I think David has provided a good outlined of the ring circuit.
Yes, the ground wire run in a ring gives redundancy in that a single break will not leave any outlet without a protective ground connection.
The same ring configuration on the phase and neutral means that a single break on either of these also results in no outlet being left without power. That's when problems with overloaded cables can start. I encounter such breaks in ring continuity on a fairly regular basis.
In cases where I find that both phase
and neutral have no ring continuity, it almost always turns out to be somebody's DIY attempt at adding outlets which has left the ring broken.
I should also add to David's explanation the fact that our Regs. allow a ring to have "spurs." A spur is a single cable feeding a single or duplex receptacle which is connected to the ring at an outlet or junction box. The spur cable is also 2.5 sq. mm.
Although the IEE considers it unlikely to happen, it would be possible to connect two 3kW loads to a double socket and overload the spur cable.
Some months ago, we also discussed the exact distribution of current around a ring. The fact is that the ring is not completely foolproof. Given heavy loads connected close to one end of a long ring, it is still possible to exceed the cable rating on the short leg.
care must be taken that the fault current is high enough to trip the breaker within a short period of time (no more than 5 seconds
For some circuits BS7671 requires a disconnect time of under 0.4 sec., although 5 seconds is acceptable for lighting circuits, fixed appliances, etc.
Re the breakers, we generally use type B in all residential applications.
We used to use metal cable clips. These were nailed to the surface first, then the cable laid in and the strip bent around the cable and back on itself to secure it.
These days, the plastic saddle with a single nail driven on one side of it is standard.
