ECN Forum

UK cooker/RCD problem

Posted By: agaricus bisporus

UK cooker/RCD problem - 09/15/05 01:58 PM

I have an old but virtually unused AEG cooker. When a ring or oven/grill is switched on the RCD trips after about half a minute. Even if the ring is turned off it will not then reset. After a couple of hours however the cooker works for 30 seconds, then trips off. Checks with a multimeter reveal no obvious anomalies.

Is this a common problem? Can it be fixed?
Posted By: aland

Re: UK cooker/RCD problem - 09/15/05 02:47 PM

Sounds like an element fault, probably registering through the neutral to the elements. Multi-meter as useful as a chocolate tea pot. You need insulation tester to show fault up. Sounds like a job for an electrician not recomended for the DIY.
Posted By: gideonr

Re: UK cooker/RCD problem - 09/15/05 08:03 PM

Can also be insulation failure elsewhere in the cooker, or even in the wiring to the cooker, triggered by a temperature rise... ...I'd stop using this cooker!

As it's not just one ring causing the trip, I'm doubting an element fault.

Edit: Duh, you can only use it for 30 secs anyway!


[This message has been edited by gideonr (edited 09-15-2005).]
Posted By: Paulusgnome

Re: UK cooker/RCD problem - 09/15/05 09:19 PM

An interesting problem this.
In NZ and Australia the wiring regs exempt cookers and ranges from requiring RCD protection, and I have always assumed that the reasoning for this is that cooker elements have a naturally high earth leakage current. This makes some sense, as elements constructed with a conductive core and sheath separated by mineral insulation which seems like a good recipe for high leakage.
Can agaricus bisporus advise us is the RCD required by code? If not, then the best bet may well be to remove it.
Posted By: agaricus bisporus

Re: UK cooker/RCD problem - 09/16/05 12:17 AM

Thanks for the replies everyone.
Can't see it as a result of thermal changes in the general fabric of the cooker as it seems to happen within the same timespan regardless of whatever unit is energised.

No regs require an RCD, just seems prudent - and no, I'm not a professional electrician and I won't risk aq dodgy cooker if the RCD says it doesn't like it. Sad thing is my gut feeling is there's nothing wrong with the cooker and the RCD is being overly sensitive. Don't want to trash a good cooker for that reason.

Additionally I now use on the same circuit, a Baby Belling that used to fire the RCD in my parent's house but works as good as gold next to this damn AEG cooker...

Ain't no continuity here..!
Posted By: aland

Re: UK cooker/RCD problem - 09/16/05 07:25 AM

AB this is why you need a sparky! He will have all the right equipment to test both the RcD and the cooker. Very sensible not to remove the RCD until you have proof that its faulty. Please! get them checked out.
Posted By: Texas_Ranger

Re: UK cooker/RCD problem - 09/16/05 05:41 PM

A good sparky should have a nice big tester that can tell if your cooker is faulty or your wiring and besides can measure and draw up a graphic trip curve of your RCD.
Posted By: Trumpy

Re: UK cooker/RCD problem - 09/17/05 07:32 AM

I'm with the majority here,
It could be to do with moisture, but you really don't know.
A-B, take our advice and get a good Electrician.
Best of luck, mate!. [Linked Image]
Posted By: pauluk

Re: UK cooker/RCD problem - 09/17/05 03:05 PM

Yep, it's hard to really be any more specific without testing.

I'd have my megger (high-voltage insulation tester) on the stove to check for leakage, then with the back removed isolate each section in turn and test again to localize the problem.
Posted By: djk

Re: UK cooker/RCD problem - 09/19/05 08:11 AM

While an RCD isn't required by the regs, a 30mA RCD shouldn't really trip with a modern cooker.

I would be particularly concerned if the element tripping the RCD is a halogen / burried in a ceramic hob.

