I have approval from my DNO (UKPN) for installing the Multiplus 2 in grid parallel mode, with the full export limit approved and no G100 requirements. However I was interested in installing it with a consumer unit operating as a protected/backup setup, and this is where Ive been bamboozled by different electricians and MCS people telling me different things…
Ive been told the Multiplus 2 is not approved for working in island mode in the UK, since it does not disconnect the DNO earth from grid, and the grid don’t allow you to connect an earth rod to their network and risk exporting fault currents to their earth… That said I have no idea how this is significantly different from earth bonding a gas pipe that goes into the ground, and clearly that is allowed/required…
Ive read that technically the Multiplus would need to be operated in TT mode for approval in both grid-tied and island mode, or work in a grey area that the earth rod is just supplemental bonding for DNO, but a proper earth rod when viewed by building control(?) for approving the island mode… though this is potentially suboptimal given I live in London in a terraced house with no doubt closely connected pipework from neighbours…
Ive been told MCS is impossible since I bought the kit myself, and not through the installer, but another who claimed it was possible. I know I dont ‘need’ MCS unless I export, and even then Octopus will allow you to ‘buy-in MCS approval’ with their admin fee… But presumably would create issues if selling the house.
Ive been told my submain is insufficient, which is probably technically true since it is only 16sqmm on a 100A fuse, but I could very easily limit things at 80A since I go nowhere near that anyway… And yet other people dont care about this…
I tried asking the DNO to enable a PME earth for me (so I can add an earth rod to their earth), but they visited and assessed the TN-C-S supply that I had was not documented in their system and converted everything to TN-S since the documentation didnt allow them to confirm it was TN-C-S. Not sure how that changes things, but it certainly confused one of the NICEIC electricians I spoke to, so he didnt want to help.
I am an electronic engineer so I get the concepts, but don’t have Part P of course, and it is actually very confusing to have multiple people say different things with confidence!! Thoughts very much appreciated!
lol first the Multiplus 2 is compatible and completely legal for DNO connection running island mode They are also my DNO, also to note that approval G99 means they have just said that you can connect the device to there network lol as long as that is the device specified on the DNO application.
Grey area I asked an electrician on YouTube about this and apparently to him the DNO likes you to install an earth rod and connect to the DNO’s earth as well but think there has to be a relay disconnect for the DNO earth in a grid down situation, so why would they want you to do an earth rod and still connect to there earth? What you have done there is make a nice new PME connection for them which I’m not a fan of others fault current going through my install should the PME fail between properties meaning mine was the only fault party to connect back to the star point of the transformer. I installed an earthrod but you have the convi disk I think it’s called but you have to dig a big hole but it does give a really good earth. I used rods much easier and I went down 4 and half rods so that’s 4 and half meters deep so my earth is really good for a TT which is normally bad other thing to note is if the paper work to the property is metal then it’s not really a TT system as the metal pipes make supplementary bonding which still connects to the PME’s in the ground.
Depends on your needs the multiplus2 5000 can do whole house but it’s close well at least for me even when I designed it with the washing machine dryer and EV on the unmonitored side so it didn’t run through the inverter. I’m now running a 10kVA which is beautiful whole house with dryer and washing machine. EV is still not monitored.
If the DNO has confirmed 100amp you’re good! Call your energy supplier, I’m taking it that you are talking about 16mm2 at the service head then connected to the smartmeter then connected to an isolation switch then to the CU? If no isolation switch I believe that the energy supplier is responsible for supplying it for safe isolation as the electrician technically can’t remove the DNO fuse in the service head for safe isolation. At point of smartmeter install or the isolation switch the energy supplier should be replacing the 16mm2 for 25mm2 then you need a sparky to replace from isolation switch to the CU in 25mm2. Does that answer everything?
Can you post a pic of the service head and earth so we can have a look? PS I’m not a spark but have good working knowledge when it comes to this
Thank you @Daza - very useful. I cant describe how frustrating it is that so electricians say different things!! And they are the ones who are supposed to know things…
If you have yours configured for island mode, have you added a DNO earth relay disconnect? I know it isnt internal within the Multiplus 2 - they disconnect L/N from grid and also connect earth to Neutral, but nothing about earth switching…
The Multiplus could probably do my whole house, but I dont have the wiring for it (from consumer unit to inverter is only 10mm), and Im not fussed about that tbh, though it would have been nice to get some of my circuits on backup - hence the plan was for one of my consumer units to be backed up.
