High Integrety CU - Internal cabling

[SUNRAY]

I have mentioned them a few times

I recently sheared my modulo head on my torque driver the maker replaced it free and give me some surprising news relating to modulo head screws in dist boards, if your interested i will try and pm it to you as i dont want to publicly announce it

Yes please me too

 

[JohnW2]

I have mentioned them a few times

Fair enough,but if yiou just talked about "modulo head screwdrivers",I wouldhave had a clue as to what you were talking about

I recently sheared my modulo head on my torque driver the maker replaced it free and give me some surprising news relating to modulo head screws in dist boards, if your interested i will try and pm it to you as i dont want to publicly announce it

Yes,I'd be interested. Thanks.

... but how do these 'modulo head screws' differ from the things which we all know and love?

 

[JohnW2]

Are you sure? All those I recall have 3 neutral bars, admittedly one is usually quite small

Maybe some dual RCDs have a third neutral bar, but I don't recall having seen that, and nor do I really understand why they would have done it - since, without 'mutilating' the CU (at least, it's bus bars), one can't have non-RCD circuits in a traditional dual RCD board.

 

[Harry Bloomfield]

I have mentioned them a few times

I recently sheared my modulo head on my torque driver the maker replaced it free and give me some surprising news relating to modulo head screws in dist boards, if your interested i will try and pm it to you as i dont want to publicly announce it

Yes please!

 

[SUNRAY]

Maybe some dual RCDs have a third neutral bar, but I don't recall having seen that, and nor do I really understand why they would have done it - since, without 'mutilating' the CU (at least, it's bus bars), one can't have non-RCD circuits in a traditional dual RCD board.

Well for a start, some dual RCD boards take the feed to the rcd's from the neutral bar.

 

[plugwash]

If they have a neutral bar for the "non-rcd" section, then they can use the same earth/neutral bar setup and the same cabling kits for both "dual RCD only" and "high integrity" configurations. Only the live busbars would need to be different.

 

[SUNRAY]

Well for a start, some dual RCD boards take the feed to the rcd's from the neutral bar.

And some dual RCD boards come with just one MCB bussbar and has to be cut to fit whatever combination is required.

 

[SUNRAY]

If they have a neutral bar for the "non-rcd" section, then they can use the same earth/neutral bar setup and the same cabling kits for both "dual RCD only" and "high integrity" configurations. Only the live busbars would need to be different.

AFAIC the term high integrity started when split load boards had the second RCD installed to become dual RCD. FWIW I've adapted a number of dual RCD boards to be non RCD protected, ie for SWA submain etc.

 

[JohnW2]

If they have a neutral bar for the "non-rcd" section, then they can use the same earth/neutral bar setup and the same cabling kits for both "dual RCD only" and "high integrity" configurations. Only the live busbars would need to be different.

Yes, that would be a manufacturing advantage, but it doesn't alter the fact that I don't recall having seen a 'dual-RCD CU' (i.e. one in which, as factory-configured, all of the slots were supplied by bus bars from one or other of the RCDs) which had a third neutral bar...

.... but maybe that's just a matter of my limited experience/exosure?

 

[SUNRAY]

Yes, that would be a manufacturing advantage, but it doesn't alter the fact that I don't recall having seen a 'dual-RCD CU' (i.e. one in which, as factory-configured, all of the slots were supplied by bus bars from one or other of the RCDs) which had a third neutral bar...

.... but maybe that's just a matter of my limited experience/exosure?

I don't know the answer, I'd have said they all have 3 N bars as that's my perception. Even to the point when I fitted a board with a total of 8 slots and a duall RCD kit... That's a main switch, 2 RCD's and 2 MCB's. There actually wasn't enough space to fit them all which real didn't matter as 2 of them at least were not required

 

[ebee]

I don';t think it is - a dual-RCD board is a dual RCD board, and has two neutral bars (one for each RCD).

This extraordinary term "high integrity board/CU' (don't ask me ) seems to refer to a board which has two RCDs, but also has provision for a few (often only two) non-RCD circuits - hence three neutral bars.

As it happens, most of thee CUs in my house are these 'high integrity' ones!

Kind Regards, John

Yes of course you are correct there John , Dual RCDs and 2 or 3 plain switched fuseways.

 

[ebee]

Yes please!

Yes Please from me too

 

[ebee]

If I understand the comments correctly then yes I have noted the 3 N terminals strips. N1 being the output of the DP Main Switch which in turn provide a N connection for both RCDs plus 2 or 3 extra terminals for use on MCB (or RCBOs if you wish) circuits. then the N2 being for RCD A/ circuits and N3 being for RCD B/ circuits.

So, speaking randomly, you might well have one chance in three of not creating the dreaded "Borrowed N Scenario"

 

[DetlefSchmitz]

I have mentioned them a few times

I've had a set of those since I redid my house wiring many years ago. I don't know how you are supposed to cope with a consumer unit otherwise.

The history seems somewhat vague, as witnessed by the variety of names: modulo, plus-minus, positive-negative, zeno SL/PH or zeno SL/PZ etc etc. They may be modeled on pozidriv or philips. But it seems that the original development of the screws was, as one might expect, simply to make it easier to use the first screwdriver out of the toolbox without having to think. The screwdrivers seem to have come about because the MCB etc manufacturers became more fussy about correct torquing and the first screwdriver out of the box wouldn't give accurate torque without damaging the screw, so they came up with screwdriver bits.

Wikipedia says (somewhat incompletely):
"Combination Drives.
Some screws have heads designed to accommodate more than one kind of driver,sometimes referred to as combo-head or combi-head. The most common of these are a combination of a slotted /Phillips head, often used in attaching knobs to furniture drawer fronts and combined
slotted/pozidriv heads which are so ubiquitous in electrical switchgear to have earned the nickname "electrician's screws". (The idea is that first screwdriver out of the toolbox isused, and the user does not have to waste valuable time searching for the correct driver). Slotted/Phillips (as opposed to slotted/pozidriv) heads occur in some North American-made switchgear.
Their rise to popular use has been in spite of the fact that the head is weaker and neither a flat screwdriver or Pozidriv/Phillips screwdriver as appropriate is fully successful in driving these screws to the required torque. Some screwdriver manufacturers solve this problem offer matching screwdrivers and call them "Modulo", "Plus-minus", or "contractor screwdrivers", although the original concept of not needing to search for a particular driver is defeated.
Other combinations are a Phillips and Robertson, a Robertson and a slotted, a Torx and a slotted and a triple-drive screw that can take a slotted, Phillips or a Robertson."

BS EN 60898 for MCBs, on the subject of screws for external conductors, simply says that whatever type they are they ought not to break when you tighten them up. So their use doesn't come from there.

 

[Harry Bloomfield]

Maybe some dual RCDs have a third neutral bar, but I don't recall having seen that, and nor do I really understand why they would have done it - since, without 'mutilating' the CU (at least, it's bus bars), one can't have non-RCD circuits in a traditional dual RCD board.

My new one has three separate neutral bars. None RCD + main loops to the two RCD inputs, on the left. It wouldn't be too difficult to add one of the RCD neutral bars, directly to the none RCD bar, if one wanted to swap it over to RCBO's.