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I’ve had a brief exchange with Ohme to establish how much of my current (excuse the pun) house electrical system complies with their installation procedure. However, until they carry out a survey its only provisional.
I believe I can start the order process three months prior to my current lease ending. Can Ohme carry out the survey prior to that in case the charger is not compatible or going to cost to much due to requiring further work.
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Basically, you order a new vehicle and will be sent an online survey to fill out or you can ask for an engineer survey which takes a bit longer. If there a cost to you beyond whats included, you can choose to cancel the order and place a new order on another vehicle.
It’s the time differential between ordering the EV car and establishing any cost for the charger install that is the issue. I assume if it all goes belly up and I choose to cancel the EV with a week before the end of my lease, I can keep my current car until I reorder?
Yes, though I wouldn’t expect it to take nearly 3 months to decide, especially if you do the survey yourself.
Are there any issues to having a charger you know about?
Put a pic up of your meter cupboard if you want and I’ll have a scant over.
My main CU is no longer made, So you cannot get the correct RCD required. My second CU is on 16mm tails but serves the heat pump and the garage, so would draw close to the 60 amp limit. The run from the CU to the selected charger site could well be 5 metres over the 15m offered.
So I could require a 3rd CU mounted on the outside wall (no room left for another CU in the house). Thus collectively, I need an idea of the cost.
My main CU is no longer made, So you cannot get the correct RCD required. My second CU is on 16mm tails but serves the heat pump and the garage, so would draw close to the 60 amp limit. The run from the CU to the selected charger site could well be 5 metres over the 15m offered. So I could require a 3rd CU mounted on the outside wall (no room left for another CU in the house). Thus collectively, I need an idea of the cost.
The charger install won’t come from your house consumer unit, instead it’ll similar to how the heatpump consumer is connected in the electric box where the our meter tails are split in whats known as Henley blocks and each consumer is fed from that point, if that makes sense.
If any work is required to upgrade your incoming supply, this will be carried out by the DNO and will be free of charge for EV chargers, solar, heatpumps and whats ever else it determine as green for the planet.
Your house consmer unit although perhaps out of date on the spares front, isn’t obsolete where the BS7671 wiring regulations are concerned. In the future should you ever wish to upgrade, your locall sparky is the best bet.
If your house consumer unit is labled you could if wanted give me the name of the circuit and MCB rating (amps), plus that of your heartpump consumer unit, I can work out you current maximum demand and new maximum demand with an EV charger installed. If you know your incoming cut-out fuse rating, I could give a better idea of whats work would be needed, if you wanted to.
Interesting. I had a brief email exchange with Ohme to get an idea of their costs (which they didn’t give). They did, however, indicate the supply would come from the main CU ‘if’ the installer could get a suitable ‘Type B RCD’. The CU is supplied with 25mm tails from a 100amp DNO fuse and has spare capacity for the breaker(s). However, that CU is an F&G concept which is now defunct, although there are plenty of used breakers available, but nothing new that is compatible.
My second CU has no capacity for an EV Charger. The idiot so called ‘Napit and other multiple certified bodies’ sparks he is a member of used 16mm tails when it was expressly stated 25mm to accommodate a future EV Charger. If often draws 30-35 amps in its current state, so a further 32 amps is out of the question (hence it should have been 25mm tails). Changing the tails is out of the question, they were installed into the wall cavity during building work and he clipped them to the inside of the internal wall leaf (seriously !).
So, if there is no way around the issue with the defunct CU, I’m left with a third CU. I have no room for another CU inside the property, so it would have to go outside. Also, I insisted the double pole Henley block the electrician installed was removed and replaced with two single pole units, so space is going to be tight in the meter box for a third set of tails. (Long story, but I’ve witnessed my neighbour’s house go up in flames due to a recently fitted double pole HB failing.
Looking around an IP66 CU fully loaded for an EV Charger is around £40, and an extra 5 metres of SWR isn’t that big a deal. However, trying to establish what Ohme will charge for that is like pulling teeth.
I’m a spark and being so for over 40 years and never seen a 2 pole Henley block be responsible for burning a house down, providing terminals are tightened to the correct specifications and torque, which still applies to single pole blocks.
