"Pretty" or "Smart" consumer unit options.

[MJPD29]

Smart real time data on earth leakage current etc is absolutley available right now as I'm have recently installed such devices but in a domestic setting they are a huge cost if going one per circuit etc, as will wiring radial per room which really isn't nessecary imo

 

[pc1966]

Smart real time data on earth leakage current etc is absolutely available right now as I'm have recently installed such devices but in a domestic setting they are a huge cost if going one per circuit etc, as will wiring radial per room which really isn't necessary imo

What module, etc, was that?

The only ones I have seen at the rather expensive adjustable EL add-ons for tripping MCB/MCCB where they give you an idea of how close to threshold it is running.

 

[MJPD29]

I'll take details and a few photos of it tomorrow for you as I'll be headed back to site. Was supplied to me to be fitted on a bank of 200kw EV chargers due to recent issues with tripping. Didn't set up smart side but seen their remote monitoring for it, looks a decent bit of kit.

 

[mrwkuk]

Smart real time data on earth leakage current etc is absolutley available right now as I'm have recently installed such devices but in a domestic setting they are a huge cost if going one per circuit etc, as will wiring radial per room which really isn't nessecary imo

Of course its not nessecary. Neither are RCBOs, or AFDDs. RCDs are fine (at the moment, until the regs madate otherwise). But like RCBOs, Radials give you more granularity of control over your power, and make isolating faults a lot easier and mean you can have lower rated breakers in the CU which is safer. Yes it costs more, but its a one-off cost for an ongoing benefit.

Ring mains are primarily a legacy configuration from cabling resource limitations of post-war britain. Most eu countries, where those limitations never happened, have radials everywhere instead because they just make more sense.

As I said though, I am not definitely doing that, but I am considering it, subject to discussion with whichever spark i get to do the work.

 

[pc1966]

Ring mains are primarily a legacy configuration from cabling resource limitations of post-war britain. Most eu countries, where those limitations never happened, have radials everywhere instead because they just make more sense.

It is more complicated than that.

The difference is we have fused plugs. So we can have a 32A supply and still use 0.75mm cables to appliances quite safely (even 0.5mm with a 3A fuse) and the added diversity means we can typically have more sockets and appliances than the x1.5-2 factor in supply rating w.r.t. EU radials suggests.

Given the high cost of AFDD the RFC might be quite a saving! True it wont detect a serial break but then that is not arcing enough to be detectable and the evidence from widespread use suggests it is not a common fire risk.

Also the RFC has greater fault tolerance due to the two connections of the CPC at each point, sadly tested by many builders & DIY modifications, and in the days before RCD were common that helped reduce the risk of an open CPC causing a fatal shock.

However, the prevalence of TN supply in the UK along with the historical insistence on reliable polarity (i.e. neutral really is the one referenced to Earth) and prompt disconnection on earth faults (due to design for worst-case fault current and over-current protection) also meant RCD were a bit slower to appear in the UK. Much of the EU was on TT supply where RCD are often the only reliable means of disconnection, so that pushed faster adoption there.

 

[davesparks]

But like RCBOs, Radials give you more granularity of control over your power, and make isolating faults a lot easier

Instead of spending money on the cost of installing a lot of radials you could spend money on a good electrician and prevent faults by having a good quality installation.

Breaking an installation down to help isolate faults suggests an assumption or acceptance that the installation will be susceptible to faults and faults will happen. A better attitude would be to have a good quality installation which is inherently far less likely to suffer a fault.

and mean you can have lower rated breakers in the CU which is safer.

Lower rated breakers are not safer! A good quality installation is safer.
A properly installed 63A circuit will be far safer than an improperly installed 6A circuit.

 

[mrwkuk]

Breaking an installation down to help isolate faults suggests an assumption or acceptance that the installation will be susceptible to faults and faults will happen. A better attitude would be to have a good quality installation which is inherently far less likely to suffer a fault.

