Hiya guys will an RCD or RCBO work if there is no earth in the house?A fellow worker said to me today that there is no need for an earth in a house if the board has an RCD or is controlled by RCBOs as they work on the inbalance of the live and neutral.
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PAUL M
Tell Your Mate He Is Talking Out His ---,of Course You Have To Have An Earth,they Work By Detecting Earth Leakage.
Thats what i said to him bud but he was adamant cause he had done his 17th and ive no i started questioning myself.
C
Cirrus
Or any quals!!!
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wayne
the guy has the half baked opinion that sends us to the text boooks to check
correct me if i am wrong here, but its not that they detect the earth leakage persay, but of an imbalance of the neutral and line, due to current flowing via earth... ?
Luke
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MacSparky
why do you need a seperate earth to make rcd,s and rcbo's work?
an rcd will actuate at around 22-30 milliamps, either of the phase conductors could come loose and touch exposed metal work which would allow the cpd to work,(connected to cpc or not),..... surely as scotty mentioned its a minute inbalance that would trip them....earth leakage that is. Non rcd/rcbo cpd's would require cpc for sure. Hope i'm not missing the point here
an rcd will actuate at around 22-30 milliamps, either of the phase conductors could come loose and touch exposed metal work which would allow the cpd to work,(connected to cpc or not),..... surely as scotty mentioned its a minute inbalance that would trip them....earth leakage that is. Non rcd/rcbo cpd's would require cpc for sure. Hope i'm not missing the point here
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Shakey
everyone is a bit right - and some are a bit wrong here.
An RCD does not need an Earth per se, but needs an EARTH PATH
it is quite conceivable to have a house with no incoming earth, but there would be an alternaive path though the CPC to the MET, through the protective bonding and down to earth though any extraneous conductive paths (gas, water pipes etc)
as long as that path is 1667 ohms or less, the RCD would trip before the fault voltage reached the magical 50V, and even with a path of 7666 ohms or less would still trip.
Of course we need an earth path for CPD's to work correctly, but an RCD, with ANY path to earth as stated above, will trip off
and before anyone starts thumping the keyboard, I am NOT suggesting using an RCD means you dont have to have an incoming earth
An RCD does not need an Earth per se, but needs an EARTH PATH
it is quite conceivable to have a house with no incoming earth, but there would be an alternaive path though the CPC to the MET, through the protective bonding and down to earth though any extraneous conductive paths (gas, water pipes etc)
as long as that path is 1667 ohms or less, the RCD would trip before the fault voltage reached the magical 50V, and even with a path of 7666 ohms or less would still trip.
Of course we need an earth path for CPD's to work correctly, but an RCD, with ANY path to earth as stated above, will trip off
and before anyone starts thumping the keyboard, I am NOT suggesting using an RCD means you dont have to have an incoming earth
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PAUL M
yes i know that but if there no earth path what then.
Listen mate im on your side lol.Hes a wee know it all ---- who has done a 17th course and is spouting out all this crap all the time.trouble is he is so sincere about it half the guys at work are starting to believe him.He is adamant the new regs say that if the board is protected by an rcd or if individual circuits all have rcbos then there is no need for an earth because the rcd/rcbo will operate on the imbalance of live and neutral.
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Shakey
ok, I have explained how an RCD COULD work without an incoming earth with an extraneous path of 7666 ohms or less (but probably not in the required time), but that is an accidental by-product of there being no earth in the first place
How the hell does this guy think ADS will be achieved
I teach 17th edition, and this guy is talking utter tosh
he has no doubt misenterpreted something he was told on the course
along the lines of RCD protected circuits only needing a Zs of 1667 ohms or less for their 60898 MCB's etc etc
If you want to 'douse his flames' a little, ask him for the relevant regs numbers to back up his 'theories'
M
Moog
I agree it will trip if the phase and neutral currents are not the same, however I would not sign off an installation without an adequate earth path unless it was SELV for instance You sure this guy isn't on about bonding? not done my 17th conversion yet but there was take about there not being a requirement for bonding in bathrooms anymore
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Shakey
bit more complicated than that Moog, for bathrooms, but yeah, if all conditions are met, then no supplementary
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WarrenG
O.K. it seems that there is some agreement on the workings of an RCD on this post.
An RCD protects by constantly monitoring the current flowing in the live and neutral wires supplying a circuit or an individual item of equipment.
The supply and the load are both connected to EARTH
Under normal circumstances, the current flowing in the two wires is equal. When an earth leakage occurs due to a fault in the circuit or an accident with the equipment, an imbalance occurs and this is detected by the RCD, which automatically cuts off the power before injury or damage can result.
If there is an imbalance in a circuit protected by the RCD, the leakage current has got to be going somewhere. If there is no earth path to take the current to earth, what is going to take it there? a person who recieves a shock from live metal work?
