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Voltage Drop at outlets on a Custom Residential Home

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    #61
    Originally posted by LarryFine View Post
    It's not a matter of polarity, it's a matter of reducing shock risk. For example, by making sure the neutral is the conductor supplying the screw shell of a lamp or fixture socket, the risk of shock while changing a bulb is greatly reduced.

    A partially-unscrewed bulb's screw-shell is exposed while it's still in contact with the socket's screw-shell. The ribbed conductor of the lamp cord is connected to the screw-shell, so it will be connected to the neutral via the wide plug blade.
    It's hard for me to imagine working on equipment these days without my trusty no-contact voltage sensor. Yes, I do test on known live circuits quite often.
    The 95% of people that you can't trust give the other 5% a bad name.

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      #62
      Originally posted by LarryFine View Post
      It's not a matter of polarity, it's a matter of reducing shock risk. For example, by making sure the neutral is the conductor supplying the screw shell of a lamp or fixture socket, the risk of shock while changing a bulb is greatly reduced.

      A partially-unscrewed bulb's screw-shell is exposed while it's still in contact with the socket's screw-shell. The ribbed conductor of the lamp cord is connected to the screw-shell, so it will be connected to the neutral via the wide plug blade.
      Originally posted by growler View Post
      Yes, I remember those days well. A lot of the engineers that worked for the company would make the same argument, "no real polarity".

      Even though I did a lot of electrical work in those days I wasn't working as an electrician. I would have been considered more of an electronics technician. We did a lot of bench work and sometimes with the equipment hot (for testing ) and sometimes with equipment cold (change out parts). Many of the techs would just turn off the switch on the equipment and think that it was safe.

      Think about it for a second. If your switch only breaks the neutral ( which is really just a return path for an AC circuit) what do you still have that's live in the equipment ? Answer is everything.

      After burning up an expensive circuit board one day my boss decided that I was right and the switch really should break the hot conductor to prevent accidents.


      It's really best to unplug equipment or turn of a breaker to make sure the power is fully disconnected. But remember that 40 years ago people didn't even wear their seat belts and some even thought a helmet for riding was sissy.
      Great answers, thanks.

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        #63
        Meter Specifications

        Looking at the specifications for the meter, the accuracy of the VD measurement is +/- 2.5% +0.2%. Pretty poor accuracy for something that you are trying to measure that has a max acceptable value of 5%.

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          #64
          Luckily most of you folks are not in the peoples republic of Californika.
          In Califonika in commercial jobs we have to account and size for Voltage drop on our plans , projects.

          It's part of the energy code.

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            #65
            Originally posted by Sierrasparky View Post
            in commercial jobs we have to account and size for Voltage drop on our plans , projects.

            It's part of the energy code.

            Actually that does make sense. If you are going to worry about voltage drop the best time to think about it is when you are designing the circuits. Latter on it gets to be a moot point unless you want to spend lots of money to redo everything.
            The 95% of people that you can't trust give the other 5% a bad name.

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              #66
              Originally posted by growler View Post

              I doubt that the homeowner actually intended to bust the EC. I still remember when I got my first plug in tester to check for polarity. I found several receptacles at work that had reversed polarity so my boss who was an electrical engineer borrowed it and tested his receptacles at home and found several that had reversed polarity. Both at work and at his home we corrected these receptacles with reversed polarity. They would work without it but were not as safe.

              Who knows, if the homeowner found a voltage drop of over 14% he may have found a real problem. A problem that could be a hazard and start a fire.
              Oh, I absolutely do think he was looking for defects. But maybe he has a point. Who here goes through a new house and checks for things like reverse polarity and VD before turning it over to the owner? Never thought of it but maybe it's a good idea.

              -Hal

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                #67
                Originally posted by growler View Post

                I doubt that the homeowner actually intended to bust the EC.
                Originally posted by hbiss View Post
                Oh, I absolutely do think he was looking for defects. But maybe he has a point. Who here goes through a new house and checks for things like reverse polarity and VD before turning it over to the owner? Never thought of it but maybe it's a good idea.

                -Hal
                I to am sure he was looking for defects. I still doubt that he was intensionally going out of his way to bust the EC.