Fault finding is just one reasoning. Say, for example, we want to re-decorate a room. Its easier to isolate just that room, then we can pull the sockets, and switches off the wall and have at it without worry, than either isolating the whole floor, or not turning the power off at all, and just "being careful".

Or as someone else has suggested in this thread, maybe you wanted to just isolate part of the house that you arent using for power saving reasons. You would have to manully disconnect or power off all devices in that area.

It just seems logical, and safer, to me to be able to switch things off in more discrete chunks.

A good quality installation is safer.

Depends on what you are protecting against. A ring circuit offers less protection against overcurrent because they have to (by design) have a higher rated breaker. The much lower breaker on a radial means that in a worst case scenario (assuming a short in the socket, or some other over current situation that bypasses the local fuse in the plug) the radial would trip quicker than a ring main would.

Also things do degrade over time. It might not be an issue now but what if theres a water leak, rodent ingress, appliance fault, or workman damage, being able to just isolate a smaller area and make safe makes more sense than making the whole house uninhabitable until a sparky can come and fix it.

Ultimately I am aware all of these are edge cases. And I am not saying I AM going to switch to radials, but I am saying I can see a lot of benefits from doing so.

Regardless of that, I do still need a few extra circuits installed above and beyond what we already have, and I do still want to add a couple of smart modules at the very least. That will require a replacement/bigger CU which will be visible to everyone, so the original post still stands.

 

[littlespark]

What is on the other side of the wall? Possible to move the CU into another room, so it isn’t in view as you come into house?

You can make the CU as pretty as you like, but you might still see a great ugly distributors head, fuse, meter and tails.

What about a well made cabinet around it all?

 

[pc1966]

A ring circuit offers less protection against overcurrent because they have to (by design) have a higher rated breaker. The much lower breaker on a radial means that in a worst case scenario (assuming a short in the socket, or some other over current situation that bypasses the local fuse in the plug) the radial would trip quicker than a ring main would.

This is not true.

If correctly designed both situations (RFC or radial) will have sufficiently low fault impedance Zs such that the breaker hits the "instant" magnetic trip point and then it will disconnect in typically 10ms or less. The disconnection speed once in the magnetic trip fault zone (rather than thermal overload trip) is not very sensitive to the degree of over-current.

In all cases for a typical UK home on TN supply the design has to disconnect in under 0.4s under hard fault conditions and in the case of MCB (and related RCBO) that always means hitting the magnetic trip point. There is some difference if fault let-through energy between MCB ratings (see below) but surprisingly small, but again the basic principle of electrical design is the cable size has been selected to meet both the operational current and the worst-case fault condition's heating effects.

As @davesparks has already said the key is to have it correctly designed, installed and tested so it is known that everything is meeting the regulations and nothing has a loose / high-resistance connection or dodgy insulation. Oddly enough this is an aspect where the RFC is better as the figure-of-eight test is very sensitive to even small excess resistance since every socket should be identical during the test so spotting a bad joint or socket with a dodgy switch, etc, is easier.

If you want multiple circuits to allow rooms to be isolated individually, etc, then radial make more sense than the RFC which is better suited to a whole floor, etc, that naturally forms some sort of a loop, but to characterise the radial as safer is completely wrong.

 

[mrwkuk]

This is not true.

If correctly designed both situations (RFC or radial) will have sufficiently low fault impedance Zs such that the breaker hits the "instant" magnetic trip point and then it will disconnect in typically 10ms or less. The disconnection speed once in the magnetic trip fault zone (rather than thermal overload trip) is not very sensitive to the degree of over-current.

In all cases for a typical UK home on TN supply the design has to disconnect in under 0.4s under hard fault conditions and in the case of MCB (and related RCBO) that always means hitting the magnetic trip point. There is some difference if fault let-through energy between MCB ratings (see below) but surprisingly small, but again the basic principle of electrical design is the cable size has been selected to meet both the operational current and the worst-case fault condition's heating effects.

