HELLO IM SEAN GRIFFIN A NAPIT MEMBER PLEASE CAN ANYONE ANSWER THIS QUESTION ON ZE TESTING THE RULES SAY 0.8 OHMS ON TNS EARTHING SYSTEM TRUE. THE VOLT IS AT 230V TRUE. MAIN FUSE IN A HOUSE IS 100AMP FUSE TRUE. THE RULES STAT THE DISCONNECTION TIME ON A 100 AMP FUSE IS 5 SEC. TRUE TO BLOW A FUSE IS 5 X THE FUSE SIZE AND PLUS 100AMPS = 600 AMPS OF FAULT CURRENT. TRUE WELL AT 230V / 0.8OHMS = 287.5 AMPS OF FAULT CURRENT. TRUE SO THE FAULT CURRENT ON 0.8 OHMS ON A TNS SYSTEM ISNT LARGE ENOUGH TO BLOW THE FUSE IN ITS CORRECT TIME.
It looks like your using a "typical" value. In reality Ze would usually be much lower so the fuse would blow at less than 5s. It's really up to the supplier to get this bit right, but yea, as you say, they are under no legal obligation to maintain the Ze at any time, so it can vary. I would imagine that if the bonding is done correctly all the touch voltages would be about the same for the length of the fault. From the charts a bs1361 would take about 15 seconds to pop at 287v.
had reading at 0.4 ohms the pfc is 575 amp on ze read will pass but disconnection on main fuse wont blow within its time, if the installation for water was in plastic piping there wont be much bonding done ... and if the phase line got cut into the problem still stands. tns should be lowered to 0.35ohms ish to correct this . correct ? 18th edition page 364
The supplier does not work to BS7671 they work to ESQR and the main fuse is to protect their cables not the installation.
The service fuse protects the service cable against overload only (by the consumer). It protects the meter tails and meter against both overload and short circuit.