Is a SPLIT LOAD CONSUMER UNIT compliant with BS7671? - Electricians' Q&A
Consumer unit requirements change with each iteration of the IET wiring regulations BS7671. Joe Robinson looks at the specifics regarding split load configurations.
🕐 TIME STAMPS 🕕
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00:40 - Split load consumer unit with 2 RCCB's
00:55 - Selectivity formally know as discrimination
01:53 - Excessive protective conductor currents
03:47 - Several circuit maybe protected by one RCD
04:38 - Compliant circuit layout of a split load consumer unit with 2 RCCB's
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❌ This content on this channel is for electrical professionals.❌ ==================================
📹 Presented by
Joe Robinson - Technical Director - eFIXX
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#efixx #electricians
The selectivity normally refers to protective devices which are in series, the protective device next to the fault shall trip, and not the level above. This is also mentioned in the part of BS 7671 shown in the video as a "NOTE". In case of a, for example, 30mA RCD this would require a RCD which is time delayed and at least 3 times the tripping current of the 30mA RCD (in that case a 100mA). Making groups of RCDs is sufficient here in Germany to meet regulations, but the best way to go is to install RCBOs for the circuits. That particular thing isn't in the DIN VDE 0100 (Low voltage electrical installations), it is in the DIN 18015 (electrical installations in domestic dwellings). This reg also regulates by the living area in m² how many outlets must be in the different rooms, numbers of circuits, and the size of the distribution board (at least 4 rows, each row 12 units wide, 1 width unit=1 standard MCB), number of general circuits for outlets and lighting (depending on area in m²) and dedicated circuits for several named appliances. They also now want that we install one distribution board per floor, I actually did that back then when it wasn't necessary. I got a board in the cellar with the circuits for the cellar and the ground floor. The circuits in the 1st floor are in a sub-board installed on the first floor. Lighting circuit tripped, you are in the first floor and the lights in the staircase aren't working. And the board is on the ground floor. Worst case: You fall down the stairs because your kid left the roller skates on the stairs... The best words describing using the RCBO for each circuit instead of RCD groups is: Operational availability, or reliability.
Great comment, thanks. 😊
Just saw this and it reminded me of doing rewires of systems about 50 years old (in UK) where they had sub boards on different floors. Sometimes the regs just go round in circles 🙃
Full RCBO is a preference, but split load CU is still safer than a nackered old rewirable board for less well off customers. I personally think the IET should be proscribing ring final circuits before mandating RCBOs (or SPDs, AFDDs, etc.). It's the 21st century, let's have socket radials exclusively already.
Some good points there.
You need to understand ring final circuits and their advantages.
As usual the regs are as clear as mud. I would have interpreted 314 differently, and someone else could have another view, just say what you can and can't do, it would make things a lot easier, then we may all be singing from the same hymn sheet.
I've said this before with the regs seem to sit on fence a lot ,but are these regs retrospective do I need to rip out my dis board everytime a new regs book comes out ?
It's as bad as Legalese.. but the opposite way. Legalese is not designed for 'regular' people to understand but trained legal experts to remove ambiguity. But these regs seem to be the opposite. Not designed for 'regular' people OR trained tradesmen to understand. If only 1% of your target audience cannot understand the regs, you have either wrote it wrong, or you need to re-think who your target audience is.
@@ColinRichardson The other thing I cant get my head round is that no current should flow to earth, but some equipment does so we have to have individual earth leakage breakers so that the main trip doesn't operate ,how cockeyed is that ?
@@raychambers3646 equipment with any type of heating element inherently leaks some current to earth
@@raychambers3646 no they are not retrospective, the same way your car is tested for its mot to the standards at the time of it's manufacture
This is a very informative video and i really enjoyed it as this is a hot topic at present!
Thanks for commenting 👍
My mum had a single RCD board. When she needed some sorting out done, rather than rip out a perfectly serviceable CU we put RCBOs on one socket circuit and one lighting. So it's split load: RCD one side, RCBOs the other. Much more affordable to upgrade one or two at a time. Eventually they could all go into a new, same brand CU.
Top tip, thanks very much!
Haven’t fitted a twin load RCD board in 7 years, RCBO’s are better in my opinion. clients can understand that if that circuit trips it’s that circuit that’s the problem. Simples😊
Manufacturers such as Lewden and FuseBox make opting for a full RCBO board very affordable.