It's well worth getting it professionally checked out.
Posted By: Alan Belson

Re: UK cooker/RCD problem - 09/19/05 08:19 AM

Mushroom,
Dud RCD?. Try another item on the RCD and see if it trips out after 30 seconds.
Alan
Posted By: aussie240

Re: UK cooker/RCD problem - 09/20/05 01:23 AM

When you think about it, 30mA is quite a lot... 7.2W of leakage...enough to fully light one of those miniature incandescent nightlight bulbs.
Water heaters are a classic case of this especially when the copper element casing has split open and keeps working. Depending on how close the split is to the active end, the fuse may blow soon after or the increased current blows the element instead...or if it's at the neutral end it may keep going for years.
30mA is certainly not acceptable leakage for a dry heating element in my opinion. It could be lethal should the earth connection fail.
One way to locate the problem is to simply insert a 15W lamp in series with the active feed, with the neutral disconnected, and to turn on each element one by one. The brilliance of the lamp will indicate if it's just one element or a cumulative effect. The earth still has to be connected of course.
One other thing of course is what else the RCD is supplying.
A classic example of what I mean is in our computer laboratories... the problem has been active to earth current flowing via the RFI suppression capacitors in the computers and their peripherals. Individually, the leakage current is negligible, but with 16 computers it was sufficient to occasionally trip the RCD. Problem was solved by creating mutliple RCD protected power circuits.
I'm just wondering if the RCD supplies other things which are already contributing, say 20mA, live to earth leakage and the cooker's leakage is the the last straw so to speak...in this case, disconnecting everything else supplied by the RCD and only running the cooker would verify it.
Posted By: djk

Re: UK cooker/RCD problem - 09/20/05 09:20 AM

We've everything on several 30mA RCDs and I can honestly say that we've never had any of the problems that I have heard regarding false tripping.

Two fridges, two freezers, washers, dryers, cookers, multiple computers etc.. none of them trip the RCD
The only thing that has ever done it is the iron when water got into the terminals at the back!
Posted By: kiwi

Re: UK cooker/RCD problem - 09/20/05 10:57 AM

I'm of the opinion that all electrical equipment should be protected by RCD.

New heating elements can have a high leakage due to the insulating powder being too damp after the manufacturing process. This is rectified after a couple of hours use as the powder dries out.

Heating elements inherently pose a high risk of high resistance earth faults. Yet our regs here exclude them from RCD protection because of nuisance tripping.

I agree with DJK, these appliances CAN be supplied by RCD. If an element trips an RCD then it should be investigated.

No leakage is good leakage. If its tripping an RCD then it should be disconnected !
Posted By: Trumpy

Re: UK cooker/RCD problem - 09/22/05 12:02 PM

With all this talk of complete RCD protection.
How do you figure Refrigeration Compressor leakage currents fit into that?.
Are we supposed to throw out our fridges after 5-10 years use?.
RCD protection is a joke, in normal conditions RCD's trip too quickly to give anyone that uses them a decent shock.
Sure I could be wrong but, that would help people to realise the actual effects of the current and make true corrective measures.
Don't take me as an egg-head or anything, but with the number of Power Company incidents I've been to that RCD's would not have helped, yet the RCD is championed as the be all and the end all to public safety.
In my opinion it's just slackness on the part of the Authorities.
Posted By: aland

Re: UK cooker/RCD problem - 09/22/05 10:50 PM

I thought an Rcd was only to be classed as a supplementary form of protection against indirect contact!
Posted By: aussie240

Re: UK cooker/RCD problem - 09/23/05 05:32 AM

Proponents of RCD protection tend to gloss over the fact they won't protect you if no current flows to earth. You can put yourself between live and neutral all day long standing on a wooden floor and the RCD is just going to think you're another balanced load and do nothing about it. The hairdryer falling in the bath is always used as a demo...but I wonder...what if the bath is a modern plastic one with a PVC drain? How will the requisite current flow to earth and trip it? I think it does need to be publicised that the RCD will not prevent all electrocutions.
As for leaky appliances, I've been lazy and not got around to replacing the leaky RFI bypass caps on my General Radio beat frequency oscillator...I just plug it into an isolating transformer so it doesn't trip my workshop supply.
Instead of the 'whole house protected by RCD' approach, I prefer to protect individual circuits or appliances. The HPM Electresafe (and their Clipsal equivalent) GPO's are great for that.
Posted By: Texas_Ranger

Re: UK cooker/RCD problem - 09/23/05 02:12 PM

Quote
Are we supposed to throw out our fridges after 5-10 years use?.

Why??? We've been using an ancient 1960ies fridge on a 100mA RCD without ever tripping it! Our recent fridge/freezer combo is 14 years old and never ever tripped the 30mA RCD. So what?
Posted By: pauluk

Re: UK cooker/RCD problem - 09/23/05 04:12 PM

Quote
I think it does need to be publicised that the RCD will not prevent all electrocutions.


