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  1. #1
    Eric Palmer's Avatar
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    Default high voltage drop under load

    My home is long and skinny with the service entrance at one end. I've noticed that when my wife irons at the far end, lights dim more than I'd expect. I have a Kill-A-Watt device that you plug into an outlet and it will display voltage (and power, current, pf as well).

    Under load with just the iron, voltage drops from 120 to 115. As I turn on lights and fans at the end of the house, I can get it down to 105V for a 12.5% drop. I realize most appliances are rated to run at 100V, but this still seems like a big drop.

    Was my house miss wired with too low a gauge wiring? House is 14 yrs old.

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  2. #2
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    Default Re: high voltage drop under load

    Check your outlets for back-stab connections. Each connection along the way can drop voltage by adding a bit of resistance. Resistance equals heat which is not a good thing as far as safety goes. Just changing from back stab to using the screws on the sides of the outlets can yield some pretty impressive results. There are other issues to consider but that would be my first stop.

    Jim Luttrall
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    Default Re: high voltage drop under load

    Quote Originally Posted by Robert Meier View Post
    The NEC has a suggested maximum drop of 5% at the last outlet but this is only a recommendation since in this case voltage drop compensation is a design issue not a code issue.
    "not a code issue"

    Sort of correct and sort of not correct.

    - 110.3 Examination, Identification, Installation, and Use of Equipment.
    - - (B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

    - Equipment. A general term, including material, fittings, devices, appliances, luminaires, apparatus, machinery, and the like used as a part of, or in connection with, an electrical installation.

    - Appliance. Utilization equipment, generally other than industrial, that is normally built in standardized sizes or types and is installed or connected as a unit to perform one or more functions such as clothes washing, air conditioning, food mixing, deep frying, and so forth.

    Most modern equipment will have a voltage range for their operation, and 105 volts is below the range for many appliances. As such, the appliance CANNOT BE INSTALLED AND USED in as required by 110.3(B), and if the appliance CANNOT BE INSTALLED AND USED in accordance with it listing or labeling information, then the appliance and the installation of it does is not in accordance with its listing and labeling, and THAT ... is a code violation.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: high voltage drop under load

    Quote Originally Posted by Eric Palmer View Post
    My home is long and skinny with the service entrance at one end. I've noticed that when my wife irons at the far end, lights dim more than I'd expect. I have a Kill-A-Watt device that you plug into an outlet and it will display voltage (and power, current, pf as well).

    Under load with just the iron, voltage drops from 120 to 115. As I turn on lights and fans at the end of the house, I can get it down to 105V for a 12.5% drop. I realize most appliances are rated to run at 100V, but this still seems like a big drop.

    Was my house miss wired with too low a gauge wiring? House is 14 yrs old.
    .
    Call your Power Company and ask them to check your Electric Meter connections.
    .

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    Default Re: high voltage drop under load

    Quote Originally Posted by Robert Meier View Post
    Not really, it just means that you may not be able to use it plugged into that circuit. That doesn't make it a violation of the NEC.

    If I have a 15 amp circuit with 7 amps of lighting and I want to plug in a 10 amp heater to a receptacle also on that circuit does that make the circuit a violation?
    You dare to question the great and powerful OZ?

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  6. #6
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    Default Re: high voltage drop under load

    Quote Originally Posted by Robert Meier View Post
    Not really, it just means that you may not be able to use it plugged into that circuit. That doesn't make it a violation of the NEC.

    If I have a 15 amp circuit with 7 amps of lighting and I want to plug in a 10 amp heater to a receptacle also on that circuit does that make the circuit a violation?
    Nope - because there is nothing in the code that says you cannot do that. You can turn any of the lights off you want, or all of the lighting load off you want, or leave the lighting on and plug the heater in. The code tells you what the circuit is RATED for, but it does not tell you that you cannot do that - what WILL tell you that you cannot do that is the 15 amp breaker will trip after a while that 17 amp load on it ... not right away, mind you, but it will trip. That 15 amp breaker should not trip with 15 amps on it, it should eventually trip with greater than 15 amps on it ... how long it takes to trip all depends on the inverse time curve of that particular breaker.

    There is a code section regarding what I posted, and that IS then a code violation.

    Two completely different things.

    Are you allowed to have a duplex 15 amp receptacle on a 20 amp circuit?

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  7. #7
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    Default Re: high voltage drop under load

    Quote Originally Posted by Robert Meier View Post
    Yup my point exactly, a design issue not a code issue. I could plug in 2-15 amp loads, it won't work for very long but that doesn't mean that the installer put in a non-compliant circuit. Code says it's compliant, also says that I can have a 200' run of 14/2 on a 15 amp multiple receptacle circuit that doesn't men that the last receptacle on that circuit has to allow a 15 amp load to operate at full load.

    This brings us back to the OP where I said "If there is no physical problem with the circuit, like what Jim has mentioned, then it's possible that the circuit was installed to the code minimum" that doesn't mean that you cannot have voltage drop along the circuit path or are required by the NEC to limit it to specific value.
    Not necessarily correct on all counts.

    It may meet the minimum requirements for minimum safety, however:
    - 90.1 Purpose.
    - - (B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.
    - - - FPN: Hazards often occur because of overloading of wiring systems by methods or usage not in conformity with this Code. This occurs because initial wiring did not provide for increases in the use of electricity. An initial adequate installation and reasonable provisions for system changes provide for future increases in the use of electricity.

    Then we go to 110.3(B) where the installation of appliances IS REQUIRED TO MEET 110.3(B), and that DOES make it a code violation if one cannot meet 110.3(B).

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  8. #8
    Eric Palmer's Avatar
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    Default Re: high voltage drop under load

    I'm new to this forum and in awe of the number and quality of replies. I have an electronics background, so know a little about electricity but zip about construction. My first step will be to begin checking outlets for "stab type" connections.

    Thanks to all who responded!


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