As @davesparks has already said the key is to have it correctly designed, installed and tested so it is known that everything is meeting the regulations and nothing has a loose / high-resistance connection or dodgy insulation. Oddly enough this is an aspect where the RFC is better as the figure-of-eight test is very sensitive to even small excess resistance since every socket should be identical during the test so spotting a bad joint or socket with a dodgy switch, etc, is easier.

If you want multiple circuits to allow rooms to be isolated individually, etc, then radial make more sense than the RFC which is better suited to a whole floor, etc, that naturally forms some sort of a loop, but to characterise the radial as safer is completely wrong.

View attachment 104770

Ok I mis-spoke, saying a ring will trip "quicker" was perhaps poor wording. Obviously the breakers will all break at similar speeds.

I meant that with an increasing current situation, a smaller breaker will trip at a lower current threshold, i.e. "sooner".

So the plugs are rated at 13a, if you plug in a device that (for whatever reason) doesnt break the fuse at 13a and pulls say 25a, a 16a or 20a radial will trip, but a 32a RFC wont. It will keep feeding the full 25a to a 13a socket (potentially overheating it and causing a fire).

In this, admittedly very unlikely, scenario a radial is "safer" than a ring because the design implies a lower rating of breaker and that gives less headroom for unexpectedly high loads.

 

[mrwkuk]

What is on the other side of the wall? Possible to move the CU into another room, so it isn’t in view as you come into house?

You can make the CU as pretty as you like, but you might still see a great ugly distributors head, fuse, meter and tails.

What about a well made cabinet around it all?

It could be possible. I hadnt considered that, but it would mean raising it up higher, meaning my partner couldnt access it in my absense.

All the meter and tails are in the cupboard outside, the only stuff inside is the CU. I dont mind trunking and other boxing around the CU, as that can be tidied. I was just looking for nicer options for the CU itself.

There is already a kind of cabinet around it, but if we enlarge the CU, theres not really enough space for a surround on the bit of wall that the CU will be on, hence why it would likely be exposed where it currently isnt (hence my interest in making it look better).

 

[nicebutdim]

Ok I mis-spoke, saying a ring will trip "quicker" was perhaps poor wording. Obviously the breakers will all break at similar speeds.

I meant that with an increasing current situation, a smaller breaker will trip at a lower current threshold, i.e. "sooner".

So the plugs are rated at 13a, if you plug in a device that (for whatever reason) doesnt break the fuse at 13a and pulls say 25a, a 16a or 20a radial will trip, but a 32a RFC wont. It will keep feeding the full 25a to a 13a socket (potentially overheating it and causing a fire).

In this, admittedly very unlikely, scenario a radial is "safer" than a ring because the design implies a lower rating of breaker and that gives less headroom for unexpectedly high loads.

The breakers in your board aren't there to protect appliances fitted with a 13A plug, but to protect the cables supplying power to each of those plugs. There are many members with vastly greater experience than me, but I doubt many (if any) will have experience of the situation described above.

As @davesparks has stated, the best way to protect against faults is to have a well designed installation installed by competent electricians. Householders can further assist by learing about cable safe zones, to avoid unintended damage to the installation, and avoid potential fires by not directly importing unsafe electrical appliances. Of course appliance fires can also happen when every possible step is taken to mitigate the possibility, but these are generally attributed to design flaws and not the sort of situation you describe.

I'm not trying to be contrary, but simple don't see any merit in your argument.

 

[Joules]

You may find a CU that looks pretty smart but finding an electrician to compliment it is altogether another matter and remember electricians run businesses so their profit motive comes first, not you. In the UK the profit motive obliges the electrician to recommend a CU filled with RCBO for every circuit courtesy of 17th Edition Regs, its a win for both electrician and customer but is very expensive. There will be little or no nuisance tripping and the electrician does not need to go to the expense of buying an earth leakage instrument such as a Megger DCM 305E.

