Tall vs compact RCBOs

[JohnW2]

All the recent discussions about CUs and what goes into them has reminded me of something I have been wondering ....

... as far as I can make out, most modern CUs are tall enough to fairly comfortably accommodate the original ('tall') format of RCBOs but, for most of them both 'tall' and 'compact' RCBOs are currently widely available, the latter generally only been slightly more expensive.

It's therefore probably tempting ('obvious' ?) to pay the little more for compact ones, hence leaving the inside of the CU even less 'crowded'. However, I wonder if anyone has any thoughts about the relative 'reliability' of the two formats, since I would think that it's far from impossible that 'cramming the works' into a smaller space could have a negative impact on reliability?

Kind Regards, John

 

[Murdochcat]

Compact every time. Cost is irrelevant

 

[pete01]

Aren't the compact double pole....fusebox anyway.

 

[JohnW2]

... reconsidering my response

 

[JohnW2]

Compact every time. Cost is irrelevant

As I also said, the (small) cost difference is irrelevant, but I wonder if cramming all the works (some of which probably generate at least some heat) into a smaller case might have a negative impact on reliability?

 

[JohnW2]

Aren't the compact double pole....fusebox anyway.

It seems that you are right, at least of FuseBox. I had taken ...

• Double Pole RCBO 1P+N (switched)

... to mean that only 1 pole was switched, but elsewhere it says ....

benefits from Double Pole switching (Switched Live and Neutral)

... which couldn't be clearer ..... but I think that probably strengthens my 'wondering', since if they have not on'y 'crammed in' the same amount if works as exist in (usually SP) 'tall' ones, but have also managed to squeeze in a second pole of switching, the potential for 'impairment of reliability' is perhaps even greater than I had been thinking?

Is the same true of other brands of compact RCBOs?

 

[davelx]

Also many brand's compacts are bi-di

 

[pete01]

Is the same true of other brands of compact RCBOs?

I'm not sure, do Schneider do a compact rcbo?

 

[333rocky333]

Without smashing them open, was there actually any important bits within the tall skinny bit

 

[Ragnar_AT]

1P+N usually means that the neutral is switched but doesn't have overload protection. At least that's what I've been told.

 

[pete01]

1P+N usually means that the neutral is switched but doesn't have overload protection. At least that's what I've been told.

Rcbos don't have overload protection???.......oh S%$#

 

[Ragnar_AT]

Rcbos don't have overload protection???.......oh S%$#

Not on the neutral, only on the live. Double pole means both poles have thermal and magnetic protection, which is necessary if you've got 230 V between two phases and some places require the neutral to be fused in TT installations.

 

[plugwash]

1P+N usually means that the neutral is switched but doesn't have overload protection. At least that's what I've been told.

For overloads, this is somewhat academic because if the neutral is overloaded and the phase isn't that means you have a bunch of residual current.

For high current faults though, it may be relevant. The "switched neutral" likely has far less ability to break fault currents than the phase does.

 

[JohnW2]

I'm not sure, do Schneider do a compact rcbo?

I didn't realise any of this! Having just had a quick look around, it's clear that I need a much more careful look, since the situation appears rather confused and confusing.

In a good few cases, it's not clear from a seller's information as to whether a n RCBO is SP or DP (and the same even seems true of some manufacturer's information). It also seems that some manufacturers do both SP and DP compact RCBOs (and sometimes also SP 'tall' ones) - e.g. Hager 's SP compact RCBOs can be had for under £14, whilst their DP ones seem to cost anything up to about £30 - but then what on earth is this 2-module animal (with an 'interesting' price!) I found on the Hager website? ...

I'm very confused about Wylex ones. Screwfix sell what they describe as NHXS1Bxx compact DP ones for about £35, but also sell 'tall' SP ones, described as NHXSBS1Bxx, for the same price! Toolstation sell both 'tall' ones and compact ones for £30 - £37, describing them as NHXSBS1Bxx and NHXS1Bxx respectively, but without indicating whether they are SP or DP. Finally, to throw a cat in amongst the pigeons, TLC sell ones they describe as NHXS1Cxx and seemingly DP ("Single pole with switched neutral") for only about £17 (incl VAT).

So, as above, I'm more than a bit confused - particularly with the Wylex ones, since it appears that I could pay double for an SP 'tall' one than I would have to may for a DP compact one. Something 'feels wrong', so I think that I need to do some more reading and investigating!

 

[JohnW2]

For overloads, this is somewhat academic because if the neutral is overloaded and the phase isn't that means you have a bunch of residual current.

True, but I don't think you need to invoke that - even if it were just an MCB (hence no resdiusal-current sensing), I don't think that there would real be a need for 'overload sensing' in the neutral - unless there were (incredibly improbable) a prize **ck-up in th wiring or a 'cross-circuits fault, if there were an overload current flowing in the neutral there would be a similar (usually identical) current in the L - after all, that high current 'as to come from somewhere

For high current faults though, it may be relevant. The "switched neutral" likely has far less ability to break fault currents than the phase does.

If I understand you correctly, and if that were true, it wouldn't be a very good thing, would it - since with an 'overload' L-N fault, the same high current will usually be flowing in L & N ?