Earth Continuity Query

Being a gentleman (though not learned), i will let the others answer this. ^{Moreover, i don't know the answer anyway}

What type of loads the 5 sub DBs feed,why didn't you lay neutral cable?.

There may be lose terminals/connections on the earth circuit. Temperature gives raise to resistance, may be check the earth condcutor temperature. Also, try disconnect the nuetral from the MEN at the main DB, and redo the test. Incase the multimeter may be reading a connected coil/some meter on the neutral.

The Australia/New Zealand 3000:2000 standard states;

"Cluase 6.3.3.2.2: The resistance of protective earthing conductors shall be low enough to permit the passage of current necessary to operate the overcurrent protective device.The resistance of the main earthing conductor shall be not more than 0.5 Ω."

Appendix B4 FAULT-LOOP IMPEDANCE and Appendix B5 MAXIMUM CIRCUIT LENGTHS, IN METRES, THAT WILL ENSURE CORRECT OPERATION OF PROTECTIVE DEVICES TO PROVIDE PROTECTION AGAINST INDIRECT CONTACT.

No apologies for rating this as not a good answer - I should have marked as off topic as you do not answer the question. Did you read the OP? Resistance of earth 0.3 ohms (35mm aluminium conductor).

No neutral form the DB to sub boards -motor control equipment requires no neutral so no neutral included. Admittedly this is not the best method.

Obviously I am no engineer and this is first project of this scope I have put together as the electrician. I won't whinge about the lack of engineering support, probably why the company is now outsourcing the engineering sign off. Oh shoot, I just whinged about it...

Fault loop impedence calculations have been done, maximum impedence for 22kW motors of 1.38.

You did not mention 0.3 ohms in your post, and you stated that the DB was the MEN point. Have you understood your problem before rasing your question? Besides, electricians are good trouble shooters...have not developed such skills...there is nothing stoping you from learning...

CR4 gives opnions, guides, which could lead to solving engineering problems at work/home, via discussions. One has to do his homework as well to better find a solution. Experts who have dealt with similar issues will advice on solutions.

I'm guessing that this problem/idiosyncrosy(?) is a little odd and unknown due to the 181 post reads and less than a handful of responses.

Ron, I thank you for your honest response and I'm figuring that referrals to AS3000/3008 is not completely unwarranted (didn't know they use same standards in PNG?).

The problem was solved (circumvented) by isolating each earth conductor and testing individually. We figure it had something to do with the negligible voltage provided by the multimeter, although we did not test with a MegOhm meter which in hindsight would be interesting if nothing else. And maybe some sort of parallel resistance thing.

In short I can not explain it. I can identify that what we found is not an issue, not a fault, and that the installation is safe in accordance with local regulations. I'd stake my livelihood on it, and I have.

Happy new year y'all

Chook,

At least we dicussed the issue as a CR4 Cyber Team. It's all team work with our respective work teams and the CR4 Cyber Team.

Your most welcome, and Happy New Year to you.

Chook,

Look for a DC voltage floating around, you may have electrolysis. The earth stake is the most likely culprit. Also be sure you have accounted for all zero errors.

What measuring tool you use is also an influence, using your megger or other analogue meter if it has the right scales simplifies the whole matter as it is simple to zero out the leads that you are using (including say a roll of earth wire).

I probably won't see this post again as I've just unsubscribed from CR4