Earth clamp on incoming cable

[Vicario]

A few weeks ago my electrician found that I had virtually no earth connection when he did the readings prior to installing a new CU. He removed some of the covering from my incoming cable just below the cut out and fitted a clamp attached to a new earth wire which now goes into the CU. The reading after he had done this was 0.23MΩ according to the report I got.
But I have read that there are better ways to do this and I'm interested to know what those might be.
Also, since it was fitted in 2008 I regularly tested the RCD on the electric shower and it always tripped, so was I protected or not? The electrician who did the inspection did say that the reading he got was unsafe and insisted on rectifying it before he left the house.

 

[EFLImpudence]

A few weeks ago my electrician found that I had virtually no earth connection when he did the readings prior to installing a new CU. He removed some of the covering from my incoming cable just below the cut out and fitted a clamp attached to a new earth wire which now goes into the CU. The reading after he had done this was 0.23MΩ according to the report I got.

That is far too high. Is it not 0.23Ω?

But I have read that there are better ways to do this and I'm interested to know what those might be.

Not sure what you mean - as long as he has done it correctly.

Also, since it was fitted in 2008 I regularly tested the RCD on the electric shower and it always tripped, so was I protected or not?

Presumably - if it works within the prescribed time.

The electrician who did the inspection did say that the reading he got was unsafe and insisted on rectifying it before he left the house.

Maybe he meant it operated too slowly but that is nothing to do with the earth.

RCDs do not use the earth wire nor earth connection to work so, again, not sure what is meant.

 

[Vicario]

Oops! Yes, 0.23Ω. I thought that RCDs needed an earth connection to work properly.

 

[EFLImpudence]

Oops! Yes, 0.23Ω.

I thought that RCDs needed an earth connection to work properly.

No, they just measure the difference between L & N - primarily for when YOU are the earth.

 

[SUNRAY]

I thought that RCDs needed an earth connection to work properly.

No, they just measure the difference between L & N - primarily for when YOU are the earth.

The early RCD's did but I've never looked to se what it does.

 

[bernardgreen]

The early RCD's did but I've never looked to se what it does.

They had two "earth" terminals, one terminal was connected to a ground rod in the real Earth and the other was connected to the CPC ( earth wiring in the house ).

If the voltage difference between the two "earth" terminals was more than 50 volts then the trip mechanism activated and disconnected the supply.

 

[EFLImpudence]

Hardly an RCD then.

 

[333rocky333]

Also, since it was fitted in 2008 I regularly tested the RCD on the electric shower and it always tripped, so was I protected or not?

I assume you mean by using the test button, that would work with no earth in most cases, on the Rcd will be a drawing showing how the test resistor is wired across L Load and N supply or similar

 

[bernardgreen]

Hardly an RCD then.

hence the label VOELB Voltage Operated Earth Leakage Breaker ( or similar )

 

[EFLImpudence]

Yes, but Sunray said early RCDs did use an earth and you answered by describing something that is not an RCD.

 

[Vicario]

The reason for my original question is that I watched a YT video about an electrician who found a property with no earth. He trimmed the incoming cable and fitted a clamp. Some of the comments from viewers said that this is wrong and is not recommended. One suggested that he should have called the DNO and another mentioned possibly causing a fire. I'm just interested to know why.

 

[bernardgreen]

The first RCDs used a current transformer to compare the Live current with the Neutral current. These currents flowed through two opposing primary windings. When eaqual they produced no magnetic flux in the core an hence no current in the secondary winding which fed the trip mechanism. No earth was needed.

Then the current transformer was replaced by electronic sensors supplied by a power supply module fed from the incoming Live and Neutral. This improved the operation of the RCD in regards of the accuracy of the trip current and also allowed the mechanism to be more robust mechanically.

A problem was soon noticed..... If the incoming Neutral supply was not there on the RCD's terminal then the RCD could not operate as there was no power to the electronic sensors. Yet the Live was there in the but problems on the incoming Neutral all the Neutral wiring in the house could become Live when any lamp or appliance was turned on.

A "functional" Earth was added to the design to supply the sensors with power from Live and Earth when the incoming Neutral had failed.

There is more to it than that basic explanation.

 

[Harry Bloomfield]

No, they just measure the difference between L & N - primarily for when YOU are the earth.

Which still assumes there is an adequate earth attached to you.

 

[Harry Bloomfield]

The reason for my original question is that I watched a YT video about an electrician who found a property with no earth. He trimmed the incoming cable and fitted a clamp. Some of the comments from viewers said that this is wrong and is not recommended. One suggested that he should have called the DNO and another mentioned possibly causing a fire. I'm just interested to know why.

The comments made, would have been the correct way. You are not permitted to interfere in anyway with anything before the meter tails.

 

[Vicario]

But my EICR now says that my installation is satisfactory. (Same guy who fitted the new earth). So what is the 'correct way' Harry? How would the DNO have done it differently?