Unusual Reading on CU change

[Octopus]

Been doing a CU change today and all the testing was going well until I got to the kitchen/utility ring. The end to end readings were:

R1 = 0.68
RN = 0.69
R2 = 0.56

So back tomorrow to look further - any suggestions as to how to locate what appears to be a "short cut" in the CPC?

Brain dead so any ideas welcome!

 

[SirKit Breaker]

Sometimes easy to overlook the obvious. Had a similar problem a couple of weeks back, rN and r2 normal readings, and r1 335 ohms. My eyes popped out. after 2 or 3 smokes and half an hour of head scratching went round the circuit and found several loose connections, the reading kept coming down with every re secured terminal, and about half way round found the line conductors in the socket tube but not even a bit tight.

Cheers..........Howard

 

[pushrod]

Nice thought but all the appliances were definitely unplugged, and for what its worth the CPC at the CU was'n't connected so the "parallel" path suggests 2 links!

In future can easily check if it is at least a possibility, by checking the continuity of the disconnected r2 to the MET.

 

[telectrix]

Update: went round the offending circuit, tightening up all sockets etc and hey presto all the 3 the readings dropped (sorry don't the actual figs to hand). Thanks for all the ideas.

i thought the R1 and RN were high. hopefully the new readings shoed R2 as higher than the phase r's.

 

[pushrod]

However, an r1 of 0.68 suggests a very long ring (c100m). Could it be loose connections on the L & N giving high readings and the cpc is correct?

With a cpc of 1.5mm² suggested length is actually less than 60m

 

[PC Electrics]

With a cpc of 1.5mm² suggested length is actually less than 60m

Oh dear!

According to my books:
r1 is RFC line resistance end to end.
Admitedly the OP didn't state the cable size, but typically an RFC in most houses is 2.5mm line and neutral.
According to GN3, 2.5mm has a resistance of 7.41 milliohms per metre. So we have:
L = (0.68 / 7.41) * 1000 = 91.8m

Better get up earlier.

 

[pushrod]

Oh dear!

According to my books:
r1 is RFC line resistance end to end.
Admitedly the OP didn't state the cable size, but typically an RFC in most houses is 2.5mm line and neutral.
According to GN3, 2.5mm has a resistance of 7.41 milliohms per metre. So we have:
L = (0.68 / 7.41) * 1000 = 91.8m

Better get up earlier.

LOL oh dear in deed! - that'll teach me to watch the telly and reply on here at the same time. Apologies Guess i was thinking r2, or not even thinking at all!!!

 

[telectrix]

it's sometimes better to think wrong than not to think at all.

 

[pushrod]

it's sometimes better to think wrong than not to think at all.

I try to think, guess the red wine doen't help too much lol

 

[telectrix]

need to buy better quality wine, not the cheap frog plonk

 

[Amp David]

Has there been a conservatory or extension built on?