16mm tails are standard for heatpump & charger installs. Heatpumps also use Type B or F RCD/RCBO, where as Chargers typically use Type A and are fitted to the non RCD side of a consumer unit, as you see in split or individual CU’s however, if you agreed to pay for a larger split CU and 25mm tails, theres no reason why they couldn’t do it
As explained, you need a Type A RCD/RCBO, that has 6mA DC protection for an EV charger. A Type B RCD/RCBO is Type AC and doesn’t have DC protection. In the highly unlikey event, you can find a single pole Type A RCBO for your F&G CU, you would still require at least 2 spare ways to fit an SPD (surge protection). That said, you’ll find the installer would disagree with what customer service have told you via email, as they don’t have a clue, and would in 99.9% of cases prefere the seperate CU route, which frankly, it keeps it seperate to your house CU and would be my prefered route of install. You could replace the heatpump CU to a split board, but it won’t come cheap through Ohme!
Arranging through Ohme for any upgrade work that isn’t needed for the charger, would be by far way more expensive than getting a couple of quotes and getting a local spark to carry out the work.
As Motability pay for the EV charger, the extra cost from Ohme may still be much less than paying for my own EV Charger and installation.
The second CU arrangement is Tails > Type A RCD (100/30-A 100 Amp Double Pole 30mA 10kA) > SPD followed by the individual circuit breakers. It also has 4 slots available. So may have been ideal if the 25mm tails had been fitted 🙁 However, as you note, what Ohme say and what the electrician say’s when they’re on site are two different things !
I wont say anymore about the electrician and the 16mm tails except to say ‘they’ no longer benefit from any form of accreditation.
Re the HB, the block /insulation was found to be at fault between the two poles according to the report from the fire investigators. We were watching TV when we heard the cracking and the power dipped in the street. Within 10 minutes their house was ablaze.
As Motability pay for the EV charger, the extra cost from Ohme may still be much less than paying for my own EV Charger and installation. The second CU arrangement is Tails > Type A RCD (100/30-A 100 Amp Double Pole 30mA 10kA) > SPD followed by the individual circuit breakers. It also has 4 slots available. So may have been ideal if the 25mm tails had been fitted
However, as you note, what Ohme say and what the electrician say’s when they’re on site are two different things ! I wont say anymore about the electrician and the 16mm tails except to say ‘they’ no longer benefit from any form of accreditation. Re the HB, the block /insulation was found to be at fault between the two poles according to the report from the fire investigators. We were watching TV when we heard the cracking and the power dipped in the street. Within 10 minutes their house was ablaze.Your second CU, I take is for the heatpump -Do you know if your heatpump is inverter driven and what MCB A supplies the heatpump?
[A downstream protective device may protect a conductor against overload, but it can’t protect it against faults, for that you’re reliant upon whatever is upstream, which in this case is the DNO’s fuse. Therefore in theory it’s just a matter of calculating based on the fault current, characteristics of the protective device and the adiabatic behaviour of the conductor.]
Another approach is not have fault protection, BS 7671 only allows that in very specific circumstances – conductors less than 3m in length, installed in such a manner to reduce the risks of faults to a minimum and reduce the the fire risk or danger to a person. The get out is only for protecting the conductors against fault currents , not protecting people against shock as a result of a fault, so likely care is still needed with metallic containment/enclosures seen on modern 18th edition CU’s.
The other issue is, the DNO’s fuse is really outside of the scope of BS 7671 and the DNOs tend to like to keep their options open for future purposes. Meaning an installation that’s supplied by a 60A cut-out fuse today might be supplied by something else in the future (80A or 100A). The DNO won’t want to start, or is it in their scope to start having to re evaluate the designs of consumer’s installations every time they upgrade a fuse. Hence the reason, you commonly see DNOs recommend the likes of maximum (with the exception of an isolator) of 3m of 25mm² tails on a 100A fuse or 16mm² on a 60A fuse and will refuse to connect/upgrade if smaller tails are found.]
It doen’t matter what you understand of that rant, but 100A cut-out > 16mm tails > 100A RCD, does not afford protection and question the use of a Type A RCD, if your heatpump is inverter driven.
You won’t get any logical sense out of Ohme customer service, they are just office staff.
The second CU is for the heat pump which is indeed inverter-driven. From memory (not at home at present), the MCB is a 20 Amp 6kA C Curve. This CU also feeds the garage for some tech gear I work on which is power hungry, and will be also be used for a future 3.5kw PV array (still to be installed).
I was under the impression that a Type A RCD was the minimum you could use (although Type B is the prefered device).
I didn’t have any input in this installation as I wasn’t at home when the work was carried out. It took a year to have the whole installation ripped out and redone after an audit. To this day I am still finding bodge’s to the wiring.
I was under the impression that a Type A RCD was the minimum you could use (although Type B is the prefered device).
