End to end testing on cpcs ring circuit.

[Deleted member 26818]

Surely that gives you r1 / r2 not end to end of the CPC ?

Yes R1+R2.

 

[steve-the-hat]

I'm probably being dense here but am I right in thinking you:
- joined the cpc connectors together in the cu and to nothing else.
- are breaking the ring at each socket in turn and measuring the continuity between the two cpc connectors.
- have checked there's nothing plugged into the ring or connected through a fsu.

 

[Engineer54]

It is normal to just measure the end to end at the CU. Although there is no reason why you can't measure the end to end at each accessory.
You would however expect each measurement to be the same.
From what you have described, it sounds as if you are not measuring end to end at each accessory, but between different conductors at each accessory.

That was what i was hinting at...lol!!

 

[schoe]

Could you confirm exactly what you did please?:thumbsup

Are you just testing the CPC or have you interconnected with a Line or Neutral?

I was just testing the cpc. One cpc in one croc clip the other in the second croc clip. And I got this reading. I did the same after with the live and then neutral but these results were fine.

The low reading couldn't be due to parrell paths in the earth?

 

[schoe]

I'm probably being dense here but am I right in thinking you:
- joined the cpc connectors together in the cu and to nothing else.
- are breaking the ring at each socket in turn and measuring the continuity between the two cpc connectors.
- have checked there's nothing plugged into the ring or connected through a fsu.

Yep cpc connectors were jointed together in the consumer unit, in the main earth terminal.

I'm them breaking the sockets at each point and testing them between the two cpc's. When I did the test there would have been a fridge plugged in and a kettle, and there are 2 switched fuse units on the ring?

 

[Deleted member 26818]

The CPC should be in a ring.
A measurement taken at any point on that ring, should be substantially the same as another measurment taken at any other point on the ring.
To obtain results where the further you are from the CU, the higher the reading, would be expected if measuring between two conductors (e.g. L & E) that are joined together at the CU.

 

[steve-the-hat]

Yep cpc connectors were jointed together in the consumer unit, in the main earth terminal.

When I did the test there would have been a fridge plugged in and a kettle, and there are 2 switched fuse units on the ring?

OK it sounds like you've got parallel paths there. You would need to make sure that nothing eles was connected to the cpc for the readings to be the same wherever you broke the ring.

 

[schoe]

Would having things plugged in and having switched fuse spurs switched on affect the results of an end to end on the cpcs?

 

[steve-the-hat]

Would having things plugged in and having switched fuse spurs switched on affect the results of an end to end on the cpcs?

Yes. If one of the items was, say a boiler, then you could have a circuit from the MET through the water pipes, to the boiler, up the boiler's lead, through the fsu, round the ring and back to the MET.

 

[Deleted member 26818]

It is possible I suppose, but it shouldn't really.
I would expect there to be substantial differences on L-L readings, as many appliances have capacitors which would soak up the test voltage.

 

[schoe]

OK it sounds like you've got parallel paths there. You would need to make sure that nothing eles was connected to the cpc for the readings to be the same wherever you broke the ring.

Thanks Steve that's what I have done. I've broken into a socket while further around the ring there are 2 switched fuse spurs feeding an aga and a dishwasher. So even with these connected if I carried out my end to end in the consumer unit instead of breaking into sockets would my readings be ok?

 

[schoe]

As I said before my end to end results which were carried out in the consumer unit were,

Live to live 0.93

Neutral to neutral 0.90

And earth to earth 1.46

Which all seem to be acceptable.

It's only when I broke into the sockets in the ring did I get a different result on the earths

 

[steve-the-hat]

You really cannot test a ring satisfactorily with anything connected to it. You could have a break in the cpc masked by a parallel path.

If your dishwasher was in the first socket and the aga in the last, then the cpc could be missing from all the sockets between them and the fault would not show up when you tested at the cu.

 

[schoe]

My results were taken before the aga, and dishwasher were plugged in via a switched fuse spur. That's why I thought everything was ok till I tested them the other day.

If I unplug everything and turn the switched fuses off will this prevent parallel paths?

 

[schoe]

Sorry one last point, so if I disconnected everything from the switched fuse spurs and plugs then carry out the tests I should get the same results in the consumer unit and if I was to test from a socket.

Thanks everyone