zs result varing when testing garage DB

[isk57]

HI
Ive just installed a new board in a garage on 12mtr 6mm 3c swa and when testing im scratching my head
ive got
Ze of .34 at the main db -tested
Zs of .74 at the garage db - tested "sometimes its up and down"
and a R1 + R2 at of the swa as .10
to me this is way out ,does anyone know what the problem could be ?

 

[westward10]

You dead test of 0.10 indicates your earth fault loop impedance test is the issue, are you using the soft test or high current test.

 

[isk57]

Soft test as it’s got a rcd on it .

 

[westward10]

Guarantee that is the problem.

 

[Silly Sausage]

Soft test as it’s got a rcd on it .

Where?
Not the main DB I hope.

 

[isk57]

Yes at the DB it’s a split load with no facility for a mcb only which I would have preferred and put a rcd in the garage

 

[Andy78]

Could be an accuracy problem due to the low current test, I know I get that a lot.
Could also be a high internal resistance of the RCD so you could try and rule that out first.

 

[isk57]

I will try it without the rcd tomorrow.

 

[Deleted member 9648]

If the measured reading meets the requirements, Ze and dead tests are as expected then pack your tester away and on to the next one. Life's too short mate.

 

[Stevie g]

Another thing to watch out for is your test leads faulty. They do not last like they use to.

 

[rolyberkin]

Why have you put an RCD in the garage board?

 

[DPG]

It's a split board

 

[rolyberkin]

It's a split board

Sorry my bad, read it as thouigh there was an RCD in both.

 

[isk57]

Well update on this I changed the leads and got about .10 better result and changed the rcd to a main switch and got .25 at garage dB so I’ve learnt something new about contactum rcds