High earth loop impedance

[Nickj]

Hello all,

I am studying to be an electrician but outside of the classroom I have little experience.

A friend has bought a house and during the buying process had an eicr with unsatisfactory result.

Reading the report it shows the ring and shower circuit to have high earth loop impedance.

I ran the test myself today and the earth loop impedance on the ring and radial are around 40 ohms, which is what the eicr also shows.

I have checked the wiring of all the sockets and all seem to be terminated correctly.

r1, rn and r2 for the ring all seem fine.

According to the report the Ze is also fine.


What could be causing this?

I suspect a problem with one of the other circuits, would I be going down the right alley with that assumption?

Thanks,

Nick

 

[Andy78]

Hi Andy,

i did did not measure those, the eicr has the cooker at 0.43 and the central heating at 1.44.

the eicr has the radial at 0.83, however I recorded the radial at 42 so unsure if the electrician doing the eicr did all but the radial, central heating and cooker by calc.

Those could be worth investigating to see if the high loop readings are consistent across all the circuits that are protected by the RCD. If not then a point of high resistance common to the first three circuits would seem logical. It's not unknown for breakers to be installed incorrectly on the busbar, or for multiple sections of busbar, or even cable links, be used to make up connections between breakers for instance.

 

[Nickj]

Thanks a lot for your help. I shall check it all this weekend and see if I can find the issue.

 

[davesparks]

Hi davesparks low current no trip test. I had pretty much the same reading as the one noted on the eicr.

Cheers

Try a high current test using the alternative method to avoid the RCD and see how the result differs.

 

[Nickj]

Just a quick update to thank you all for your help.

I solved the problem today and it was caused by a very high Ze. The electrician that wrote the eicr stated he measured a Ze of 0.3. This was clearly made up because when I checked the cable was tarnished and the resistance of the cable alone was > 2 ohms! (I forget the actual reading).

I used some wire wool to clear the tarnish and re-ran the earth loop impedance on all circuits. All well within allowed values now.

Thanks again

Nick

 

[Midwest]

Think its a bit late for me, but I don't understand any of that.