High Zs value with 2 sockets

[Midwest]

If you do end to ends at these sockets with a higher Zs reading, and you don't get continuity, then this socket will more likely to be a spurred socket. Importance of doing dead tests in the correct order. Although understand what you were trying to achieve, pre CU change.

Edit, as suggested by the other chaps!

 

[TheCodboy]

From your readings it will not be the same as at the board, they may well be open circuit.

I think a return to the property on monday and get some socket fronts off....

 

[Midwest]

I think a return to the property on monday and get some socket fronts off....

Think, as the chaps have been saying, your higher Zs readings are because the sockets have been spurred. Easy assumption to make when you see two cables at a socket. (See my post #8).

 

[Midwest]

Think, as the chaps have been saying, your higher Zs readings are because the sockets have been spurred. Easy assumption to make when you see two cables at a socket. (See my post #8).

Least I hope it is, anything else might be more stressful

 

[TheCodboy]

Least I hope it is, anything else might be more stressful

Me too!!!!

 

[ChrisElectrical88]

L=0.92 N=0.92 E=1.83
Measured Ze 0.14

These reading are too high for a RFC to be below 100m

 

[Midwest]

These reading are too high for a RFC to be below 100m

My CG 2392 course workbook suggests circuit length of 45-50m circuit length (2.5 + 1.5mm), then there's the old dodgy socket connections?

 

[ChrisElectrical88]

0.92/7.41 x1000

124m

Also the CPC is greater than 1.67x the r1 and rn which would suggest a loose connection on that somewhere

 

[westward10]

Or 1.0 cpcs.

 

[ChrisElectrical88]

Don't know the 1.0mm resistance off my head (1.5 is 12.41) I'm sure if someone could do that calculation and get close to 124 then it would confirm that.

 

[TheCodboy]

Don't know the 1.0mm resistance of

1mm 18.10 Table B1 GN3

 

[bigspark17]

I think a return to the property on monday and get some socket fronts off....

Is the customer paying for all these pre test.?

 

[TheCodboy]

Theres 2 rings in the bungalow. One for the kitchen and one for the rest of the house Kitchen readings were r1 0.49 rN 0.49 r2 0.83. So even these figures seem a bit high then? MFT has been calibrated recently and checked it against my Cal card the other day.

 

[TheCodboy]

Is the customer paying for all these pre test.?

I put the pre test on the price but told him any faults would need rectified and would be extra.

 

[Wilko]

Theres 2 rings in the bungalow. One for the kitchen and one for the rest of the house Kitchen readings were r1 0.49 rN 0.49 r2 0.83. So even these figures seem a bit high then? MFT has been calibrated recently and checked it against my Cal card the other day.

If you are measuring the rfc loop e2e and it's made from 2.5 /1.5 then these seem ok to me as 0.49x2.5/1.5 = 0.817, so practical reading of 0.83 gets a tick
This would indicate an rfc about 65m length end to end and added to your Ze 0.14 should give Zs of around 0.47 ish which is fine for 32A. Is that roughly the Zs you've measured?

 

[TheCodboy]

If you are measuring the rfc loop e2e and it's made from 2.5 /1.5 then these seem ok to me as 0.49x2.5/1.5 = 0.817, so practical reading of 0.83 gets a tick
This would indicate an rfc about 65m length end to end and added to your Ze 0.14 should give Zs of around 0.47 ish which is fine for 32A. Is that roughly the Zs you've measured?

Yep, 0.46 was my highest value in the kitchen. My calcs work out for the other ring (apart Zs sockets) work out, but r1 r2 & rN values are high if you put them against cable resistance table in GN3. See post 12 for other values.

 

[Midwest]

Is the customer paying for all these pre test.?

No but the electrician needs to do some, or he/she will pay for them in the long run

 

[bigspark17]

No but the electrician needs to do some, or he/she will pay for them in the long run

Not zs every socket...

 

[Toneyz]

The socket with the highest reading had 2 x 2.5 T&E. Took L-L, N-N, E-E reading at the consumer unit. r1 + r2/4 + Ze = 0.82 Ze was measured at 0.14. The calculated Zs of 0.82 was very near what i was getting all around the ring. 2 sockets were a bit lower (0.45 & 0.55) and apart from the 2 that were high, the rest were virtually spot on. ( My end to end values were L=0.92 N=0.92 E=1.83)

Td to end is a bit higher than expected calculation of 1.55 this may be down to loose/bad connection or 1.0mm cpc(or in part of) that aside did you do a R1 +R2 dead test this will prove that these two sockets are spurs. Midwest posted a good point in post #21 put the ends together at the C.U. and do a ring test at the high reading socket will prove it. You posted that there was still two cables at the highest reading socket my feeling is that there is another socket/outlet from this you have not located maybe in loft just a thought. Let us know what you find out on Monday

 

[TheCodboy]

Td to end is a bit higher than expected calculation of 1.55 this may be down to loose/bad connection or 1.0mm cpc(or in part of) that aside did you do a R1 +R2 dead test this will prove that these two sockets are spurs. Midwest posted a good point in post #21 put the ends together at the C.U. and do a ring test at the high reading socket will prove it. You posted that there was still two cables at the highest reading socket my feeling is that there is another socket/outlet from this you have not located maybe in loft just a thought. Let us know what you find out on Monday

I hope its not in the loft, its covered in insulation. Two layers, And there's hardly any space to move....