Continuity

[Gasman1015]

Circuit is 2.5 / 1.5
Tested at DB
Cpc / Cpc 0.34
Neutral / Neutral 0.05
Phase / Phase 0.05

R1 + R2 0.25

The figures seem to be all over the place, was testing before making alterations, Trying to calculate the circuit length.

0.34 x 1000 = 340 / 12.10 = 28 metres
0.05 X 1000 = 50 / 7.41 = 6.74 metres

Double checked readings five times, zeroed meter, still pulling my hair out.

Could use some experienced views please.

 

[Lectrician]

Not using a fluke 1652 are you?

Instinct says the L and N seem a little low - are you sure the leads are correctly zero'ed? The CPC value seems about right for a standard sized ring. It could be simply that the CPC is a little high resistace, due to a dodgy termination somewhere.

Where in Devon are you?

 

[RF Lighting]

It sounds very fishy.

How big is the area served by the ring circuit?
These are the readings before you carried out any work?
The readings (as I presume you realise) sound wrong. It strikes me that someone may perhaps have tried to extend a ring and got it wrong?

Whatever the cause, it needs further investigation, and at least you have covered your a**e by finding there is a possible fault before you modified the circuit

 

[dingbat]

It sounds very much to me like you've incorrectly nulled your test leads. Un-null them and take the circuit readings again. Then measure the resistance of the clips, several times if necessary. When you've got a reading that is repeatable and makes sense, subtract that and then see if your circuit length calculations work out.

(And take heart that at least you realised there was something wrong - plenty would have just written down the values as measured and thought nothing of it.)

 

[Gasman1015]

Firstly, thankyou for the replies.

No, I have'nt made any alterations yet. I wanted to be sure of the condition of the circuits beforehand. I test everything before starting, comes from experience with gas installations.

Really not 100% confident with my test meter Megger MFT1502, ten months old, anyone want to buy it, absoluteley certain of it being zeroed, I suspected loose connections, will return to job later in the week, everything isolated at the moment, owners live abroad.

Large three bedroom terraced property, expected ring to be about 50/60 metres, 11 points, 1 circuit for down and upstairs.

Will maybe try to borrow another meter. I'm in Torquay.

Would really like to try out the Fluke, but are they any better than the Megger.

 

[Bright_Spark]

i use alphateks stuff. theyre owned by metrel and i find their stuff good

www.alphatek.co.uk if ur interested.

 

[Gasman1015]

Thanks, seems they are not up and running yet.

This web site is under major development. Please check back soon.

 

[Pensdown]

Not using a fluke 1652 are you?

Because our fluke 1652's were in for null faults on a regular basis we thought we would try the megger CM500. Nice piece of kit but it measures low by about 0.4ohm. It's brand new out of the box and it is supposed to be calibrated.

Gasman's post highlights the problems with test kit because if you don't trust the readings then you don't know if there is problem with the installation or not. 10/10 Gasman for spotting the irregularities.

I would suggest that a few more circuits should be tested either on site or at home and if the readings are all suspect it may be the test kit.