Not all clients are able or willing to pay for an all rcbo board. I do prefer them personally
it is getting very expensive with all the new regs. If and when the regs say you must fit an spd. or afdd
SPDs are turning out to be very affordable, mainly thanks to manufacturers taking the regs on board so quickly and acting as if they were mandatory. AFDDs are a different matter..it they become mandatory for a domestic CU upgrade, it could easily add £500 to your average upgrade overnight. Given the tech stuffed inside those things I reckon it will take years for the price to fall. So just as people are starting to wake up to EV being the future, and given that often coincides with a property needing a CU upgrade, how many domestic customers are actually going to be able to afford all of this.. I can see a real problem of energy poverty creeping up on us.
I would. But sparks didn't listen and not worth having them come back
I was asking my Qualifying supervisor about this as I had a couple of consumer unit fails recently( Old rcd not disconnecting and cover taped on). I was saying do we fit a Dual rcd splitload consumer unit as we only get paid a set amount standard order rate (sor) from the client which is a housing association. Or do we install all rcbo's which would go over the rate,he said that we have to fit all Rcbos now with bs7671. I wasn't going to look it up or argue it as I prefer rcbo's myself. On the splitload consumer units with the dual rcds I would of done the same as Joe with the lights and sockets and put the shower and cooker on the separate dual rcd's and the immersion heater if there was one separate from the shower as well.
Seems like a law degree/module would be handy for electricians.
Definitely recommend RCBO’s, been installing these for over 3 years now, rcbos have come down in price drastically, lewden for just over a tenner each, wouldn't install anything else now for practicality and usability
👍
Where are you getting them for that price, have never seen RCBOs for less than £16
In an ideal world all electricians would prefer to use SPD's and RCBO's in a CU. However, not all clients can afford the associated costs involved. So until the RCBO's become a little more affordable, RCD's will continue to be offered as a cost effective method (albeit not perfect) to protect the varying circuits within an installation. Nice job of explaining Joe. #StaySafe
Thanks Brian, that's pretty much the message I was going for. 👍
Do you offer both solutions when quoting, or do you assume the client can’t afford RCBO option without offering? What saving do you offer for a dual board vs an RCBO board ( genuinely interested in reasoning)
Would love to see a video on ccus underneath wooden stairs
I think in time, more and more equipment will be IT orientated and at some point you won't comply with the 30% natural leakage to the point where you will be needing RCBO's. Several years ago i had to replace a dual split due to various earth leakages in combination from about 8 pieces of equipment generating nuisance tripping
That’sall well and good splitting circuits up with selectivity and rcbo’s provided there are no borrowed neutrals. Prime examples are two way lighting on landing light. Boiler that have been replaced with live and switched live, where the permanent live has now been added from downstairs and control gear from the airing cupboard upstairs.
If you're aware a circuit has a borrowed neutral would that not be something that you'd fix anyway?
I do like to have more then 2 lighting circuits for that reason spliting up and down. The regs could get silly one rcbo for each socket each light. What might we need 25 to 40 way fuce box cu. Imagen a office 203 way that would be a fun installation job.
I would still install a split load as there is nothing really wrong with them if you divide the circuits correctly, but I would always prefer separate RCBOs as its cleaner and less disruptive should an RCD trip. My issue here is that the general vibe seems to imply the RCDs are always tripping, but in a healthy circuit you rarely ever see that.
Great comment, some really valid points made there.
I hear that, but circuit can become defective via dodgy appliances plugged in, water heaters elements going down etc. & finding faults on a bank of circuits via a RCD takes time to eliminate the fault as you will need to check all circuits addressed to said RCD, client always like a cheaper option but over engineering is always the best solution in the long run, but will cost more upfront
My parents house had 1 30ma rcd protecting the whole house. And never really had issues. I could probably count on 1 hand when it tripped in 10 years. My dad was in to tech so had 15+ machines with switch mode power supplies. Chinese odd power supplies all over the place. And the only things that used to cause it to trip was once me drilling through a cable. My mum cutting the lawn mower cable. And a couple of times when the outside light would literally explode. Other than that never had a problem.
Indeed, I've had a split load board for ten years and it's only tripped the RCD once when someone went on an adventure with a knife in a toaster..
The reality of fitting a CU means that you don’t always get to make those choices over which RCD a circuit goes on. The position and length of the existing cables often dictates things, and if you’re installing a split load board to reduce costs, it means you’re not likely going to be able extend the cables safely and tidily. Also, lots of older properties have shared neutrals on the lights anyway, so regardless of board type, the lights are going to be on one RCD/RCBO anyway.
During an eicr if you measure current flowing to earth and you have 10ma of more flowing to earth via one rcd does that become a c3?
