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Thread: Excessive voltage loss under load results

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    Site Caretaker Dave A's Avatar
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    Excessive voltage loss under load results

    We're finding quite a few properties with excessive voltage loss under load problems.

    Here's an example:
    Voltage no load: 231.2 V
    Voltage test load (16A): 223.8 V

    And that's tested at the meter.

    For the record:
    Neutral voltage: 0.86 v
    Loop test: 0.5 ohms
    PSC: 0.5 kA
    Main supply limited to 60 A

    Anyone else having problems like this?
    The trouble with opportunity is it normally comes dressed up as work.

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    Bronze Member ACEsterhuizen's Avatar
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    Hi Dave i might be wrong but if Vdrop (V) = Iwire (A) Rwire (Ω) = Iwire (A) (2 L(m) Rwire (Ω/km) / 1000)) and since all remains constant and you can proof it eg the 16A, the length of the wire, the only variable would be the resistance of the wire. If the resistance of the wire increases your voltdrop will increase. I have come across total breakdown of conductivity of copper and Al wire.

    ps have you tried different brand meters?

    (8.7.5 Earth fault loop impedance at the main switch
    8.7.5.1 At the main switch, the impedance shall be such that an earth
    fault current double the rated current (or higher) of the main protective
    device automatically disconnects the supply to the installation.)

    Your voltdrop under load is <5% (3%) and your loop test is more than double the rated current for the main protective device.
    Last edited by ACEsterhuizen; 17-Dec-14 at 01:23 PM. Reason: mistake

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    Diamond Member AndyD's Avatar
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    It could be a poor termination somewhere in the supply cabinet on the street. There could be a bottleneck, it wouldn't be the first time the council use a piece of 6mm wire as a jumper somewhere on a 60A supply. Might be that the council/Eskom HV transformer is a long run from the property. Either way if your tests were done at the meter I'd give the results to the homeowner and get them to log a fault of low voltage with the council/Eskom.
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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by ACEsterhuizen View Post
    Your voltdrop under load is <5% (3%)
    For the test load (16A), true. But with the maximum load (60A) the volt loss would be 27.75 V, or 12% in the above case

    Quote Originally Posted by ACEsterhuizen View Post
    ps have you tried different brand meters?
    I'm seriously considering going down that route. We have two testers which we test against each other from time to time, but unfortunately both the same model. Most of the time the readings we are getting are well within spec though, so I'm not sure it's the meter.

    I probably should point out that we test at the main switch first. It's only when we pick up problems that we then test at the meter to identify whether it's the municipal supply or the consumer's main feeder cable. So by the time we start getting concerned about the quality of the municipal supply, we're already up to two tests.

    What's really starting to concern me is we're finding it more and more often of late.
    The trouble with opportunity is it normally comes dressed up as work.

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