Recently I tested a property, it was a 3 story townhouse built in 1995 located in Yateley, Hampshire. The previous owners had the home under offer and approached me when they were asked to provide an electrical certificate.
The initial test revealed some test results that would not be expected so I needed to flag them as further investigation required. In addition to this there was no RCD protection which meant a C2 (you can read more about what this electrical classification code means HERE) for the ground floor ring main / ring final circuit.
In addition to the old consumer box, I also found heat damage on the neutral tail from the meter.
Because of these findings my recommendation was to find the fault/s and replace the consumer unit with a full RCBO replacement. This meant that each circuit would be fully independent from each other. This is better for a number of reasons, but from your point of view it means that if a fault develops later on or you have a faulty appliance, only that circuit would trip out, leaving the rest of the circuits on meaning you don't lose all the power in your home!
When I carried out the fault finding on the ground floor ring, it was interesting as a conservatory had been powered by a split into the ring from a socket in the breakfast room. This was located on the 1st floor through the cavity and adding a larger resistance to the ring.
In addition, the garage had been converted to a room which had also added resistance to the ring
After re-terminating and fixing back all the sockets on this ring to correct loose connection I managed to reduce the resistance slightly and improve the test results to a satisfactory level. This meant that this part of the unsatisfactory EICR Report was rectified.
The 2nd ring main covered the kitchen, front room and 2nd floor with 20 socket outlets on this circuit. With the addition of 20 more sockets on the other ring, this was quite an available load capability and certainly required ring continuity to cover the 2.5mm rating allowed on a 32a ring main. On a radial a maximum of 20amp is permitted.
During my fault finding, I located a double socket with a 1.5mm twin and earth cable connected to a switched fused spur above, this on closer inspection revealed open live ends that just sat in the void space with some degraded masking tape for protection!
Clearly not good !!
Next it was time to find the fault on the 2nd ring final circuit which had an end to end r1 rn and r2 reading of 0.00 which had me questioning my test equipment!
As every meter of cable has a known resistance value, and since this was a ring final covering 2 floors in a large house wired in 2.5mm cable, I expected to see a minimum value of 0.50 on both live and neutral, and approx 1.67 x that value on the 1.5mm earth r2 end to end results. (2.5 mm milliohms per metre is 7.41 mili ohms per metre )
The only explanation for 0.00 was either faulty test equipment, which later that evening I tested my tester with my approved megger test box, and my values were spot on. As an NICEIC approved contractor I carry out monthly checks on my test box to keep track of any problems with my tester.
To locate the 0.00, in my experience the explanation had to be extremely close due to the readings of 0.00. My hunch was that both legs of the ring had been connected together above the consumer unit so I got the camera out and this is what was found:
Interested in the rest of this investigation?