In replacing kitchen cupboards I had to re-arrange some tiles, underneath I spied some capping at a distinct angle! Exposing the run revealed cooker FTE at >5 degrees to the vertical with regulations requiring <3.5 degrees since 1987 IIRC.
The capping had a notch out of it where the fitters drill had passed. So close.
The cable has been moved to 0.0 degrees to the vertical from wiring accessory.
Checking further, this run of 6mm FTE is very short with a 2.5mm CPC.
- 2m of 6mm FTE CU to CCU - could actually be 1.2m
- 1m of 6mm FTE CCU to CO
- 2m of 6mm H07RNF Cooker to CCO (new)
Fault Current...
a) Taking max Ze for TN-C-S of 0.35ohm, Uo nominal 230V
- EFLI Zs = Ze + (R1+R2) = 0.42 ohm
- Fault Current = 548 Amps
b) Taking measured Zs of 0.21ohm, Uo of 247V
- EFLI Zs = 0.21 ohm at CCU
- Fault Current = 1176 Amps
Adiabatic calculation for minimum CPC size.
a) 0.4sec disconnect time, k = 115 at 70oC for copper CPC
- CPC minimum = SQRT (548^2 * 0.4) / 115 = 3.01mm^2
b) 0.4sec disconnect time, k = 115 at 70oC for copper CPC
- CPC minimum = SQRT (1176^2 * 0.4) / 115 = 6.46mm^2
It can be seen that the 2.5mm CPC in 6mm FTE is undersized.
However, considering CPD Trip Characteristics...
- Type-B CPD trip characteristic disconnects 5*In in <0.1sec
- For a 32A Type-B RCBO that is 160A in <0.1sec
- So the CPC is thus sized ok.
Assuming your CPD *is* an RCBO and not just a switch
))
Q - So I can rely on the fast trip characteristics of a Type-B CPD?
Otherwise upgrades are difficult.
- 4mm 6491X could be added - only easy option
- 10mm FTE does off 4mm CPC, but backbox on CCU & CO are 35mm (6mm cable), wall 1-brick-depth
- 6/10mm H07RNF would fit re bend radius in 35mm backbox and BS7671 permits flex with bootlace ferrules
I know most people & PIRs have a fit on use of flex in fixed wiring, even if to BS7671. IR tests ok on the existing PVC cable.
Aside - in 1967 the cable was VIR, protected by 30A BS1362. Old kitchen fitter changed cooker faceplate, wired LE across the switch. On operating the switch in blew the CCU & tiles off the wall, plus the 63A BS1361 cutout.
The capping had a notch out of it where the fitters drill had passed. So close.
The cable has been moved to 0.0 degrees to the vertical from wiring accessory.
Checking further, this run of 6mm FTE is very short with a 2.5mm CPC.
- 2m of 6mm FTE CU to CCU - could actually be 1.2m
- 1m of 6mm FTE CCU to CO
- 2m of 6mm H07RNF Cooker to CCO (new)
Fault Current...
a) Taking max Ze for TN-C-S of 0.35ohm, Uo nominal 230V
- EFLI Zs = Ze + (R1+R2) = 0.42 ohm
- Fault Current = 548 Amps
b) Taking measured Zs of 0.21ohm, Uo of 247V
- EFLI Zs = 0.21 ohm at CCU
- Fault Current = 1176 Amps
Adiabatic calculation for minimum CPC size.
a) 0.4sec disconnect time, k = 115 at 70oC for copper CPC
- CPC minimum = SQRT (548^2 * 0.4) / 115 = 3.01mm^2
b) 0.4sec disconnect time, k = 115 at 70oC for copper CPC
- CPC minimum = SQRT (1176^2 * 0.4) / 115 = 6.46mm^2
It can be seen that the 2.5mm CPC in 6mm FTE is undersized.
However, considering CPD Trip Characteristics...
- Type-B CPD trip characteristic disconnects 5*In in <0.1sec
- For a 32A Type-B RCBO that is 160A in <0.1sec
- So the CPC is thus sized ok.
Assuming your CPD *is* an RCBO and not just a switch
))Q - So I can rely on the fast trip characteristics of a Type-B CPD?
Otherwise upgrades are difficult.
- 4mm 6491X could be added - only easy option
- 10mm FTE does off 4mm CPC, but backbox on CCU & CO are 35mm (6mm cable), wall 1-brick-depth
- 6/10mm H07RNF would fit re bend radius in 35mm backbox and BS7671 permits flex with bootlace ferrules
I know most people & PIRs have a fit on use of flex in fixed wiring, even if to BS7671. IR tests ok on the existing PVC cable.
Aside - in 1967 the cable was VIR, protected by 30A BS1362. Old kitchen fitter changed cooker faceplate, wired LE across the switch. On operating the switch in blew the CCU & tiles off the wall, plus the 63A BS1361 cutout.
