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Insulation Resistance Testing

Chivers
Hi,


I work as a Maintenance Electrician and part of my Testing role is to complete Insulation resistance testing on Supply cables between Metal cabinets on Highways Equipment - Normally Armoured or similar.


I have had 2391 since 2006 and at no point in my Testing Course did i ever come across something a colleague of mine seems to be insisting we all do. That is "Conductor to Ground Testing". I have in the past completed Phase to Neutral, Neutral to Earth and Earth to Phase and recorded these on my test certificates (All supplies are single phase). As far as I know there is nowhere to record such tests on any software or sheets I have seen. Am I missing something fairly obvious or does this seem pointless to others too? 


Regards Chivs
  • 0
    This might only be case of differing terminology.

    The presently performed tests between the phase or neutral conductors and earth might be what is required ?

    For an already installed SWA  cable, it is a reasonable assumption that "earth" means the armouring and that this is already connected to the general mass of earth, hopefully deliberately, but at least fortuitously if the intended connection is missing or defective.

  • 0
    When I say Conductor to Ground, it's testing IR between the Metal Cabinets (with the Earth removed) and one of the Conductors.
  • 0
    If the metal cabinet or column is making contact with earth and you keep the connection in place it would seem to me that a test between live conductors and earth would also test to ground. If not then perhaps nearby fencing or the like.
  • 0
    It is normally advised to do insulation tests (of the L+N to E flavour described by the OP) if possible after  the circuit CPC is connected to an electrode and/ or bonded to plumbing or what have you.

    A test for live cores to CPC  is one thing, but in non-armoured cable, or at the ends of an armoured one where the cores separate off, it is possible, though rare, that a damaged jacket may expose live copper to true ground, or to the fabric of the structure, but not actually to the metal of CPC core or armour  itself.

    I suspect you already knew this, but the form of words may be confusing.
  • 0
    I often test the armour of an SWA to real earth (screwdriver in grass) to test for the integrity of the sheathing. I agree with Lyle and cannot see the point of the test with the cabinet earth disconnected unless there is a low resistance live to earth when you would want to find out if it is the cable or the cabinet.


    Perhaps a sensitively phrased question to determine the purpose?
  • 0
    100% agreed on sensitively phrased.... this thread has brought up a few points i'd not considered, but people, especially in this trade, seem to hate their 'normal routine' being questioned (myself included)

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