Continuity Test Results

[peterb20]

Another DIYer trying to a professionals job!.....

I switched the main breaker, have removed a socket, and have tested the resistance on the circuit. It came out at 1.2ohms on each wire.

I know this figure shows there IS continuity, but will it also be able to tell me (or someone out there!) whether i have any bad connections? Surely if a wire was barely into a junction box then the resistance would be higher?
Im just interested to know the relavence of this 1.2ohms and if this how a qualified sparky would run the test.

Our house is probably 50sqm upstairs and 50sqm downstairs with only 1 ring on it.

 

[ban-all-sheds]

Between which points did you measure the resistance?

And with what?

 

[GaryMo]

To prove correct connection of conductors on a ring final......

You need an accurate low ohm meter, not a multimeter.
You've proved that a cable goes out and comes back but that could also be an interconnect (imagine a figure of 8 or a H).

Measure end to end continuity r1 (live), rn (neutral) and r2 (cpc).
Assuming your ring final is wired in 2.5/1.5 t&e?
If so then r2 (cpc) should read 1.67 times that of r1 (live) and rn (neutral) conductors.

You would then need to cross connect the incoming live to the outgoing cpc and vice versa at the consumer unit.
With an accurate low ohm meter first zero your leads then measure resistance between live and cpc at each point of the circuit.
Assuming a healthy ring you should see the same reading at each point.
This reading is otherwise known at R1+R2 which should be very similar to (r1+r2)/4.

Now cross connect the incoming live to the outgoing neutral and vice versa at the consumer unit.
With an accurate low ohm meter first zero your leads then measure resistance between live and neutral at each point of the circuit.
Assuming a healthy ring you should see the same reading at each point.
This reading should be very similar to (r1+rn)/4.

 

[peterb20]

wow good answer! although im a little sceptical about taking wires from the connections in the consumer unit - i presume thats what you mean be cross connect?

Also when you say interconnect do you mean an erronous connection between the live and neutral connecting them both together for example? or that they are connected to the wrong terminal in a socket somewhere? i cant see how a test could discover the latter, and the MCB would trip for the former wouldnt it?

ban-all-sheds i have measured the resistance at a socket part way around the ring, with a bog-standard multimeter set to resistance.

 

[ban-all-sheds]

1) The cross connections that Gary described are ones that you temporarily make in order to take different measurements.

See here: http://www.tlc-direct.co.uk/Book/8.4.2.htm

2) Also as Gary said you've proved that some kind of continuity exists, but not what sort, and also your "bog-standard multimeter" might not be accurate enough. 2.5mm² cable has a resistance of 7.41 milliohms/m, so 1.2 ohms implies a circuit length of 162m, which is (a) unlikely and (b)too long.

 

[peterb20]

ah right - well its more than likely the multimeter isnt accurate enough - its only a £10 jobbie from uni!

Thanks for the info guys!