Verifying polarity on radial ccts

[Hudson]

Hi
I've got my 2391 assessment at the end of the week and I've managed to confuse myself (and not for the first time)
I get how performing R1+R2 and R1+Rn on a ring also confirms polarity.
The thing that is confusing me is how does performing only a R1+R2 on a radial socket cct (and operating switches to make sure it breaks) confirm polarity.
I get it confirms you are not switching the neutral but it doesn't confirm that the line and cpc are not swapped over. I can't see what dead test would confirm this isn't the case and you don't want to be energising a cct if the line is connected to the CPC terminal!
Thanks

 

[Lucien Nunes]

I always test R1+Rn during commissioning, not least because it seems daft not to verify each conductor that you have just installed. And as per the above explanation by PC1966, the combination of testing R1+R2 and R1+Rn proves the line conductor is right so therefore the other two must be right.

 

[pc1966]

Exactly. You would not IR test only one of the L/N conductors, so why only check loop resistance of one?

 

[radiohead]

There is no requirement or even suggestion in GN3 or Bs7671 of carrying out a R1+Rn test on radials (as far as I am aware), which is why I don't, and I would suspect I am not alone given the deafening silence from many of the forum stalwarts on this thread. I am confident that a combination of 'required' testing and visual inspection is sufficient when verifying my own work, but taking on board the comments on this thread I will consider carrying out the additional test in future, particularly when verifying radials in which others have been involved in the 2nd fix.

 

[pc1966]

To be honest I never clocked that GN3, etc, did not included that for radials as I just assumed it would be the same idea (check all 3 wires) but without the figure-of-8 loop or the end-end r1/r2/rn checks.

I see the point that if you know the L & E are not swapped from inspection then R1+R2 is your key point for over-current ADS to be measured and compared to the MCB Zs, but having had the odd bad socket in the past always though it wise to check them all.

Without wanting to upset anyone over testing strategies, it might go some way to explaining the common argument that radials are much faster to test than RFC!

 

[Vortigern]

Good points above. For myself, I do not check continuity of L-N. There are two scenarios where such checking may take place a new installation and an existing installation.

A new installation means I connect the various cables to the termination points. I know by visual sighting that the Earth is connected to the earth point at the socket, likewise the Neutral and Live. Therefore I just do R1/R2 on all sockets. On commissioning the circuit loop test confirms polarity and correct connection. The R1/R2 test also shows that I have not connected the N to the L or E terminal. Which I already knew when I wired the socket.

Existing installation; What am I doing there? EICR or fault finding. The first test I usually do by way of investigation as it is easiest is EFLI and L-N loop test. This tells me that All cables are teminated (or not) correctly, it confirms (or not) polarity and shows up any sockets that are defective. Any anomalies are picked up and investigated from there.
Anything wrong with that?

Bottom line; As you may all know there are occasions when you may be fitting up to fifty or more sockets in dado trunking, are you really telling me you will do R1/R2 R1/Rn when you know you just wired all those sockets when you could just pick up any problems with EFLI test, your meter will complain if you get it wrong!

 

[davesparks]

Exactly. You would not IR test only one of the L/N conductors, so why only check loop resistance of one?

The only conductor we are required to check continuity of during testing is the CPC, the R2 test is sufficient for this and acceptable, an R1+R2 test is more normally carried out because it is easier, and it checks polarity at the same time.
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The thing that is confusing me is how does performing only a R1+R2 on a radial socket cct (and operating switches to make sure it breaks) confirm polarity.

The R1+R2 test proves two things, the continuity of the CPC and the polarity.

If the polarity was reversed then you would not get a reading as there would be no continuity.

Remember the polarity test is confirming that L and N are the right way round.

 

[radiohead]

The only conductor we are required to check continuity of during testing is the CPC, the R2 test is sufficient for this and acceptable, an R1+R2 test is more normally carried out because it is easier, and it checks polarity at the same time.
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The R1+R2 test proves two things, the continuity of the CPC and the polarity.

If the polarity was reversed then you would not get a reading as there would be no continuity.

Remember the polarity test is confirming that L and N are the right way round.

The OP's point was that if L and E connections at a socket outlet are reversed the R1+R2 test will not indicate that, it may only be apparent when EFLI tests are carried out, in which case a dangerous fault will be energised before being discovered.