testing Ra

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Ok then here's another daft question.When I measure loop impedance of a socket on a TT installation is the reading I get the resistance of the current path from my tester through the cpc of the socket, through the cpc of the domestic ring circuit to the consumer unit then down through the earth via the earth rod and metal bonded pipework and onward through the general mass of the earth to the supply transformers earth, then back along the phase from the transformer to the consumer unit in the house and back along the phase of my ring circuit to the live red probe on my tester.

Is this a fair assessment of the path of my earth fault current?

Is this the circuit from start to finish?

And is 18 ohms the figure for the resistance of this circuit?

Cheers.

Yes, that's your Earth Fault Loop Path.

If 18 ohms is the reading you're getting, then that's the Zs for your Ring Final (IF the socket that you are testing is the mid/furtherest point of the ring)

The reading is the 'Loop impedance' of the circuit, not the 'resistance'

 

[Andy™]

Ok then here's another daft question.When I measure loop impedance of a socket on a TT installation is the reading I get the resistance of the current path from my tester through the cpc of the socket, through the cpc of the domestic ring circuit to the consumer unit then down through the earth via the earth rod and metal bonded pipework and onward through the general mass of the earth to the supply transformers earth, then back along the phase from the transformer to the consumer unit in the house and back along the phase of my ring circuit to the live red probe on my tester.

Is this a fair assessment of the path of my earth fault current?

Is this the circuit from start to finish?

And is 18 ohms the figure for the resistance of this circuit?

Cheers.

thats the short version of it.

but the fault path can take many other routes back to star. i.e if your neighbour has TN, and you share a metallic service pipe, then fault current will take path of least resistance, which will be from your earth, through shared service pipe, through their bonding to MET and back to star.

 

[la poste]

[quote name='Andy