RCD trip mode question

[emeritus]

Re the noise coupling issue, I recall that my late mother found that the TV picture blipped whenever she started her sewing machine motor. This was in the 1970's before the use of regulated power supplies in TVs, which meant that they were rather sensitive to drops in mains voltage. She was worried in case it was interfering with the neighbours' TVs, and to establish if it was simply due to loading of the ring main or radiated interference, I tried running her machine from the cooker point in the kitchen via a heavy duty extension lead ( 2.5mm cable). This completely fixed the problem, operation of the motor then having no discernible effect on the TV. She then happily ran it from the cooker point until the TV was replaced by a colour set that was immune from mains voltage blips.

[Station X]

Originally Posted by cmjones01

I can think of three pieces of equipment in regular use in my workshop - isolating transformer, variac and a big battery charger - which almost always caused the 16A breaker to trip when switched on

Could it be that you require MCBs with a 'C' or 'D' curve rather than the usual 'B' type?

[cmjones01]

Yes, that would probably fix the problem, but in a rented house I don't have much choice. There's a similar situation in my office, where the whole room is on a 10A breaker so I have to be a bit careful. The breakers are all 'B' type ones, as is the 25A (!) breaker which feeds the whole house. That one's in a cupboard on an outside wall, and is also prone to tripping on inrush currents. It's really annoying when it trips and it's raining outside...

Chris

[Herald1360]

What about an inline soft start box? Big green crinkly 10R resistor in the line with a suitable relay/contactor latched by a pushbutton with a contact across the resistor to short it. Could be more or less automatic depending on how far you want to go........

[cmjones01]

Yes, that would work, too, but I've gone for the built-in option because on all three troublesome devices it's useful to keep their outputs shut down until the soft-start process has done its thing. The idea is exactly the same, but with some extra contacts on the relay!

Chris

[julie_m]

Originally Posted by Tractorfan

There's no requirement in France for ovens or cookers to have a local two pole isolator. It seems to be a peculiarly British thing.

I always thought it was a requirement for a cooker isolating switch to be positioned to one side or the other of the hob, so that you would never have to reach over the top of a burning chip pan to turn off the power.

But the last time I was in Wales, every electric cooker I saw had its isolating switch mounted centrally above and behind the cooker

[ben]

Thank you all for the responses!
I will give some more background information - my setup seems very like the Polish one mentioned by Chris. The consumer unit consists of four MCBs :
- one of 10A (!) for the sockets and lighting in the living room, passageways, bathroom and two bedrooms. Two air conditioning units are also plugged in but rarely in use, and hardly ever at the same time.
It's a sort of `main ring` for the flat, excluding kitchen. It is probably the original late 60s setup dating from when the flat/block was built. I believe these sockets are unearthed.

- One of 10A for the 4 kitchen sockets which are used for fridge, microwave and toaster. I believe these sockets are earthed.

- One of 20A for the cooker (no UK style isolating switch; I've lived in Germany and France and never saw one there either)

- and another of 20A for the washing machine.

These last three rings were installed in the 1990s. They are downstream of the main RCD which is rated 40A and when off, cuts power to everything. It is only this that has been doing the odd `tripping`. None of the MCBs have been tripping.

Today I did a little test, I switched off the MCB for the flat ring and cooker, and left the kitchen sockets (fridge etc) and washer MCBs ON, set a load of washing and nothing tripped after 15 mins or more. I then set the cooker MCB to ON and turned the grill on. Sure enough, after 6 mins or so the power was cut - the main MCB did its weird internal cut off thing. That would suggest the cooker is indeed playing a main part in this scenario.

Since then I have switched off the grill, (leaving the cooker MCB ON) and have had the air con, fridge, washer etc. on continuously with no trouble.

When the washer finishes I will just run the grill or oven alone, and post back with results.

[matthewhouse]

Originally Posted by ben

Thank you all for the responses!
None of the MCBs have been tripping.

Sounds like they are made by Federal Electric! Either that or you only ever use one appliance at a time.

Any chance of a photo?!

[julie_m]

All this makes me realise just how generous we are with our amps in the UK

Of course, most of the rest of the world has mains-pressure domestic hot water -- none of your namby-pamby cisterns and ball valves for the Continentals! -- so has little need for that most power-hungry of appliances, the electric shower. (It takes 70 watts to make water flowing at one litre per minute one degree hotter, and that isn't about to change any time soon.)

