Testing question

M

Murrreid

I was testing a ring main today.

3 double sockets
2 spurs, one for fridge, one for fan.

I test from one of the sockets.

R1 - .054 ohms
R2 - 18.8 ohms

This is where I stopped, I buzzed out Neutral & Earth, they were buzzing out. So a high reading on the R1. R2 & CPC were ok readings, and neutral and earth buzzed out.

I turned on the breaker and everything worked fine.

Can someone please help out my confusuion !?
 
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M

Murrreid

All sockets and spurs connected, apart from one. Connected at the board.

At the one socket - the last to get done- 2 legs, tested between live and live, neutral and neutral, and cpc and cpc. Then I usually take the live from leg one and put it with the cpc from leg 2, and same with the other live and cpc, and test between them to get my R1 + R2. Do it using Ohmmeter

So I tested live and i got a reading of over 18.8ohms

Neutral was a usual 0.51 ohms
cpc was about 0.78 ish ohms

So i guessed there was a prob, so I got the buzzer and buzzed between live and live, there was a ring, same with neutral, and earth. Then between neutral and earth, and it buzzed, so I guessing that they are connected somewhere - maybe back at the substation ?

connected everything, turned on breaker, and everything worked tho
 
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So I tested live and i got a reading of over 18.8ohms

Neutral was a usual 0.51 ohms
cpc was about 0.78 ish ohms

Using a buzzer or 'beep' tester won't give you a definitive answer.The clue lies above - you have a high resistance Phase loop which is possibly a loose or bad connection somewhere.This needs investigating ASAP as the ring will continue to function apparently normally but there could be overload/heat issues.

Isolate, split the ring somewhere near the middle and measure each leg until you narrow it down.
 
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With the cross connections in, where are you testing across to get the 18ohms? Do you mean r1?
 
M

Murrreid

Testing at a socket in the kitchen.

So if there is a loose connection then a high reading is obtained ?

So tomorrow I should go and check all sockets on the ring and check connections ? Could this be a problem with an appliance?
 
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Yeah, a loose connection or a damaged cable can give a high reading.
 
M

Murrreid

Define damaged cable ?

Screwed ?

Any ideas about the neutral and earth buzzing out ?
 
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Forget the buzzer, you need to measure r1, r2 and rn. r1 (live) should be very close to the same value as rn (neutral).
Damaged cable, nailed, screwed, damaged with hammer etc

R1 - .054 ohms
R2 - 18.8 ohms

R2 is the max resistance of the CPC, midpoint or spur??
 
M

Murrreid

Yeah, they usually are the same. So whats the best way to go about finding where exactly the fault is. I haven't done alot of testing in my time, and the stuff I have, I haven't encountered problems such as these.

Do I go around all the sockets and test the Live legs ? Find the highest and thats where the fault is ?
 
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At the CU, disconnect both legs. Connect one leg live to CPC. Go around measuring the resistance between the two noting the reading at each point.
Disconnect the live to CPC and connect the other one. Go around and do the same again. This should hopefully get you to within 2 sockets.
 
M

Murrreid

Ok, So what is it I am looking for readings wise ?

Also, there is 4 wires going into the breaker. 2 are the ring, as for the other 2 I have no Idea.
 
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You are looking at the readings and assessing where the fault is, where the jump of resistance starts on one leg and where it starts on the other leg indicates the two points where the fault will be between. You will need to have an idea of the route of the circuit. As for your 4 wires, could be anything. A couple of spurs? 2 rings into the same MCB? Could be anything!
 
M

Murrreid

Cheers for the advice, I will check out all the sockets on the ring tomorrow. I am against time, but if it needs to be done then it needs to be done. Hopefully I find something.

High reading = loose connection/damaged cable
 
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As I read it you were testing N+E from a socket outlet and they belled out.

Were the cables connected (but the CPD out) at the CU??
 

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