Splitting left & right on domestic works for rings, thus half the sockets in a room are on if the RCD trips. Similar can be done with lighting. Separate circuits for kitchen & bathroom on RCBOs
If you're in your own home you should know where everything is in the dark
@@user-wk7wv8rn8h What if you’re just visiting or house sitting?
Split load RCD could also alert someone quicker that a circuit has gone down and has a fault as half the property will loose power, these circuits could have vital equipment pump or freezer for example and is more likely to go unnoticed with an RCBO, this is the only real benefit other than cost to have a split load RCD
Another good point. 😊
I like to see a max of 4 circuits per RCD, even better would be double pole MCBs, I have fitted them and it makes fault finding easier.
Great video. Presumably the IET are happy for us to continue to use dual RCD boards for the time being, as they are still shown as an option in the OSG (fig 3.6.3 (ii)). RCBO boards are undoubtedly less inconvenient in the event of a fault, but there is one very slight advantage to dual RCD boards: Depending on what tripped (MCB, RCD, or both), you can get an idea as to what sort of fault you're dealing with. This can be very useful for those intermittent, difficult to find faults that don't show up under test.
You'd get an idea what fault you're dealing with with an RCBO?
@@user-wk7wv8rn8h I think he means if a MCB tripped it would suggest a different fault to that if an RCD tripped. If an RCBO trips, it could suggest a neutral earth fault or a short circuit so you'd be looking for both.
@@JC-NUFC would a competent electrician not be able to figure that out within a few minutes of testing
@@user-wk7wv8rn8h not really. For a dual RCD board, an overload or L-N short would trip the MCB, while an earth fault would trip the RCD. A line to earth short would probably trip both. So you can at least get an idea of what sort of fault there is by what device tripped. An RCBO will trip for all the above faults, so it gives no clues as to what caused it to trip
@@user-wk7wv8rn8h Yes, and someone competent at reading would have noticed he said RCDs offer a "slight advantage" which isn't incorrect of him to say.
I know some one who’s house has one big ring main supplying both upstairs and downstairs cu full of RCBOS, his son has a medical condition and has to have a number of medical monitors . If god forbid there’s a short that young lad would be in serious trouble so I think ring-mains should be a necessity and split load CUs a personal choice. Great video joe thank you.
Or just put the medical equipment on a separate MCB radial with the feed in Galv conduit or deeper than 50mm in a wall...
@@jongurney Have two rings or radials to the same room, with DP RCBOs, with lots of sockets. If a circuit is down, plug into another.
or make sure its on a decent ups backup supply...
DP RCBO with no earth fly lead. The best.
Agree with that, but no DP RCBO for us in England. You must be in a European country
I fit rcbo 90% of the time bit sometimes budget means split rcd board. Ive used the logic that if the big Manufacturers still make and sell these boards they must meet with the regs im sure these guys go through the book thoroughly to make sure they are not making itmes they cant sell. As soon as a reg comes out suggesting split boards are not good enough they will stop making them. Spiltting the lighting circuits always trips the rcd when the property is sharing a neutral for two way switching.so on occasion ive had to put them on the same rcd.
Spot on for both comments.
No mention of not being able to install a split load board on a TT earthing system?
Seem to be making simple house wiring into rocket science!
It's definitely getting more complex but we got this!
@@efixx normally the job is scoped out for you by office engineers you do the install and let them worry about the regs ,testing is usually done by the test team.
Rcbo is obviously better but not necessary in most cases where the property has 3 or 4 power circuits and 2 lighting ones, putting the lights “upside down” compared to the power circuits is a good solution.. would only go full rcbo board in an office for example ( all radial circuits, no funny 32A ring mains ). The only issue money wise for the customer is that I only use Hager.
What about the maximum amount of leakage current on a RCD being no more than 15mA. This was not mentioned in this. How can we guess what the leakage will be on a split load board. I still fit dual RCD but try and sell RCBO’s to customers and i usually get around 40% come back and say lets go and fit RCBO’s and surge protector.
There is guidance for this with regards to IT equipment but you could also just carry out a measurement before fitting the board.
I like to fit high integrity consumer units and full rcbo consumer units. Have to way up how many circuits and how big is the property. ..fitting dual rccd consumer units has a problem with a circuit tripping off there is no we here else to put it temporarily on a non rccd side.. just a thought ...
Interesting thoughts, thanks very much. 😊
Well, if it’s tripping the RCD, there’s a potentially dangerous fault, so you you shouldn’t really be putting it on a non RCD protected breaker at all.... Temporary fixes have a way of becoming permanent. I know of a customer that has over a 100ma going down the main earth where the previous spark did a “temporary fix”, but the customer doesn’t want the hassle of changing his board.