I think your friend should study the 16th Edition before trying the 17th Edition.
I think your friend should study the 16th Edition before trying the 17th Edition.
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Shakey
Like I said Warren, there may be an 'accidental' earth path through any extraneous paths, which, if 7666 ohms or less, would still allow the RCD to trip, but it is most defintely NOT in the 17th that you dont need an inscoming earth because of it
I think your mate is confusing a Main supply earth and equipotential bonding. The 17th does not require you to install equipotential bonding to pipes such as a bath room basin as long as the circuits in the bathroom are protected by an RCD. Every installation must have a main earth.
Sorry, meant supplimentary bonding not equipotential.
Sorry, meant supplimentary bonding not equipotential.
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W
wattsup
Perhaps it's a double insulated house
A
alancp
shakey, i understand about the 1667 ohms bit, but, shouldnt it be lower than that (exact figure not known at mo) to do away with an unreliable earth path??
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Shakey
depends what you mean by 'do away with'
No value would allow you to do away with an unreliable earth
Or are you refering to the value of 200 ohms for TT earth electrodes?
This is the max value at which it could be condidered a 'stable reading', but is not a max value as far as the RCD is concerned
there is no 'leeway' for an unreliable earth
D
Dinosaur
No Earth path - No electric shock???????????
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tony.towa
Technically an RCD will operate without any form of earth path being installed. It operates. as stated in other answers, by monitoring the phase and neutral and reacting to an imbalance between them. Normally this imbalance is as a result of an "earth fault" be it to a back box, cpc, or as a result of external influences like moisture. It is possible to have a created imbalance, for example where wall lights have been installed and the live is taken from the lighting circuit and the neutral is taken from a socket on the final ring circuit protected by an RCD (16th edition style split load board with protected and unprotected ways). By switching the wall lights on an imbalance is created on the final ring circuit which will trip the RCD. Whilst not a common fault it is a typical "lash up" job by a "Barry the Bodger".
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Shakey
yup, done a few like that Tony
"just installed a new circuit, RCD trips as soon as i switch it on"
Investigation finds that the guy didnt know there was seperate neutral bars
Doh!
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greekislandlover
Not sure certain CU manufacturers are aware of this fact either! I've found several new CU's to have the neutrals connected arbitrarily to whatever bar suits at the time of manufacturer.
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Carter
Modern (current controlled) RCDs make the assumption that any imbalance in line and neutral currents must be flowing to earth (because generally there isn't anywhere else for it to go) they don't actually measure anything with reference to the main or cct cpc's. However it still doesn't remove the fact an earth path must be present or there would be no residual current and the device would not operate.
I think the older voltage controlled ELCBs sensed voltage on the cpc but they were effectively proscribed in 1981 as it was realised that a parallel earth path would render them inoperable under true fault conditons.
Ask your man to draw out the FULL fault path and ask him were exactly does he thinks that inconvenient stray, 'residual' "I delta n" tripping current is going.
I think the older voltage controlled ELCBs sensed voltage on the cpc but they were effectively proscribed in 1981 as it was realised that a parallel earth path would render them inoperable under true fault conditons.
Ask your man to draw out the FULL fault path and ask him were exactly does he thinks that inconvenient stray, 'residual' "I delta n" tripping current is going.
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weyboy
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SteveF1
As stated, there has to be an Earth path. That Earth path could theoretically become you.
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SteveF1
The Only THEORETICAL reason that I can think of is that, if the fault trip coil on the RCD was to become faulty and the RCD did not trip then the touch voltage on a faulty piece of equipment may rise above 50V. Thus EEBADS would come into play.
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The Only THEORETICAL reason that I can think of is that, if the fault trip coil on the RCD was to become faulty and the RCD did not trip then the touch voltage on a faulty piece of equipment may rise above 50V. Thus EEBADS would come into play.
SteveF1 gather you have not done the 17th yet as there is No such thing as EEBADS any more its ADS
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SteveF1
ian.settle1
Your assumption that I have not done the 17th Edition is incorrect. Yes you are correct that EEBADS has been replaced by ADoS as an acronym buit there will always be EEBADS. Although it is not refered to in the 17 Edition it does not mean "ther is no such thing any more" Equipotential bonding will always be required where protection against electric shock (indirect contact) is provided by Earthed Equipotential Bonding and Automatic Disconnection of Supply (EEBADS).It will also be used where disconnection times for circuits cannot be met, and where circuits with differing disconnection times come from a common distribution board.
I think you missed the point of the original post.
Hiya guys will an RCD or RCBO work if there is no earth in the house?A fellow worker said to me today that there is no need for an earth in a house if the board has an RCD or is controlled by RCBOs as they work on the inbalance of the live and neutral.
Regards
Steve F1
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