Is an RCBO an adequate replacement for an isolator?

[John Rumm]

No, this is an area where you can't generalise without knowing the specifics. Firstly you are confusing fault protection with some nebulous concept of "safety". Fault protection has a specific meaning and there are specific requirements. SP and DP devices both fulfil these requirements.

To extend the discussion to safety in general, then you need to look at a wider picture, like can the neutral take on a noticeably different potential to the local earth? For many cases (i.e. TN-C-S / TN-S) the difference between DP and SP is moot, and even with TT it is negligible.

The time that DP device does have a clear advantage is that you can also use it for isolation (something that requires DP switching).

[John Rumm]

Ah, so you mean you were actually agreeing with Dave when he said "There never was 'unmetered' power in the UK"

[John Rumm]

a recommendation, since I have never used the brand)

[John Rumm]

Indeed they do, BS1363 among them.

This has nothing to do with it being a ring, and everything to do with it being a 32A circuit.

How does the appliance fuse protect the appliance flex?

Appliance fuses, where used are pretty much universal across the euro zone. Appliance fuses also offer less protection outside the UK, since you can only assume they are in the live wire 50% of the time.

Indeed. Many modern appliance flexes will also be sized (and restricted in length) to ensure that they have adequate fault protection from a 13A fuse (and 16A circuit breaker) - even if the overload protection required by the appliance is lower.

One area where this is less desirable however is with small portable appliances, where there is benefit to being able to use smaller lighter flex than would otherwise be required.

The scope for abuse these days is greatly reduced since appliance plugs come pre fitted and fused, and fuses rarely need replacement.

The appliance is protected by its own fuse. You will be relatively hard pushed to many devices fitted with 3A flex that are capable of overloading the flex.

So a radial with a disconnected or high resistance earth connection somewhere along its length is better than a ring with the same fault?

[Tim W]

Doctor Drivel wibbled on Thursday 12 November 2009 22:37

Even when the appliances all have 0.5mm2 flexes?

Do you strip your wires with a hacksaw too? Go back to plumbing, at least you'll only get wet...

[The Natural Philosopher]

Which puts a neat upper limit on our power consumption doesn't it?

[Steve Firth]

As another poster sig mentions, Malthus was right. Predicting when the inevitable collapse will happen is more difficult. Governments have already shown they can't even take difficult decisions over energy supply. Taking much more difficult positions over nitwits who think a religion allows them to breed like bugs is never going to happen.

[Owain]

But absolutely useless for practical purposes. We'd end up like the Americans, having to work out which combinations of sockets and appliances don't trip anything.

I didn't think ring abuse was that widespread so as to be a problem.

Owain

[Owain]

Lighting circuits are safer where Drivel lives - they're all tamper- resistant ligature-free recessed fittings

Owain

[Tim W]

Owain wibbled on Friday 13 November 2009 10:11

I'm doing that at the moment, running my entire house (bar water heater) off

1 32A temp ring and a rather unhealthy assortment of extension leads.

SWMBO's been "instructed" as to which fan heater to turn off to run, say the washing machine...

It's quite a weird existence (and a right PITA if I didn't know it would be ending soon), but it's amazing how much stuff you can run with a single maxed out 32A circuit. Not for long. Next week, I should have 3 final rings done properly...

It's almost amazing the nice meals you can conjure up with one combi microwave, a rice cooker (apart from the bloody thing drips condensate on its own IEC plug and trips the RCBO(!) and a slow cooker. Wondering whether to bother getting a real cooker ;-O

In case anyone says "wire your rings, lazy git", today's task was clearing all the gutters (I like bungalows in this respect) - got fed up with the waterfalls everywhere :)

Next task is have a bath. The get son from nursery, set up tonight's meal in the slow cooker and clear up a bit so I can get round to do the wiring next week.

Cheers

Tim

[Doctor Drivel]

I am not. If the device activates and cuts out all electricity conductors (L&N) it must by definition be safer. In fact if the earth is isolated even better, then all electrical conductors are isolated from the appliance or circuit.

yep.

[Doctor Drivel]

You lack common sense. I woudl let you near my house. There again I do all my own.

[Doctor Drivel]

When a wire becomes loose in a ring it is difficult to trace. As it is fed from two ends. It could mean one section of cable in the ring is cooking as the other section is isolated because of a wire coming loose.

If daisy chained sockets on a radial, and one has loose wire those downstream will not operate. On a ring all appears fine until a high current appliance is connected.

Ring abuse is widespread. I have noticed square 3-pin plugs with no fuses being sold (prob illegally). That means the appliance, which could be a table lamp, is only protected by a 32A fuse or mcb.

[Doctor Drivel]

And this is lecturing people on electricity. Amazing. The man is a walking fire hazard.

[Doctor Drivel]

Lighting circuits are safer where Drivel lives - they're all tamper- resistant ligature-free recessed fittings

[Doctor Drivel]

I not agree with loonies and plantpots.

[Doctor Drivel]

This one need tagging. What a pervo!

[ARWadsworth]

No.

Only the live and neutral are the electrical (phase) conductors. The earth is a circuit protective conductor. The earth connection does it's job properly by not having it's circuit broken.

You would not want for example a lump of metal such as a combi boiler and it's copper pipework to have all it's live, neutral and earth connections isolated when you turn the power off to it.

That would mean that a fault elsewhere, such as a live cable from another circuit touching a copper pipe would make the combi and it's pipework rise up to 230V.

Adam

[ARWadsworth]

It is not that difficult to trace if you have the experience and equipment.

What happens if it is the earth terminal that is loose?

It is in the Catholic church.

Adam

[Doctor Drivel]

Missed the point. It can be there undetected and home owner thinks all is fine, switches on a few the 3kW fires and the cable is cooked.and then a fire. On radial if a socket does not work then the alarm bell rings.

Safety is impaired. You can use 4 core cable and have an earth returning from the last socket. Or an earth wire back from the end socket.