[Herald1360]

Whatever the heating fuel is it takes less energy to heat the water for a shower directly than in advance over a longer period, since there are no storage losses. For full rate mains flow hot water you'll need about 20kW whichever way you do it. Supply current limitations simply mean you have either to store the hot water or use a different energy source.

What's so interesting about Federal Electric? Have they got a different tripping characteristic from other makes- less closely rated tripping current?

[AC/HL]

None of which is helping Ben, please keep on topic.

[Radio Wrangler]

The combination of the cooker on and one of the other high current appliances would fit with a conductor-to-metal-casing fault in one element of Ben's cooker, close to the neutral end of the element.

This is essentially a neutral to earth fault, but it is only when both the cooker and something else takes appreciable current that the neutral potential rises due to the resistance of the neutral wiring, enough to trip the RCD.

David

[ben]

Thanks for the other contributions. Here is an update as I think I have found the answer.

Despite noticing that the power went off when the cooker was on, something still didn't add up because neither the RCD nor the MCB tripped at any time. As I said, the RCD was replaced with exactly the same symptoms continuing.

So I did a bit of probing. Next to the CU there is a housing for an ICP (Interruptor Control de Potencia), which under Spanish law must now be fitted to all properties. It limits the amount of power you consume by cutting the supply if you exceed, say, 2.3kW. This was empty.

I discovered that this was removed because the meter in the main supply area downstairs is a newer digital type and has the power limiter incorporated. So it looks like this was what was causing the cuts in the supply!

I have never seen this setup in the UK. Basically it allows the greedy electrical companies here to charge you more each month, as the power contracted to homeowners is a fixed charge on your bill, (like the line rental of a telephone) which has nothing to do with the amount of kW/h you actually use. At the moment, due to the recession, people have been more careful to switch things off and since the kw/h unit consumption has fallen, the power companies just raised the costs of these fixed power tariffs to compensate!

The solution is pay for an increase in contracted power, but that would probably mean improving the house ring as it may well fail the current regs (as you can see from the picture, there's not a lot of separation!)

Will have to give it a think I suppose. It's still a bit strange how the cuts only began to happen a few months ago, but I suppose the aging of the appliances may have had something to do with it.

[matthewhouse]

At least you know what the problem is now. If you have a clamp meter you can measure the current drawn to see if it is tripping early.

There's some English information here. The standard 3.3KW supply sounds rather stingy, no large Christmas dinners in an electric cooker there.

I've not come across a set up like that before though.
The only current limiting I've ever heard of is when homes had a separate tariff for lighting and power to stop people connecting all their appliance to the cheaper lighting rate. The Current limiter was automatic and was a relay with its coil connected in series with the supply and the relay contact also connected in series. When enough current was drawn to pull in the relay the contacts opened and closed, flashing the lights.

[Nickthedentist]

That's interesting. My parents have a flat in Spain, and recently had a letter explaining that their place was to have such a meter installed. It implied that it was not self-resetting, and if it tripped, one would have to reset it manually. The trouble is, nobody knows where this meter is situated - presumably in some locked service cupboard.

The whole flat, built in the early 1970s, is fed via a single 16A MCB (yes, honestly).

N.

[mole42uk]

These current limiting breakers are standard in central France where I've done some electrical work. Basically, Ben is correct in that the householder is charged a flat rate for the capacity of the supply, then a kWh rate for the electricity consumed. The French ones have a manual reset button that you use when you have switched off the extra demand that caused it to trip.
I was told it was done this way to allow the electricity distributors to maintain a large enough distribution network to service the maximum demand without overloading. Certainly, when we have requested an increased supply capacity, there's all sorts of Gallic shrugging about whether it's possible or not!
In the UK, we do a similar thing by maintaining the networks with a huge overload capacity. At least, we used to. Since the 1980s that overload capacity is smaller than it was.

[ben]

On the subject of resetting the limiter, it must be automatic as after every 'trip' I managed to get the power on by turning the main RCD off then back on again - must be about a 5 or 10 seconds 'grace' period.

[matthewhouse]

Perhaps it waits for all loads to be removed before switching back on?

[Nickthedentist]

Yes, maybe I misunderstood the letter (in Spanish). It could well have said switch your own incomer/RCD off then on again to reset it.

N.

[ben]

If you scan it and email it to me, I'll tell you what it says exactly.