testing TT systems

[andy]

as much as i hate to ask, how are you susposed to test the earthing on a TT syste,?

 

[comms]

test earth rod resistance, using earth loop impedance tester.
isolate final circuits,disconnect main earthing conductor from met. Connect efli tester between phase conductor at source of tt installation & main earth conductor take reading, result is earth electrode/rod resistance.
Then continue with rest of tests after reconnecting main earthing conductor.
Is that what you were after ?

 

[andy]

test earth rod resistance, using earth loop impedance tester.
isolate final circuits,disconnect main earthing conductor from met. Connect efli tester between phase conductor at source of tt installation & main earth conductor take reading, result is earth electrode/rod resistance.
Then continue with rest of tests after reconnecting main earthing conductor.
Is that what you were after ?

i was thinkin it was summit like that, but ive never had to test TT systems yet so wasnt sure

 

[securespark]

Why didn't you ask your boss?

 

[andy]

Why didn't you ask your boss?

week off work....

well prob be doin it at col soon anyway

 

[comms]

Thats how I knew, we've just done it.
Did take a look at GN3 before posting reply though.

 

[mapj1]

Remember that some of the difference between the loop test value, and what you might measure with the magic box and the three spike method will be partly due to the resitance of the company spike, where the earth the neutral at the transformer end - that could be as high as 21 ohms before they come out and add another dompany spike in paralell. Though it usually less than 10 ohms - they normally either have many rods or buried tapes or wires.
Three spike test may be needed on new buildings if no local supply connected yet, but in terms of setting RCD characteristics and fault voltages, the loop method is more useful, as in terms of being realistic, it is nearer to what happens in a real L-E fault condition.