di-log earth leakage clamp

[JohnW2]

But bubachuba said he had heard that this model could be affected by other wires outside the clamp.

Ah, I missed that. Nothing in this world is perfect, and I doubt that it would be possible to design a clamp meter that was totally immune to large electromagnetic fields from nearby conductors which were NOT within the clamp but which were carrying large currents.

Kind Regards, John

 

[JohnW2]

You would think so wouldn't you, but i have heard other sparks claim that this does happen when in close proximity of other loaded cables which is one of the reasons of me asking about this particular model: I wondered if the more expensive models (like the Kewtech 2434) were less suscepticle to such allegations!

As I just wrote, I think it inevitable that any clamp meter will be to at least extent influenced by nearby conductors carrying large currents. I don't think it's possible to do much, design-wise, to mitigate that, but I suppose it's possible that some expensive ones have found a way of reducing the problem.

Ironically, the larger the jaws of the clamp (hence the less convenient to use), the less will probably be the problem, since that will limit how close any 'nearby conductors' can get to the centre of the jaws!

Kind Regards, John

 

[bernardgreen]

Depends on the method use in the sensing.

The output of any current transformer will be susceptible to magnetic fields generated external to the core by adjacent cables. The effect is almost insignifcant and depends on how the core is made and what screening, if any, has been included in the design.

A core with a Hall Effect semi-conducter device that measures the magnetic flux in the core will be less affected by external magnetic fields but the last time I looked ( several years ago ) Hall Effect devices were not very sensitive.

 

[bubachuba]

Clamped around the CPC of a cable they may give a reading of leakage current when that circuit is completely free of any faults.

Current from a earth fault will divide at the earth bar in the CU and flow along all available parallel paths to ground. Leakage from ( for example )the kitchen sockets flows back to the earth bar and then most flows along the main earth direct to the MET. But some will also flow ( for example ) from the earth bar along the CPC to the boiler, across the gland plate to a water pipe. along the water pipe to the main water bonding point and then along the bond wire to the MET. and also via the gas pipe from boiler to bonding of the income gas pipe and thus to the MET. Boiler is free of any fault but there is current flowing in the CPC to the boiler. Likewise immersion heater and electric showers.

Another great point, thanks Bernard. As you say parallel paths introduce extra factors whilst troubleshooting earth leakage so something else to bear in mind.

 

[bubachuba]

As I just wrote, I think it inevitable that any clamp meter will be to at least extent influenced by nearby conductors carrying large currents. I don't think it's possible to do much, design-wise, to mitigate that, but I suppose it's possible that some expensive ones have found a way of reducing the problem.

Ironically, the larger the jaws of the clamp (hence the less convenient to use), the less will probably be the problem, since that will limit how close any 'nearby conductors' can get to the centre of the jaws!

Kind Regards, John

Thanks John, that makes perfect sense. I think i will make a purchase of the one EFLI kindly linked to and let you all know how it goes.

 

[JohnW2]

Thanks John, that makes perfect sense. I think i will make a purchase of the one EFLI kindly linked to and let you all know how it goes.

Fair enough. It obviously makes sense to try to avoid situations in which there are very nearby (single) conductors which may be carrying high currents - but that's probably only a situation likely to be encountered within a CU/DB, if anywhere. If you were ever suspicious of readings obtained, you could always 'temporarily extend' the conductor(s) in question so that they could go through the clamp meter at a position remote from any possible interference.

Kind Regards, John

 

[EFLImpudence]

Yes, it is, of course, very difficult to get the clamp around L & N in a CU - especially a nice neat one.

 

[bubachuba]

Fair enough. It obviously makes sense to try to avoid situations in which there are very nearby (single) conductors which may be carrying high currents - but that's probably only a situation likely to be encountered within a CU/DB, if anywhere. If you were ever suspicious of readings obtained, you could always 'temporarily extend' the conductor(s) in question so that they could go through the clamp meter at a position remote from any possible interference.

Kind Regards, John

Indeed, that is one way of clarifying that there is nothing interfering with the results. I also have an extension lead with the insulation removed on section which can help clamps function as a PAT tester which has been useful on occasions.

 

[Monkeh]

A core with a Hall Effect semi-conducter device that measures the magnetic flux in the core will be less affected by external magnetic fields but the last time I looked ( several years ago ) Hall Effect devices were not very sensitive.

Hall effect devices can be very sensitive, and therein lies the problem. They are quite readily upset by other nearby magnetic fields, including that of the planet we're parked on (turn one over and you can get quite a substantial offset).

Traditional current transformers are not so easily upset. I'm unsure how Rogowski coils behave with external fields, but they can be even more finicky than hall effect with regards to conductor placement.