Hear hear! Far too much of the advertising I see here seems to leave people with the impression than an RCD is some kind of magical device which will prevent one from ever receiving a dangerous shock.

Sure, phase-to-earth shocks are the most common, but at you say, an RCD won't do a darned thing for somebody who manages to get across phase and neutral, unless there is simultaneous ground current. That's not to mention the fact that a current through the body of a little under 30mA can still be quite dangerous given the right (wrong?) circumstances.

Quote
Instead of the 'whole house protected by RCD' approach, I prefer to protect individual circuits or appliances.


I'd like to see a move toward this approach too. You could base the leakage trip current on the circuit served, maybe 100mA for more "leaky" devices and down to 10mA for sensitive areas (e.g. outlets powering outdoor equipment). It would eliminate the accumulative effects we see now which affect a main RCD, and it would eliminate an entire house being plunged into darkness because an alement on a stove trips the main.
Posted By: aland

Re: UK cooker/RCD problem - 09/23/05 05:13 PM

Agree entirely Paul! Why we dont use rcbo's
more redily I will never know. Money,Money Money all the while I suppose.
Posted By: jooles

Re: UK cooker/RCD problem - 09/23/05 09:02 PM

The "whole-house" thing may be more dangerous than none at all for another reason.

Take a scenario where at bedtime something in the house (someone mentioned old fridges? could be anything actually) causes a nuisance trip. There was no actual electrical danger to anybody, but it has now plunged the whole house into darkness.

In the course of making your way to the meter cupboard to reset the pesky thing, you trip over the cat on the stairs, fall to the bottom, and sustain a broken leg, or worse.

The dangers of having fixed lighting circuits protected in this way seem way out of proportion to the (very small) chance that someone will get a fatal shock off a ceiling fitting.

Perhaps more debatably, nor would I be very keen on the idea of a deep freezer full of food getting knocked offline by a nuisance trip while we went away for two weeks in the middle of summer. I wonder what the insurance broker would have to say about the claim for replacement. They will certainly pay the claim if the freezer itself develops a fault, but when we talk about the electricity being turned off for some other reason, there's too much wriggle room there for my ease of mind.
Posted By: aland

Re: UK cooker/RCD problem - 09/24/05 12:05 AM

Jooles, Good point thats why we have split load type boards, Lighting on None Rcd side or 100ma. Socket circuits and other vulnerable equipment on 30ma trip. If you do put a 30ma trip across the whole lot. You might leave yoursefe open to being sued in the event of a tumble.
Posted By: pauluk

Re: UK cooker/RCD problem - 09/24/05 11:20 AM

Quote
Why we dont use rcbo's more redily I will never know


I think we're in something of a Catch-22 situation at the moment. People will balk at installing RCBOs until the prices come down on them, but the prices won't drop until they're more widely used.
Modern split-load boards help, but they're not without their own problems out here in rural TT-earthing land. By the time you factor in a 100mA time-delay RCD for the main on top of the 30mA RCD sub-main, it can start getting quite expensive.

There's always the option of converting to PME and installing a "normal" split load board, but that's likely to be just as expensive when much of the bonding then needs to be upgraded.

There are still a lot of houses around here on TT with an old voltage-operated ELCB.
Posted By: Trumpy

Re: UK cooker/RCD problem - 09/25/05 09:07 AM

AB,
Quote
Checks with a multimeter reveal no obvious anomalies.

I'd get the thing meggered, this could show up a few things
Posted By: pauluk

Re: UK cooker/RCD problem - 09/25/05 10:31 AM

Yep, a low-voltage ohmmeter test will not always reveal problems that a high-voltage test will show up.

I had an outdoor pond pump like that recently in which damp had gotten in via a crude splice. A low-voltage ohmmeter test showed resistance over 20 meg, yet putting it on a 500V megger revealed the problem instantly.
Posted By: Wolfgang

Re: UK cooker/RCD problem - 09/25/05 08:47 PM

A cooker unused for a longer period of time!

I know internal recommendations of a well known manufacturer, that you are supposed to run and heat the equipment for some time in order to reduce leakage current.

