Originally posted by sparky:
hmmm,
I've messed up here!
Paul, could you please review the N & G of your system and the ELCB application ?
It happens to the best of us. Re-reading the thread, it looks as though some quotes got attributed to the wrong person at one point. Let's try and straighten things out:
In our main panels there are ALWAYS separate neutral and ground busbars/strips with no link between them. There are three distinct grounding methods still in use, depending upon the type of distribution network.
1. Armored underground feeds, found on older services in towns. The ground busbar is bonded to the armor of the supply cable, which in turn is grounded at the utility's xfmr. The incoming neutral goes ONLY to the neutral busbar, there is no N-to-G link on the customer's premises & no ground rod is needed. ELCBs were NOT fitted as standard. (Note: When installed, these town systems had the neutral grounded ONLY at the xfmr star-point.)
2. Overhead twin lines. Standard service for decades in rural areas. Again, incoming neutral goes ONLY to the neutral busbar and there is no N-G link. The house ground is provided by a local ground rod, and because of the resultant high loop impedance, an ELCB was/is almost always used. (As above, originally the only ground on the neutral was at the utility's xfmr.)
3. PME (Protective Multiple Earthing). Used since the 1930s in some rural areas, with overhead feeds. This is the only system with a N-G link at the house. The neutral & ground are still separate at the main panel, but instead of the main grounding lead running to cable armor or a gnd-rod, it is bonded to the incoming neutral AT THE SERVICE BLOCK. This is located before the meter, and is the only point of contact between N & G. No separate rod or ELCB is needed. (With PME the utility co. has ground rods on their neutral along its route at regular intervals.)
When reading this, keep in mind that compared to U.S. residential service we tend to use a smaller quantity of larger xfmrs to feed a given number of homes.
Since the 1980s, most of the LV distribution networks have been converted to allow PME operation, but many of the houses retain their original grounding method.
Does this help, or have I made it worse?