Hypothetical: I have two circuits that are being powered from the same electrical service. They both have a hot and a neutral wire from the same transformer.
- The first circuit and the transformer are earth grounded locally with a ground rod.
- The second circuit is earth grounded on the other side of the country with a second ground rod.
Assuming the voltage drop is acceptable for circuit #2:
- Are these equivalent circuits?
- What problems could occur when a circuit is grounded elsewhere than where its electrical service is grounded?
Hypothetical Schematic
simulate this circuit – Schematic created using CircuitLab
Best Answer
Not really. The resistance between G and N on CCT#1 is likely to be very low. It may be less than an ohm.
The resistance between G and N on CCT#2 is likely to be much higher. With a simple rod hammered into the ground, it could be anything from a few tens of ohms to a few kilohms. Dirt isn't a good conductor, especially if it's dry.
The first supply would be classified as "TN-S", the second is "TT".
You haven't said what circuit protection devices CCT#1 and CCT#2 have. A short between L and G on CCT#1 will cause a large current to flow. This should trip a circuit breaker or blow a fuse.
A short between L and G on CCT#2 is unlikely to pass enough current to trip a breaker or blow a fuse, unless you have an unusually good earth rod. Such circuits really need to be protected by an RCD/GFCI to be safe (RCD and GFCI are the same thing under different names).