My war against dual rcd boards

Do we not get into a merry-go round of confusing desired (designed in) 'leakage' such as that from EMC filters (tripping undesired), and the undesired 'leakage' fault currents, particularly accidental touch based leakages for which tripping is clearly desired?

It wasn't clear to me what the 30% figure alluded to. Is it the lowest level of leakage (either style) that might trip the RCD? Could it be the maximum level of designed-in leakage from all the filters?

The steady inclusion of more an more EMC (HF) filters can greatly increase the level of 'leakage' with the potential for nuisance trips. And that's before any of the Heat pump EMC filter problems (the ~1kHz band). 

The modern house is definitely a complex system that needs some thought.

I think the 30% comes from 531.3.2 - so avoiding "Unwanted tripping" - as RCDs can trip anywhere between 50% and 100% of their residual rating, I suppose it gives a bit of a margin.

I'd be wary of blanket bans on "shared RCDs" - there are situations - i.e. RCD protection on a sub-main in TT systems, where one RCD "shared" across several final circuits in pretty much unavoidable - and can be OK if done carefully.

By the looks of it BS 7671 already provides enough evidence that multiple high leakage appliances on a single 30mA RCD isn't compliant.

   - Andy. 

Hmm, 10mA of idle state leakage on a 30mA RCD spanning many final circuits is not great design even so. Elsewhere (not the UK)  I have seen RCDs for general loads chosen based on 0.1%  - so 1mA per amp - 30mA RCD on a 30A circuit etc.
Does not really work so well here as a rule of thumb with with ring finals and single phase 100A boards.

Mike.

I think that Andy has summed up the engineering succinctly.

If the leakage currents in the dual-RCD boards are excessive, then there would be a lot of nuisance tripping. Is that actually the case?

What is the economic argument? I doubt that margins are so fine on new-build developments that all-RCBO boards cannot be provided. With after-market solar PV installations costing £thousands, once again a few £tens more on a board change hardly matters.

Of course, should nuisance-tripping materialize, the householder would have to stump up the cash to rectify the problem. That may seem like money well-spent, but would hardly be fair on a tenant.

Philip,

Based on your last sentence, that must be why in the In the UK we have "Domestic Installers"! to deal with those complex systems.

Cheers GTB

Is the issue due to installer or system designer.  I would say the installer does what the designer has prescribed

Chris Pearson said:

What is the economic argument? I doubt that margins are so fine on new-build developments that all-RCBO boards cannot be provided. With after-market solar PV installations costing £thousands, once again a few £tens more on a board change hardly matters

Try and compare a Hager (other brands are available) split load CU against a Navits CU

https://www.navitascp.co.uk/product-page/10-way-100a-mainswitch-consumer-units-c-w-t2-spd

The economic argument goes out of the window (other Apertures are available) 

I see no reason why a fully RCBO and SPD type2 CU can not be designed and installed in the average UK dwelling

Sergio,

In my exeprience and despite what standards and regulations say, in majority of cases in domestic dwelling house work there is no "Designer". The installer or somebody may be signing paperwork as "Designer". But attitude is still very much "Its only a dwelling" what can go wrong?.

Cheers GTB

Or need that little bit extra clarity, particularly about the distinctions between requirements, regulations and specifications (there's a separate thread on that  Requirement Structuring )

Or need that little bit extra clarity, particularly about the distinctions between requirements, regulations and specifications (there's a separate thread on that  Requirement Structuring )