EICR - main earth and neutral

Andy raises an interesting point - what do you need to consider for fault protection (adiabatic) in this case?


It's entirely possible (and perhaps more likely) that a line to neutral or line to earth fault will only short line to a single strand of the neutral or earth (or perhaps a few strands).


In a 25 mm² split-concentric cable, the equivalent CSA of each neutral strand (11 x 1.7 mm) is 2.27 mm², and that of each cpc strand (4 x 2.25 mm) is 4.0 mm².


Immediately you can see the neutral fault is the worst-case. So if you're using BS 88-3 fuses,


The next step depends on which of the following scenarios you follow:

1. The neutral strand is broken so fault current flows only one way.

• The neutral strand is not broken, so roughly half the fault current flows in each direction and in the case of the downstream current returns down the other neutral strands.

Supposing either is possible, then 1. is the worst-case from an adiabatic perspective.


Using BS 88-3 fuses to protect the cable, the lengths of the cables are limited by the minimum prospective fault current:

• for 63 A BS 88-3 fuse, the minimum prospective fault current is approx 900 A and max length of run is 2.8 m with 1 kA pfc at building network origin, or 24 m with 5 kA pfc at building network origin

• for 45 A BS 88-3 fuse, the minimum prospective fault current is approx 430 A and max length of run is 34 m with 1 kA pfc at building network origin, or 55 m with 5 kA pfc at building network origin

• for 32 A BS 88-3 fuse, the minimum prospective fault current is approx 160 A and max length of run is 135 m with 1 kA pfc at building network origin, or 156 m with 5 kA pfc at building network origin

Andy raises an interesting point - what do you need to consider for fault protection (adiabatic) in this case?


It's entirely possible (and perhaps more likely) that a line to neutral or line to earth fault will only short line to a single strand of the neutral or earth (or perhaps a few strands).


In a 25 mm² split-concentric cable, the equivalent CSA of each neutral strand (11 x 1.7 mm) is 2.27 mm², and that of each cpc strand (4 x 2.25 mm) is 4.0 mm².


Immediately you can see the neutral fault is the worst-case. So if you're using BS 88-3 fuses,


The next step depends on which of the following scenarios you follow:

1. The neutral strand is broken so fault current flows only one way.

• The neutral strand is not broken, so roughly half the fault current flows in each direction and in the case of the downstream current returns down the other neutral strands.

Supposing either is possible, then 1. is the worst-case from an adiabatic perspective.


Using BS 88-3 fuses to protect the cable, the lengths of the cables are limited by the minimum prospective fault current:

• for 63 A BS 88-3 fuse, the minimum prospective fault current is approx 900 A and max length of run is 2.8 m with 1 kA pfc at building network origin, or 24 m with 5 kA pfc at building network origin

• for 45 A BS 88-3 fuse, the minimum prospective fault current is approx 430 A and max length of run is 34 m with 1 kA pfc at building network origin, or 55 m with 5 kA pfc at building network origin

• for 32 A BS 88-3 fuse, the minimum prospective fault current is approx 160 A and max length of run is 135 m with 1 kA pfc at building network origin, or 156 m with 5 kA pfc at building network origin