Neutral in the High resistance earthed systems

What is the resistance of ZN?

Sparkingchip said:

What is the resistance of ZN?

"sufficiently high" according to BS 7671 (411.6.1) ... sufficient for what purpose seems less clear to me...

   - Andy.

The earth fault current is limited to 1A, around 25ohms

The earth fault current is limited to 1A, around 25ohms

Ah, as I know only too well,  the danger of doing sums in an open forum is that some smart!755 like me corrects you ;-) 

Now, I reckon 230 V / 25 Ohm  is closer to 'about' 10A  To limit to 1A you'd need more like 230 ohms ;-)

(Much like the current limit for a hard fault on a single 4ft rod TT system typically an amp or three flows in in the electrodes ,and fuses never blow, just RCDs trip.)

I of course now am at risk of being corrected myself  if I have misunderstood the intent of the answer.

Mike,

The earth fault current is limited to 1A, around 25ohms

Ah, as I know only too well,  the danger of doing sums in an open forum is that some smart!755 like me corrects you ;-) 

Now, I reckon 230 V / 25 Ohm  is closer to 'about' 10A  To limit to 1A you'd need more like 230 ohms ;-)

(Much like the current limit for a hard fault on a single 4ft rod TT system typically an amp or three flows in in the electrodes ,and fuses never blow, just RCDs trip.)

I of course now am at risk of being corrected myself  if I have misunderstood the intent of the answer.

Mike,