When is an earth not an earth?

Discussion in 'Electricians' Talk' started by dingbat, Dec 13, 2006.

  1. dingbat

    dingbat New Member

    My latest favourite DNO cock-up...

    Went to a property yesterday to find (unusually) a separate, DNO-fitted MET, adjacent to the cut-out. Of course it wasn't connected to the consumer unit earth terminal; it had only been there ten years or so, after all!

    But it was at 245V - just as well it was enclosed.

    I got YEDL out within fifteen minutes (I kid you not!) to discover that it wasn't incorrectly connected in the housing; the live connection to the split-con earth conductor was made outside, in the street...

    ...they're digging the street up today.
     
  2. thripster

    thripster New Member

    Ding,

    Let us know what they discover.......

    I presume the 245V was wrt to the incoming neutral or another known 'earth' reference?
     
  3. dingbat

    dingbat New Member

    So far it's been ascertained that the supply was once shared with next door but separated some years ago. Next door has the remains of a lead-sheathed TN-S system, but the area has been PME for some years. (Leeds has an enormous backlog of work to supply reliable means of earthing.)

    The property in question is now supplied via a split-concentric cable, with phase and neutral in the correct places (no reversed polarity) and the supposed earth conductor connected to an external MET. Somewhere under the ground the earth conductor is connected to the incoming phase (thankfully, not a different phase!!)

    The same voltage is present on the phase and earthing conductors relative to neutral and to the main bonding. Thankfully, the MET wasn't connected to anything inside the property (as usual) because it ain't fused at installation level!
     
  4. Adam_151

    Adam_151 New Member

    Should've kept quiet, TT'ed it, and made use of the unmetered phase...

    Seriously though... that sounds rather bad, could've been nasty if someone had touched it before testing :O , sounds a weird fuckup for them to make :s

    Anyway if the area is TNC-S sounds odd that they have brought split-con to the cut out rather than the plain stuff, though I have heard of it before... what does the supply type go down as OOI? In my mind it would be TN-C-S (but think some DNOs insist this arrangement should be counted as TNS... sounds wrong to me)
     
  5. dingbat

    dingbat New Member

    Well, it's fixed now; I just went back to test it.

    The YEDL fella who came to sort it tested with, yes you've guessed it, a neon screwdriver! (At least the fella yesterday had an approved test lamp.)

    When I got to the trench I saw three new joints. "Had any problems?" I asked.

    "Yeah, mate," he said, amiably, "bloody great flash when the digger went through the cable!"

    The trench is still there... it's contracted out to another firm to fill it in and make good... shame it's fifteen feet long, four feet wide and right across the doorway of the house!

    (It's going down as TN-C-S, Adam, as there's only two conductors until the joint about five feet from the CU.)
     

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