Ring main r1+r2 reading really low - 0.01?

[tomodo]

hi guys just wired up a new ring main for a house, confused on the test results though, firstly all other ring mains in the house that are new are okay and have came out as expected, tester has just been calibrated and batterys are okay and the ring main is a true ring... am using a metrel tester with the easy switch adaptor and have connected up right for testing at board.

Results for dodgy ring main are as follows
L-L 0.80 ohms
N-N 0.81 ohms
E-E 1.25 ohms

R1+rn 0.52 ohms
R1 + R2 0.01 ohms

Does anybody have any ideas why the r1+r2 reading is so low? I have read else where it could be to do with the metal backboxes being bonded making a parrellel path is this common?

Cheers for reading be grateful for any replys

 

[SparkyChick]

I suspect you have a short between line and CPC.

Do a quick IR test... L-N, L-E, N-E... I think you'll get good readings for L-N and N-E and a very poor result for L-E.

To find it, try linking line and CPC at the board on one leg only... Test the outlets and record the results. The further you get from the board, the results should go up, increasing the further you get from the board. If you find they go up and then down... check the accessories with the lowest values as there's likely to be a short in the back box or on the leg of cable between the two with the lowest values.

 

[Octopus]

I have an easi switch, but gave up using it a long time ago .....

Are you 100 % sure you connected it all correctly to the 6 ends?

 

[PEG]

Hi bud,have you done any other testing,apart from at the board?

...It is also only a matter of time,before the terminology police begin r1r2/R1R2 questioning...

 

[Strima]

I'm with SC on this, short between L&N at an accessory.

 

[telectrix]

agreed. seems like a L-E short. pretty close to wherever you're getting the reading at. the R1+R2

 

[123]

What is an easi switch?

 

[Strima]

With a reading of 0.01 ohms it would be less than a meter away if using 2.5/1.5.

R1+R2 of 2.5/1.5 is 0.019 per meter.

 

[Strima]

What is an easi switch?

It's a device for those with more money than sense: A 1214 EASI Switch: Metrel d.d. - http://www.metrel.co.uk/productsuk/electrical_installation_testers/single_function_testers/a_1214_easi_switch.html

 

[telectrix]

either that or OP has nulled leads with circuit connected.

 

[telectrix]

It's a device for those with more money than sense: A 1214 EASI Switch: Metrel d.d. - http://www.metrel.co.uk/productsuk/electrical_installation_testers/single_function_testers/a_1214_easi_switch.html

another possible source of error. if i got the 0.01 reading, the next thing out the van would be the alternative megger BM continuity tester to confirm or not.

 

[PEG]

It's a device for those with more money than sense: A 1214 EASI Switch: Metrel d.d. - http://www.metrel.co.uk/productsuk/electrical_installation_testers/single_function_testers/a_1214_easi_switch.html

Beat me to it £200+ to avoid swapping some connections...but can really confuse things,if any of those connections are incorrect.

 

[Strima]

I don't know why people find ring testing so difficult.

 

[Strima]

either that or OP has nulled leads with circuit connected.

I have done it myself in the past.

 

[tomodo]

I tripled doubled checked i had it connected right! But thanks i will try that tomorrow, l-e did have a lower IR at 500v then n-e and l-n it was around 100M ohms though so well in allowance but normally i would expect over 999Mohm could the 100Mohms be low enough to be giving me the bad r1r2 readings? And also circuit works fine live?

And 123 the easy switch is from metrel does all your ring main tests in one go without having to mess about with connector blocks , not sure if id reccomend though yet

I will let you know the outcome

 

[Amp David]

Are you testing you R1R2 at the consumer unit or at a socket?

You sure you havent got you 2 cpcs touching if test at the CU and they’re not fully sleeved or seperated?

 

[Octopus]

And also circuit works fine live?

Interesting strategy .......... issue with dead tests - so lets go live!

 

[Octopus]

Did you set the Metrel in the "auto" function when using the easi switch?

 

[buzzlightyear]

 

[Gavin John Hyde]

had a similar scenario a while back when replacing a part of a damaged RFC, the electrician who did the original install had twisted the 2 cpc's together in the back of the consumer unit, they were then separated out and sleeved to the earth bar in the CU, so at first glance appeared separate, it caused a little confusion at first, as soon as i untwisted the wires so they were not touching, I got sensible results.

 

[buzzlightyear]

And 123 the easy switch is from metrel does all your ring main tests in one go without having to mess about with connector blocks , not sure if id reccomend though yet

don't,bin it. ill always do it the old way.

 

[AJshep]

Is this going to be a 20amp ring ?

 

[AJshep]

Yep I know it is funny I only mentioned it because I had the pleasure of seeing a mock new 2391-51/52 mutiple choice question paper recently, a similar question was written on it
Strictly text book, taking you as far as the design scope of the course (not allowing diversity for maximum load from the centre of the ring)
Assuming a ridiculous scenario of the ring running at full load (32amps ×R1+Rn) the R1+Rn would already fail the maximum permissible 5% volt drop, and that's before you add the correction factor for the circuit running at 70°c. (a multiplier of 1.2 to R1+Rn)

Really just mentioned it for the trainees as I thought it was a bit of a silly question.