In case of a TT installation with rcd tripping it is recommended to isolate the cooker/oven and to unmount (!) PE conductor in order to achieve drying. Better don't touch it in this phase.

It is not worth to meg the device (if it has not a low ohm failure) before half an hour of ordinary service.

This is not my personal idea!
Posted By: marcspages

Re: UK cooker/RCD problem - 09/26/05 10:41 AM

Hi Guys,

Yip, heard of this one too (disconnect the Protective Earth so as to stop the ECLB/RCD/RCBO - take your pick!) from tripping. Once had a case where this was done and tester/operator was receiving "mild tingles" (i.e. shocked like hell!). It revealed the knobs were conductive!

Solution: Not to disconnect the Earth, but to rather have a non RCD line (or to bypass the RCD) feeding the cooker for the burn-in period but to monitor the leakage current to ascertain the burn-in was complete. If an element failed (shorted) during this time it would either pop the fuse in the cooker (some older cookers had fuses per circuit) and/or trip the main current breaker (usually at the same time the filament tried to escape through the element casing!).

I have continued this practice through all cases of earth leakage problems (especially cookers) by bypassing the RCD but monitoring the leakage current. When the leakage falls below the required mA, return the circuit to normal (reinstate the RCD) and leave behind one very happy customer (and no-one shocked in the process). You'd be surprised at the number of central heating pumps that need this treatment too.

M.
Posted By: kiwi

Re: UK cooker/RCD problem - 09/28/05 01:05 AM

I haven't seen any advertising claiming rcd protection is the " be all and end all " solution to electric shock danger.

When I say all equipment should be rcd protected, I actually meant in the domestic situation. Obviously some equipment in industry will have its exclusions

Single RCD main switches never really took off in NZ. Most sparkies here will have a few in the domestic DB ( 2 lights & 2 power ) or use RCBOs. Eliminating the "plunged into darkness" scenario.

RCDs are just one more tool to minimise electric shock risk and shouldn't be ignored just because of a little nuisance tripping.
Posted By: marcspages

Re: UK cooker/RCD problem - 09/28/05 08:41 AM

Kiwi,

I am fully with you that RCDs are in no way a protection against electric shock, that's what the protective Earth conductor is for.

I believe RCDs are mis-sold. I personally view an RCD as a means to detect latent faults i.e. where a current carrying conductor is attempting to return to its birth place (i.e. Earth/Ground). Usually this involves a high-ish resistance (such as water) and if it was not for the RCD the fault could escalate to a point where it becomes threatening (such as fire).

In short; The RCD is simply another component within the distribution system to protect the electrical installation and devices connected to it, and not as a means to prevent electric shock.

M.
Posted By: Wolfgang

Re: UK cooker/RCD problem - 09/28/05 09:36 AM

In this discussion do not forget that in certain power grids a protection in case of an isolation fault can only be realized by means of an RCD because the loop impedance is to high. In typical TT-systems (France, Belgium for instance) earth leakage even in case of a full short to earth is that weak that a fuse will never trip.

That's why in France RCD's are usually integrated in the mains switch delivered by the PoCo.

So the RCD discussion is not the same for everybody.

[This message has been edited by Wolfgang (edited 09-28-2005).]
Posted By: aland

Re: UK cooker/RCD problem - 09/28/05 11:06 PM

Hi Wolfgang,
Welcome to the mad house.
You mention Belgium and France as having predominantly TT systems, what type do you have in the VERY WEST OF GERMANY? And where is the very West of Germany? Do you have Rcd's fitted as standard by the PoCo?
This thing about it being normal to have a current passing to earth still seems alien to me. Yes,if you have all the equipment to monitor it and logicaly deduce that it's O.K. fine. But so many people buy second and third hand equipment nowerdays nad it gets connected. For Instance the other day I did an inspection on a property; testing revealed that the cooker circuit did not have an earth connection to it,15 years it had been like that. The cooker had been changed once,re-conected by a well known supply house,it turned out to be an earth connection broken off for 15 years. If the cooker had developed a fault, who knows!!! If it trips out it needs proper investigation and thats the end of it as far as I am concerned. regards aland
Posted By: kiwi

Re: UK cooker/RCD problem - 09/29/05 12:02 PM

(France, Belgium for instance) earth leakage even in case of a full short to earth is that weak that a fuse will never trip.

