Voltage operated ELCB - what's wrong with them?
- Thread starter davetheglitz
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It's not pedantry, they are 2 different terms for 2 different things. I've never said that they aren't mostly used interchangeably and that TN-C-S does generally mean PME in the UK as you won;t get one without the other in most cases. Still doesn;t mean they are still one and the same though.
The Hoover and Electrolux reference is not comparable, neither PME nor TN-C-S are brand names.
The key point of importance with the old voltage-operated ELCB is to make sure that the earth reference electrode is completely outside the resistance gradient areas of any other electrodes (including unintentional electrodes such as buried supply pipes which are bonded to the installation's earthing system).
If the electrode overlaps the resistance area of any electrodes which are connected to the "F" terminal of the ELCB, then it is desensitized and requires a higher voltage before it trips. If the electrode is within the resistance area of any electrodes on neighboring installations, then you can get nuisance tripping due to a fault on that neighboring installation.
For the same reason, that's why the old Wiring Regs. also specified that the conductor between the "E" terminal of the ELCB and the electrode should be insulated.
If the electrode overlaps the resistance area of any electrodes which are connected to the "F" terminal of the ELCB, then it is desensitized and requires a higher voltage before it trips. If the electrode is within the resistance area of any electrodes on neighboring installations, then you can get nuisance tripping due to a fault on that neighboring installation.
For the same reason, that's why the old Wiring Regs. also specified that the conductor between the "E" terminal of the ELCB and the electrode should be insulated.
Getting a bit fed up of people making 'random' statements, without explanation
Then, people who read the posts take these points as gospel - which is how the 'fairy stories' start. (earths to outhouses lol)
So, if you don't mind:
Explain, please
Explain, please
Then, people who read the posts take these points as gospel - which is how the 'fairy stories' start. (earths to outhouses lol)
So, if you don't mind:
Explain, please
and
Explain, please
What's random about N-E touching and tripping RCD, its an everday occurrence as observed by anyone who works on RCD protected circuits. When I'm feeling keen I disconnect N at CU for circuit as well as isolating L to avoid such nuisnace tripping. If you want a technical explanation say so - I'm sure someone will oblige, unless you want to provide one yourself or give a counter argument? :| ?:| ? :| ?:|
It isn't an everyday occurrence on ALL RCD's, only on those where there is a potential difference between N and E. My RCD doesn't trip on N-E faults IIRC.
I think that's what he was getting at, the fact you made an incorrect statement.
I want to be perfectly clear what you are claiming here before giving a counter argument.
17th edition board, main switch closed, RCDs closed, MCBs open.
Are you saying that touching neutral to earth on any of the 'isolated circuits' will trip the RCD? (ie neutral/earth fault)
And if you are right, why is Davetheglitz claiming that a neutral to earth fault won't trip an RCD - in fact it will disable it? What's the earthing system got to do with it?
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Generally I find if you touch neutral to earth on most systems even with circuit switched off RCD will trip exception is TN-C-S system which may not. I do not know how others can get away with it not happening but it does happen to me and thats the honest truth guvner.
Are you an escapy from some other forum?? I don't have time to spend numerous hours correcting and contemplating every word or phrase used. It's pretty obvious what I mean - deal with it and kindly stop being bleeding predantic
Precisely :^O
I'm not being pedantic - I asked if what I described is what you are saying.Are you an escapy from some other forum?? I don't have time to spend numerous hours correcting and contemplating every word or phrase used. It's pretty obvious what I mean - deal with it and kindly stop being bleeding predantic
By taking this approach, all you are proving is that you have no idea what you are talking about.
And No, it's not obvious what you mean - coz an RCD won't trip every time on an isolated circuit, by touching neutral to earth.
You make a statement and then can't back it up with an explanation.
An RCD monitors current out against current in - nothing to do with the CPC - so, in the scenario that I posted, if there is no current flowing in the circuit (isolated), then there is no current to monitor, so it's not going to trip anything!! Now that's 'pretty obvious'
davetheglitz
Electrician
Getting a bit fed up of people making 'random' statements, without explanation
So, if you don't mind QUOTE]
This was not a random statement - it was pertinent to point out that all systems have their limitations. The subject has been talked about on the forum before - and I thought my posts have been nerdy enough without going into the detail. If we took this to he Nth degree then there would be no free flow of conversation on here. However the way I look at it is as follows:-
Re RCD's and N-E faults. Consider a TT system with a N-E fault. The earth rod is now effectively shunted by a very low impedance. This means that if someone touches live there is now no mechanism for the RCD to detect this as you are now effectively connected bettween live and neutral - not good.
The only way you would know about the fault was if 30mA of current flowed through the shunted earth path.
Assume a rod with Ze of 500 ohms carring 30mA. This means the voltage across this would be I x R = 15v. Considering the shunt path to neutral - possibly 0.2 ohms - this means that 30mA would flow through the earth rod when 15/0.2 A flows through the neutral path. This is 75A - probably in most houses this never occurs.
Upshot is the RCD is effectively disabled - but the test button will still work as this is not reliant on an earth connection.
It's easy to put on a N-E fault during routine maintenance - side screws on metal light fittings especially.
Figures here illustrate the point - but if the Ze was 50 ohms the RCD would trip when 7.5A was flowing in circuit - this would manifest itself as an intermittent trip on the TT systems which seems to have no single cause. The fault has nothing to do with any one circuit as such - it's just that the load is sufficient to get 30mA of difference in the neutral current.
davetheglitz
Electrician
Absolute star post!!!! The earth rod and the gas bond at this place are at the opposite diagonal of a large bungalow - so it seems that I've got away with it in this case - particularly as the water comes in on plastic. Thanks again!
S'funny how every one else knows what I'm on about.I'm not being pedantic - I asked if what I described is what you are saying.By taking this approach, all you are proving is that you have no idea what you are talking about.
And No, it's not obvious what you mean - coz an RCD won't trip every time on an isolated circuit, by touching neutral to earth.
You make a statement and then can't back it up with an explanation.
An RCD monitors current out against current in - nothing to do with the CPC - so, in the scenario that I posted, if there is no current flowing in the circuit (isolated), then there is no current to monitor, so it's not going to trip anything!! Now that's 'pretty obvious'
One other point though Dave, given that the units are now at least 30 years old, I wouldn't trust them anyway, or a 30 year old RCD on which no one ever presses the test button. Intersting post from PBC-1966. Is that your year of birth PBC
davetheglitz
Electrician
Agree completely - but my customer was adamant that there was nothing wrong with it - and unfortunately he was right in this case!!!! Was hoping for a board change at a later date - but never mind!!
