Today's conundrum,
Supply is TT, new 100ma time delayed RCD, then split via henley blocks to two CU in the kitchen, and one in the garage/office. The two kitchen CU have their main earth in the MET along with the cable to the earth rod. The cable to the garage DB has its earth terminated in one of the kitchen CU earth bar.
I've Measured Ze in the two CU in the kitchen from the phase to the rod cable (disconnected from the MET).
In the garage, am I right in thinking that I should be taking Ze as the measurement from phase in that CU, direct to the rod via the earth in the distribution cable.
i.e. connect the earth from the garage DB direct to the rod cable for the test?
Out of interest, if the garage CU was run from a breaker on one of the kitchen CU, would Ze at the garage CU become the Zs of that circuit, with any parallel paths included.
The reason I ask is because the supposed NICEIC approved contractor who certified the new kitchen CU in 2005 put Ze down as ~16ohm and while that is what I get at the MET, disconnecting and using just the earth rod for the test gives me 185ohm, whereas the mains water gives ~18 and Zs on the final circuits is about 21 ohms.
None of the texts I've read seem to offer much advice on completing the cert in these sort of circumstances, so hope wiser heads on here will confirm I'm on the right lines?
Thanks
Gavin
p.s. Hope the above makes sense, but if not in my defence its late!
Supply is TT, new 100ma time delayed RCD, then split via henley blocks to two CU in the kitchen, and one in the garage/office. The two kitchen CU have their main earth in the MET along with the cable to the earth rod. The cable to the garage DB has its earth terminated in one of the kitchen CU earth bar.
I've Measured Ze in the two CU in the kitchen from the phase to the rod cable (disconnected from the MET).
In the garage, am I right in thinking that I should be taking Ze as the measurement from phase in that CU, direct to the rod via the earth in the distribution cable.
i.e. connect the earth from the garage DB direct to the rod cable for the test?
Out of interest, if the garage CU was run from a breaker on one of the kitchen CU, would Ze at the garage CU become the Zs of that circuit, with any parallel paths included.
The reason I ask is because the supposed NICEIC approved contractor who certified the new kitchen CU in 2005 put Ze down as ~16ohm and while that is what I get at the MET, disconnecting and using just the earth rod for the test gives me 185ohm, whereas the mains water gives ~18 and Zs on the final circuits is about 21 ohms.
None of the texts I've read seem to offer much advice on completing the cert in these sort of circumstances, so hope wiser heads on here will confirm I'm on the right lines?
Thanks
Gavin
p.s. Hope the above makes sense, but if not in my defence its late!