Say it aint so Wolfgang. If I lived in France or Belgium where a full short to earth doesn't blow the fuse, I would emigrate
Posted By: Alan Belson

Re: UK cooker/RCD problem - 09/29/05 12:09 PM

Course it don't blow the fuse! Ridiculous! The meter melts first!

Alan
Posted By: Wolfgang

Re: UK cooker/RCD problem - 09/29/05 12:36 PM

It possible that Alan has got an untypical installation in Mayenne.

But in a typical TT system the local Protective earth is connected to a ground electrode and notbonded to the neutral at any place. (It is forbidden!)

So any current taking the "earth path" has to enter the ground via local electrode and leave via transformer electrode.

So impedancies (is that English, = sum of all inductive, ohm and capacitive resistors in a loop) will be often 50 ohms or more in what we call the "fault loop". As Voltage against ground in France is 230 V (Belgium often 133V) a current of 230 V/50 Ohm = 4,6 Ampere will result. For any fuse or breaker this will be just a normal load.
So it is quite obvious that the only way to guarantee 0.4 seconds until circuit is switched off (harmonized European norms) can be achieved by means of one or nowadays two RCD in a row.

@ Alan Btw You mixed two locations: Sable d'Olonnes and Île d'Oléron

PS: As to France, I heard that formally it is not TT but IT, as often an impedance is between transformer neutral and transformer ground electrode. Usually this is to compensate capacities of the pole-mounted, but isolated cables they use. But practically it works as TT, as long as a definite voltage and current against ground is guaranteed.
Posted By: Wolfgang

Re: UK cooker/RCD problem - 09/29/05 01:40 PM

@ Alan D:

The very West of Germany is just the western border to Belgium and the Netherlands around Aachen.

German power grids have a long history of many little power companies (here used to be 3 of them in one city).

Nevertheless the probably most typical grid is TN-C-S. This means that you got four wires entering your house. One of them is ground and neutral at the same time (in Europe called PEN). The other have 230V against ground and 400 against each other at 120°.

In older installation until 1971 the combined PEN usually continued 'til wall outlet or lamp. So you got just two wires, but one is the earthed Neutral, usually bridged in the outlet between one pole and earth brackets of Schuko! In pre-computer times this worked quite well, if only skilled persons worked on it. Main danger is a breaking PEN leading to full phase voltage on the (metal) bodies of faulty devices. Now it is obsolete as the difference in potentials by high currents using the PEN is a problem for electronic equipment.

Unearthed circuits are usually pre-WW2 or GDR.

Now in an actual installation you separate N and PE at the entrance in a house and bond it to a ground electrode in the foundations (mandatory for new houses). A PEN is today formally only allowed for more than 10mm2 but uncommon. In older houses it is very typical, however.

Actual minimum for a new meter is a 3 phase-63 A mains or 43,5 kW. This is usually enough for 6 of them ,but ...
Fuses become rare and more and more replaced by selective breakers. The N is normally never switched nor protected.

Protection by RCD is for TN-C-S in residences only mandatory for bathrooms and similar and outlets used also from the outside of a house (30 mA).

But in certain regions you also will find TT-grids with different designs.
For TT it is more or less necessary as the principal rule is the above mentioned 0.4 seconds. After that period of time fault voltage must be below 50 VAC. Without RCD it would need a very very good ground electrode system.

That might be enough for the moment. Feel free to correct my technical terms in English, as this is not simple in German already.


[This message has been edited by Wolfgang (edited 09-29-2005).]
Posted By: Texas_Ranger

Re: UK cooker/RCD problem - 09/29/05 03:53 PM

Quote
In older installation until 1971 the combined PEN usually continued 'til wall outlet or lamp. So you got just two wires, but one is the earthed Neutral, usually bridged in the outlet between one pole and earth brackets of Schuko!

Basically TN-C, IMHO a scary system! Some parts of Austria did use it, but it was never very common, personally I haven't seen a TN-C system all my life! I was told about one by a friend, but that was definitely a hefty rural bodge job. He even seemed to be proud of it...
Posted By: Wolfgang

Re: UK cooker/RCD problem - 09/29/05 05:05 PM

As a matter of fact this is all primarily a historical problem.

