What would you do??

[Deleted member 26818]

If you were to contact the DNO, they would likely tell you that the 0.35 and 0.8 values are only guidlines.

 

[mechelec]

There is no relation to max Ze TNC-S of 0.35ohms to the cut out fuse values... It is considered to remain the same value regardless!!

Interesting? The higher the fuse rating the lower the Ze for a given disconnection time. The relationship between Ze and cutout fuse size is to ensure a disconnection time of 5 seconds for a fault between the cutout fuse and the consumers installation, The figures for max Ze quoted by my DNO (revised due to decared voltage change to 230V) are :

100A = 0.38ohms
80A = 0.52ohms
60A = 0.73ohms
45A = 1 ohm

These figures are very close to table 41.4 in the regs for a BS1361 fuse 5 second disconnection time. FYI These Max values quoted are measured at the cutout with the customers earth disconnected not the consumers installation. I hope this makes sense.