There's no longer anything in the regs about it that I recall. (The concept of earth resistance area isn't even mentioned now that voltage operated ELCB's aren't in the regs any more, except for a dangling reference in the index which points to the Part 2 definition which is no longer there;-)
However, it would still be a good thing to do, but not for the sake of the RCD which doesn't care.
The 14th Edition regs may have said how to measure it (sadly I've lost mine). I don't have the exact definition to hand, but ISTR it was the area round the earth rod where a voltage difference was measureable (relative to some more distant point in the ground) as a result of leaking current into the earth rod under test. I can't remember how much current you were required to leak into the rod for the test.
However, as I said, this isn't so critical for RCD's which won't nuisance trip if some portion of someone else's nearby earth leakage is finding its way back up your earth rod due to overlapping earth resistance areas.
1 protect against electrocution from the earthed wiring ( a very real and serious problem with TT installs),
cut the supply if leakage is excessively high, which also to some extent acts against high bills caused by earth leakage. However this is secondary to 1.
Number 1 is the whole reason theyre installed. Why else?
I gave these details above, explaining they also dont protect against live conductor touches... I dont understand how exactly youre saying all this is false, or what extra explanation youre giving.
I've lived with both: ELCB 1 nuisance trip per 20 years, RCD long lost count. Both nuisance trip, but RCDs are orders of magnitude worse.
The ELCB is there to protect against high earth fault loop impedance due to high earth resistance, typical of earth rods. It measures the product of the leakage current and earth resistance (which happens to be the voltage between the house earth zone and real earth), and if it gets too high for the fault current protective device (fuse/MCB) to reliably trip, the ELCB trips instead. They do not protect against electrocution at all -- earth bonding means you can't get electrocuted even if there's an earth fault and the ELCB wasn't installed.
That bit isn't false, but the idea that they are to protect against electrocution is false. They are to protect against high earth fault loop impedance, which would otherwise prevent fault current protection devices operating and could result in cable damage and fires.
Others have different experiences. I've installed loads of RCDs amongst friends/family who would certainly tell me if they had ever tripped, and I've never had a single incident of a nuisance trip -- the one trip which has happened was a genuine fault. I would suspect you have a real fault if you have RCD's tripping frequently.
On 18 Jun 2005 00:52:56 GMT,it is alleged that snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) spake thusly in uk.d-i-y:
I can second the differing experience part with RCDs. Others say they nuisance trip, can't say I have experienced that. The times mine on the shed and garage tripped were in one instance a burned out connection box, which caused phase/earth flashover, thus a genuine fault, and the other occasion that both of them tripped together was a lightning strike next to the local substation. The surge fried the PBX and 2 tvs, so that probably counts as a 'genuine trip' too:-)
but what is being protected? Only the human user, and against what?
yup
no it does not. Even crossbonding everything does not produce safety against electrocution from a live earth cpc. Why? Stand on a damp concrete bathroom floor and find out. (well, dont, but...) Use a metal bodied drill outdoors and find out...
Having the earth system rise up near live voltage is very much a risk, and it is precisely this that ELCBs protect against. The 1st thing they protect in these situations is the user from electrocution. The 2nd is the user from fire, if the fault gets hot. And almost incidentally, a correct trip tells the user there is a fault leading to a high bill, thus it causes this to be avoided.
And electrocution. The cable is already damaged, its just electrocution and fire.
This is to be expected. I didnt say every install suffers nuisance trips, just that RCDs have orders of magnitude more problems. Most people are ok, but many have endless nuisance trips, a problem far rarer with ELCBs.
Usually these nuisance trips are due to normal safe leakage levels on appliances that normally leak, such as cookers, washing machines, immersion heaters etc, plus the total leakage of other appliances. None of these constitute a genuine fault in the majority of cases. Sure they trip when there is a fault, but they too often trip when there isnt.
If I had to choose between one single ELCB or RCD for a whole house install, I'd choose ELCB... unless I had an electric shower, then I'd go for the better cover of RCD.
1st this problem can only occur if they are incorrectly installed, with the earth rods of 2 houses in close proximity.
2ndly One also has to get near 240v on the foreign earth to get the problematic 50v on your sense earth. This will of course be detected and rectified very quickly, either as a result of the neighbours ELCB or RCD, either of which is universal on earth rod protected systems. Or even if the neighbour has a 1930s install with no protection, they will soon get a shock and get it fixed. Either way its a self fixing problem, even when the thing was installed wrongly.
2nd this is a lot rarer than RCD nuisance trips.
3rd it is usually self fixing, and in the exceptional case that its not, its probably easier to fix than RCD troubles:
ELCB nuisance trip fixing: hammer in new earth rod further along wall, extend earth wire, done. Expect no further problem.
RCD nuisance trip fixing: PAT test all appliances replace an often satisfactory appliance or Trace neutral/earth connections throughout install trace borrowed neutrals throughout install. Insulation test install Rewire any problem ... and know in either case that nuisance trips may occur in future.
