RCD feeding RCD thoughts.

[JohnW2]

I agree with that, I can't find enough information either, and like you I would note it in report, but likely would not give it a code.

Agreed. In fact, I think it's the only honest approach (unless some people hve managed to discover a lot more information than I have).

As things are, I really don't think that (in relation to a standard domestic installation) I could honesty say that I yet know enough to be able to even "recommend" that a Type AC RCD be replaced (C3), let alone that I knew enough to declare that it was sufficiently "potentially dangerous" to require "urgent remedial action" (C2).

However if I find some one else has given it a code, I could not say that's wrong either.

True, with our degree of relative ignorance, we could not say that it was necessarily "wrong", but I think it would be appropriate (and justified) for us to ask for an evidence-based justification for the coding.

As far as I am concerned, the type of RCD we have been using extensively (almost universally, I think) in the UK for 30-40 years (or whatever) "remains innocent until proven guilty" - so, from my viewpoint, it is down to the person who 'codes' a Type AC RCD to justify what they have done. Their argument obviously has to be good enough to over-ride ...

531.3.3 Types of RCD
Different types of RCD exist, depending on their behaviour in the presence of DC components and frequencies. The appropriate RCD shall be selected from the following: ......
For general purposes, Type AC RCDs may be used.

Kind Regards, John

 

[SUNRAY]

This one has the earth lead:
https://www.diynot.com/diy/threads/another-shed-botch.468100/#post-3774461

 

[JohnW2]

This one has the earth lead: (click for link)

It does, but I have to say that I've never personally seen one on an RCD, only on RCBOs (which made little sense in relation to those who believed there was a 'need' for them in RCBOs)!

Kind Regards, John

 

[SUNRAY]

It does, but I have to say that I've never personally seen one on an RCD, only on RCBOs (which made little sense in relation to those who believed there was a 'need' for them in RCBOs)!

Kind Regards, John

I'm going to stick my neck out and say there was a period when RCD's with earth leads were probably running about 50:50 and I'd like to say it was when they first became the 2 unit format we now expect, so after the rotary lever style, and cuboid blocks such as these:

So maybe mid 80's ish?

 

[JohnW2]

I'm going to stick my neck out and say there was a period when RCD's with earth leads were probably running about 50:50 ... So maybe mid 80's ish?

Quite possibly. I don't think my first person encounters with RCDs were until around mid-80s, which might explain why I'm unfamiliar with things which came before then.

However, I still don't really understand why functional earths were seemingly fairly common with RCBOs when the first started becoming 'popular', even though the same manufacturers continued to make and sell RCDs without them. As I implied I would have thought that the (rather 'barrel-scraping') argument for their being need would apply as much to an RCD as to an RCBO, wouldn't it?

Kind Regards, John

 

[ericmark]

I seem to remember the whole idea of the active RCD was to fail safe, as at 50 volt (under 50 volt not required) the units could fail to operate due to not enough voltage to work the electronics, a RCD in a distribution unit was unlikely to have a volt drop problem, but a portable RCD fitted at the end of an extension lead an earth fault could also cause a volt drop, so must work at 50 volt.

The 110 volt versions even harder, as the 55-0-55 is a split phase supply, I remember having problems with generators, RCD's and mag mount drills, the generator was designed to tick over until there was a load, the volts and frequency dropped, and the magnets in the mag mount drills were not drawing enough power, so generator was dropping to tick over and drills falling off, and then the RCD would also auto switch off and needed manual resetting.

It was a case of the quartz 300 watt lamp tube would blow, then the drill would fall off and mayhem evolved. Why some one had decided we needed RCD's with 55-0-55 I don't know, maybe as it had been found we had some USA imported equipment which was 110 - 0 - 110?

Like the supplying of a shaver transformer from a RCD protected supply, the RCD clearly can't work through an isolation transformer. I had a lot of problems with yellow brick and blue brick transformers, so items would not work on 110 volt, but safety officer said must have 110 where ever possible, so a RCD fed a 13 amp socket, which powered a yellow brick 55-0-55 which had a run of yellow cable to a blue brick which transformed it back to 230 volt with a 13 amp outlet, and earth faults would not trip the RCD of course, but I could not get the safety officer to understand.

 

[JohnW2]

I seem to remember the whole idea of the active RCD was to fail safe, as at 50 volt (under 50 volt not required) the units could fail to operate due to not enough voltage to work the electronics ...

That reasoning would make sense, but .....

.... a RCD in a distribution unit was unlikely to have a volt drop problem ....

Nothing can avoid the 'voltage drop' due to the Ze. An L-E fault fairly close to (or in) the DB could result in a near-zero L-N (or L-E) voltage at the DB.

... and furthermore, in the context of the discussion above, a 'functional earth' would be of no use/value in that situation.

Kind Regards, John