Why do we do it the way we do in the UK?

[Electrics]

Was just watching a video of an RCBO install and found it weird that the breakers are double pole yet still have to have a fly lead.

Why don't we do it like this:

Ignore the gibberish coming out of his mouth and take a look at the unit. L+N coming from the supply, feeding the bottom of the first RCD. All the RCD's are linked together by the linking bars running down the left, giving them all L+N feed. The feed then goes through the RCD out the top, into the bus bar that's linked across the tops of all the MCB's. The L+N of each circuit comes out the bottom. This does away with the need for a neutral bar (there is one but they are used when there is no linking bar employed and you have to run an N to each RCD), several main neutral cables and the need to fill the unit with loads of extra cabling, not to mention cost saving on the materials.

Why, even with dual pole RCBO's, do we still make them use fly leads when we could simply link them all to N via the main RCD in? Makes no sense to me.

Having said that we're still the only country i know of that uses rings.

Anyone think we'll eventually catch up and stop doing things in such weird ways? Although i guess one drawback of the way they do it in Europe is that their multi tier units are standard for almost any regular sized home and they are anywhere from £3-700.

 

[Electrics]

Like on this video, why don't they just have the N going through the bottom, then you could simply do L+N in the top of the RCD from the supply, L+N out the bottom of the RCD via bus bar into the bottom of the RCBO's then L+N out the tops for the circuits. That would do away with 10 extra N cables.

Or do these exist and i've just not seen them?

 

[Mike Johnson]

Hager double pole RCBO's do not have a fly lead anymore, and I think most others are doing away with them, or will eventually.

Hager CDA240U 40a 2p 30ma Type A RCD

Buy online Hager CDA240U 40a 2p 30ma Type A RCD with 24 hour delivery from Edwardes

www.edwardes.co.uk

 

[Mike Johnson]

Sorry wrong link, this is the right one: Electrical Wholesaler - Hager 2 Pole 6kA B-25A 30mA A Class RCBO AD925J - https://www.electricalwholesaler.ie/products/switchgearfuses/switchgeardistribution/rcboresidualcurrentbreakers/hagerrcbo2p1pn6kab25a30maaclassad925j

 

[pc1966]

I agree 100% that there should be a neutral bus-bar so no abomination of flying leads.

Why does Europe have them already? Probably as they have often mandated DP MCBs due to a historical lack of a "strong correct polarity". The UK has had polarised plugs since well before WW2 and often only a switch or fuse in the line, as neutral was usually well--earthed (though you do occasionally see pre-WW2 cut-outs with a fused neutral - a bad thing these days). So when we had fuse or MCBs there was never a need for DP operation, so no neutrals going through them and no need for a neutral bus-bar.

That has changed with RCBOs, even though the majority of them in the UK are single-pole switching (I strongly believe in DP switching like the Wylex, Crabtree and Fusebox compact RCBO) it would be massively easier with a neutral bus-bar.

As for the RFC, arguments over it can be found here and it will run and run. But the key difference as to why the UK (and former commonwealth) has them and other don't is we have fused plugs and they don't. That massively changes the way you chose to rate the supply OCPD and manage the cable volt drop and rating. Also it means no single point of failure in the fixed wiring for the CPC (weakly with single terminal sockets, strongly if dual-terminal 'high integrity' sockets are used).

 

[timhoward]

By the way, SBS make one....
I've been thinking about trying one when I find the right job for it.

 

[Lucien Nunes]

There are lots of historical influences on design of these things. @pc1966 mentions some of them, including the important factor that DP and SPSN MCBs became popular in Europe before RCBOs, because of wider use of TT.

We are used to being able to supply all the socket-outlets of a domestic installation with a small number of circuits, as each 32A circuit (whether ring or radial) offers 7.3kW. A small home will function perfectly well with just one 32A circuit; we would consider that bad design now but it was quite standard in the past. Using 16A circuits, more than two would be required to achieve the same level of utility since there is less diversity and any concentration of load can easily trip a 16A. Hence four or more circuits might be desirable to cover the same load and area, increasing the number of ways needed in the CU. This is all the more important in areas using supplies in the 110-127V range (which included parts of France until a few decades ago) which obviously only get half as much power per amp as those using the 220-250V range.

Some locations standardised on 3-phase for domestic supplies, with main fuses as low as 25A, leading to 3-phase cookers etc. with a corresponding increase in the number of outgoing ways. The result of these and other factors is that large multi-row CU's are fairly standard abroad, whereas we tended to stick to little boxes with as few as six outgoing ways even in the 1980s, bought as a complete thing and used as-is instead of being built as a system with a view to expansion.

 

[Electrics]

There are lots of historical influences on design of these things. @pc1966 mentions some of them, including the important factor that DP and SPSN MCBs became popular in Europe before RCBOs, because of wider use of TT.

We are used to being able to supply all the socket-outlets of a domestic installation with a small number of circuits, as each 32A circuit (whether ring or radial) offers 7.3kW. A small home will function perfectly well with just one 32A circuit; we would consider that bad design now but it was quite standard in the past. Using 16A circuits, more than two would be required to achieve the same level of utility since there is less diversity and any concentration of load can easily trip a 16A. Hence four or more circuits might be desirable to cover the same load and area, increasing the number of ways needed in the CU. This is all the more important in areas using supplies in the 110-127V range (which included parts of France until a few decades ago) which obviously only get half as much power per amp as those using the 220-250V range.

