I know, in the vaguest kind of way, the theory of why you MIGHT need an A Type RCD. (Each item of equipment that uses a DC component can drip, drip, drip, a little bit, or a lot, of dc current (back?) onto the L&N, sort of back up the AC waveform, saturating the RCD coil with DC, and as we do for testing Zs on an RCD, will fool the RCD into thinking that there is, in fact, no fault at all......So the theory is sound. Moving forwards install Type A RCDs........... no problem. BUt what to do if - as Alan B has found - an AC RCD is in existance already, how to quantify the risk? 

If this final circuits' attached equipment did blind the RCD, (which you, nor I,can really know before hand if it will or not - just that its a theoretical maybe it might? or collectively with a myriad of other electrical items might gang up to do so,  all it means is that for the time while the oven is on, the RCD may not function (in part or ever - does anyone know? Blinding the rcd - does that mean if we gave it a 0.5A or 5A or 500A fault current it would stubbornly fail to function because it is blinded by DC) we still have the MCB functioning and for 95% or the day the RCD will function as normal. 

Surely, especially in a standard household, anything other than an EV charge point or solar, isn't going to blind the RCD?

I know there is probably one inverter per household good, and inverters are the worst culprits, but really.......its going to blind all and any RCDs? 

I really require a design figure to operate on. An Average figure of various item manufactured in 2023 and updated each year as modern practices change. 

x amount of RCD blinding per white goods inverter,

x amount of RCD blinding per LED lamp

x amount of RCD blinding per TV, X box, Tablet or phone

Is this really as huge a danger as its made out to be? On Facebook groups it certainly seems like the end of the world is nigh........

I know, in the vaguest kind of way, the theory of why you MIGHT need an A Type RCD. (Each item of equipment that uses a DC component can drip, drip, drip, a little bit, or a lot, of dc current (back?) onto the L&N, sort of back up the AC waveform, saturating the RCD coil with DC, and as we do for testing Zs on an RCD, will fool the RCD into thinking that there is, in fact, no fault at all......So the theory is sound. Moving forwards install Type A RCDs........... no problem. BUt what to do if - as Alan B has found - an AC RCD is in existance already, how to quantify the risk? 

If this final circuits' attached equipment did blind the RCD, (which you, nor I,can really know before hand if it will or not - just that its a theoretical maybe it might? or collectively with a myriad of other electrical items might gang up to do so,  all it means is that for the time while the oven is on, the RCD may not function (in part or ever - does anyone know? Blinding the rcd - does that mean if we gave it a 0.5A or 5A or 500A fault current it would stubbornly fail to function because it is blinded by DC) we still have the MCB functioning and for 95% or the day the RCD will function as normal. 

Surely, especially in a standard household, anything other than an EV charge point or solar, isn't going to blind the RCD?

I know there is probably one inverter per household good, and inverters are the worst culprits, but really.......its going to blind all and any RCDs? 

I really require a design figure to operate on. An Average figure of various item manufactured in 2023 and updated each year as modern practices change. 

x amount of RCD blinding per white goods inverter,

x amount of RCD blinding per LED lamp

x amount of RCD blinding per TV, X box, Tablet or phone

Is this really as huge a danger as its made out to be? On Facebook groups it certainly seems like the end of the world is nigh........

tattyinengland said:

Surely, especially in a standard household, anything other than an EV charge point or solar, isn't going to blind the RCD?

That's not the case. A fault to earth (PE or FE connected to mains Earth) on any single-phase electronic product downstream of a rectifier on the mains (bridge or half-wave) requires a Type A RCD ... see items 3 and 4 in Fig A53.1 (page 195 of BS 7671).

Now, a huge proportion of modern electronic (household) products have that kind of arrangement ... if the product has no connection to mains earth, which may lead you to think the risk of blinding is gone completely ... but a fault leading to exposed live parts might not operate a Type AC RCD when someone touches the product downstream of the rectifier.

So, even with electronic devices without connection to mains earth, with Type AC RCDs, there is potentially no additional protection according to the objectives of Reg 415.1 ... and of course usually where BS 7671 requires RCDs with residual operating current not exceeding 30 mA, it states 'additional protection' being provided by that RCD (e.g. 411.3.3, 411.3.4, 522.6.202, 522.6.203, 701.411.3.3, etc.)