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Thread: SANS codes.

  1. #41
    Diamond Member AndyD's Avatar
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    Quote Originally Posted by Dave A View Post
    My turn to explain - my point was around what the real hazard is...

    I've got a door handle in my office that hands out a fairly dramatic static jolt from time to time, but hasn't killed anyone yet.
    This is a common problem easiest way to fix this problem is to wear high heel shoes with a pair of rubberised odour-eaters inside them :-)

  2. #42
    Site Caretaker Dave A's Avatar
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    Sounds enticingly kinky, but I'm not sure my dodgy back could take the high heels...

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    I've got a new one...Has anyone come across this before?

    Overhead lines across the road, feeds down the pole and under the street to a house more than 100 years old (assuming). The cable runs up the wall and in under a galvinised roof. A makeshift connection is done at this point and a 10mm earth cable runs back down the cable to a spike about 50cm from the house. Inside the house the db sits surface mounted with one entry hole only. L+N cables comes through this hole and only 3 earth wires. The ceiling is also steel.

    Without having done any faultfinding yet, here's the problem...I'll go back there in the daylight to see whats happening.

    The house constantly gets hit by lightning. The lightning however fires blue flames out of all the socket outlets and the lightswitches, which are all steel. You can see the evidence by looking at the black burned coverplates and walls surrounding the S/O's and switches. Now, not having done a loop impedance and a spike test yet, i'm in 2 minds about this.

    When lightning hits your house it searches for the fastest possible route down to earth, it also hits your house because it is grounded. It hits often because it is grounded, and everything is metal, but, the blackening of all the electrical equipment indicates that the lightning hits the house and rather than running down to earth (with some damage to equipment), it fires out at every end. It would seem that there is no ground on the house, and the lightning actually follows the live conductor, hoping to piggyback to an earth????? But then again, with no ground, why does it get hit so many times????? There are plenty of other houses very close?
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  4. #44
    Site Caretaker Dave A's Avatar
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    Two things come to mind on the regular strikes -

    The roof of the house could be sitting at a different potential to the houses around it due to not being earthed back to the transformer, or

    There's a sharp metal point somewhere on the roof which intensifies the electromagnetic field and could be atrracting the unwanted attention.

    The sparks are probably because the earth is floating too far off the neutral during the strike. The loop impedance test should pick that up. You might get an interesting voltage reading between neutral and earth too.

  5. #45
    Diamond Member AndyD's Avatar
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    I like Dave's theory, sharp edges or acute angles etc might attract lightning.

    I'm not sure if I understand the layout you're working with here. There's an earth spike close to the house, does the earth wire from the spike go directly to the DB earth bar or is it bonded with the neutral where the supply wires enter the house? Is there a meter somewhere on the premises or is it an ED?

    The lack of earth wiring coming from the DB is not uncommon in old installations where the steel conduit was the earth and it was common practice to just bond all the conduits at the DB with straps and a single earth wire. I woul test the earth spike first and post the results if you feel like it. The neutral - earth bond resistance would also be nice to know as well as the neutral - earth voltage when there is a load on the system.

    Is the roof steel sheet construction? If it is then maybe the roof is bonded to earth by physical contact with the steel conduiting. If it is then this might make it more attractive to lightning. If you can 'unearth' the roof so it's just at floating potential and perhaps you can install a separate earth spike far away from the electrical earth and install a lightning conductor.

  6. #46
    Site Caretaker Dave A's Avatar
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    I suspect metal roofs are supposed to be bonded to earth i.t.o. the regulations - and for good reason.

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    I've got some work to do on the premises, but will only go back once the builders do their thing. The entire roof and ceiling is metal. I do not believe the earth is joined with the neutral at all anywhere close to the premises at least, it looks like a TT system (can never tell as you don't know if council used the armouring as earth......which is allowed if the impedance is low enough.....but from a visual perspective....TT). I went to council and they said that if I don;t come right, they'll come join the N+E at the pole.

    The E to N voltage was the first thing I tested in the house, to make sure E is not Live all of a sudden, and touching a SO may be the last thing I touch.

    What I did see, thought it was strange at the time, but pondering over it the last few days: "the main cable runs up the wall and a 10mm earth runs back down to a spike about 50cm from the house".....wrapped around the earth was a small 2.5mm earth wire - bare - all the down and also joined. What I think they did: the council supply runs up the wall, where the armouring is earthed and runs back down. From the DB a 2.5mm wire runs down the earth wire, and is connected to the spike. "Potentially", if this is true, that thin 2.5mm earthing the entire house, and being so damn flimsy, could have broken off by the last guy that walked through the roof?
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    This though...still leaves me with the question, if my hypothesis is correct....why all the strikes on a floating earth???
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  9. #49
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    Sory Andy, you were asking about the meter....it sits about 10 cm from the db on the wall, with a CB with open ends next to it (main), luckily they put is around 2.2m, so a normal person would not accidentally bump the exposed main feeder!!!!!!!!
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