When the 18th Edition Regs came along two options presented themselves: the first carried across from 17th Edition in that the board must be entirely filled with RCBO. The second option allowed an RCD to protect a group of MCB just as long as the total leakage current measured down stream was less than 9mA. This allows for a split neutral board to be installed albeit with a risk of nuisance RCD tripping. There is however a third option which is a hybrid combination of the first two.

The CU is split into three parts each with separate neutral bars. The first is to leave spare module slots after the main breaker to accommodate RCBO. The second is for an RCD to monitor a group of MCB power circuits and the third an MCB to monitor another group of MCB for lighting. Have installed or as a prelude to install an audit of leakage currents is undertaken. Circuits like ring mains that feature higher leakage currents use RCBO as do any PV inverters and so on. The cost to the customer of such a CU should be around the £350 mark as opposed to between £700-£950 for a 17th Edition full RCBO board.

Youtube's eFIXX electrician explains the pros and cons of this in his Earth Leakage Currents video.

 

[westward10]

You may find a CU that looks pretty smart but finding an electrician to compliment it is altogether another matter and remember electricians run businesses so their profit motive comes first, not you. In the UK the profit motive obliges the electrician to recommend a CU filled with RCBO for every circuit courtesy of 17th Edition Regs, its a win for both electrician and customer but is very expensive. There will be little or no nuisance tripping and the electrician does not need to go to the expense of buying an earth leakage instrument such as a Megger DCM 305E.

When the 18th Edition Regs came along two options presented themselves: the first carried across from 17th Edition in that the board must be entirely filled with RCBO. The second option allowed an RCD to protect a group of MCB just as long as the total leakage current measured down stream was less than 9mA. This allows for a split neutral board to be installed albeit with a risk of nuisance RCD tripping. There is however a third option which is a hybrid combination of the first two.

The CU is split into three parts each with separate neutral bars. The first is to leave spare module slots after the main breaker to accommodate RCBO. The second is for an RCD to monitor a group of MCB power circuits and the third an MCB to monitor another group of MCB for lighting. Have installed or as a prelude to install an audit of leakage currents is undertaken. Circuits like ring mains that feature higher leakage currents use RCBO as do any PV inverters and so on. The cost to the customer of such a CU should be around the £350 mark as opposed to between £700-£950 for a 17th Edition full RCBO board.

Youtube's eFIXX electrician explains the pros and cons of this in his Earth Leakage Currents video.

Your second option is not really permitted by BS7671 in residential installations.

 

[Joules]

Your second option is not really permitted by BS7671 in residential installations.

Your interpretation of BS7671 stands as personal opinion. In the best interests of the OP please provide members with evidence to support your view so that it may undergo peer review

 

[westward10]

@Joules that is exactly what I will do when I get home. You are new to the forum so I will let your attitude pass.

 

[littlespark]

@Joules that is exactly what I will do when I get home. You are new to the forum so I will let your attitude pass.

Attitude?

He did finish with a smiley face. I’m sure no “attitude” was inferred.

Merry Christmas, Scrooge.

 

[Electro-tech]

This is a hotly contested debate amongst electricians. Dual RCD & split load boards were popular under previous versions of BS7671. Whilst these never really met the requirements for division of circuits, they were a safe compromise.
It should be recognised though, especially since RCBOs are so plentiful and relatively cheap, that an RCBO board is really the properly compliant with consumer unit regulations, specifically the parts of BS7671 related to dividing circuits to minimise inconvenience in the event of fault.
For a regular 30mA RCD the regular leakage current must not exceed 10mA under normal circumstances.
RCBOs not only minimise inconvenience to the end user, but they allow for much faster fault finding & rectification of issues as it obvious from the get-go which circuit is involved. Dual RCD boards do not allow this, each RCD can cover a multitude of circuits, thus complicating locating faults.

 

[JBW175]

I don’t know anyone installing split load boards these days, I’ve not done one for over 4 years.

I only ever quote for full RCBO boards with SPD.

 

[mrwkuk]

You could fit one of these, adapted for single phase usage. Plenty of room for 'smart accessories)
View attachment 104696

I missed this post on the first pass. What make/model is that ?