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Safe Disconnection to Undertake Work.

Zoomup
Scene. An old farm building now used as a double glazing frame maker's workshop.


The supply comes from an old shed about 40 metres away, where the meter is. The old shed has some 70s/80s rusty M.E.M. isolators that feed several S.W.A. cables that exist the shed in many directions underground. I suspect that one feeds the main farmhouse, another a rented cottage and the others various farm buildings. There is no clear labelling of the isolators.


What is the best way to locate the frame maker's  building supply where I have to work?


Somewhere I have a circuit i/d set, if I can find it, but that will need access to the live parts and I do not wish to turn off the wrong isolator.


Z.


  • 0
    Well done.


    All the farms around me I have been on are PME even when they are dairy with PME milking parlours. It makes any modifications difficult. Not so many still milking though.
  • 0
    Chris Pearson:
    Zoomup:

    I kept all of my original hair. No shocks or explosions occurred.


    You and BOD are getting very unruly. ?


    What I want to know is whether the motors will go round and round in the correct direction. ?




    The word is 'are getting' emotionally close.....

    I have a solution to Zoom's dilemma, I've been chatting with one of his relative's,  Zoom, and it was suggested that he should use a electronic tracker, as Andy suggested. The one we use has no torrid coil detector so has to be hard wired in series. We once used it to good effect, followed a very interesting cable route and a couple of buried JBs. The tracking instrument is french at a frequency of 25kHz, but works perfectly well on UK electrical circuits. It does help if you can understand French instructions.....

    Legh


  • 0
    Chris Pearson:
    Zoomup:

    I kept all of my original hair. No shocks or explosions occurred.


    You and BOD are getting very unruly. ?


    What I want to know is whether the motors will go round and round in the correct direction. ?




    The new machine is to be delivered nest week. It is a sort of chop saw thingy that mitres the corners of double glazing U.P.V.C. unit edges. I haven't seen it yet. I suppose that if it rotates backwards it adds material rather than removing it.


    Z.


  • 0
    kfh:

    Well done.


    All the farms around me I have been on are PME even when they are dairy with PME milking parlours. It makes any modifications difficult. Not so many still milking though.


    That is interesting kfh, What astounded me though was that the main three phase cut out has two S.P. Henley blocks placed side by side connected to Neutral, by the main fuses. They are linked together with a very short length of 16mm2, or imperial equivalent, cotton covered single cable. These two Henleys are used as earth terminals. How does that date things Watson?


    Z.


  • 0
     

    The word is 'are getting' emotionally close.....




    I bet it's that Doris in accounts. She has a gob on her like the Dartford tunnel.


    Z.


  • 0
     

    I have a solution to Zoom's dilemma, I've been chatting with one of his relative's,  




    Oh ek, is he out already. Doesn't time fly.


    Z.


  • 0
    That is interesting kfh, What astounded me though was that the main three phase cut out has two S.P. Henley blocks placed side by side connected to Neutral, by the main fuses. They are linked together with a very short length of 16mm2, or imperial equivalent, cotton covered single cable. These two Henleys are used as earth terminals. How does that date things Watson?

    I've seen setups like that in rural areas (or more likely both N and PE into one Henley block) - often PNB rather than PME though.

       - Andy.
  • 0
    AJJewsbury:
    That is interesting kfh, What astounded me though was that the main three phase cut out has two S.P. Henley blocks placed side by side connected to Neutral, by the main fuses. They are linked together with a very short length of 16mm2, or imperial equivalent, cotton covered single cable. These two Henleys are used as earth terminals. How does that date things Watson?

    I've seen setups like that in rural areas (or more likely both N and PE into one Henley block) - often PNB rather than PME though.

       - Andy.


    There is a single black cable running from the Henleys down 

    into the ground, possibly about 16mm2.  The supply is from  newish A.B.C. overheads.



    Edit. Add. So Andy, are you saying that the earthing of the Neutral is at the installation head position only and not at the supply transformer star point? Is that P.N.B?


    2nd Edit. Add https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=47661&STARTPAGE=4&FTVAR_FORUMVIEWTM


    The PNB discussion is very long and convoluted.


    Z.


  • 0
    Edit. Add. So Andy, are you saying that the earthing of the Neutral is at the installation head position only and not at the supply transformer star point? Is that P.N.B?

    Yup - that's traditional PNB anyway (with one consumer per transformer). Think TN-S but the electrode and N-PE link are at the intake position rather than out on the pole. The overhead lines are little more than extensions of the transformer windings. It's convenient not only for keeping the consumer's N-PE voltage low, but also keeping the LV earth electrode well away from the HV one at the transformer. But unlike PME there's little danger from a broken supply N - as the consumer's end remains at 0V.


    I think you sometimes get a similar arrangement on industrial sites with a private transformer - N-PE link at the first distribution board rather than the transformer.


    I gather from some DNO documentation that sometimes they extend PNB to serve up to 4 customers - I'm not sure of the physical layout then - I suspect they'd earth the N at the first point where the supplies to different customers diverge and then run either a separate N and PE or CNE from there. UKPN might be able to enlighten us.


    Or of course what you're seeing might be conventional PME but with an additional electrode connected at the cut-out instead of out in the street (sometimes that's preferred when it's a long service cable).

       - Andy.
  • 0
    I still don't understand a pair of cottages with an earth adjacent to the transformer and no other. DNO says PME, so that must be what it is.

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