RCDs in series

On Tue, 21 Aug 2007 13:55:12 +0100 someone who may be "Tim Downie" wrote this:-

Yes.

It would work in that it would disconnect the supply. However, it is likely that the main one would also work.

In this sort of situation you need a time delayed one on the main board, but this gives rise to other difficulties.

Hmm, sounds like it will be easier to wire the pond into a circuit & RCD of its own. I was hoping for a "lazy-man's" solution. ;-)

Tim

Isolate pond circuit when going away on holiday?

cheers, clive

.=2E.such as the fact that they are scarily expensive. Cheapest I found was from CPC a couple of years back. =A385 + VAT IIRC.

Jon.

Or put the deep freeze on its own unprotected circuit as I have done.

Interersting post though as my garage, workshop and greenhouse systems are all on their own rcd's but seperate from the house one.

Rob

Same here on both points. Also computer & lan stuff on their own circuit.

Run the pond stuff off a 1:1 isolating transformer (with an RCD on the secondary if you wish).

You don't want any outdoor circuits sharing an RCD with anything indoors, for this sort of reason. Also a fridge/freezer is not something which needs to be RCD protected at all. You have a fault and the RCD appropriately detected it, but the circuit design for the property would not appear to limited the effects of that fault in a desirable way. Both issues need fixing.

Best have a CU with double pole RCBOs on it instead of and have Continental radial system instead of the silly at times ring circuits. If any problem only the one RCBO trips not the whole house.

Separating these risky circuits out such that they are protected by independent RCDs is generally a good thing to do. RCBOs are one of several ways of doing this.

The use of a ring or radial circuit does not really have any relevance though.

Yup, you don't want to start from there! ;-)

You would.

alas no.

Read the sections on discrimination, mitigating the effects of nuisance trips, and system design using RCDs here:

There is also a fair bit or relevant info in this one:

True an RCBO can be on a ring. Rings are still silly and cheap; one of the reasons they were adopted..and to have higher currents for electric heaters post war as the nuclear policy was all electric using unmetered nuclear power. Although radials may have high currents at the sockets too.

I recall a German looking at a British system; the RCD protecting all of the house and the fused spurs above the worktops with a fuesd plug hidden behind the appliance. He thought the system was mad and said it was clearly cheap at the CU but expensive (and ugly) in fused spurs.

About time we went the same way as the rest of the world. On the Continent each appliance has an RCBO at the CU. So much easier to isolate. The only advantage of the UK system is that 3kW kettles are common, whereas in Europe they only go to around 2kW max. BUt they fill their kettles with hot water from the combi to make the heat up cheaper and faster.

Today's ring circuits represent a very good bit of engineering design.

Even if this were true originally, one has to look at how design has evolved and been refined to where we are today. The ring final circuit we have now is very well suited to diverse power provision over a wide area.

No sure what his nationality has to do with it. The system you describe would not be to standard in the UK wiring regulations, and would rightly be due criticism. Appliances in kitchens with concealed sockets etc should have independent switching above the worktop. Use of whole house RCDs is also long since deprecated.

Rich coming from a German, have you seen their plugs and sockets?

Your logic seems as confused as ever.

Engineering? Daisy-chaining sockets together? Are you kidding? I said to this guy we have two ways back to the meter in earthing. He said if you are that paranoid run another earth back from the furthest socket on a radial circuit. He said "use 4 core cable and use the 4th core for the return earth, that will do it". He was amazed we had an unsheathed eath wire in the T&E cable. He said "that is cheap".

You mean a high current circuit on a 32A MCB. Duh!

With a socket under the worktop with an inaccessible fuse in the plug, that might blow. Duh!! The fused spurs looks hideous as well.

Long since? Like a few years then.

Fused spurs can ruin an nice kitchen worktop.

Get to know the merits of a system the rest of the world use. Duh!

Mo, not at all. Do the sums and see how it out performs other circuit topologies under wide ranging loads and the majority of fault conditions. This with economy of materials.

Anyone can build cheap and anyone can build strong, but it takes engineering finesse to do both at once.

Which is also standard practice in the UK for high integrity radial circuits.

Does not get you the advantages of dual conductor paths for the phase an neutral though does it? You would also need 6mm^2 cable in many circuits to make and equivalent radial. Far less practical from an installers point of view.

Which is good obviously.

You don't need a fused spur on the wall, just a switch. These look perfectly acceptable:

some 20 odd, yes.

Fuses in plugs don't routinely blow unless the appliance develops a fault. You probably won't be repairing that in situ under the worktop either, so not really a problem is it.

So don't use them - no need.

What and lower our standards and safety record to match theirs you mean?

You could start with understanding ours before you go trying to compare with others.

They do not have countless sockets on one radial. In France it is 8 maximum on a 16A MCB.

You mean cheap, having all the downsrairs sockets on one 32A MCB. They would have that split into many 16 MCBs. Better. Divider and rule.

More a few years. I have seen many new builds with RCDs on the whole CU.

They CAN blow and when they do an appliance has to be dragged out.

Theirs superior.

I understand ours and it is cheap and nasty. In France to isolate a dishwasher you go to the CU and throw the RCBO. Any problems and they throws.

As one German said to me when I said rings are legal in Germany. "why run a ring off one MCB when this can be run in two runs (radials) and have two MCBs protecting each. To him it just did not add up. He was right.

Would this explain why, proportionately to population, the number of people killed by electrical accidents in Germany is 3 times greater than the UK and in France is about 10 times greater?