ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Ring circuits revisited again

Ah yes..... Our "whole-house" RCD is another angle I would like to see addressed. In rural areas such as where I live, TT is still by far the most common system (I'd say about half the houses in my small settlement are still on voltage-operated ELCBs), so split-load units aren't that common.

I'd like to see the wider adoption of TN-C-S (PME), and a move toward the American idea of individual branch GFIs, in place of just one or two main RCDs.

Good point about the rcds Paul, I have fitted a lot of boards in the past few years with either an rcd on the main incomer or a split board, my own house has both ring circuits protected by individual rcds and the rest just on standard breakers, the problem is a lot of the time people just want the cheapest and take a board with an rcd on the main as they reckon they will be covered, I had one recently where a lamp in the loft which had been left on had shattered the bulb and tripped the main rcd in the process, the rcd would not reset and they spent the rest of the night in the dark, it was pretty straight forward for me to locate the problem but it demonstrated to them the inconvenience of a main rcd, I am waiting to replace their main rcd with a standard breaker and fit a couple of individual circuit rcds.

edit for spelling mistake

[This message has been edited by Ever Ready (edited 05-27-2004).]

The inconvenience of a single main RCD was demonstrated to me when I first moved into my present house. The element on the shower decided to short out one night while I was using it, leaving me to stumble about in the dark trying to find a towel and then fumble my way around the place to the main panel to restore power.

Dave,
Sorry, I missed that question first time around.

Have a look here for our typical flush mounting boxes.

Deeper boxes are available as you can see, but this is the box used for a twin socket (duplex receptacle) in the average house:

In English units, that box is approx. 5" long, 2.7" high, and only 1" deep.

Yes, GFI-style outlets have become available in recent years. This one is supposed to fit in the same 1" deep box as a regular outlet.

Thinking on this I install ring circuits often in US buildings.

That is a class A fire alarm system.

OK there are a couple of big differences, the fire alarm circuit is power limited and the integrity of the loop (ring) is constantly monitored.

Yes, that's certainly a horse of a different color, but they are somewhat valid points on power distribution as well.

We have HV rings distributing power around cities, so some may ask why I don't like LV rings within a house. The difference is that those HV rings are PoCo controlled, and closely monitored for loads at strategic points.

By contrast, the LV domestic ring could develop a break in continuity and run like that for a considerable time, perhaps overheating the cables regularly but always just escaping a fire. Then somebody finally throws a hefty load on an already hot cable and that's the final straw.

And as we've discussed in the past, even with good ring continuity, it is still possible (even if the IEE considers it unlikely) to put a heavy enough load at one end of a ring to overload the short side of the cable while still not exceeding the 30A OCPD rating.

I can see this happening where the main panel is in the kitchen (fairly common here) and the washer, dryer, dishwasher etc. are all on outlets very close to one end of the ring.

* Another note for our U.S. friends: Washers and dishwashers here typically incorporate a 3kW heating element, so the load is considerably higher than an American washer.


[This message has been edited by pauluk (edited 05-28-2004).]