Some locations standardised on 3-phase for domestic supplies, with main fuses as low as 25A, leading to 3-phase cookers etc. with a corresponding increase in the number of outgoing ways. The result of these and other factors is that large multi-row CU's are fairly standard abroad, whereas we tended to stick to little boxes with as few as six outgoing ways even in the 1980s, bought as a complete thing and used as-is instead of being built as a system with a view to expansion.

I always thought (coming from a French background) it prudent to do something like 2x radials on 20a MCB's + 32a ring for the kitchen, for a smaller house up to 100sqm.

Sound like something that is doable over here?

In France we basically use radials and then everything in the kitchen gets its own dedicated circuit, including washing machines and dishwashers.

 

[westward10]

I can sense a picture coming.

 

[Mike Johnson]

No chance, been posted too often. ?

 

[Electrics]

I can sense a picture coming.

Lol nah i'm a trainee without an employer, trying to get as much info as i can to the many hundreds of questions i have ?

 

[telectrix]

my thinks......average house.RFC for kitchen, rest of sockets on 2/3 20A radials.

 

[Electrics]

my thinks......average house.RFC for kitchen, rest of sockets on 2/3 20A radials.

That's what i woulda thought - is it true that you're only allowed one radial per 50sqm area? I've heard this said but struggling to find the rule written down.

I thought RFC for the kitchen just because of the load being drawn if eg toaster, kettle, dishwasher and washing machine are all on at the same time.

 

[pc1966]

That's what i woulda thought - is it true that you're only allowed one radial per 50sqm area? I've heard this said but struggling to find the rule written down.

There is no rule as such, just some guidance for "typical" usage. From memory it is 50m^2 for 20A radial, 75 for 32A radial and 100 for 32A RFC.

Recent tradition is one floor of a house would be on a RFC. More recently came the idea of one just for the kitchen as more power-hungry accessories came in to common use.

In truth the RFC is very robust, many place have everything on one and it is just fine. the more recent trend for more separate radial socket circuits in the UK is probably driven more by RCDs and accumulated leakage.

I thought RFC for the kitchen just because of the load being drawn if eg toaster, kettle, dishwasher and washing machine are all on at the same time.

I would agree. Some prefer 4mm radials but that is marginal if much thermal insulation, and by 6mm it is hard to wrnagle or fit pairs in to socket terminals..

But more often than not the main issue/guidance that seems relevant is separate single sockets per appliance, not doubles that seem to burn out more.

In Scotland the building regs say there must be accessible means of isolation for white goods, so you probably would have an RFC around 20A DP switches and each running 2.5mm to an unswitched socket behind the appliance, etc.

 

[Simon47]

By the way, SBS make one....
I've been thinking about trying one when I find the right job for it.

Yes, they are nice boxes, and he's very flexible.
Also does some nice glands. The 25mm tail set he does fits in a 32mm hole, and there's an adapter if yo have a 40mm hole. The last one I got from the wholesaler (CEF) was 40mm an by the time you added an adapter down to 32mm it was a horrible monstrosity.

 

[pc1966]

Yes, they are nice boxes, and he's very flexible.
Also does some nice glands. The 25mm tail set he does fits in a 32mm hole, and there's an adapter if yo have a 40mm hole. The last one I got from the wholesaler (CEF) was 40mm an by the time you added an adapter down to 32mm it was a horrible monstrosity.

CEF appear to do a 32mm one, though the image does not seem to match as it does for the 40mm one:

32mm Plastic Cable Gland LSF with Multiple Insert, Locknut and Blanks IP68

Flame protection Glow wire test 750° C acc. to EN 60695-2-11

www.cef.co.uk

40mm Plastic Cable Gland LSF with Multiple Insert, Locknut and Blanks IP68

Flame protection Glow wire test 750° C acc. to EN 60695-2-11

www.cef.co.uk

They also stock the Wylex one but at quite a price:

32mm Plastic Cable Gland with Multiple Insert and Locknut

Moulded cable gland kit for metal consumer unit to provide additional support and supplementary insulation similar to Class II construction for the incoming cables

www.cef.co.uk

 

[Mikegh]

Its all DP 2-mod rcbos here

Takes up more space ,.main boards are always at least ,2-row

Better job on an rcbo board to be breaking both live poles for a fault I reckon

 

[Mike Johnson]

As I understand it, the double pole RCBO's only monitor the Phase side, the neutral side is just dragged along on a fault condition, so as you say it does break both.

 

[Mikegh]

As I understand it, the double pole RCBO's only monitor the Phase side, the neutral side is just dragged along on a fault condition, so as you say it does break both.

You mean the MCB side of it ?

It'll be just on the L pole

 

[pc1966]

Its all DP 2-mod rcbos here

Takes up more space ,.main boards are always at least ,2-row

Better job on an rcbo board to be breaking both live poles for a fault I reckon

You can get DP RCBOs in single width, like the compact Wylex, Crabtree, and fusebox RCBOs so they take no more space then traditional UK style MCBs.

I really prefer DP ones for various reasons:

• They isolate both L & N so you can IR test the circuit without having to unscrew anything
• If you have a TT style arrangement with an up-front delay RCD the you don't trip that on a N-E fault downstream (as N is isolated)
• If you are really unfortunate and have reversed polarity, you still get some hope of a fault being interrupted (but you really don't want to test that out as the I2t of the relatively slow RCD opening action will be horrendous)