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AMD 2 - insulation testing

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.
  • I can foresee a lot of justified departures coming up with the addition of all of these frivolities.
  • When smart homes are in full swing, I can see that carrying out insulation resistance tests during EICRs or minor works will become practically impossible - at best you'd be checking N-E using an [L+N]=E test, as semiconductor switches or electronically controlled relays won't be "on" when you do the test.


    The idea of the test after install of a section of a wiring system is to check it wasn't "snagged" on pulling in or similar.


    After energization, any issues should be picked up by a protective device (RCD or OCPD - or perhaps AFDD).



    Electrical installations have changed over time, along with the appliances they have served, and the way both the installation and the appliances are used.


    We just need to accept that, whilst basic physics won't change, some of our working practices and designs definitely will.
  • [q]"After energization, any issues should be picked up by a protective device (RCD or OCPD - or perhaps AFDD)."[/q]


    The BANG TEST has returned ?


    Regards


    Geoff Blackwell
  • Perhaps ... in a way ... but what choice do we have once our circuits are littered with control devices? 3-day EICRs ?
  • I am not against the BANG TEST as such, but perhaps the whole issue needs to be revisited in light of the changing nature of electrical installations.


    Regards


    Geoff Blackwell
  • To be be accepted it needs a natty abbreviation , like the old EEBADs and DR ABC for first aid.


    I struggled with that

    Perhaps
    Begin by Activating Network Gingerly

    Or
    Basic Active Noise Generation  when it goes wrong



    Joking aside we have the same problem with the PAT of things that do not fall neatly into a proper category but are not dangerous.

    Also it is unwise to rely on meggar results to tell you a cable is intact - there are plenty of nasty ways to compromise a cable or junction with ham fisted installation, that will still pass the electrical tests.

    regards Mike.

  • Over twenty years ago I was taught that I may need to insulation test as I assembled an installation, even a simple neon indicator in a switch will stop full testing on completion.


    Has that changed much?
  • That is the advice that was / is given, but how well it is followed is another matter.  It's fine on small installations but on installations with many fittings that need to be connected to complete the circuits (e.g lighting fittings, socket outlets with usb outlets etc.) - it is easier said than done.


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


    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," ......


    So it is not meant to be a collection of single circuit or part wired circuit tests.


    Disconnecting current using equipment is problematic if that equipment is actually part of the fixed installation (eg socket outlets with usb outlets).


    I don't have any solutions other than to say that perhaps the great and the good should look at the requirements for testing and the type of testing again.


    Regards


    Geoff Blackwell 

     

  • 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 don’t get a high insulation test result with one connected as they have a reference to earth.


    ?