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faulty cable between switchboard and power point, how to fix??

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  1. #1
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    Default faulty cable between switchboard and power point, how to fix??

    3 story block building, middle unit, power point on perimeter wall, dedicated aircon power point, stopped working the other day. breakers are all on, but no power at the power point.
    electrician called, came, looked, said faulty cable between switchboard and power point. he gets a reading of 35v at the power point instead of 240v.
    now how the F do you replace that??
    2000 built building.
    will it have conduit going right up to the top of the building into the roof then across into the top wall and into the switchboard?? or do they run the cable in the slab floors making it impossible??

  2. #2
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    Frankly if the electrician who was actually there looking at the problem can't tell you, it's a a vain hope that some internet la la land interlopers can.
    Before you speak, ask yourself: Is it necessary, it is true, does it improve on the silence? - Baba

  3. #3
    Community Moderator phild01's Avatar
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    Did he check the connectors or just measure voltage.

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    Cable failure is pretty unusual without other issues eg cb tripping, rcd tripping, is that the $800 electrician who told you that?

    I would suspect termination at the GPO, high resistance at CB or heaven forbid inaccessible Jboxes.

  5. #5
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    Quote Originally Posted by John2b View Post
    Frankly if the electrician who was actually there looking at the problem can't tell you, it's a a vain hope that some internet la la land interlopers can.
    he sort of did, but wasnt sure if was possible or not until he investigated and tried. just asking.
    Quote Originally Posted by phild01 View Post
    Did he check the connectors or just measure voltage.
    he pulled power point and check connections, he pulled switchboard off and checked connections and them measured voltage and came to that conclusion, asked if i wanted to continue further into the roof etc.. and more tests, denied, had to goto unit owner to get his permission. he suspected cable fault somewhere.
    Quote Originally Posted by Bros View Post
    Cable failure is pretty unusual without other issues eg cb tripping, rcd tripping, is that the $800 electrician who told you that?

    I would suspect termination at the GPO, high resistance at CB or heaven forbid inaccessible Jboxes.
    no other one, my usual one, the one i dont annoy with useless quotes and dont want to loose because someone wants continual quotes to piss people off.

  6. #6
    Community Moderator phild01's Avatar
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    Don't have rats do you!

  7. #7
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    Reading 35V at what load? If it's the 10M ohm input of a multimeter that would indicate a broken connection where the conductors are almost touching and you're just getting capacitive coupling. If you're getting 35V under amps of load, that means your dropping 200V somewhere, and I suspect the problem would be where you notice the walls on fire.

  8. #8
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    Quote Originally Posted by wozzzzza View Post
    3 story block building, middle unit, power point on perimeter wall, dedicated aircon power point, stopped working the other day. breakers are all on, but no power at the power point.
    electrician called, came, looked, said faulty cable between switchboard and power point. he gets a reading of 35v at the power point instead of 240v.
    now how the F do you replace that??
    2000 built building.
    will it have conduit going right up to the top of the building into the roof then across into the top wall and into the switchboard?? or do they run the cable in the slab floors making it impossible??
    You stated "he gets a reading of 35v at the power point instead of 240v."
    Now, between which "conductors" and with what equipment did he get any such "reading".

    He should have measured the Voltage between the
    Line and Neutral conductors (240 V)
    Line and Earth conductors (240 V)
    Neutral and Earth conductors (Zero V - or near to that.)

    He should have done this with a "Low Impedance" meter - NOT with a "High Impedance" digital Volt-Meter.

    (Digital Volt-Meters are good for measuring High-Impedance voltages in sensitive electronic circuits - so as not to disturb the operation of such circuits!
    However, they are sensitive to "stray" (induced) Voltages in "high current" electrical supply circuits - such as socket-outlets - and should never be used on them to get a realistic "reading" - without a suitable low-impedance "shunt".
    The 35 V "read" (on a digital meter) is that which is often termed a "phantom voltage".

