supply earthing and PIR'S

Discussion in 'Electrics UK' started by andy1984, 5 Dec 2006.

  1. andy1984

    andy1984

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    hi, couple of questions i have regarding a PIR our firm had done if anyone would be so kind,

    1, the Inspector has the IR tests all as above 200M ohm, thats about 300 circuits and not one below 200 (in a 30 year old factory).
    also he's only done phase-earth (has others as LIM) tests but i no for a fact he never turned any power off, made up surelly or is there some other way he could have done it?

    2, the building has 2 supply's, one 400A three phase and the other is 400A three phase. the system is TNS, however the 400A supply has no earth around the armour bringing it into the installation, niether is it glanded off correctly. the other supply is earthed through the armour as should be and this is the earth for both supply's. is it aloud to have '1' earth for both supply's???

    also the earths are no bigger than 50mm, a little undersized surelly?

    cheers.
     
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  3. industryspark

    industryspark

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    1, sounds like the guys made them up to me! naughty.

    had a similar thing a couple of years ago at my firm when i was still an apprentice, all IR tests above 250M ohm - was a complete load of sh*te, i know because i tested aome after and some were low..... even below 2M ohm!

    on the visuals also i could have noted hundreds of code 2's but we ended up with a sheet of about 20.

    this thing kinda annoys me with PIR's, when there are so many limitations that its effectivelly worthless or when a guys expected to do 70 circuits per day.

    2, not sure on this to be honest, would think though that each supply should have its own earth. 50mm is undersized yeah
     
  4. ricicle

    ricicle

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    Are the supplies from the DNO or from a privately owned transformer?
     
  5. andy1984

    andy1984

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    thankyou for the comments so far.

    The supplys are from the DNO. Forgot to mention, coming out of the ground with the first supply (unearthed) is a bare cable (about 25mm).


    This connects to a terminal on the outside of the meter but goes nowhere from there. could this be the earth? and it is infact our fault/job to link it all up?

    Still, A bit small for the supply isnt it if this is the case?
     
  6. ricicle

    ricicle

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    Its hard to comment without seeing but any idea what the Ze is of the suspect supply (with no possible parallel paths connected)
    This at least might give you an idea of the integrity of the earth
     
  7. ample

    ample

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    I'm afraid made up results and very poor inspectors are very common these days. We frequently get involved in projects where someone has done a recent PIR and theyre that far from reality its hard to believe they were actually testing the same building?! I personally think you need to have been in the industry a long time, know BS7671 to a high level and have your C&G 2391 to have a chance of doing it right. How many sparks have you seen doing an R1+R2 test at the furthest point only or doing an R1+R2 at "furthest point of a ring main?!". I personally think the NICEIC are largely impotent at keeping tabs on this, I've seen way too much crap work slip through the net from supposedly approved contractors. I recently saw a certificate from an NICEIC approved contractor who actually gave 2 code 1s for the shop having no fire alarm or emergency lighting! They had actually missed the fact, amonst many others, that the installation had a maximum demand after diversity of well over 100A on a 100A fuse, and that the poor old paper lead was dripping down the wall!
     
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