Regulation 643.3.3 (ii) clarification

Question

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.

Sparkingchip · Accepted Answer

Line and neutral are both live conductors, the test should really be carried out at the meter tails with line and neutral joined together to earth with the installation completed and all earthing and bonding in place. 
 In the IET GN3 it says on page 69 &ldquo;An insulation resistance test of line and neutral (L&N) connected together to Earth (E) will ensure all the circuit conductors are tested.&rdquo;. 
 But that is not what is shown in the Figure 2.21 at the bottom of the page. 
 When I started work the Electricity Board meter installer working for the Midlands Electricity Board would do an insulation test at the meter tails before connecting them into the meter to test the entire installation to earth, but these days the meter operative just installs a main switch and it&rsquo;s the electricians responsibility to test and make the final connection, absolving the meter installer and the electricity supplier of any responsibility it there is a big bang when the new installation is energised.

Sparkingchip · Answer

The IET OSG page 120 is much clearer when explaining the three-phase installation insulation resistance test. 
 Quote &ldquo;Test to earth from all live conductors (including neutral) connected together.&rdquo;.

Chris Pearson · Answer

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!

Regulation 643.3.3 (ii) clarification

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