Ring Main Extension Ohms

[loopy66]

I posted similar to this before where I extend the ring main to fit 5 new sockets upstairs and then get high Ohm readings. Well, I stripped it all out and started again, brand new cable.

I put 5 new sockets in, run the cable around and back to where I will cut it into the main (when the sparky puts me in a new consumer unit).

I tested from socket to socket and get 0.2ohms, which is about right all the way around.

My issue is, when I test the circuit as a whole, ie, the test going from the start of the cable, through the 5 sockets to the other end of the cable, get 2ohms.

I am going mad with this... surely I should get 0.2ohms end to end or even 0.x and not a whole 2?

 

[EFLImpudence]

2.5mm² conductors have a resistance of 7.32mΩ (0.00732Ω) per metre.

0.2Ω would mean 27m. It can't be that long between each socket.
5 x that would be 1Ω meaning 135m.
2Ω would mean 273m so something is wrong.

Is your meter kaput?

 

[conny]

First thing I would do is replace the batteries in your meter. If that doesn't work borrow/hire a meter that is calibrated and working correctly then re-test.
If you are still getting the same/similar readings then clearly there is something amiss.
Loose/bad connection somewhere?

 

[AndyPRK]

Need a milli ohm meter

 

[bernardgreen]

Errors occur due to contact resistance between meter probe and the terminal being probed,

Most accurate way to measure cable resistances is to use a constant DC current source to drive a current through the cable and then with a high impedence voltmeter measure the voltage at the various points along the cable. For the other probe use either a long lead back to the current souce. Then using R = V / I calculate the resistance

Because there is no significant current flowing in the voltmeter leads their resistance does not significanly affect the results.