I suppose that the TN-C system was sort of trick to introduce a grounding in an existing ungrounded pre-war two wire installation at a time when RCD were merely ideas, as first working and payable RCDs were developped in the 60's.
And properly done, with a majority of devices with metal bodies or frames it was a lot safer than before.

Nevertheless, in Germany TN-C up to the level of an appartment or house main switch panel is still quite normal for everything that is more than 20 years old. And on the level of PoCo it is probably the majority.
Posted By: Alan Belson

Re: UK cooker/RCD problem - 09/29/05 05:26 PM

Most French 230v domestic installations have a primary 500ma RCD and a relais de decouplage fitted before the consumer unit. The meter does not really melt, that was a just a joke. [Linked Image]
Les Stables d'Oblong. Yes, sorry, another typo!
Oh, and they weren't Lusitaniens either, ( according to my present wife ), but Pure-Race Spanish horses. The Lusitaniens were Portugese. Or was it French? Anyway, they had four legs.

Alan

[This message has been edited by Alan Belson (edited 09-29-2005).]
Posted By: Alan Belson

Re: UK cooker/RCD problem - 09/30/05 05:12 PM

Wolfgang,
50 ohms between a domestic earth arrangement and the transformer, leading to the assumption that only about 4.5A could flow at 230v. I don't think the current flow to earth needs to go back to the transformer per se. I would expect an earth rod, properly installed to a suitable depth, to achieve 5-10 ohms resistance.

Alan

[This message has been edited by Alan Belson (edited 09-30-2005).]
Posted By: Wolfgang

Re: UK cooker/RCD problem - 09/30/05 06:08 PM

@ Alan Belson

TT-system: transformer neutral grounded, Consumer neutral grounded, no conductor but ground/earth between both electrodes. Voltage against ground equal voltage against neutral.
Quite a lot of power grids use this system all over Europe, particularly in rural areas.


IT-system(ideal): transformer neutral not grounded at all. No voltage against ground (at least in small systems without capacitive connections). First fault allows to continue service.
Typical for hospital emergency sections, sensitive industrial processes, isolation(insulation?) checking device (continuously, with alarming) mandatory.

Conclusion: Without a grounded transformer neutral there will no reasonable current on PE conductor to ground at all in case of a fault.

In France maximum resistance of ground electrode is limited to 100 Ohms by Normes Francaises. They typically use tiny, handy 1m long rods and a 6mm2(?) conductor to connect the PE of a domestic installation.

I got a small house in the Gard (30). There I measured the loop impedance of all the houses around by means of my Amprobe Genius 5080E installation tester:
My house has got a loop impedance of 314 Ohms or a maximum current of 0.8A on PE in case of short to PE! This is really above limit, but protected by a second 30mA RCD.
My neighbours got a very new installation and about 57 ohms. A friend downhill 143 Ohms.

Okay this region is rather dry, but I made the measurements at Easter after a wet winter. As it is down there, nobody bothers as CONSUEL has passed already.

For the 100 Ohms limit I have a very simple explanation:
Voltage of the bodies of faulty devices against ground shall be limited to 50VAC by harmonized norms. 50 Volts/100 Ohms equal 0.5 Ampere and zhis is exactly what you find on the EDF-RCD in the "branchement", also in yours, as you told us.

To achieve 5 Ohms on a ground electrode is not that simple at all. More difficult furthermore, to guarantee this value all over the year. Even in much wetter Germany no one expects that value for much longer and thicker electrodes than used in France.
Posted By: Texas_Ranger

Re: UK cooker/RCD problem - 09/30/05 08:52 PM

Only most recently Vienna's distribution is being changed over from TT to TN, so there was no way to do TN-C. To make things even nicer, until the late 1970ies large parts of Vienna ran on a 127/220V grid without neutral (I assume wye connected transformers with grounded star point, but the neutral was not supplied to the customers).
So the most common way of grounding at least kitchen and bathroom outlets was until 01/01/01 running a ground wire to the nearest available water pipe, using it as a grounding electrode (or in better cases just as a grounding conductor up to the equipotential bonding in the basement). Even though such systems have to be replaced I'm pretty sure many of them are still around. I've seen one today... too bad the water mains are all PEx tubing... [Linked Image] Think that would affect the ground resistance? [Linked Image] [Linked Image] [Linked Image]
In Austria we're limited to a maximum of 165 ohms.

