Checking Earthings Without Open Land

Hello pret_p

I understand you are properly trained and qualified.

If you are not both, and your Assistant the same, do not attempt this following procedure.

It is easy to do, but you need to check the type of electrical system at your factory, and ensure that no other persons are present, while you do the Earth test this way, have an assistant with you, and both wear rubber gumboots.

I am presuming that your transformer is deltastar connected, with the neutral/star connection at the secondary being earthed properly at the transformer site.

After you have established the transformer connection:

Ensure that no other persons are present, while you do the Earth test this way, have an assistant with you, and both wear rubber gumboots.

I presume your factory Voltage Mains are 230/400V or similar, if not, do not test this way, without further advice.

When testing, take readings quickly, do not allow current to pass through the Earthing Connection Cable for more than a few seconds.

Little equipment is needed:

1. Assistant, for safety reasons, and to write down the readings
   
2. Rubber gumboots for yourself, and Assistant
   
3. Tools for disconnection/reconnection
4. Ammeter
5. Voltmeter
6. Standard Heater Element (High Wattage Resistor approximately 30 Ohms
   

Method:

1. Turn off the Factory Main Switch
2. Carefully disconnect the main Earth Connection, at the Main Switchboard
3. Using a standard heater element, around about 30 - 50 ohms resistance.
4. Measure the resistance of that element, and write it down
5. Disconnect carefully at the Main Switchboard, the Main Earth Connection Cable
   
6. Connect one end of your high-wattage resistor, (standard heater element), to the disconnected earth connection which runs to the earth electrode/s now hidden beneath concrete and plaster
7. Connect in series with that, an ammeter
8. As an alternative to ( 6) above, connect across (In parallel) the standard heater element, a voltmeter
9. Apply mains voltage to the other end of the ammeter, or if the voltmeter system is used, to the free end of that standard heater element
10. Current will flow
    
11. Take your current or voltage reading quickly, write the reading/s down
    
12. Turn off the Power
13. Remove the standard heater element, meters
14. Reconnect the Main Earth Connection Cable
15. Check your Ammeter or Voltmeter readings
16. Remove gumboots
17. Now the answer is easy to establish, using Ohms Law, to calculate the actual Earth Resistance at your Factory Site.
18. Write your report.

The above system of measuring actual earth connection is safe, providing you take careful precautions as mentioned.

I have previously used this method, when no other was available.

Hope that assists you.

Kind Regards....

Thanks to provide assistance.

Pratik

Hi Sparky. You are braver, than expected, but as I like, you are a DOER!

I have just some caveats. If there are multiple groundings, and others carry significant current when in operation, they will not show up in this measurement, as the whole facility is now without power. I did run into that - it had the very good reason to exist that the facility was big, and the grounding for RF reasons had to be short - so that the facility had multiple groundings. It was fun to watch our Power Engineer solve that! The other note is, that the measurement sez little about the AC voltage on the wire running to the Ground in normal operation. If there are similar grounds nearby, they will induce voltage onto our ground. That is a real bitch to sort out. But for people who feel it it is quite real.