Ze

[oohthatslive!!]

hi is it possible to have a Ze reading thats higher than a Zs reading? 40ohms Zs and 90 Ze.

 

[ricicle]

Yes, due to parallel paths.You test Ze (or should) with the main earthing conductor disconnected from the CU, but Zs is tested with the Main Equipotential Bonds in place.

 

[oohthatslive!!]

yes thats right. main earth disconnected. test between phase incoming,consumer unit off and earth. test Zs with plug in loop tester

 

[ricicle]

That'll be that then

 

[Podooser]

I have read that it is better to determine a realistic and therefore more useful Zs value with the main earth bonding disconnected. Does anyone do it this way?

 

[ricicle]

I have read that it is better to determine a realistic and therefore more useful Zs value with the main earth bonding disconnected. Does anyone do it this way?

Although that would make sense, it is not the correct way to do it as you must have bonding in place as the Earth fault loop impedance test can introduce voltages on to exposed metalwork.
Anyone in contact with this metalwork could receive a shock.

 

[ptuwacha]

Ze test should be done with the earthing conductor disconnected. Zs should be done with the main bonding and equal-potential bonding conductor disconnected. so as to remove parallel paths.

Ze TT SYSTEAMS 21 ohms
TN-C-S 0,35ohms
TN-S 0,8 ohms

 

[RF Lighting]

No it shouldn't.

Probably sorted after 5 years anyway.

 

[ricicle]

Ze test should be done with the earthing conductor disconnected. Zs should be done with the main bonding and equal-potential bonding conductor disconnected. so as to remove parallel paths.

Ze TT SYSTEAMS 21 ohms
TN-C-S 0,35ohms
TN-S 0,8 ohms

1]Why resurrect an old post ?

2]Why post incorrect advice ?

 

[vibrobullit407]

Zs should be done with the main bonding and equal-potential bonding conductor disconnected. so as to remove parallel paths.

Great advice there ptuwacha, energize an unsafe installation and carrying out live tests with no bonding! Fantastic!

 

[Lectrician]

And 21ohms for a TT is the DNO's declared maximum for their side of the TT, yours is likely to be far higher. Anything below 200ohms is considered stable.