Help!!!!!!!!!!!!!!!!!!!!!!!

[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. ​

 

[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

 

[Had8Lives]

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.

 

[wattsup]

Perhaps it's a double insulated house

 

[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??

 

[Shakey]

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??

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

 

[Dinosaur]

No Earth path - No electric shock???????????

 

[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".

 

[Shakey]

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".

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!

 

[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.

 

[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.

 

[weyboy]

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.

what about disconnection times?

 

[SteveF1]

As stated, there has to be an Earth path. That Earth path could theoretically become you.

 

[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.

 

[ian.settle1]

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