200 Ohm ?

[luka B]

Hi Everyone ,
I'm always confused that One ohm or less is a must for circuits supplied by a company earth .

But when its an Earth Rod then up to 200 Ohm is acceptable ...
Surely the rod is much inferior so should be less acceptable resistance ..

I know we now have RCD's but Rods were in place long before .

Just curious ..

 

[Megawatt]

Hi Everyone ,
I'm always confused that One ohm or less is a must for circuits supplied by a company earth .

But when its an Earth Rod then up to 200 Ohm is acceptable ...
Surely the rod is much inferior so should be less acceptable resistance ..

I know we now have RCD's but Rods were in place long before .

Just curious ..

Luka you are right in the US we use 2 ground rods and it’s less than 1 ohm but I think in the UK has sandstone which is very resistant. I understand that UK power companies have different arrangements than we do and I guess that’s your answer and welcome to the forum

 

[static zap]

Before current operated RCDs ,they were effectively
Voltage operated ... but ...
Their big problem was you needed a voltage for them to operate.
Parallel paths to earth could quite easily "supress"
the voltage from ever occurring .
Causing a change of strategy to monitoring the currents in and out , balancing !
( opinions may be available on adequacy /stability ? of 200 ohms -but not from me ! )