Paul,
I'm in total agreement with what you say regarding ring continuity.
Breaks are usually as a result of botched DIY, growl! [Linked Image] (I'm on the soap box again!)

There are times when I wish we could go back to radial circuits, but these are only when I am pulling my hair out attempting to locate a break in continuity, normally caused by the above.

I have to say that generally I like ring circuits for a number of reasons:
1) Permits relatively long cable runs, with limited voltage drop & low earth loop impedance (TN-S & TNC-S).
2) High integrity earthing, required to comply with section 607 of BS 7671.
3) Providing it is correctly designed, it allows a lot of sockets to be installed on a circuit with little chance of over-loading.(Kitchens excepted.)
4) In the event of a cable fault, you can disconnect the faulty section & temporarily restore power until a permanent repair / replacement can be made. Obviously precautions would have to be taken to prevent over-loading.

I was grateful of #4 above when I was called out this morning.
A ring main serving bedroom sockets in a nursing home went faulty, tripping the 32A MCB in the sub panel & also the 63A sub main MCB at the main panel.
I traced the fault to a live (phase)/ earth cable fault between the sub panel & 1st socket on the ring. Disconnecting this cable at the sub panel & 1st socket enabled me to re-energize the circuit, using a 16A MCB to prevent over-loading.
Next week I will go back & replace the faulty cable (after the joiner lifts chipboard flooring) & install a new split load sub panel incorperating RCD for the socket circuits.

I don't think unfused spurs should be allowed on a ring, they tend to be extended indiscriminately by those who know no better.

Breakers for ring circuit are normally "B curve" for residential, "C curve" for commercial / industrial. Nothing to prevent you installing "C curve" for residential, providing you can achieve the lower loop impedance values.
Generally socket circuits on TN systems have to disconnect within 0.4 second.
Socket circuits on TT systems must be protected by a 30mA RCD, also sockets which may reasonably be expected to supply equipment used outdoors on TN systems require 30mA RCD protection.

I have a policy of installing 30mA RCD protection to all residential socket circuits, in new work & when replacing an existing board (panel).

BTW what's "THHN in PVC flex conduit"?


[This message has been edited by David UK (edited 10-14-2002).]