Testing a ring

[rainydays]

Hi all, just a quick query with regards to testing a ring main.

With the legs cross connected the reading at each socket outlet should all be substantially the same excluding spurs etc.

Could someone clarify what sort of ohmic value tolerance one would deem acceptable. i.e. how much of a difference between sockets would one not deem as substantially the same, before thinking that it could be a spur.

Many thank`s

 

[green-hornet]

This is a hard one in the respect that most readings will be almost identical, the spur could have a difference of 0.05 to 0.whatever! dependant on the length of the spur.

The end to end readings r1, r2, rn should be recorded first, then with phase and cpc conductors cross connected the highest reading is put on the certificate and this should be (r1+r2)/4. One of the best ways to see the differences is by experiance, I do know that with most test walls in training for testing the spurs will have a very little difference from the rest of the ring.

As a guide I almost always get my ring readings to around 0.02 difference on new installs.

Another problem could be the tester used and your confidence in its readings, low batteries sometimes gives some "funny" readings.

Any high readings you get from one socket may not indicate a spur but a faulty connection or even as I have sometimes found a faulty new socket outlet.

 

[ianmacd]

... and this should be (r1+r2)4.

Shouldn't that be (r1+r2)/4?

Ian.

 

[green-hornet]

Shouldn't that be (r1+r2)/4?Ian.

You are right Ian a typo from me I think I did not spot it.

Thank you

 

[seajayess]

All readings should be within + or - 0.05 ohms of the R1+R2 measurement if you get readings higher it could be a spur hope this helps CJS

 

[SPECIAL LOCATION]

The only points I would add here are..

1/ the age of the circuit you are testing

2/ the type of connection for your readings

both can give some apparent errors.

e.g.

a brand new circuit with all new socket fronts should be much closer than an older circuit with sockets that have been in normal everyday use. Especially if using a plug top adaptors e.g. something like this sort of gizmo...

http://www.screwfix.com/prods/31565/Hand-Tools/Detection-Equipment/Kewtech-Kewcheck-R2-Socket-Testing-Adaptor

you can get more variation on your readings due to the resistance of the contacts between the pins & the socket itself.

I have also had tests on a switched socket where you get one reading..

but if you operate the switch a few times the resistance can change!

Obviously if you are opening up your sockets and sticking your probes direct on to the back of the socket.. tolerance should be tighter.

 

[tymark]

I was demonstrating testing a ring for my assesment on metalclad sockets and couldn't get the readings down to within tolerance (0.05 ohms ) using a socket front adapter but got them down to within 0.02 from the back of the sockets - after the assesor had gone i ran a 3KW heater on all of the sockets for a little while and rechecked them with the socket adapter and they were all within tolerance.

 

[spinlondon]

I've had big differences between the 2 sockets on a double socket before now.

I prefer to test at the back of a socket, allows me to check for sleeving on the earth, and loose terminals.

 

[Janice]

I've had big differences between the 2 sockets on a double socket before now.I prefer to test at the back of a socket, allows me to check for sleeving on the earth, and loose terminals.

If you can get the damn thing exposed enough! Some sparks wire sockets so tight, it's a wonder they ever managed to get a screwdriver in there to tighten the screws up, let alone a pair of test prods.

J.

 

[SPECIAL LOCATION]

If you can get the damn thing exposed enough! Some sparks wire sockets so tight, it's a wonder they ever managed to get a screwdriver in there to tighten the screws up, let alone a pair of test prods.J.

Those are the jobs where the wall was built after the socket & back-box were fitted!]Blushing:_|

 

[Andy™]

Those are the jobs where the wall was built after the socket & back-box were fitted!]Blushing:_|

or the socket was terminated before plastering, cables pushed back out of socket, then clipped/capped after socket front screwed back

 

[AK-UK]

I agree with SPECIAL LOCATION's, the reading values depend on several variables. I find that the most important thing is that the hiest value of Zs will be in tolerance, the meaning is that even in the worst scenario the MCB/RCBO will trip.

 

[SPECIAL LOCATION]

I agree with SPECIAL LOCATION's, the reading values depend on several variables. I find that the most important thing is that the hiest value of Zs will be in tolerance, the meaning is that even in the worst scenario the MCB/RCBO will trip.

so do I....

oh he is nice! ]Blushing:O:^O:^O:^O