Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 48 replies
  • Subscribers 32 subscribers
  • Views 3928 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

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.


Parents
  • 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.
Reply
  • 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.
Children
No Data

Community Rules & Guidelines