Understanding what this means on the megger 1731

[davesparks]

Doesn't this current leak through either the main earth or the bonding conductors?

In an ideal world it would yes, but in reality some will flow elsewhere too. Parallel paths, fortuitous connections to earth or even the fault you are trying to find could be diverting the leakage current elsewhere.

 

[Bobster]

In an ideal world it would yes, but in reality some will flow elsewhere too. Parallel paths, fortuitous connections to earth or even the fault you are trying to find could be diverting the leakage current elsewhere.

I imagine the easiest way of imagining it is a bonding conductor connected to a pipe for example, is just a potential divider.

 

[Strima]

When you say clamp around all live conductors at once do you mean both the supply live and neutral? If so, why will this reading be different to clamping the main earth and bonding conductors?

Both live conductors will have magnetic influence on each other due to current draw but these are cancelled out by each other. If there's some leakage going a different route there will be a part of the magnetic field that isn't cancelled out giving you a reading.

I tend to test with all conductors clamped, both lives and earth, then just the live conductors. This gives a ball park figure of what is finding parallel paths and what is going back down the main earth conductor.

 

[Midwest]

Thought the best method for earth leakage testing, was clamping around live/neutral supply?

Edit beaten to it.

 

[AJshep]

I would clamp around the L-N of the outgoing problem RCD.
I tried to say this earlier in the thread but after re-reading my previous doesn't make much sense.