Different Type RCD’s have different characteristics and depending what its for. The well known RCD for many years is the Type B, which is classed as Type AC. Have a read here for a better explanation-
The problem with MCS is it was easy for someone with a bit of cash, to go on the course, with no experience what so ever as a sparky (PV) or Heating Engineer (HP), pass the course, sign up to a regulatory body and get basic liability insurance and then be let loose on customers premises and soon go out of business and restart up again or in something else. I could go on, but you get my jist and the likes of Brydo on here no all to well of the consequences.
When you eventually have PV, its essential to do your homework to a persons background and how long they have been in the electrical industry and also to ensure you get an insurance backed guarantee, as your covered for crap or if they go out of business.
The joys of the domestic sector has never interested me lol.
Indeed, I’m well versed with the MCS / Trustmark / NICEIC and many of the other kwangos. I had to deal with them all at some point over the past year!
You prompted me to look at my Heat Pump installation specs, and it clearly states “type A and AC RCD protection are not suitable. ” The one thing I established over the past year from all the legal arguments, is that the manufacturers instructions – assuming they meet the required standards- are sacrosanct and have to be adhered to first and foremost.
So guess what I will be doing this week !
Indeed, I’m well versed with the MCS / Trustmark / NICEIC and many of the other kwangos. I had to deal with them all at some point over the past year! You prompted me to look at my Heat Pump installation specs, and it clearly states “type A and AC RCD protection are not suitable. ” The one thing I established over the past year from all the legal arguments, is that the manufacturers instructions – assuming they meet the required standards- are sacrosanct and have to be adhered to first and foremost. So guess what I will be doing this week !
I’m NICEICregistered, well I have got to be and on its own, it prooves competance and in the experienced quality to. yet throw in TrustMark and MCS together it can go rapidly downhill depending on ecperience and time in the trade. Thats why it’s vital to do your homework and always thinking the cheapest quote is the best, whils’t at the same tim nt get ripped off.
Well, an EV Charger question has raised concerns over another aspect of an already fraught electrical installation!
My heat pump has a measured DC current leakage of 10ma so should require at least a Type F RCD. The PV inverter I have awaiting installation requires a Type A RCD. They will both co-exist in the same small CU, where from my inexperienced viewpoint cannot see how two RCD’s (Type A and B), SPD, and the three circuits can fit, let alone an EV Charger.
The heat pump manufacturer only published the DC spec and advised a Type F or B RCD this August. Prior to that they were silent on the matter (so I’ve no comeback on the installation company).
I think my EV journey has come to an abrupt halt. I wouldn’t have know any of this without your advice. Now to work on a solution……!
The only way of installing a Type A, B or F RCD in one CU, is having a split load board i.e having 2 busbars or cutting the exising one in half and prividing a gap between them, so they are seperated. However by doing so, you will typcally double the space required for the SPD’s alone as 2 will be needed if your going to installing them on the PV side, so in most cases a new split load board will be required to accomondate the number of useable ways.
By rights, if you have for example have a MK CU, you should use MK RCD’s, MCB’s etc, as they are type approved (type tested) to be used in the CU housing, this however, is not always followed and there are many other manufacturers RCD’s MCB’s etc that will be cross compatible.
Type F RCD’s are among the most expensive and depending on brand can be considerably more expensive than say Type B or Type A RCD’s, so potentially it cold be far cheaper to by a new CU by Fusebox or WCED, which are cheaper to beging with and still approved for use and with a Type A RCD installed, so you only have to buy one for the HP. However, not knowing the design characteristics of you HP, I can’t say for sure whether you should opt for Type B or F RCD*, if you remain uncertain to the system characteristics ring manufacturer helpline for advice. Note heatpump Type B RCD’s have different characteristics than your bog standard typical Type B AC RCD and are more expensive than Type F’s.
If it helps you can get single pole RCBO’s where the RCD and MCB are combined along single pole SPD’s but still need MCB for SPD – possibly freeing up valuable space.
Indeed, everything you say makes sense and aligns with the HP and PV manufacturers.
I have now identified the issue.
· My Heat Pump manufacturer states that if an RCD is used it should be either a type F or B (Type B is the preferred option).
· My PV Inverter states the RCD ‘can’ be a Type A or B (because it has Type B RCD on board), however, it requires a 100-300ma RCD due to potential tripping if a 30ma RCD is installed.
