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Possible Power surge damage

  • 24-09-2011 8:49am
    #1
    Carlow52
    Closed Accounts Posts: 2,389 ✭✭✭


    Over here I posted a query re a water pump which stopped working after a power cut cause by a car crash which sheared a wooden pole and cable all crossed over etc etc.

    Now it seems as well as the pump, a fone charger and the sky box are not working either, my friend is checking other stuff in the house.
    Could a 'power surge' from the falling cables have caused this?
    Thanks


Comments

  • #2
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Carlow52 wrote: »
    Over here I posted a query re a water pump which stopped working after a power cut cause by a car crash which sheared a wooden pole and cable all crossed over etc etc.

    Now it seems as well as the pump, a fone charger and the sky box are not working either, my friend is checking other stuff in the house.
    Could a 'power surge' from the falling cables have caused this?
    Thanks

    Is it a house on its own or a few houses supplied by 3 phase overhead lines? Power surges are possible when short circuits occur.

    Another cause of the above is if the neutral broke, but 2 or 3 phases stayed on, assuming there are several houses connected to 3 phases where you are. Then different houses get different proportions of 400v depending on whats on in each house.


  • #3
    Carlow52
    Closed Accounts Posts: 2,389 ✭✭✭Carlow52


    Its a row of houses lon Dublin Road in Malahide., the crash happened across the road from the cricket club in Malahide at 0700 on Thursday 22nd Sept


  • #4
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Possibly a surge caused by lines shorting briefly or more likely the neutral was broken in the crash into the pole. I seen the neutral failing before causing most electronic items in the house i was called to being ruined. When i got there it had 350 volts L-N, caused by neutral failure at the mini-pillar outside. Only happens where more than one house is being supplied with different houses on the different phases.

    If one house has a heavier load on in the broken neutral scenario, such as cooker, and the next house on another phase just has just maybe the tv on, its the one with the tv (smaller load) that will receive the higher voltage ratio of 400v max, and will see the tv or similar loads ruined.


  • #5
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    +1 on what Robbie says above. Electronic equipment would be designed to withstand these voltages for a very short period, but if the fault is sustained there will be issues.

    It's an interesting one, cause the earth electrodes would try keep the neutral down near ground. But would depend on thier impedance ect... Also might not be fitted if houses haven't been re-wired etc....


  • #6
    westom
    Registered Users, Registered Users 2 Posts: 39 ✭westom


    Carlow52 wrote: »
    Could a 'power surge' from the falling cables have caused this?
    A 33.000 volt wire fell on local distribution. As a result, at least one hundred electric meters were blown from their pans. This type surge is electrically similar to a direct lightning strike. Therefore many neighbors suffered damaged appliances, blown power strip protectors, and other damage. At least one had failed circuit breakers.

    My friend knows someone who knows this stuff. He only had one properly earthed 'whole house' protector. Therefore he had no damage except to his meter. Even the protector remained functional.


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  • #7
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    DublinDilbert wrote: »
    It's an interesting one, cause the earth electrodes would try keep the neutral down near ground. But would depend on thier impedance ect... Also might not be fitted if houses haven't been re-wired etc....

    In practice though, earth rods wont keep the broken part of the neutral down at ground potential, unless the load is very small on it, if it did work perfectly, then broken neutrals upstream of the neutralising point of a house would go un-noticed. We know the earth as a conductor has an infinite CSA, but the connection that earth rods make is very finite.

    Even in the example i gave of a house i was called to 2 years ago had the neutral in the house at 350v from the phase, even though the minipillar where the neutral failed would of had a few earth rods connected to it, as well as the earth rods of every house connected to that neutral bar.

    I often seen neutrals fail as well at mini pillars which are just the neutral of the actual concentric cable, so that a single house just loses its neutral, and nothing in the house will work properly, even though in theory there is a neutral path down the earth rod. A single cfl or 2 might work, but anything more than that and the earth rod path is simply too high an impedence path like you suggest. With the neutral break in this example, there is only a single earth rod in the circuit.

    But the main neutral feed to the mini pillar failed in the house(s) i was at, and still the neutral went above earth potential, even though there would of been multiple rods. Its actually a group of houses connected in an unbalanced star but depending on the earth rods as the neutral to carry the imbalance when the main neutral failed in my example.


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