    Apart from using a "low impedance" analog meter, if all that one has is a digital meter it is necessary to place a load across Line and Neutral while taking the reading.
    This can be done by connecting a "load" (such as a table lamp) using an extension lead with a "piggy back" plug or a "power board" and measuring the voltages concerned at the plug or an unused "power board" socket-outlet with the load switched ON.)

    I strongly suspect that there is an open-circuit in either the Line or the Neutral conductor - at either the socket-outlet or the switchboard - with the socket-outlet being the most likely.

    (Never forget that the Neutral conductor is necessary to complete the circuit and is just as prone to problems as is the Line (Active) conductor.)

  9. #9
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    That is one of those horrible jobs where the choices are either (plan A) disconnect and run an alternative circuit or (plan B) keep throwing time and money at finding the fault. Both cost $$$ so you need the cost of plan A then decide how much of this to spend on plan B before abandoning and going back to plan A. I don't think that anyone would give you a firm quote for plan B so the "three quoters" will just have to live with it.

    Wierd things happen, so find out if any work (not only electrical) was done prior to the fault appearing. As an example I was "emergency" called to an upstairs light not working all the time. New tenants... hmmm. No power at the switch, cables from the light fitting don't look like the cables at the switch, is it two way switched from anywhere? Don't know!

    The final answer was a two way switch with some dodgy rewiring such that the downstairs switch had to be ON before power was supplied to the upstairs switch. Who did it? Why?... no-one knows (perhaps the owner or a previous tenant) but the new tenants had at various times turned the downstairs switch on or off and didn't know what it was for and didn't make the mental link to the upstairs light not working. Nothing to do with your problem, but a good example of NEVER ASSUME that things are done properly or normal.

    Just saw FrodoOne's post which happened while I was writing mine. Yep, that is exactly what "plan B" should be.
    Last edited by chalkyt; 22nd Jun 2022 at 06:51 PM. Reason: To endorse FrodoOne's response

  10. #10
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    rats i need to get in the roof and check, not sure.
    not sure what meter electrician used as i want not there at the time.
    yes i understand this cant be quoted as its a how long is a piece of string thing
    no wiring or building or renovations done to the place, only thing that was done was the box aircon it runs was replaced 6 months ago, slid old one out and in with new, no interference at all with wiring.
    he checked wiring behind socket and all ok but no power there

  11. #11
    4K Club Member Marc's Avatar
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    If the sparky checked switchboard and powerpoint connections, then there is most likely a junction box somewhere with a "finger twisted" cable connection. All other scenarios are also possible including rats. You need another sparky willing to do the job. Visit your local real estate property manager and ask for their electrician. They are used to deal with pesky property owners. How far is the switchboard from the pp? Is it on the same floor?
    https://www.amazon.com.au/Global-Warming-Climate-Change-Hoax-ebook/dp/B00JPU8332

  12. #12
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    Quote Originally Posted by Marc View Post
    How far is the switchboard from the pp? Is it on the same floor?
    unit on middle floor, board about 8m away from it on same floor in same unit. but how far the cable runs is the other question.

  13. #13
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    Unlikely to be rats without any other clues. Rats will gnaw the cable and will cause a CB trip or RCD trip.

  14. #14
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    Agreed about rats unlikely, but you never know.
    I remember rewiring a restaurant (full brick and all conduits) that had the main switchboard in the next door apartment building. The switchboard was on a large marble plate, some 30mm thick and about one square meter, hanging from two horizontal steel bars concreted in the wall and poked into two large holes in the marble. To access the back you needed to slide the contraption forward on the bars, far enough to reach behind to do your connection.
    The request to rewire the joint came because they had a recurring fault no one could fix, so they thought rewire everything and be done with. As I slid the marble away from the wall, I found two massive rats, mummified on the exposed connections. Yum ... what's on the menu today?

    If the board is so close and in the same unit, the job should be a breeze. Get someone else to do it.
    https://www.amazon.com.au/Global-Warming-Climate-Change-Hoax-ebook/dp/B00JPU8332

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