OK
1.Instead of an RCD you can use a MCB as FAULT PROTECTION "IF" the Rod Resistance is low enough to do so.
BUT supposing your Rod Resistance was 50 ohms? 230/50 =4.6A on Fault. This wouldn't be enough to trip a 5A Breaker or fuse.
Answer? Fit a Time Delay RCD Type S ( time delay 100mA ) as...
If you had a high Rod impedance is what I am referring to. If you did have ( for instance 99 ohms )
or less and an overcurrent device would not suffice in protecting your install , how would you have fed a Ring and a Cooker Circuit ?
lets just say it was 20 ohms would you feed the supply through...
in the Regs 411.5.2. Fault Protection. if your Earth Rod Impedance is low then you can rely on a overcurrent device but the Earth Rod changes all the time depending on the ground conditions, always err on the side of safety. ( my motto ) you do as you like my friend but I am devout RCD man on TT
The TT supply must have an RCD of 100mA Time Delay or a 300mA rcd. The circuits downstream must have an RCD of 30mA for Discrimination ( now called Selectivity )
The RCD is an Earth Leakage Device the older types now banned and obsolete were Voltage operated circuit breakers
you don't need an rcd unless you are supplying the equipment via a socket outlet of 32A or less. If you are wiring through a local isolator to fixed or immovable equipment you do not need an RCD. A 16A tp mcb will do just fine probably type C
It seems you are confused here. the R1+R2 figure is combined with Ze to give Zs. The insulation resistance readings have their own columns.
The IR of 3.17 Megohms is more than enough to satisfy the current regs.
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