TT Ze reading

[vertigodj]

sank an earth rod today to see if we can get a lower value of earth resistance, reading we had came to 80.1 ohms. Nothing is connected proper yet to this new earth as the system is still using the old earth, (in the process of upgrading) figures quoted in on-site guide say max of 200 ohms. Without getting to complicated would you be happy or not with that

 

[londonboy]

I'd be happy with it, its well within the allowance isn't it.

However its not my name on the certificate, its yours

 

[vertigodj]

I'd be happy with it, its well within the allowance isn't it.

However its not my name on the certificate, its yours

ok, tell me this, Ra divide by 30mA = less than = to 50v
so 80.1 / 30mA = 2.67 Volts
still learning and getting my head around it all

 

[RF Lighting]

Not quite.

Max permissible touch voltage is 50V

RCD operating current is 30mA

So using ohms law (V/I=R)

50V / 0.03A = 1666Ω

That is the max theoretical Zs to operate your RCD in an earth fault condition.

In reality though, anything over 200Ω is not considered to be a stable reading, and could end up above the theoretical limits due to changes in climate etc.

Ideally you should be aiming for a reading below 100Ω which you have acheived, so all is good.

 

[Electrifying]

I'd be happy with it, its well within the allowance isn't it.

However its not my name on the certificate, its yours

ok, tell me this, Ra divide by 30mA = less than = to 50v
so 80.1 / 30mA = 2.67 Volts
still learning and getting my head around it all

I guess it's not your name on the certificate, either.