Verification of Ring not adding up

[RobFurn]

ok here we go : Testing a final ring circuit today cross connecting phase and CPC to get R1+R2 value etc. The value recorded at the ring mid point (socket outlet) was 0.6ohms
Prior to the cross I did the intital check for continuity at the ends of the ring i.e phase OUT to phase IN neutral OUT to neutral IN and CPC OUT to CPC IN

phase OUT to phase IN measured: 0.1ohms
CPC OUT to CPC IN measured:0.17ohms

so the loop resistance was : 0.27ohms

My question is why is the (cross connected) socket outlet reading 0.6ohms when it should be 1/4 of the Phase + CPC loop resistance

My guess is a multiple loop (loop within a loop) cause by DIY over the years. Its defo not loose connections belive me I took all 13 sockets off and tightened the lot.

Cheers

 

[Qedelec]

Only way to prove the loop in loop theory is th open the ring and check continuity on the two cabled terminating at that socket.

 

[Adam_151]

How did you measure at the socket? probes behind on the terminals or a BS1363 lead for your tester/plug with holes drilled in it

If the later then a worn socket could be to blame and it should be replaced (and this is why you should test it this way, as opposed to going on the back, to pick this kind of thing up)

 

[Qedelec]

Also a Poor contact on a well used switch could be to blame.

 

[RobFurn]

How did you measure at the socket? probes behind on the terminals or a BS1363 lead for your tester/plug with holes drilled in it

If the later then a worn socket could be to blame and it should be replaced (and this is why you should test it this way, as opposed to going on the back, to pick this kind of thing up)

I use a fluke 1653 with the 3pin plug lead connected directly to the socket. I did think of worn contacts so whilst I was tightnig ALL of the connections on EVERY socket I tested on the reverse as well with the same result .
Im baffeled just wondered if this is common in old installations. In case your wondering it was a CU changeover.

 

[RF Lighting]

How big was the ring circuit (floor area & points served)?


0.1 ohms sounds a bit low for the end to end reading on the phase conductor.

Was the neutral end to end reading roughtly the same?

 

[RobFurn]

It was the upstairs ring on a normal 3 bed semi 13 points served.
Cant remember what the Neutral reading was Im going back tomorrow or Sunday to investigate further.
I know what your saying it does seem a bit low bit I checked it god knows how many times and ZEROd the the meter every time. This it why Im thinking has the ring been buggered about with and a ring within a ring has been created thus introducing a parallel phase path between sockets thus reducing the loop resistance and therefore increasing the "cross connected" R1+R2 resistance.

 

[RF Lighting]

when you had the ring cross connected, were the R1+R2 readings the same at every socket?

 

[RobFurn]

when you had the ring cross connected, were the R1+R2 readings the same at every socket?

Glad you asked that RF. No the results were all over the place should have mention that as I know they should be substantially the same at each socket outlet. Any thoughts?

 

[Spark123]

Interconnected ring, spurs all over the place, test interconnection incorrect. What were the R1+Rn checks like?

 

[RobFurn]

The R1+Rn (cross connection) results were much the same as R1+R2 a little lower but you would expect this due to the N CSA being bigger than CPC.

Also the Rn loop resistance was much the same as R1 and measured 0.1ohm

Think I may trace the whole ring out opening the ring at each socket outlet and finding out what connects to what etc. Ballsaching I know but I would like to get to the bottom of it regardless.

What would YOU (anyone) do? in this situation put it right or forget about it, after all the Zs was well below 1.2ohms

 

[securespark]

Put it right or at least notify the customer in writing.

Now you know it's wrong, you can't walk away without doing one of those things.

 

[Spark123]

Zs isn't the problem, you may have an imballance in the ring which may, depending on the setup, cause an overload of a leg. When I said R1+Rn, I meant cross connecting the phase and neutral conductors at the consumer unit and carrying out a check of the resistance P-N at each socket. All the readings of sockets on the ring should be roughly the same and be a quarter of the sum of the end to end resistance of the phase and neutral conductors (r1+rn)/4. The R1+Rn will be higher for spurs.

 

[RobFurn]

Yeah gonna rip its guts out and sort it
Trouble is the downstairs ring is the same
Must have had a numpty in to add sockets at some point and buggered it up.

Thankfully the kitchen (on a seperate ring) is fine so I can rule out any testing errors from myself.

Anyone elses views are very welcome .

 

[RobFurn]

All the readings of sockets on the ring should be roughly the same and be a quarter of the sum of the end to end resistance of the phase and neutral conductors (r1+rn)/4. The R1+Rn will be higher for spurs.

Yeah i uderstand the theory its just that the sum of r1+rn is 0.2ohms but the (cross connected) results tested at the socket outlets are much higher so even if spurs existed which the most certinaly do as the results differ on some of the sockets it doesnt explain why Im getting over 0.4ohms it should be reading 0.05 ohms. I can only think a ring within a ring exists or something more sinister.