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AMD 2 - insulation testing

AJJewsbury
Looks like the DPC has made a bit of a change about insulation testing where some devices might be vulnerable to a 500V test voltage or distort the results. Previously we were allowed to either disconnect the item concerned (or do the test prior to initial connection) OR carry out a 250V test (with a 1MΩ limit to meet).


As I read it, a full 500V test will soon be required prior to connection of such equipment PLUS an additional 250V test (with a 1MΩ limit to meet) will be required after it is connected.


I can see the sense in that, in that it doesn't 'excuse' the rest of the circuit from a full 500V test, but I'm slightly uneasy about some equipment not being happy with a relatively long duration 250V d.c. test L&N - PE - especially if it has to meet a 1MΩ limit. Does anyone have any thoughts on that?


All strictly speaking for an initial verification - for a periodic we still seem to have the flexibility of choosing 'appropriate' tests (however that's going to be interpreted...).


Seems it's going to be a bit of extra work, especially if you've a house full of USB power sockets....


   - Andy.
  • 0
    Note that the insulation resistance test as described in BS 7671 (643.3.2) is meant to be applied to the assembled installation, i.e .... "the main switch board and each distribution circuit tested separately, with all its final circuits connected but with current-using equipment disconnected," ......

    And then confused and bemuddled by model generic schedule of test results asking for insulation resistance results per outgoing circuit.

     
    Perhaps we need to question just what it is we want to achieve.

    +1 for that!


       - Andy.
  • 0
    An Am Dram group I was involved with some years ago used a local theatre which had an optional orchestra pit - which could be opened by removing the (very heavy) downstage floor panels. When we exposed the pit, we found that every single SRCD in the pit was dead. Turned out that during the annual summer shut down, someone had done a 500V IR test but didn't know about all the outlets hidden below the stage.
  • 0
    Chris Pearson:

    I have a couple of SRCDs. The manufacturer's instructions say that the product should be removed from the circuit prior to insulation resistance testing. That's fine if you have only one in a ring, it's on a spur, or is at the end of a radial circuit, but a bit of a problem otherwise.


    You've got to ask whether that's fit for purpose in a BS 7671 installation at the present time ... but perhaps an indicator of the way things will change in future.


  • 0
    wallywombat:

    An Am Dram group I was involved with some years ago used a local theatre which had an optional orchestra pit - which could be opened by removing the (very heavy) downstage floor panels. When we exposed the pit, we found that every single SRCD in the pit was dead. Turned out that during the annual summer shut down, someone had done a 500V IR test but didn't know about all the outlets hidden below the stage.


    Again ... do we think that's fit for purpose for a permanently-connected accessory?


  • 0
    I am surprised that the SRCD didn't survive insulation testing, but apart from that the insulation test result must have been a massive fail and would like to see what the report had to say and the test result recorded.
  • 0
    Around twenty years ago I was repositioning a cooker circuit in an uncompleted barn conversion, the electrical installation had been completed, but I was installing the first ever kitchen in the new home.


    There was a cooker switch with a neon, so I tested each half of the circuit live to neutral with the switch disconnected, then refitted the switch and did live to earth of the whole circuit with it in place. When I turned the power on the switch literally blew up as it had a dead short in it.


    You just cannot win them all!

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