ELCBs arent the ultimate in earth leakage protection, but they do have real advnatages over RCDs as well as cons, and are in some respects the better device. And it is better in some cases not be replace them with an RCD.
Confirming Andrews remarks about VOELCB nuisance tripping often being caused outside the dwelling. We had one some years ago which tripped every time the farmer down the line switched on certain bits of equipment. Couldn't actually prove it but it happened when his milking parlour lights were on which strongly suggested it was the milking machine. Disconnecting (temporarily) the water main and immersion heater earth as a test stopped the problem. Easiest and cheapest solution was to fit a current operated breaker (when they were still called current operated earth leakage breakers) IIRC correctly they tripped at 500mA in those days
You may have room to relocate your earth rod but in many village cases this was a luxury simply not available.
You make the mistake of assuming a degree of sense in some people which is simply not there. I used to come across cookers which often gave shocks to people stirring a pan and this was accepted as part of the way of things with electricity. Stupid but thats joe public sometimes!
Except when you are one of the sufferers. I have personally had nuisance tripping from a VOELCB in one house I lived in.
You have been fortunate.
Nuisance tripping "usually" comes down to cookers or immersion heaters. The early concept of 30mA whole house protection was found to be unsuitable because of nuisance tripping, which is why split load CSUs were developed and the use of 100mA time delayed breakers gives discrimination from downstream 30mA "instant" types. Horses for courses as with all things. The use of TN-C-S systems in rural areas has rolled out to nearly everywhere now so with the exception of ensuring that sockets liable to supply equipment outdoors and "some" shower makers recommendations the argument is becoming academic.
Double pole switching especially on such as cooker grills could sometimes cause sensetive trips to operate if the neutral closed after the live and an imbalanced inrush took place.
Earth leakage circuit breaker things? Yes. But most are now incorporated in to a Residual Current Device (RCD), which works on both earth leakage and load conductor imbalance. Just a step forward in the technology used in the ELCB.
Not at all. Overlapping earth resistance areas is only one of many reasons they can trip. It's not at all uncommon to find substantial ground currents in many places, and these can cause repeated tripping. Lightning is another source, albeit the cause of the trip being more instantly obvious (if you are there when it happens).
Most of them trip well below 50V. 50V was the 'must trip by' voltage.
Can easily make no difference, or make things worse. Also you missed out the part where you diagnosed that the problem is nuisance tripping and not a real fault. That's not at all easy -- actually it was almost impossible unless you are lucky enough to get the trip happen at the same instant you operate some appliance.
how is this possible? A terrace house, since theyre the densest, has several metres of both frontage and backage... one would have to remarkably unlucky to have 2 neighbours both with live earth systems, one with a rod on the corner next to your house at back, and one similarly at front.
Of course there are always idiots, but most people dont accept that and do fix it.
whether one suffers or not makes no difference to which happens more often. An RCD trips on a range of non-fault and fault conditions an ELCB does not.
not relevant.
If you have tens of volts (upto 50v) between house cpc and the sense rod, you have a problem that needs fixing. The ELCB removes the power for a reason.
The fact that it can not always determine wheher this is caused by a neighbouring install is true, though usually they will. But despite their limitations they still nuisance much trip less than RCDs. That is why, despite the millios of ELCBs in use, we regularly get asked here how to sort out RCD trip problems, and almost never get asked how to sort out a nuisance tripping ELCB. ELCBs are dramatically superior in this respect.
It may be in 50 years time, when the millions of present TT with ELCB installs are finally rewired. But clearly not now.
I also would not completely rule out a return to ELCBs from RCDs. Probably wont happen, but there is a case to be made.
you can only have an imbalanced inrush if you have an earth leakage issue. The reason this scenario can cause tripping is that below par insulation near the neutral end will conduct very little when on, since there is very little v diff across it. Now apply live but not neutral, and suddenly there is 240v ac across them, and current flows.
RCDs trip more in these cases of course. An RCD will trip at 15-30mA leakage minus other leakges on the same circuit. An ELCB will only trip when there is so much leakage current that the house cpc v rises. Pros and cons.
this has been covered already. I said _this_ problem, not any and every trip.
how will moving your earth rod away from teh neighbours nearby one make things worse or make no difference? The only situation in which no difference occurs is when there is a real fault, and the ELCB is acting on it.
its a lot easier than RCD trip disgnosis. Apply multimeter to ELCB earth terminals... the rest is obvious enough.
some are real, some are nuisance. The majority are just nuisance trips.
You do not seem to have seen a village terrace with electricity supply via twin Vic on porcelain supports, 3 ft wide paved footpath in contact with the front house wall, then tarmac road immediately across the front of the terrace and house width in the order of 3 to 4 metres. These houses still exist and are now often listed. I grew up in such a village albeit not in one of the terraces, and its still there. The electricity was fed in above the front door straight into an undertakers service unit and meter.
In your world, unfortunately there are others. This is not to say I personally find it acceptable.
