Tall vs compact RCBOs

[plugwash]

Given that you seem to agree that, today in the UK, 'neutral is nearly always neutral', I would say that the agument for not fusing both L & N greatly outweighs (today in UK) the argue for doing that, doesn't it?

If you are designing an item that will only ever be used in the UK, and you don't need to meet specific standards that may require otherwise, yes.

And if you are designing a fixed installtion in the UK you will be working to BS7671, where fusing neutrals is forbidden.

 

[JohnW2]

If you are designing an item that will only ever be used in the UK, and you don't need to meet specific standards that may require otherwise, yes.. And if you are designing a fixed installtion in the UK you will be working to BS7671, where fusing neutrals is forbidden.

Quite - and, since this is the "Electrics UK" forum, when we are talking about acceptable wiring practices, I think it pretty reasonable to just stick with the "fusing neutrals is forbidden in UK" concept, isn't it, particularly given that, as I've said, they are 'forbidden' for reasons which, in the UK, seem to be very good reasons?

 

[Ragnar_AT]

However, our debate started with the difference between 1-pole + N and double pole. To my knowledge, both types break line and neutral simultaneously but only the latter has current sensing in the neutral path, the former merely a mechanical switch.

 

[JohnW2]

However, our debate started with the difference between 1-pole + N and double pole.

It did.

To my knowledge, both types break line and neutral simultaneously ....

I'm now all-but-certain that such is the case.

.... but only the latter has current sensing in the neutral path, the former merely a mechanical switch.

That would make sense, but I'm far from convinced that it's universally true (of how products are described) - i.e. I'm far from convinced that all products described as "DP" do actually have neutral current sensing.

As we've discussed, the 'ideal' (which 'covers all bases') is to have neutral sensing as well as DP switching -although, as also discussed, I think that (at least in UK) the real 'need' for neutral current sensing is probably debatable.

Kind Regards, John

 

[Ragnar_AT]

I agree, there‘s absolutely no need for neutral sensing in the UK. If there was, no one could use single-pole MCBs either.

 

[JohnW2]

I agree, there‘s absolutely no need for neutral sensing in the UK. If there was, no one could use single-pole MCBs either.

Quite so - and where, amidst the tens of millions of UK domestic installations, would you find a significant number (if any ) of double-pole MCBs, I wonder?

 

[Ragnar_AT]

Quite so - and where, amidst the tens of millions of UK domestic installations, would you find a significant number (if any ) of double-pole MCBs, I wonder?

That’s precisely my point - if they were somehow required, you‘d expect to see a lot more of them.

RCBOs do often seem to be DP but for no apparent technical reason.

 

[JohnW2]

That’s precisely my point - if they were somehow required, you‘d expect to see a lot more of them.

Quite so - and precisely my point, too

RCBOs do often seem to be DP but for no apparent technical reason.

That does seem to be increasingly the case and, like you, I can't see why. In terms of 'required', the only thing I can think of is their use in TT installations, so that they could be used ('compliantly') for isolation!

They've obviously found a way to do it, but I have to say that cramming DP switching, as well as the current and residual-current sensing, plus associated electronics, into a 1-module wide 'compact' RCBO seems to be pushing things a bit - not the least because the L & N poles of the 'switching' presumably can't be very far from one another!

 

[Ragnar_AT]

The oldest DP RCBOs I‘ve seen, from the late 70s I think, were no less than four modules wide. An Italian spark gave one to me for my collection of electrical oddities. They were made by Stotz Kontakt (SK) in Germany, who also made the plug-in MCBs for Wylex CUs for a while.

 

[JohnW2]

The oldest DP RCBOs I‘ve seen, from the late 70s I think, were no less than four modules wide. An Italian spark gave one to me for my collection of electrical oddities. They were made by Stotz Kontakt (SK) in Germany, who also made the plug-in MCBs for Wylex CUs for a while.

I suppose it makes some sense that the earliest RCBOs were DP, given that (I think) RCCBs always had been, so they just added on the overcurrent sensing (in the two extra modules!).

I imagine that practicalities ('pressure from users?) then resulted in them shrinking to just 1-moduke wide, since when people started thinking of 'all RCBO CUs', even 2-module ones would have required pretty big CUs,not to mention the complication in terms of sorting out 'bus bars'etc?

 

[AndyPRK]

Euro breakers tend to be 2 wide.

They like their double stacked or triple? Countersunk CUs

 

[JohnW2]

Euro breakers tend to be 2 wide. They like their double stacked or triple? Countersunk CUs

True - but maybe because 'they don't know any better' (i.e. 'that's how we've always done it') ?

 

[Ragnar_AT]

It’s a bit more complex than that. Some European countries use all single-pole MCBs and hardly any RCBOs. Others use 1+N MCBs, most of which are two modules wide.
Single module ones are readily available but the selection of bus bars is limited. Keep in mind that many of those countries have domestic three-phase supplies, including three-phase cooker supplies (16 A). That means you can reasonably expect a mix of 4-pole RCD, 3+N MCBs and 1+N MCBs per row in a standard domestic fuse box. Fitting a bus bar to that is tricky, whereas 3+N bus bars for 2-module MCBs and RCBOs are pretty much standardised and compatible with 4-pole RCDs and 3+N MCBs. Single-module 1+N MCBs and RCBOs have non-standard terminals, wider ones have the same ones as 1-pole.

 

[ebee]

Yes, having been looking around a lot, that is clearly the case. However, the terminology can vary - I came across a SP one which was identified as such by describing it as having 'a solid neutral'.

If you follow the theory then overload protection could conceivably be at any part of the circuit L or N, ditto for short circuit protection too, it`s only the requirement for Earth fault protection puts it firmly on the L side and hence auto disconnection the L side makes us accustomed to OPD out means no dangerous L

 

[JohnW2]

If you follow the theory then overload protection could conceivably be at any part of the circuit L or N, ditto for short circuit protection too, it`s only the requirement for Earth fault protection puts it firmly on the L side and hence auto disconnection the L side makes us accustomed to OPD out means no dangerous L

Yes, I think we've covered all that and is the reason I said that, provided that one can assume that ';neutral is neutral' (and ;ine is line'), which one essentially can do in the UK, there is not really any reason (in the UK) to have current-sensing in the N ... let's face it, and as you imply, an excessive current in the N 'has to come from somewhere' - and what 'somewheres' are there other than an L (nearly always the L of the same circuit but, if you really wanted to deeply scrape the barrel of 'not impossible' scenarios, then perhaps the L of some other circuit ).