@@efixx interesting?!?! More like dangerous.
The IET never appear to worry about cost to the consumer. Individual RCBOs will cost more than split load MCB/RCDs.
About £150 extra for my installation, new in 2015. In the context of the overall cost that hardly seems excessive.
@@JimWhitaker Multiply that by the number of households who will do the same and the figure will be much larger. Also some of these will be retired and on pensions so £150 may not be a lot to you but it will be to them.
So a cheap board full of rcbos vs a better brand split load? We don't even pay for smart meter fitters to change tails so surely there's better places to put your investment
I have always done full-RCBO boards. On a normal house, the difference is an extra £90 (on a ~£500 job). It’s a much a better service. When they make us do the AFDD, that’s going to be another minefield to navigate. By all accounts one AFDD at the front of the board will keep the lights of permanently, but an AFDD on every circuit will double the price of the install. Guide us! Oh ye wise eFixx!
stay tuned for amd2 in March - from what we know it's only going to be certain types of circuit on certain types of installation.
A benefit of split-load distribution boards is it's quicker and easier to test two RCD's than test the RCD component of several RCBO's.
If you test the RCBOs at the Consumer Unit, you will do all of them in 2 min..it is not a big difference compared with RCDs, I wouldn't see this as an advantage...personal opinion 😉
It takes about 60 seconds to test an RCBO, not a major problem
I test the rcbo's at the board takes a little longer but not much
@@12000gp I would say max 30 seconds:)) E clip stays on earthing bar The other 2 probes quickly you can move from one RCBO to other..probably depends of the tester, my megger does it very quick.. i will count the seconds tomorrow:)) Anyway, this is not an issue to test the RCBOs, at least I am not seeing as being a big issue, the only one is the price (install goes quick if using mini RCBO) New installation depends, existing installation I will not take a risk and I will always install a CU with RCBOs
With DP RCBOs they are far easier to fault find.
Very balanced video I've got a split load that only ever tripped due to faulty iron and hasn't now for 3 years. My electrical installation and appliances are all good. RCBOs are an expensive overkill
DP RCBOs are *safer.* Also your freezer can be tripped off when there is nothing wrong with it.
Balance is what we were aiming for so thanks. Love RCBO boards but wanted to point out how split load can still comply.
I would rather have a garage circuit, which may have a freezer plugged in, on an RCCB. If there is a fault with the freezer, you'd hope to notice one of the other circuits off in the house before you lose your frozen food.
RCBO boards only suit properties with good wiring done by a pro .One someone starts hacking into neutrals and bad connections etc , adding a RCBO will be a nightmare .And as mentioned RCBO boards dont tell you when something has turned off .So lets say you dont notice something not working , Then you could be in trouble !!
Couple of other points I can think of referring to split loads: 1. Does both RCDS have to be both at 100amp now? What happens if they are not? 2. What happens if either RCD or both are the incorrect type for coping with DC masking/Earth leakage with present circuits or additional circuits such as car chargers, etc. Please discuss if you can with another video please.
Great questions, we'll add them to our to do list!
@@efixx Thanks. I liked that Lewden IP rated TP&N DB. Have you seen the Hagar TP&N (basic IP) with Surge built in on the busbar system adjacent the main switch? No MCB required to feed it. If all boards came built in, we wouldn’t forget about them. 🤣
If the mcbs down stream addup to less than say the 63a rcd. Surely that's OK. If they add up to more then it would need changing
It is if it’s already installed!
The regs are a bit like the bible; "An eye for an eye" or should it be "turn the other cheek". No one is going to die but I only fit full RCBO boards. An excellent video and analysis of the regs and thank you very much Jo for your time and effort.
Love that "unless amendment 2 comes along and changes it all" Definition of amendment =men in lab coats have changed there minds again!
More like industry has got an idea to sell more product and lobbies hard to those in power to change the rules to generate cash.
I'm beginning to wonder if wholesalers should stop selling pre-built standard configuration special offer dual RCCB consumer units; all too often the installer just sets up an installation based on whatever MCBs came with the board rather than what the installation would be best served by Thankfully I operate in a sector of the market where 99% of the time I can fit RCBO boards with SPD
I fit RCBO Boards all the time. Nothing other than. Just because its easier for the client and fault finding.
No it's not, it's exactly the same...
Why are we still having this discussion? Split loads are allowable but they shouldn't be. If everyone fitted RCBOs the cost would drop like a stone. As to the question of separation. What about arc fault we won't have 10 of them per board. (At first). RCBOs aren't that expensive, and I wouldn't fit anything else. (WEO essential uses alarms etc.)