With new TN-C supplies the PEN has to be grounded locally and is split up at the service entrance point (Hausanschlußkasten). Approved means of grounding are flat iron 3x30mm or round copper, 30mm in diameter and 4.5m long.
Where in Germany Schuko sockets with TN-C jumpers were retrofitted in Vienna (and most parts of Austria) the old ungrounded sockets were just left in place. Today I checked out an apartment that has one single Schuko socket on 100sq. m...
Posted By: pauluk

Re: UK cooker/RCD problem - 10/01/05 01:31 PM

Guten Tag Wolfgang,

Welcome to the forum.

In Britain we have TN-S, TN-C-S, and TT in use, which complicates earthing arrangements considerably.

TN-S was installed in the old urban areas, most of the distribution being by armored underground cables with the armor used as the separate earthing path back to the sub-station.

TT was the norm in rural areas for a long time, and necessitated the use of various earth-leakage devices just as for the TT systems common in France.

In residential applications, the voltage-operated ELCB (Earth-Leakage Circuit Breaker) was the norm for a long time, and many are still in use although now obsolete. These were superseded by the current-operated ELCB, or RCD to use the present-day terminology, which has gradually increased in sensitivity over the years.

As you say, with the high loop impedance which is possible on a TT system, the use of such a device is the only way to ensure that the power is disconnected at all, nevermind that it happens within the 0.4 second specified by the current regs.

TN-C-S was called PME here -- Protective Multiple Earthing. Its use goes back to at least the 1930s, but originally it was only used in specific rural areas in which local conditions made it very difficult to get a good ground connection. In fact the installation of a PME distribution system for an area back in the early days had to be by the explicit approval of the Secretary of State.

Gradually, TN-C-S has become more widely accepted and used, especially over the last 25 years or so. Extra earth connections have been installed on the neutrals of distribution lines, and it's now possible for any installation to be connected as TN-C-S.

Even though PME earthing is available now to all, of course there are still many properties using their own local earth and wired as TT. In my immediate neighborhood (rural Norfolk) I would estimate that at least 90% of domestic systems are still TT.

Where PME/TN-C-S is used here, the bond is at the service block just before the meter. From that point onward, neutral and earth are kept strictly separate.

There are some diagrams showing the various British arrangements here:
https://www.electrical-contractor.net/ubb/Forum15/HTML/000044.html


Quote
Voltage of the bodies of faulty devices against ground shall be limited to 50VAC by harmonized norms. 50 Volts/100 Ohms equal 0.5 Ampere and zhis is exactly what you find on the EDF-RCD in the "branchement", also in yours, as you told us.


The 50-volt figure was also the limit set for the voltage-operated ELCB here. In practice, most of them would actually trip at a much lower voltage.


Quote
So impedancies (is that English, = sum of all inductive, ohm and capacitive resistors in a loop)


Yes, in English:

R = resistance
X = reactance (capacitive or inductive)
Z = impedance, i.e. SQRT (R^2 + X^2)

Plural: impedances [Linked Image]

Quote
Feel free to correct my technical terms in English, as this is not simple in German already.


Your English is far better than our German I'm sure (Texas_Ranger excepted [Linked Image] ).

Those long technical terms in German are scary! [Linked Image] [Linked Image]



[This message has been edited by pauluk (edited 10-01-2005).]
Posted By: Texas_Ranger

Re: UK cooker/RCD problem - 10/01/05 02:31 PM

Surprisingly the letters for resistance, reactance, and impedance are the same in English and German. i think voltage (German U) and current (German I) are different. Power is P, apparent power (U*I, given in VA) is S and reactive power (unit var) is Q. Inductive reactance is XL and capacitive reactance is XC (subscript L and C).

Back to earthing arrangements... for some reason the voltage in Austria is 65V AC, not 50.

Voltage operated ELCB - German FU (Fault voltage interruptor)
Posted By: Alan Belson

Re: UK cooker/RCD problem - 10/01/05 08:21 PM

HELP!!!! This thread has given me a real headache! Wolfgang's revelations about the effectiveness of earthing via a simple rod have led me to realise that my three-phase antique woodworking machines, run off a generator, have inadequate protection against earth faults/shock.
The alternator is wired star, and makes around 400v 50hz. A full description has been been posted, (see Photos for Discussion 5-18-05), and at that time I re-wired centre star to earth on advice from the Forum. There's about 10 metres max. between the alternator and the furthest machine, and I have a 10A 3ph breaker as overload, which see. All machines are earthed using a discrete shop 4 ft copper rod into heavy clay.
Ideas anyone?