Your stance is dogmatic but is not shared by the rest of the electrical engineering world. Could it be that you are the only one in step and the rest of the world are wrong? (This is a hypothetical question BTW - dont bother to answer it)
A response which I would have epected from DIMM but you seemed more logical up till that :-(
The parallel paths to earth would hold down the voltage rise below the operating point of the unit. Real but minor faults would not show unless routine testing showed them up. Routine testing was poorly supported until of late and is still almost unheard of amongst the public :-(
Just to clarify for me - are you saying you advise customers to get rid of their industry accepted RCDs and replace with VOELCBs?
You haven't convinced me yet!
Since you are referring to old but still operating wiring and appliances many of the old grills showed low resistance to earth when turned on from cold, especially after being splashed with fat/moisture from cooking. Storage heaters with bare coiled elements similarly until they had burnt off/dried out moisture etc. Other sources of leakage include of course certain suppressor/snubber networks to be found in equipment
Exactly so! Due to the parallel/alternate earth paths mentioned above. An RCD will trip due to the more significant leakage long before forcing the cpc network to rise to these levels. Your argument relies on not actually doing the job of protecting the system which an effective Earth Leakage unit should do but relying on alternate paths holding down the voltage by shunting off the leakage current(s)
Sorry but this is not even a sensible interpretation. It would be about as sensible as me replying 'you must have never heard of a drill.'
I think you'll find pretty much everyone in the lec eng world knows RCDs trip on conditions ELCBs dont.
um, no. The traffic of questions on ukdiy about RCD trips, and the lack of qs about ELCB trips does rather confirm my position on this. There is nothing novel or unique about my view that RCDs nuisance trip more than ELCBs.
I would have picked another adjective.
Are you seriously implying that one personal experience has any relevance to determining the question of which trips more?? I sure hope not.
To which parallel paths do you refer?
And frankly its pretty obvious that the v_rise does not always stay below the ELCB operating voltage - if that were so they would never have begun being installed in the first place. Let alone end up mandated in the 14th edition of our national wiring regs.
I would suggest this is incredibly obvious. May I suggest you either wake up before posting, or wait till sober?
Yes, this has been well covered already.
I have never said any such thing. Are you being serious?
Of course, I havent even made the case. Nor do I intend to, unless you can come back with sensible answers next time.
we agree on something.
I dont see any parallel earth paths mentioned above... maybe you mean in some other post? I can honestly only think of one single earth path for your typical cooker.... down the CPC and to the earth.
Of course if the cooker were installed in a bathroom with crossbonding there might be parallel paths... I wouldnt put it past you. :)
agreed
Er, no the ELCB does it, but it does it in a very different way. It does do the job. And does it without the problems caused by RCDs.
If you dont think an ELCB provides protection, you a) dont understand ELCBs b) cant think straight enough to realise that they were mandated in the regs for a reason.
What alternate paths are you referring to?
And yes, thats what the earth is there for, to shunt away leakage currents so the device remains safe to the user. That is one of the main purposes of the cpc to earth.
We are at such different stances I really don't see the point of continuing this argument. Your assertation that VO devices are superior to RCDs is not shared by most of the industry or they would still be accepted as the way to deal with protection.
Please continue in your approach and enjoy your life also. I happen to think you are wrong but you have the freedom of expression in this country (which has RCDs mandated as our present means of protection in the British Standards and other inductry official publications.)
Thanks again, to Chipmunk and Andrew especially, and apologies for starting another NT v the rest thread.
I've had another look at the setup. The incoming supply is here:
formatting link
a closeup of the earth terminal here:
formatting link
is indeed next to the incoming neutral. There is also what appears to be a covered flat strip emerging from the incoming cable sheath immediately below the box and entering it just in front of the main cable. One the two 16mm^2 cables is connected to the upstairs flat's installation, and the other goes to an earth block with connections to the equipotential bonding of the incoming gas pipes. A smaller cable disappears under the floor.
So it's looking like a TN C-S setup? The isolator which is adjacent to the incomer and the Chilton VO trip contains a 60A fuse, which gives me some comfort about the 16mm^2 T&E to the CU.
I'm still minded to replace the CU with a split-load unit (Volex from Screwfix or GE from Toolstation - opinions?), and to connect all the green or green/yellow cables at the incomer/meter board together, with a beefed-up cable linking the "earth" of the 16mm T&E directly to the other earths rather than via the trip. Am I right that it does not matter if one of the untraced green cables does indeed go to an earth rod under the floor?
Since the earth trip will then be redundant, would it be better to remove it completely and replace it either with a Henley block or a
100mA time-delayed RCD in an enclosure? I'd prefer to avoid new tails, as even I don't reckon to break meter seals.
To allay concerns others have rightly expressed: I'm buying a copy of the On-Site Guide, and the fact that it's a flat doesn't really come into it: my daughter owns the freehold of the whole property, with the upstairs flat, which has its own meter on a different phase from the incomer, leased.
One for the rogues gallery: the isolator has a bit of length of 0.5mm^2 three-core flex poked into its output terminals to feed the bell transformer
formatting link
what to do with that - the ring main is yards away.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.