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Regulation 643.3.3 (ii) clarification

DR Darren Hughes

I want to ask if someone can help clarify the requirements on the regulation 643.3.3, notably the second para  (or ii in GN3)

Whilst it is understood that an initial insulation resistance test should be carried out with all Sensitive loads disconnected, once they are reconnected the regulation reads "Following connection of the equipment, a test at 250 V DC shall be applied between live conductors and the protective conductor connected to the earthing arrangement."

Does this mean we are conducting two separate tests, i.e. line to CPC and Neutral to CPC? Or a single test where we link line and neutral, then test that to CPC (i.e. like previous guidance). I suspect it is the letter, but would be grateful for your thoughts.

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  • 0

    There may be a slight typo, but I assume that the reference is to 643.3.1. 

    There are two tests.

    First, between the live conductors, so L-N in SP and L1-L2, L2-L3, L3-L1, L1-N, L2-N, and L3-N in TP. Once it has been established that those values are satisfactory, you do the second test.

    Second, between live conductors together and PE. PE is connected, but fairly obviously, the live conductors are not. This is a shortcut because if the IR is low, you would then have to test each live conductor individually to see where the problem lies.

    I remember: SP 3 tests: L-N, L-E, N-E; TP 10 tests: L1-L2, L2-L3, L3-L1, L1-N, L2-N, L3-N, L1-E, L2-E, L3-E, N-E.

    HTH.

  • 0 in reply to Chris Pearson

    Thanks Chris, the main thing I'm getting bogged down in is the 250v vs 500v issue for the second set of tests, and whether, in a situation where you have SELV components in a predominantly 230V circuit, and sensitive equipment cannot be removed, is it OK to conduct the test at 230V with L-N connected together? Or in other words, how likely is the probability that modern circuits could contain ultra-sensitive SELV modules  or circuitry that could be damaged by 500V? In which case, is 230V just being over cautious. 

  • +1 in reply to DR Darren Hughes

    Something a bit odd here because when I posted 20 min ago your posting of 30 min ago was not visible.

    I see exactly what you mean. Clearly for an EIC, nothing will be plugged in, but for an EICR, you may have missed something. So IR is low and you have to find it, remove it and test again. Testing at 500 V could fry the appliance, which is why the test voltage has been lowered.

    The problem with a BS 1363 socket with added USB ports is that there is nothing which you can unplug, so the default voltage has been reduced.

    In my simple mind, if a device is powered by 230 V AC, 250 V DC should not harm it. Should not as opposed to cannot!

  • 0 in reply to Chris Pearson

    In my simple mind, if a device is powered by 230 V AC, 250 V DC should not harm it.

    generally, but things that rely on inductors to limit the current will only be happy if as part of that test you reverse the 250V dc before the current has built up to a significant value and continue to do so, perhaps at 50 or so times per second ;-) 

    In practice if you cannot with confidence, remove all loads from between L and N, or L1 and L2/3 then there is no point in trying a DC test between those conductors, as the test will fail as the resistance presented by the load will be a lot less than the expected insulation, and there is a good chance some equipment will not appreciate it and may not work afterwards.

    In such a case, the only sensible test is L+N on one side of the meter, and E + bonding and electrodes  on the other. (this then also finds faults from L to the heating pipes or whatever, as well as to the CPC of the circuit with the L in it.)

    That way  no current flows  in L-N connected loads and as both L and N should be isolated from E, it is a sensible test. Even so tests at 250V where surge limiters are involved, which is not only the ones we can see in the consumer unit, but also those in the connected equipment, as you will probably trigger them with 500V.

    In an EICR there is no risk of missing an L-N short, as you are testing a circuit that was until recently energized, and the ADS would have 'indicated' such an issue had it been present, by operating.

    In a new and as yet un-energised circuit it does make more sense to test L-N and L_L as well this avoids the embarrassment of the main fuse failing on first power up, but at that point there should be no connected loads as it is under your control.  Which may mean usb sockets must not yet be fitted.

    Mike.

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  • 0 in reply to Chris Pearson

    In my simple mind, if a device is powered by 230 V AC, 250 V DC should not harm it.

    generally, but things that rely on inductors to limit the current will only be happy if as part of that test you reverse the 250V dc before the current has built up to a significant value and continue to do so, perhaps at 50 or so times per second ;-) 

    In practice if you cannot with confidence, remove all loads from between L and N, or L1 and L2/3 then there is no point in trying a DC test between those conductors, as the test will fail as the resistance presented by the load will be a lot less than the expected insulation, and there is a good chance some equipment will not appreciate it and may not work afterwards.

    In such a case, the only sensible test is L+N on one side of the meter, and E + bonding and electrodes  on the other. (this then also finds faults from L to the heating pipes or whatever, as well as to the CPC of the circuit with the L in it.)

    That way  no current flows  in L-N connected loads and as both L and N should be isolated from E, it is a sensible test. Even so tests at 250V where surge limiters are involved, which is not only the ones we can see in the consumer unit, but also those in the connected equipment, as you will probably trigger them with 500V.

    In an EICR there is no risk of missing an L-N short, as you are testing a circuit that was until recently energized, and the ADS would have 'indicated' such an issue had it been present, by operating.

    In a new and as yet un-energised circuit it does make more sense to test L-N and L_L as well this avoids the embarrassment of the main fuse failing on first power up, but at that point there should be no connected loads as it is under your control.  Which may mean usb sockets must not yet be fitted.

    Mike.

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