problems with test results

[Leesparkykent]

Had this two weeks ago in a fire damaged bungalow. I know it sounds implausible to some but a neutral to earth fault on a circuit stopped the RCD from tripping and test button wouldn't work. Dissed circuit in question...RCD now tests fine and test button works.

 

[Strima]

You will more than likely get a higher Zs through an RCD due to it's own resistance and also the test meter puts out a lower current on the no trip setting so the result isn't as accurate.

 

[chris butterfield]

pretty much lol

I think also my meter is playing uo as I'm getting different zs readings from the same bloody socket aghhhhhhhh need a vino

 

[chris butterfield]

pretty much lol

I think also my meter is playing uo as I'm getting different zs readings from the same bloody socket aghhhhhhhh need a vino

 

[davesparks]

Yeah thought it was N EARTH FAULT but what has confused me is all the circuits are in the correct side of the rcd ways but the other rcd tripped !!!!!!

Draw it out and work out where the current will flow,

 

[chris butterfield]

Right i recon i have a n earth fault on a lighting circuit on that side of the red and also a crossed n on the other

I recon this is my problem hammy

Any ideas on the different zs values I'm getting from my dialog tester on the same socket chaps ?

 

[Leesparkykent]

@Loki 2.5 T&E RFC with a R1+R2 reading of 0.48 would give an expected value of 1.15 for r2 and 0.77 for r1.

1.15+0.77= 1.92

1.92/4=0.48

To work it out

0.48x4=1.92

1.92/1.67=1.15 for r2

1.92-1.15=0.77 for r1

 

[Pete999]

You said that the Ze is 0.5
Im guessing its a tns & not tncs then as its over the 0.35 Ze max



If using 2.5 (1.5) T&E

Zs 0.98 - Ze 0.5 = 0.48

4 ÷ (2.5 + 1.5) x 0.48 = 0.3

r2 = 0.3 ohms
r1 = 0.18

Roughly lol, Am i close?

You said that the Ze is 0.5
Im guessing its a tns & not tncs then as its over the 0.35 Ze max



If using 2.5 (1.5) T&E

Zs 0.98 - Ze 0.5 = 0.48

4 ÷ (2.5 + 1.5) x 0.48 = 0.3

r2 = 0.3 ohms
r1 = 0.18

Roughly lol, Am i close?

Are you answering post 3?

 

[Loki]

@Loki 2.5 T&E RFC with a R1+R2 reading of 0.48 would give an expected value of 1.15 for r2 and 0.77 for r1.

1.15+0.77= 1.92

1.92/4=0.48

To work it out

0.48x4=1.92

1.92/1.67=1.15 for r2

1.92-1.15=0.77 for r1

Thanks for clearing that.
Think i was mixing formulas up

 

[Loki]

Are you answering post 3?

Just noticing the Ze was above 0.35 for tncs & was wanting to work out expected R1 & R2 values

 

[Midwest]

I seem to recall, I might be wrong, one of our more eminent members describing a situation where a neutral earth fault on a circuit could trip an RCD that is not protected by?