Alan
Oh, and thanks Wolfgang!
Posted By: Wolfgang

Re: UK cooker/RCD problem - 10/03/05 05:09 AM

@ Alan Belson:

Sorry, not regularly online at the moment.

1. Might be better to open a new thread?!
(Started with a leaking cooker, didn't we?)

2. Can you load up a wiring scheme of your existing installation.

3. Is that workshop in UK or F, public or completely private.

CU Wolfgang

[This message has been edited by Wolfgang (edited 10-03-2005).]
Posted By: pauluk

Re: UK cooker/RCD problem - 10/04/05 10:09 AM

Quote
Surprisingly the letters for resistance, reactance, and impedance are the same in English and German. i think voltage (German U) and current (German I) are different.


The symbol I is used for current in English too. (C is capacitance).

Voltage is normally V or E, but with harmonized standards coming into effect many "official" sources such as the I.E.E. are now using U for voltage as well.

Isn't "Spannung" the German for voltage?
Posted By: pauluk

Re: UK cooker/RCD problem - 10/04/05 10:20 AM

Quote
Might be better to open a new thread?!
(Started with a leaking cooker, didn't we?)


Yep, a good idea. I've opened a new thread here .

Wolfgang -- Alan's workshop is in France where he now lives.
Posted By: Texas_Ranger

Re: UK cooker/RCD problem - 10/04/05 02:37 PM

Quote
Isn't "Spannung" the German for voltage?

Correct. I don't have the slightest idea where the letter U is derived from.
Posted By: Wolfgang

Re: UK cooker/RCD problem - 10/04/05 06:46 PM

German Wiki says that U might be derived from Latin urgere = to drive .See English "urgent"
Posted By: briselec

Re: UK cooker/RCD problem - 03/11/06 01:11 PM

Quote
I am fully with you that RCDs are in no way a protection against electric shock, that's what the protective Earth conductor is for.


Actually the reason for having an earthing system is a bit more complicated than that. Think about it .. if you have no earthing system then what would happen if you touched an appliance with a live metal case...nothing!
Posted By: briselec

Re: UK cooker/RCD problem - 03/11/06 01:19 PM

Quote
In NZ and Australia the wiring regs exempt cookers and ranges from requiring RCD protection, and I have always assumed that the reasoning for this is that cooker elements have a naturally high earth leakage current


No it's because fixed appliances aren't regarded as being as likely to cause an electric shock as much as portable appliances.
Posted By: pauluk

Re: UK cooker/RCD problem - 03/11/06 01:21 PM

Hence also the disconnect time rules of 0.4 sec. for outlets feeding portable appliances and 5 seconds for fixed appliances.
Posted By: briselec

Re: UK cooker/RCD problem - 03/11/06 01:27 PM

Quote
I thought an Rcd was only to be classed as a supplementary form of protection against indirect contact!


That's not what our wiring rules tells us. There are certain ways you are not allowed to run cables UNLESS the circuit is protected by an RCD. It is a brilliant device but it concerns me that decision makers tend to look upon RCDs as an alternative to safe methods.
Posted By: pauluk

Re: UK cooker/RCD problem - 03/12/06 03:01 PM

Quote
It is a brilliant device but it concerns me that decision makers tend to look upon RCDs as an alternative to safe methods.


The problem is that so many memebers of the general public also seem to believe that the RCD is some sort of magic device that protects against all known shock hazards, wards off evil electrical spirits, etc. The advertising blurb has done a lot to foster that belief, and there really are those who believe that with an RCD they are totally immune to getting a shock.

Just try getting yourself across phase and neutral and wait for that RCD to protect you. [Linked Image]
Posted By: Trumpy

Re: UK cooker/RCD problem - 03/12/06 03:10 PM

Exactly Paul,
You and I have had discussions about these devices.
Are'nt they just the darlings of the PC crew.
"Prevent ALL electric shock".
My A***.
Like most things, they haven't yet been idiot-proofed.
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