The cut-out/service head, and tails to meter, and tails to islator switch are all 25mm, and were all replaced when the meter was replaced, but then from isolator to consumer unit it is 16mm twin and earth (and about 8m long since consumer unit is under stairs, while meter box is outside front door). The twin+earth goes underground a bit but very quickly goes through the wall and then wiggles its way to the consumer unit. I remember seeing it when the house was renvovated 12 years ago, but would be an absolutely massive job to replace since the whole floor (with UFH) would need to be lifted.
Hey mate I was in the same position. No I’m pure TT as my pipes to the house are plastic gas and water. So I’m not connected to the DNO earth at all. Also I used 25mm2 for the earth cable to the rod over kill but wanted the lowest resistance I could get in my budget window.
I think switching to TT earth is probably the best and safest option, so thanks for helping me reach that conclusion. I was initially not so keen given it is hard to get anywhere near the quality of earth connection that you can from DNO TN-S…
Only follow on question I guess is what I can do v.s. needing an electrician for. Installing an earth rod and running the cable to consumer unit is entirely doable, but then I guess definiing a new MET and disconnecting DNO earth is something an electrician would need to do…
I got mine to 2.15 Ohms so really good in regards to TT as good as you can get not being physically joined to transformer star point I guess. Yep save some bucks get ground work diagrams so you don’t go through any pipes or drains make sure your away from extraneous metal in the ground in order not to cause it to shoot back through the pipes in the ground. Get a decent earth pit not the stupid cover thing, go for at least 16mm for the earth but you will need your MET in a location in order to service the multi and the CU’s proteus have the best green multi block then get a single Metal MET to then branch off I’ve got about 2 8 way MET’s that one runs a feed to 3 proteus multi blocks which earth my batteries, server cabinets and lynx distro’s PS unusual cable TN-S ££££ normally it’s terra neutral combined separate a lot cheaper lol
My setup will be more simple, just funny how the requirements change as you learn more, and realise how little a lot of electricians seem to know!
Yes very old school lead sheethed cable goes virtually to my door, that was upgraded by DNO in 1990 to plastic… (according to their logs) But in the upgrade they also fed an earth cable at the same time as their ‘upgraded’ cable.
@Daza - sorry one more question, do you have an SPD on the incoming grid supply only, or do you also have one on backup consumer unit? Perhaps if you have everything backed up it is easier…
Mines still rocking the lead lol, renewables is a fast moving sector I think it’s forcing the industry to make changes almost on the fly which is leading to gaps in knowledge
@WhiteCitySolar I think the relay you are talking about there connects earth to neutral, rather than disconnecting the ‘grid earth’… So whilst that is also important, it doesnt cover the earth problem - which seems to be a DNO requirement.
But that earth looks like it’s connected to the output side which would leave OP with no earth in the back up CU which could lead to RCD’s RCBO’s not working correctly when faults are introduced
Ideally, the Multiplus 2 ‘Earth terminal’ (currently just case earth) would not be in parallel with the AC-IN Earth, that way you could have a relay which disconnects AC-IN Earth and instead connects an external earth rod to AC-OUT, but that isnt in any of the diagrams…
Hey mate it’s on every CU that I have as all the CU’s are new so it was easier to buy it in the CU as it’s almost the same price where as if you get them after the fact nearly £100 ie Hager boards like them as they haven’t changed the MCB layout forever so spares are easy to find years later
Yes you could use it as an energiser for a relay that’s going to be a beast of a relay though, and would need to be wired disconnect of out earth connect earth rod. Now that a moving part is in you have to test regularly just to make sure it always functions as intended so you may need some way to know that it has worked ie alarm or LED system to show function when you are in island mode to me seems like more hassle. For me prove the earth get the reading and job done lol
PS get a clamp meter as your back up board isn’t going to use the amperage of that inverter.
The 5000 is only 50amps pass through I put a clamp meter on my house and got 49amps running two dehumidifiers microwave computer toaster oven kettle dryer dish washer washing machine computer and all the TV’s in the house, but it’s not that that’s going to be the issue for the multi it’s the kW used that tops the multi that’s why I opted for AC solar which provides me with an extra 4.5kW of juice still looking at getting another 3kW of solar if I can in the future lol
Yup I have a clamp meter, but would put it on main incomer for preventing grid export from (a tiny bit of) solar. I dont think I will ever get close to 50A, but having half the circuits on there will also give me TONS AND TONS of capacity anyway.
Not sure how that changes things, but it certainly confused one of the NICEIC electricians I spoke to, so he didnt want to help.
