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Type A/B RCDs can you help explain the component parts?

Zs
Hello,  Long time no post but I hope you are all OK.


I'm curious about something.  Anyone know what is inside a type B RCD that is different from what's inside a type A RCD? What component parts are different and what's the physics behind the tripping of a type B that is different from the tripping of a type A?


I've heard the terms blinded and flooding being bandied around on the virtual water cooler lately so I thought I'd do a little quiet due-diligence.  The web can be rather conflicting though. Ever wish you'd never started something?  


Am I right that a type A will disconnect ac and pulsating dc and a type B does those two with smooth dc as well?  I can also find a site that tells me type A only does ac.


Also, if a type A is subject to a DC fault in one of the circuits, say a charger, they, at the water cooler,  say it will be 'blinded' and won't trip.  Well, as far as I can see that could be partially true  and it  might be unable to see other (ac) faults in the installation - but  I'm thinking there'd be a level of DC fault at which it would not go 'blind'.


Add to that the conundrum that a pulsating dc surely involves time so it will have a  level of frequency?


I've managed to get myself proper confused now and wonder if you can help with what happens inside the type B that makes it so different, not to mention expensive.

  

Zs


  










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    Thank you Graham, 


    Technical curiosity only,  and wanting better to understand. I am not about to start installing EV charging points.  But you know those conversations we overhear where person A is giving person B advice?  After hearing one such, just the other day, I came home with a few question marks. Am looking it up and I was right to question. Let me reassure you that I'm not looking to find a product that does the specified job of another. Bit surprised by that suggestion.


    We have the component parts of a standard type A RCD drummed into us so well that we can all draw a diagram and explain what is going on to make it trip and what happens when it trips. 10 points in an exam for that.  But the type B, presumably, is operating differently?


    For an installer or end-user; yes, I agree completely about the pertinence of knowing what to buy and where to apply it. that's usually enough for most and that's fine.  IMHO though it doesn't have to be a mystery regarding any difference in what's going on inside. But I sure can't find anything.


    Yes, I have anecdotal on those tests - one of my Meggers trips RCDs on various tests unless I swap the probes over which was mentioned on here some years back.  Yes, it can stop tripping them in the blink of a tea break. The other Megger has never tripped an RCD unless I tell it to.


    Zs
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  • 0
    Thank you Graham, 


    Technical curiosity only,  and wanting better to understand. I am not about to start installing EV charging points.  But you know those conversations we overhear where person A is giving person B advice?  After hearing one such, just the other day, I came home with a few question marks. Am looking it up and I was right to question. Let me reassure you that I'm not looking to find a product that does the specified job of another. Bit surprised by that suggestion.


    We have the component parts of a standard type A RCD drummed into us so well that we can all draw a diagram and explain what is going on to make it trip and what happens when it trips. 10 points in an exam for that.  But the type B, presumably, is operating differently?


    For an installer or end-user; yes, I agree completely about the pertinence of knowing what to buy and where to apply it. that's usually enough for most and that's fine.  IMHO though it doesn't have to be a mystery regarding any difference in what's going on inside. But I sure can't find anything.


    Yes, I have anecdotal on those tests - one of my Meggers trips RCDs on various tests unless I swap the probes over which was mentioned on here some years back.  Yes, it can stop tripping them in the blink of a tea break. The other Megger has never tripped an RCD unless I tell it to.


    Zs
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