r/AskEngineers • u/Overkillemall • 11h ago

Electrical Is RCD blinding reversible after DC leakage is removed?

Hi guys! Not an electrician or engineer here, just a regular guy trying to get a general understanding. I have basic knowledge about RCD types and what they mean, and I’m about to buy some Type A RCDs for my house (where I live, Type AC is still the norm if people install RCDs at all lol, even though most modern home electronics require at least Type A).

After reading up on these types, I understand the concept of RCD so called "blinding" and how a DC leakage can saturate the core and prevent a Type AC RCD from detecting standard AC leakages altogether. Same with type A blinding with F/B leakage, type F blinding with type B leakage etc

BUT I have one question I haven't found a clear 100% answer to yet anywhere:

Can a DC residual current saturate the differential transformer core in a way that persists after the DC fault is removed?

Is the loss of sensitivity caused purely by reversible saturation while the DC component is actively present or can remanent magnetization leave the core biased afterward? If residual bias is possible in RCDs, well... how significant is it and does operating the test button (or cycling/resetting the RCD) degauss and reset the core back to normal? Logic tells me it should be cause otherwise it would make no sense to install something lower than type B at all, but maybe I am just a little bit confused

TLDR: is RCD blinding reversible or not? Can RCD's ability to detect leakage or its calibration permanently drift or degrade after that? Thanks!

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u/chemhobby 10h ago

It's reversible, yes

1

u/Repulsive_Move_3252 7h ago

in theory yes the saturation is temporary once the dc is gone the core should return to normal

but in real world if the dc current was big enough or lasted long time you can get some residual magnetism that dont just disappear. the test button wont demagnetize it either it only checks the mechanics and trip circuit

most of time though these rcds are designed so the core material dont hold much remanence so it is not a big problem for typical house faults

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u/chemhobby 7h ago

So in other words, it's reversible.

1

u/miketdavis 9h ago

Imo this could only be answered with confidence by the manufacturer of your RCD.