Question bout electronics....... (Sensible one)

[Grot]

How do you test your earth ?

I don't mean how to you check to see if "XYZ" is connected to the earth wire, a monkey could do that .....

But the earth facility its self ........

I have no reason to doubt that the earth works..... But ya know ..... Might be an idea to check it

 

[comms]

Do a earth fault loop impeadance test (Ze).

 

[Steve]

Where did you get that diagram from? Its wrong on so many levels.

Earth doesn't always go to the service head.

Earth never goes to a meter.

Neutral goes THROUGH meter.

Meter has 5.1 digit readout.

Meters INVARIABLY have ALL the wires coming / going at the bottom.

 

[Spark123]

Neutral is only usually connected to the meter to provide reference for the volt coil, it doesn't need to go through the meter

 

[bernardgreen]

And there is only a "positive lead" on a DC supply.


But it is a valid question. How do you test and ensure the earth is connected to The Earth and has not at some point become detached ?

Or in the case of PME that the incoming neutral is not a few dozen volts above earth due to an un-detected fault or significant phase un-balance in the supply network.

 

[plugwash]

And the answer is that you measure the loop impedance. At least for a grid connected system.

For a non grid connected system you get into the fun of rod testers.

 

[bernardgreen]

And the answer is that you measure the loop impedance. At least for a grid connected system.

For a non grid connected system you get into the fun of rod testers.

But which loop.

To ensure the earth wire CPC is at true earth the loop HAS to include true earth and that can ONLY be by using a earth rod.

I accept that for the vast majority of systems in normal situations the CPC bonded ( by the DNO ) to the incomiong neutral or the DNO's own earth CPC is adequate for safety.

BUT if the DNO supplied earth fails to be true earth ptotential then, in the worst case, an earthed appliance held by someone in contact with true earth could become a hazard if the CPC voltage is driven up by a network phase un-balance and /or failed neutral in the network.

 

[plugwash]

Yeah I guess you could have a DNO supplied TN system where the earth and neutral were connected together and back to the transformer neutral but not actually connected to earth. I would imagine this is pretty unlikely though.

If there is a failed neutral between the transformer neutral and where your earth splits off from the neutral then the loop impedance will probablly be higher than it should be.

 

[bernardgreen]

If there is a failed neutral between the transformer neutral and where your earth splits off from the neutral then the loop impedance will probablly be higher than it should be.

But where CPC and neutral are bonded at the supply head there is no way to measure any loop to true ground without using an earth rod.

While the house is meeting the loop requirments how does one know the DNO "loop" is intact ?

Or am I being over protective ?

 

[plugwash]

a loop impedance as it's name suggests tells you the impandance of the loop through the phase conductor to the transformer, through the transformer and through either the neutral or earth (depending on how you probe) back to the tester.

If the neutral breaks between the transformer and the neutral-earth split then the only loop present will be through equipment downstream of the fault on other phases. This will almost certainly be higher impedance than the expected loop impedance.

Of course the entire supply system could lose it's connection to real earth but IMO this is pretty unlikley (except maybe on small rural setups where a transformer only feeds a very small number of houses).