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to be honest you would test at the socket.

you will get parallel paths no matter how to try to do it.

put the line of the conductor down to the earth bar for the test and test at socket.

Why would you have a parallel path? The conduit is the cpc. The OP doesn't mention that there is a separate conductor for a cpc.
 
Why would you have a parallel path? The conduit is the cpc. The OP doesn't mention that there is a separate conductor for a cpc.

the back box is earthed via the conduit and the socket is earthed via the back box :6:

and test for continuity from consumer earth/switch gear to socket
 
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Having done quite a lot of industrial conduit installs I would say a wander lead is the only way. Take the worse reading and there’s your answer.

Whatever the reading is, if the conduit has been correctly installed it will be damn low.
 
A parallel path usually means an alternative path than that of the final circuit, even if the circuit you note has separate earthing the conduit is still part of its earth return so a reading at the socket R1 +R2 is perfectly acceptable, although you would want to prove the integrity of the earth core as Tony mentions.

If for instance you had a metal clad socket bolted to a metal girder then the metal girder may constitute as a parallel path and in this set up you may need to ensure you are not getting a false positive reading when testing.
 
The hassle with that is proving the integrity of that earth core is going to need a lot of dismantling of sockets, much better to just use the conduit as the cpc. It's not like a seperate cpc will see much fault current when the parallel path of the conduit will be so much lower resistance.
 
The hassle with that is proving the integrity of that earth core is going to need a lot of dismantling of sockets, much better to just use the conduit as the cpc. It's not like a seperate cpc will see much fault current when the parallel path of the conduit will be so much lower resistance.

Depends what your testing here, your new circuit, an existing arrangement, is the conduit showing signs of corrosion etc etc ... If you are asked for a 100% test then no matter on the hassle the integrity of the earth wire needs confirming... Not really too big a deal to drop all front and possible disconnect earth tail ...might add 15mins but then its proven...

If your just giving an overview of the electrics and your satisfied with the conduit install then yes a simple R1 + R2 is fine as your have proven at least 1 good earth path exists.
 
The hassle with that is proving the integrity of that earth core is going to need a lot of dismantling of sockets, much better to just use the conduit as the cpc. It's not like a seperate cpc will see much fault current when the parallel path of the conduit will be so much lower resistance.
The fault current will share both paths with respect to their resistance, as copper has a much lower resistance it can carry a greater proportion but would need to be calculated relative to their csa and resistance per meter.... just because the steel may have a larger csa does not mean it will carry the larger part of the fault current.... but without the separate cpc the conduit would still be able to handle the current in an earth fault scenario.
 
The fault current will share both paths with respect to their resistance, as copper has a much lower resistance it can carry a greater proportion but would need to be calculated relative to their csa and resistance per meter.... just because the steel may have a larger csa does not mean it will carry the larger part of the fault current.... but without the separate cpc the conduit would still be able to handle the current in an earth fault scenario.


It will if the buildings steelwork is one big earth field, and/or has been effectively bonded to the installations MET....

Then again why would anyone be daft enough to pull in CPC's into a metal containment system in the first place?? lol!!
 
It will if the buildings steelwork is one big earth field, and/or has been effectively bonded to the installations MET....

Then again why would anyone be daft enough to pull in CPC's into a metal containment system in the first place?? lol!!

One reason I hardly ever bothered to test a conduit install. It’s a bit pointless when all the boxes are fastened to structural steelwork. Added to which trying to get your hands on one of the two Ductors was nigh on impossible. I’d be able to borrow one if I’d got an apprentice with me, otherwise, get lost! Readings from a normal meter were meaningless.

The Ductors were in daily use for M&Q statutory testing, so you had no chance of laying your hands on one.
 

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