RCD background leakage current measurement.

[ericmark]

Form this bed time reading.

Some ( heavy ) bed time reading

https://globaljournals.org/GJRE_Volume13/5-RCD-Nuisance-Tripping.pdf

Although specifically written about nuisance tripping and not country specific it does include some information about various types of RCDs ( active electronic, passive electronic and purely electromechanical ) and how they react to faults in the system

I have been considering the info given, 10 micro amps per meter leakage for cables, and 4 mA per amp for electronic appliance, which if I am doing maths correct equals 129 mA for a 32A ring feeding electronic equipment to the full 32A. It was unlikely this would happen, but with induction hobs, and microwaves the electronic power being used is increasing.

The article shows the method to measure real background leakage which it states should be no more than 30% of the tripping current of the RCD. Although it shows using a resistor with modern clamp on ammeters able to measure in the mA range I would think today it is just a case of measuring the leakage current directly.

However for an empty house it will clearly pass, only as items get plugged in with the massive 4 mA per amp be mounting up. So one RCD every 7.5 amp does seem a little OTT however the regulations state

(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.

so not to allow for the background leakage by splitting the RCD protection as well as MCB protection into circuits would be required to comply. For a domestic this requires the designer to assume some background leakage, although the article states 4 mA per amp this is not given in regulations so could be contested, to my mind it does seem rather high.

Having been out of the trade for some time, and only did house bashing when no other work was going I do not know the answer for domestic, is there a figure given for socket supply as to what to allow as the background leakage per amp of supply, where the sockets are mixed electronic and non electronic equipment?

 

[EFLImpudence]

I think your figures clearly show the article to be dubious. (I have not read it)

As some houses, with all the modern appliances, quite happily manage with one up front RCD this clearly demonstrates the total leakage is less than 15mA.

Apart from specific installations with high CPC current needing HI earthing, I would say, for 'normal' houses the matter is given no consideration.

What is the leakage per metre on a new 50m. cable with an IR >500MΩ (or even 1000) ?

 

[Spark123]

I think you are x10 out, 0.4mA per amp.

 

[ericmark]

For any socket the limit is normally considered as 10 mA so 10/13 = 0.75 per amp, so yes I agree that 4 mA per amp seems too high. At 0.4 mA per amp the 32A ring would at 106 meters = 13.86 mA which does seem more reasonable.

However again one it would seem would be limited to one ring per RCD.

I have for a time considered that a standard consumer unit should have a RCBO per ring, however having a single RCD for the rest is not really a problem. Maybe since the cooker is likely to have a high earth leakage then also one for the cooker supply, before the metal RCD you could still get the old split units with one half covered with a general RCD and other half requiring RCBO's but with the metal units the options seemed to have reduced.

At the moment I have two fuse boxes with fuses replaced by MCB's both supplied from their own 30 mA RCD. I would like to replace with a consumer unit with 3 RCBO's and one RCD to cover the rest. Although I am in no hurry, idea was to reduce the nuisance tripping, however as it is should the RCD trip the light at top of stairs lights warning me the unit has tripped as least with the main board, once changed then one has to consider warning devices to alert if a unit supplying fridge/freezer or freezer has tripped.

 

[EFLImpudence]

For any socket the limit is normally considered as 10 mA

That is only where high leakage equipment is being installed - so obviously you cannot have much more.
For normal domestic premises there is no figure.

so 10/13 = 0.75 per amp, so yes I agree that 4 mA per amp seems too high. At 0.4 mA per amp the 32A ring would at 106 meters = 13.86 mA which does seem more reasonable.

I think you are confusing different things.

However again one it would seem would be limited to one ring per RCD.

So, clearly incorrect - unless I am mistaking what you are discussing.

I have for a time considered that a standard consumer unit should have a RCBO per ring, however having a single RCD for the rest is not really a problem.

What IS the problem?

Maybe since the cooker is likely to have a high earth leakage then also one for the cooker supply,

... or - don't have one for the cooker.

before the metal RCD

You mean CU ???

you could still get the old split units with one half covered with a general RCD and other half requiring RCBO's but with the metal units the options seemed to have reduced.

Why? Do they not come with two (or three) neutral bars?

 

[Spark123]

The math at 32A only really counts if you are fully loading it, in reality a house isn't going to have fully loaded ring final circuits. The 0.4mA per amp given in the document is just really a guide in the absence of measured values.

 

[stillp]

I downloaded the file linked in the OP, and it came accompanied by malware, so I suggest no-one else should click on that link.