Zs reading issue !

[Soulsurfer]

I have a circuit of only approximately 8-9 metres from a 61009 type B 32A Rcbo to an oven & hob all run in m T&E and have got a Zs result on "No Trip" of 1.49 ohms which is not cool as I need sub 1.1 ohms to comply. Technically it's below 1667 ohms but still it's on a TN-S so efli should be well within anyway as such a short run too. Thinking I'm going to have to re-check all connections and then test again tomorrow. Still in my testing infancy and am losing confidence fast !

 

[Darkwood]

Sometimes the terminals of a outlet can be coated with a anti-corrosion layer to stop oxidisation while in storage, try doing the same test touching the copper wire direct.

 

[Soulsurfer]

Thanks DW, I'll try disconnecting them first tomorrow, test took like 15 plus seconds to finish too ! Needed all 3 leads connected ! All other circuits were like 0.70 ohms this one was a no no.

 

[Sintra]

What's the R1 + R2 of the circuit? Could be a high resistance across the OPD, check Zs each side of the 61009.

 

[Leesparkykent]

As above, if your R1+R2 is within range for the length of circuit. I would assume your getting a high resistance through the RCBO. Carry out an EFLI either side of the RCBO. Or the RCBO could be slightly loose on the bus bar.

 

[NDG Elecs]

Assuming 6mm cable used your R1R2 should be around 0.09. As all other ccts are testing fine, then the advice above is good. Check them all, it will be straight forward enough to find the cause. What's the Ze on the TNS? And does the bonding make much difference?

 

[telectrix]

or try this method. original diagram was, i think, courtesy of RBurns:

 

[Soulsurfer]

Hey all, thanks so much for all your help ! rather than a good slating lol, checked tightness on busbar and also all connections, had R1+R2 from hob connection terminals at this time a satisfactory reading of 0.43, Ze was 0.22 so calculated Zs @ 0.65 but didn't want to jinx it ! Tested from end of circuit on no trip Zs = 0.65 ! was well happy with that.

Plus had some weird results on living room, bedroom ring last week and today while finishing the whole job I got great results ! r1 0.41, rn 0.43, r2 0.78 & R1+R2 0.35 with Zs at 0.79 slightly above calculated Zs but well within 1.1 ohms Zs allowable so really happy and just completed the certs now ! time to get paid and same guy just bought another house to fix up from ground up 3 storey and put in planning for another property new build too ! No rest for me then... You're all legends for your help guys and if ever you're in Jersey I'll get the beers in.