Hi Marvo, the situation is that we have many devices that have an inherent earth leakage as part of their normal operation, computers and electronics are normally the worst culprits for this, but any coil also has this occur, such as in transformers or electrical motors that are often present in domestic appliances, let alone commercial and industrial ones. As an example case, I once did a socket swap for my father who wanted his sockets changed for ones with usb chargers. At first i thought he meant one or two, but no, he tried to get me to do the lot. Turns out if you put too many of them on, the combined total earth leakage was enough to trip the rcd, and in the end i worked out by trial and error how many made it occur, and then installed 5 less than that, to make sure that appliances plugged in didn't then contribute enough to the problem that he had nuisance tripping as an issue.
As a shorter answer, the reason it's as high as 30mA is because otherwise the nuisance tripping would be ridiculous, which would result in people refusing to get rcd's installed in their homes and businesses, and then we'd all be a lot less safe. Hope this helps
QUOTE="Marvo, post: 1751586, member: 23556"]
I see in the UK that RCBO's are more becoming a standard installation now.
I might be missing something obvious here but I've been wondering why are the commonly used RCBO's rated to 30mA leakage current when they're only protecting a single final circuit. Surely 30mA leakage on a normal domestic circuit is astronomically high especially when viewed through the lens of the whole installation having to be above a Megaohm in IR value which equates to 0.2 miliamps of global leakage. Why don't 10mA RCBO's become the norm for a single circuit? I know 30mA is the value of shock current that ought not to cause death but I'm sure anyone who's had a whack from a circuit fed by a 30mA rated protective would agree that limiting that current to a lower value would result in a significantly safer installation for the user.
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