need to have more than 1 transformer on the pole. Is that two tranformers for a wye connection and three for a delta?

    When I lived in Paranaque, I wired my house to have 110 and 220 service. I do not recall now whether there was a third wire out of the distribution transformer but I certainly got 110 service. I remember that a neighbor, who also had 110 service once had a fault with his service entrance connection. It seemed that he had a frostfree 110 refrigerator. The ref was drawing high current and eventually corroded the twisted wire connection between Meralco's aluminum service wire and the homeowner's copper entrance wire, but only on the side that connected to the ref.

    I think that Meralco now uses better connectors between the al and cu wires.

    Can you get 110 volts if the ground is floating? You will probably not get 110 volts but rather 220. Lastly, any wired ground is far better than your body connecting the 220 volt line to the floor of your house.

    Comment


    • #3
      Re: Meralco's 3-wire service entrace

      Hi Hot Daddiy. Thank you for the welcome.

      Actually, to have 110/220 only 3 wires will enter the house, not 4. The 4th would exist at the last 3 phase transformer, assuming it is Y connected, and is the neutral.

      If I remember right this is still all at a high voltage and still needs to be stepped down which is what those transformers on the posts near our homes do. Notice however that these transformers near our house only have two wires coming to them. These two wires are two of the three at the high voltage 3 phase transformer, the neutral is not distributed. Rather I believe standard practice is to connect the neutral to an earth ground. The soil is used to "distribute" it.

      A house that has 110v service will have a third wire that is taken from the center tap of the transformer near the house. This wire is THEORETICALLY at the same potential as the neutral. You can see this if you draw the circuit and take note of the symmetry. So the ground stake technique to get 110v from a 220v only circuit is theoretically sound. In practice however a potential difference exists due to circuit component variances but more so because of the unavoidable load imbalances.

      So yes it is a good thing, Meralco requiring a 3-wire service entrance. Something is better than nothing. I just wonder about the trade-offs made and how unsafe a situation can result.

      Comment


      • #4
        Re: Meralco's 3-wire service entrace

        I got this photo that shows that the transformer used by Meralco has three secondary taps. While not very clear in this photo, the middle tap is connected to the uninsulated wire, the wire that goes to ground at the subscriber's pole.

        It seems to me that what Meralco is doing is saving money. Instead of grounding each and every pole, they are making the homeowner install the ground for them. I say take advantage and bring the ground inside the house for safety purposes. You can even get 110 volts.

        Comment


        • #5
          Re: Meralco's 3-wire service entrace

          so the third uninsulated wire going to the customer's house is supposed to be a ground wire from meralco, I thought it was just some sort of a "hanger" for the two live wires especially if the house is far from the service line

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          • #6
            Re: Meralco's 3-wire service entrace

            It's both a hanger and a ground wire. I've rechecked and have found that the uninsulated wire is actually connected to the neutral tap of the distribution transformer.

            Comment


            • #7
              Re: Meralco's 3-wire service entrace

              Pheewww ! Am not sure I get all this.

              In another thread on GFI (Ground Fault Interrupter) gadgets, I asked about our local wiring system has a neutral wire or not. These GFIs only work with hot and neutral wires plus a (true?) ground.

              So, is that third tap which is both a hanger and ground wire connected to the neutral tap in the transformer connected to the ground ?? So does that make the ground and neutral wires the same ?? Oooooooo, I'm stumped !!

              Comment


              • #8
                Re: Meralco's 3-wire service entrace

                I think the confusion is that in the US with 110 volt wiring, the neutral wire (often colored white) is different from ground (often colored green). In Metro Manila, ground is often interchangeably called as neutral.

                Comment


                • #9
                  Re: Meralco's 3-wire service entrace

                  actually you can use either the neutral or the ground to run a motor or light a bulb but as the code suggests, you must have a clean neutral whereas if you use the ground for neutral, the effect will be on the electronic appliances such the computers.i think that has something to do with the harmonics.ahhh it's to broad to discuss, but that's just my piece on that matter.

                  Comment


                  • #10
                    Re: Meralco's 3-wire service entrace

                    If the hangar wire is connected to the three phase neutral then this is ideal. Now if the loads are nicely balanced among the 3 phases then it should be easy to get 110v. The added benefit is you can connect the hanger to the 3rd prong of your house convenience outlets and have true ground protection. The GFI thing mentioned earlier would also work.

                    I'm going to take a look at our subdivision's wiring.


                    About the green and white wires, I believe they are electrically connected but are both provided so that the currents if any have different paths. This is the same as the "single point ground technique" the audiophiles out there will know.

                    Comment


                    • #11
                      Re: Meralco's 3-wire service entrace

                      Also called a star ground, a technique which I always use in my home built tube amps to prevent ground loop hum.

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