I have an RCBO question ????

[LastManOnline]

From what I gather from posts on here, right up to the point they are removed, shortly after the installation has been inspected!

You may well be right. I had no knowledge of that practice. If correct, that would mark the US electrical culture out as highly unconventional. We all have gripes about some of our respective regs, but its rare to hear of someone willingly breaking them.

 

[LastManOnline]

It’s all down to the touch voltage, the regs would have to be rewritte, can you imagine

You sure about that point? Would the "touch voltage" be any different whether the rcbo rating is 30 Ma or 500 Ma?

 

[pc1966]

You sure about that point? Would the "touch voltage" be any different whether the rcbo rating is 30 Ma or 500 Ma?

Exactly, there are very few situations when you would have a CPC so poor that an RCD won't trip and a substantial voltage exists for touching that might be trip-limited.

It practice you will almost certainly get 0.5-1.0 of the supply voltage for the duration of the RCD trip time, depending on the CPC being full size on TN (so R2 = R1 and 0.5) to practically non-existent (e.g. TT case where 'R2' is very much higher than R1 back to the source so more or less 1.0).

 

[LastManOnline]

It’s all down to the touch voltage, the regs would have to be rewritte, can you imagine

Interestingly the tables for calculating touch voltage show that the rated operating current of an rcd/rcbo has no influence on the resulting touch voltage appearing on conductive surfaces during a, fault

 

[The Raving Stickman]

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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[Lucien Nunes]

I understand that 10 ma rcd, s are quite common In The USA

Functional leakage is typically lower on 120V circuits than 230V, so more appliances can be accommodated within a given tripping threshold. USA GFCI protection is often incorporated into socket outlets, but these usually have load terminals that are used to supply points downstream on the circuit. So if you have four points in one room, the RCD protection for all of them is within the first point.

One of the problems with speculatively dividing the leakage of multiple circuits that were OK grouped on a 30mA RCD into a number of 10mA RCBOs, is that there can be localised clusters of high functional leakage but low load. For example, my video playback computer systems leak about 3.5mA but consume only 500W. One might expect to be able to power two of them from one 13A socket but with 7mA total leakage that could already be in tripping territory for a 10mA RCBO, whereas it would probably be absorbed into the total on a 30mA also serving other lower-leakage loads. It's a kind of leakage diversity situation where the larger the number of loads served, the better it will all average out below the nuisance trip level.