G
geoffa
Hi, can anybody throw some light on a problem / confusion i have?
I'm in the process of installing a new TT system.
The existing earth electrode had a high resistance in excess of 2Mohms. I've inserted a new electrode in a new location and measured the resistance immediately after inserting the electrode with a Fluke 1653 MF tester which gave a reading of 140 ohms.
I also replaced the earthing conductor from the DB to the new electrode with 4mm 6491X, and replaced the main protective bonding conductors to the services with 10mm 6491X.
All ok so far i thought.
I've installed a new 4mm radial cct and the Zs reading came out at 39.6 ohms.
I expected the reading to be higher than 140 ohms. For it to be so much lower than the electrode reading i assume that the soil conditions have have caused a better conduction from the electrode during the week that it had been in the ground, even though no rain had fallen.
This is where i started getting confused as i then conducted the RCD tests. Results were as follows:
0deg at x0.5 = 310mS
180deg at 0.5 = 310mS
180deg at x1 = 310mS (this should be less than 200 mS as i understand it)
0deg at x1 = 310mS (this should be less than 200 mS as i understand it)
0deg at x5 = 50mS (this should be less than 40 mS as i understand it)
180deg at x5 = 50mS (this should be less than 40 mS as i understand it)
The RCD didn't trip for any of the tests.
I also measured the Idelta N value of the RCD and had a reading of 33mA.
Could someone explain why i got these results please.
And, would i be correct in saying that to meet the standards set out in the reg's this is acceptable so long as supplementary bonding is added to the system.
I think it would be far safer if TT systems were abandoned altogether and PME systems were a mandatory requirement. Zs would be a constant un-changing and reliable value and you have the obvious safety advantage of ADS using the MCB's together with the RCD protection.
Thanks in anticipation.
I'm in the process of installing a new TT system.
The existing earth electrode had a high resistance in excess of 2Mohms. I've inserted a new electrode in a new location and measured the resistance immediately after inserting the electrode with a Fluke 1653 MF tester which gave a reading of 140 ohms.
I also replaced the earthing conductor from the DB to the new electrode with 4mm 6491X, and replaced the main protective bonding conductors to the services with 10mm 6491X.
All ok so far i thought.
I've installed a new 4mm radial cct and the Zs reading came out at 39.6 ohms.
I expected the reading to be higher than 140 ohms. For it to be so much lower than the electrode reading i assume that the soil conditions have have caused a better conduction from the electrode during the week that it had been in the ground, even though no rain had fallen.
This is where i started getting confused as i then conducted the RCD tests. Results were as follows:
0deg at x0.5 = 310mS
180deg at 0.5 = 310mS
180deg at x1 = 310mS (this should be less than 200 mS as i understand it)
0deg at x1 = 310mS (this should be less than 200 mS as i understand it)
0deg at x5 = 50mS (this should be less than 40 mS as i understand it)
180deg at x5 = 50mS (this should be less than 40 mS as i understand it)
The RCD didn't trip for any of the tests.
I also measured the Idelta N value of the RCD and had a reading of 33mA.
Could someone explain why i got these results please.
And, would i be correct in saying that to meet the standards set out in the reg's this is acceptable so long as supplementary bonding is added to the system.
I think it would be far safer if TT systems were abandoned altogether and PME systems were a mandatory requirement. Zs would be a constant un-changing and reliable value and you have the obvious safety advantage of ADS using the MCB's together with the RCD protection.
Thanks in anticipation.
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