                Home buyers often try to find as many defects in workmanship as they can during the first year when the property is still under warranty. If they can find these defects and get them repaired it saves money out of their own pocket.

                There are plenty of things that can be found on new construction. I have found receptacles that were never fed and have no power, missing grounds, reversed polarity, loose receptacles, receptacles sticking out from the wall (also poorly installed switches), GFCI receptacles that won't trip ( some had line and load reversed), meters hanging loose with only sheet rock screws, the list can go on and on.

                Some of the time these gig list look like the dead sea scrolls.

                I don't wire to many new houses (none now ) but I always tried to check out as many thing as possible just to make sure things passed inspection and to keep the owners happy and to avoid call backs. Other contractors don't mind the occasional call back.
                The 95% of people that you can't trust give the other 5% a bad name.

                Comment


                  #68
                  Originally posted by tom-g View Post
                  Looking at the specifications for the meter, the accuracy of the VD measurement is +/- 2.5% +0.2%. Pretty poor accuracy for something that you are trying to measure that has a max acceptable value of 5%.
                  I think it may not be as bad as it first looks, but it sure can be confusing.
                  The spec on the accuracy of measured "Voltage drop (%)" is stated as ± (2.5% + 0.2%). If you compare this with all of the other measurements in the table, you can see that the first number is a percent of the measured quantity, and the second number is an added fixed error which has the same units as the quantity being measured. For example "Line Voltage" is ± (1.0% + 0.2V), so the max error is 1.0% of the reading plus 0.2V (either too high or too low).
                  Therefore
                  the error for voltage drop(%) is a percentage of the measured value, which in this case is a percent itself!
                  So for example, if 5.0% drop was measured then the maximum error would be +/-(0.025 x 5.0% + 0.2%) which is +/- 0.325%

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                    #69
                    Just moved into another house this week. Last night the wife is in the dressing room and has the makeup mirror running, she turns on the blow dryer lights get very dim, blow dryer doesn't sound happy. I pull out the old Fluke 87, no hair dryer 118 volts, with hair dryer running 102 volts. Turns out this receptacle is the one farthest from the panel in the entire house. Guess who will be running a new circuit.
                    Rob

                    Moderator

                    All responses based on the 2017 NEC unless otherwise noted

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                      #70
                      190516-2352 EDT

                      Some measurements from my home.

                      Source is 50 kVA pole transformer, some wimpy wire from that pole to another pole where our original transformer was, about 90 ft. From original pole into my main panel about 50 ro 60 ft of 0000 copper.

                      My simple test is a Fluke 27, and a 1500 W space heater. About 10 A load when warmed up.

                      Main panel is 200 A fuses followed by a QO20 to a local receptacle.

                      Meter is plugged into 1/2 of the receptacle, heater into the other half. This way the meter reads the voltage to the receptacle.

                      At main panel delta V is 1.3 V for delta 10 A. Note at 200 A this would be about 26 V. A 200 A breaker or fuse would be lower.

                      My work bench is fed from a #8 copper cable, about 50 ft, then moderate length, possibly 20 ft of #12, then two breakers and a little more wire. Drop was 4.6 V and this includes the main panel drop of 1.3 V. Thus, about 3.3 V interior drop. This is about 5.5% at 20 A.

                      To a wall outlet via main panel breaker to a sub-panel, a QO20 in sub-panel, about 40 ft of #12 after sub-panel produced a drop of 3.8 V at 10 A. Or 2.5 V at 10 A interior and calculated at 20 A a value of 4.2 %.

                      The bench would be better than the wall if the breakers were not on the bench and excess #12 on the floor.

                      .

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                        #71
                        Originally posted by hbiss View Post
                        Oh, I absolutely do think he was looking for defects. But maybe he has a point. Who here goes through a new house and checks for things like reverse polarity and VD before turning it over to the owner? Never thought of it but maybe it's a good idea.

                        -Hal
                        VD no, but polarity test, yes. If I don't catch it inspector likely will on final inspection. They typically test every receptacle with one of those plug in polarity/GFCI testers, and will press GFCI test button at any receptacle that requires GFCI protection to see if it is protected.
                        I live for today, I'm just a day behind.

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