Thanks for commenting 👍
No chance big housing developers would move to rcbo only boards until they are as cheap as split boards.
Or until the regs require them to.
I prefer Rcbo boards, but IR testing is a bit more of a pain.
If you get double pole RCBO's it ends up being easier
electrician 1: hello i can fit new rcbo board for £400 electrician 2: hello i can fit new screwfix jobby british general split board for £300 as its cheap as chips. customer : oh great £300 one fine thanks. 2 weeks later, customer : hello electrican 2 theres a fault on my sockets and now half the house cant come on and its 12pm at night and ive got a baby and this and that please come out to fix.
Rcbo all the way. I educate the customer on the benefits of the rcbo board and 9 out of 10 times I get the work.
Good man! 👍
nice thing of having 3-phase supply and 4-pole RCDs, leakage currents does not add up, instead those cancel each other out. So no false tripping. It is common to have about 10 circuits protected by one RCD. RCBOs are very rare here too, those are only used if adding circuit and there is no space for RCD+MCB
I thought most leakage is from electronics loads or motors with y-class capacitors which are line-to-ground - so not sure how 3 phase helps?
@@edc1569 when you have balanced load between all phases, there is no current in neutral wire. Same applies to leakage current to ground.
Are you saying that Earth Leakage Current/Residual Current say 12mA 'induced' on phase-A , phase-B and phase-C simultaneously will be 'viewed' by the Sensing Coil as 0mA or near 0mA as they 'cancel out' each other???🤔🤣🤣
@@piratedprivacy9052 Exactly
In my opinion all domestic houses should have a AFDD and and an rcd protecting all circuits regardless of how the set up it, might be a pain with nuisance tripping but at least its safe
I personally C2 a consumer unit if there’s no RCD protection but you can technically pass it if only the lights and sockets are protected as only circuits you can “plug” things in need to be RCD protected, but yes I agree with you all circuits should be RCD protected
@@uplightuk8924 this is incorrect, any cable at a depth less than 50mm in a wall needs RCD protection. Not just circuits that plug in
@@TheFool2cool This is what I’ve been told by NIC and the trainer on my 18th edition course, don’t shoot the messenger. I personally C2 a board if it has no RCD protection. Besides, there is no way for you to tell if cables are buried more/less than 50mm anyway, that’s a limitation
You got AFDD money?
@@uplightuk8924 you’re both wrong, it’s a C3 unless the socket is likely to be used to supply outdoor equipment. Check out best practice guide 4.
Why do they need to over simplify everything 🤦♂️
Full RCBO is better
That is what I said.
@@efixx ok sorry, I thought you said whats your thoughts about this
My apologies, I did say that. Been taking some pelters on other vids and it's made me a bit oversensitive. 😊 Sorry again and thanks for commenting. 👍
There is nothing wrong with split load boards.
There isn't really anything wrong with them until a fault develops and takes out half of the circuits. That's why rcbo boards are soooo much better
@@curtisj2165 well no that's bollocks really because if half the circuits gat taken out in a house for 5 seconds what's the problem? Turn the MCBs off, turn the RCD back on the one MCB at a Time. When it trips you.know which circuit. RCBOS only benefit is having 30ma per Circuit, which technically means its less sensitive then when it is shared over a split load.
@@adamwright5306 5 seconds? Imagine if the rcd trips while you are not at home, or worse still, while you are on holiday
@@curtisj2165 Would never happen if its tested correctly. Thats just like saying imagine it just spontaneously combusted. It never happens, it's just what ifs all the time. You hear the odd case on a forum out of millions of houses. The worst that would ever happen is your fridge might turn off. Big deal. Can't imagine people leave fillet steak in there before they go away
@@adamwright5306 would never happen if tested correctly, are you serious? Personally i would not be happy if my freezer defrosted
If you can use split load and your competition is, then you have to be competitive! RCBO consumer units are better, but always comes done to money.
It's another factor to consider for sure!
Get a proper job joe and stop with this crap.
😂 This is my proper job, I love it and I'm great at it. 💪
Way too much is being read into this, and you can bet your ass a judge would rip you apart if you listened to this advice. Just put each circuit on its own RCBO. They are cheap enough these days.
You could also point to other publications by the IET which show split load boards in use as acceptable. I think if you demonstrated the depth of knowledge of the regs shown in this video the judge would trust your engineering judgement. I agree RCBO boards are the best but split load boards aren't necessarily non-compliant.