UK AC RCD’s C2? Absolutely!

[davesparks]

Well if it has been affected by DC leakage then it still tripped so all is good and if it hasn't been affected by DC leakage then all is good too. My house has all the possible scenarios that could cause DC leakage but the RCD still trips merrily away.

Just because it trips it doesn't mean it is tripping at the right current or within the right time period.

This isn't a binary process whereby the RCD either is or is not prevented from working at all.

 

[Rockingit]

I'm wondering if this entire thread has missed the point. The OP seemed to be proposing a blanket C2 for any type AC RCD circuit, then did a bit of a back-track.

This is what really boils my P about 'inspectors' who lack the fundamental knowledge and learning to apply some engineering principles and instead just go looking for any reason to find a higher code because they think it justifies their existence.

Absolutely, there are instances where potentially use of an AC type rather than an A, B or F might be innapropriate due to bias and blinding, that's a part of mine, Davesparks and several others on here's specialism(s) every day, but it bears no relation to a lighting radial of 60W BC's in Mrs Miggins pie shop where an AC type is still perfectly acceptable as it provides entirely appropriate protection against the risk.

Sure, the lines have become murky in domesttic installations due to the changes in household and consumer appliances but if you are going to be ballsy enough to make an assertion about risk, then at least understand that risk and be able to justify it. If you think that a circuit might be compromised then simples - test it. Apply a ramp test when it's in normal use and see what happens - if your assertion that it needs a C2 due to DC blinding is true then it won't trip on a standard ramp test. If (when) it does, then you'll know to stop talking ball hooks and give it an entirely appropriate C3.

 

[nicebutdim]

I'm wondering if this entire thread has missed the point. The OP seemed to be proposing a blanket C2 for any type AC RCD circuit, then did a bit of a back-track.

Yesterday seemed to be a day for bold statements and back-tracking.

 

[Rockingit]

Yesterday seemed to be a day for bold statements and back-tracking.

I think I'm still in yesterday mate, hence my lack of patience with things like this!

 

[SparkySy]

With regard to code for AC RCD's. If it is tested with all loads connected and passes then I will C3 it, if it fails then C2 for obvious reasons.
In my working life as an electrician I can honestly say that apart from the obvious failures of RCD's I have only ever tested 3 that have been blinded by DC they were all within the last 2 years and all of them were the older BS4293 type of RCD!

It's funny as I have been having issues at a unit I have been testing with Welding plant melting the earth conductor insulation the entire length of a circuit.
That circuit is protected by an MEM 4pole 63a 30ma RCCB and a 32a MCB. The circuit has never tripped out until recently.
Upon inspection of the welders there doesn't seem to be any internal link between the main earth and the Welding plants return earth which was excellent but didn't solve my problem. I then clamped the circuit CPC and the supply cable to see if there was any leakage, there was no AC leakage.
I forgot the DC clamp meter so am going back tomorrow with it to see if it is DC that is blinding the RCD and helping to melt the earth conductors insulation!
Sy

 

[Aaron b]

I've not yet had an issue with them not tripping but I don't think it's possible to fully simulate the worst possible case either. I've never turn on someones inverter driven washing machine, rapid boiled some water on the induction hob, with the fridge left open and fired up the PC to see if it would still trip with everything going full pelt. Usually, I warn them that the power will go off so everything minus the fridge is off in fact.

I think Dave's point about RCDs being additional protection in many situations is very poignant too.

If appliance manufacturers could give more useful information regarding DC leakages we could make a much more informed decisions and the manufacturers could tell customers that their new hob will lead to firey death if that is true so we don't have to be the doomsayers.

 

[pc1966]

I expect very few items actually leak DC under normal conditions, otherwise they will fail the PAT style of test on insulation. They might inject DC components under fault conditions, but that is another matter.

My own understanding is C2 codes are for situations that are a single fault away from danger (C1 is immediate danger, C3 is not to current specifications but needs an unfortunate combination of circumstances) and as such for most cases type AC RCD are not that.

If they are on an EV or PV system then yes, a single fault could be a DC fault and then "say your prayers Blackadder, its poker time!"


Edit: Fun fact, the actor who played the baby-eating bishop of Bath & Wells in Blackadder S2 'Money' was Ronald Lacey, who also played the Gestapo officer in the Raider of the Lost Ark.