From that, I would need a split board or use single pole RCBO’ as you rightly noted. Although I’m unsure (don’t have the knowledge) how many slots that configuration would take up. My second CU is a 6 way Niglon, and they don’t have the extensive range of components like Hager.
Out of curiosity. On page 8 of the guidance document you uploaded, it notes “If Type A is selected for the heat pump circuit, the upstream RCD must be either Type A, or Type F or Type B.”
How does that relate to my heat pump MCB being a C Curve and the RCD being a Type A, does it have any significance with that statement?
Finally. I can still hold the original installer to account if I can show that they fitted a Type A RCD incorrectly. Does Amendment 2 of the BS 7671:2018 IET Wiring Regulations (BS 7671:2018+A2:2022) demonstrate that during early 2025 the electrician should have fitted a Type F or B RCD and not a Type A ?
Let’s not go down the recent debate over Type B High Performance RCDs that function at high-frequency currents. ☹
If the HP manufacturer states that Type B is the prefered option, thats the route I’d take (without any debate😂) although its an odd preffered option as Type B are nornally reserved for if the Type is unknown. Anyway enough said on that.
On the PV side of the CU, you are best keeping seperate rather than sharing on the load side of a RCCB/RCD with other circuits such as your workshop. There is varying guidance on this from regulatory bodies, so much will depend on who installs it, but I do try to keep PV/HP etc circuits seperate, as a matter of good practice.
The choice of Type B is used in PV installations which has a power supply system (transformer) without simple seperation between the AC & DC side, however nearly all Inverters are transformerless these days anyway. The RCD will go on the output side of the inverter, as its best to design the supply circuit so an RCD isn’t required as above you don’t want have RCD that is shared with other circuits, hence my mention of RCBO’s yeterday. Rather than confuse the situation, perhapd we can talk more in depth on the PV side after your HP is mind sorted:-)
Using RCBOs do not necessarily require a split board however, due to the DC pressent on both the HP and PV, its recommended the circuits are divided to reduce the risk of tripping from DC lealage. Will work out later the ideal situation for the number of ways likely required and get back to you.
Page 8 “If Type A is selected for the heat pump circuit, the upstream RCD must be either Type A,
or Type F or Type B. ” You dont have an upstream RCD supplying a downstream RCD that supplies a HP Type A RCD e.g if your HP was supplied from the RCD in house CU and the HP was supplied from a Type A RCD, the House CU must be Type A, F or B so that an RCD won’t impair the operation of another (blinding)MCB Types relate to their trip curves, where RCD’s tripping characteristics are in mA. They are two seperate things, that are combined in RCBO’s i.e Type C MCB will trip at 5 to 10 times the rated current and 30mA RCD will trip in 300ms at a fault current of 30mA.
Will have any comeback on the installer, not sure because there was an typo error in BS EN IEC 60335-2-40:2024+A11:2024, that was ammended in March 2025. However its worth contacting them with the manufacturers information questioning why they fitted a Type A on an inverter HP.
. Rather than confuse the situation, perhapd we can talk more in depth on the PV side after your HP is mind sorted:-) Using RCBOs do not necessarily require a split board however, due to the DC pressent on both the HP and PV, its recommended the circuits are divided to reduce the risk of tripping from DC lealage. Will work out later the ideal situation for the number of ways likely required and get back to you. P.
Cheers 🙂
Without going into the various varieties, as have basically been discussed:
DP RCB, which will take care of a main switch or RCD upfront and include the necessary MCB
SP SPD + MCB for the SPD
The minumum you could get away with is 4 ways for each system and depending on space depends whether you will get away with a 2 or 3 way split board (12 way in total) for HP, PV,EV or whether you need another CU or you change your house one and put you garage workshop on that or chance used F&G parts.
My preference for a garage workshop, would be to come off an appropiate size MCB in the housee and run a suitable cable to a CU in the garage woekshop.
That’s great advice and means I can plan for a complete revamp. To address the RCD issue will mean a replacement CU regardless (only 6 slots). So, I may as well bring the main board up to date at the same time, and add in the EV. In the meantime, I really need to establish if an intentional or misguided error was made with the RCD choice.
What is the relationship between:
Amendment 2 BS 7671:2018 IET Wiring Regulations (BS 7671:2018+A2:2022)
BS EN IEC 60335-2-40:2024+A11:2024
My heat pump manufacturer appears to be hiding behind the HPA March Guidance. Prior to that, they say it was up to the Electrician to fit the correct type based on BS 7671 (hinting they did not offer guidance)
Does one trump the other, or is it more complex than that?
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