16A on garage fed by 2.5mm?

[Rookieoftheyear]

Hello all,

Theoretically speaking, so I can get an idea of cost...

My garage is about a 20-30m run of SWA 2.5mm2 cable from the house. This connects into the main CU on a 16A MCB. The garage as a small 4-way CU in it. Theoretical current limits on the 2.5mm cable indicate it should handle in excess of 20-25A.

Unfortunately I’ve inherited the situation, it isn’t easily upgradable, and I have no idea why the garage wasn’t installed with a 6mm+ cable originally.

Is it possible to install a 16A device in the garage on its own MCB? Eg. A 3.7kW EV charger.

If so, would it be just the case of upgrading the MCB that serves the garage to a new 20A MCB (perhaps Type C) in the main CU? And putting a new MCB in one of the spare ways in the garage?

Thank you

 

[winston1]

Is it possible to install a 16A device in the garage on its own MCB? Eg. A 3.7kW EV charger.

If so, would it be just the case of upgrading the MCB that serves the garage to a new 20A MCB (perhaps Type C) in the main CU? And putting a new MCB in one of the spare ways in the garage?

Thank you

Not sure there would be enough discrimination between a 16 amp and 20 amp MCB especially if other loads in the garage were on at the time.

 

[flameport]

Is it possible to install a 16A device in the garage on its own MCB? Eg. A 3.7kW EV charger.

Probably, but there is no point in having any MCB for it in the garage if the whole lot is already supplied by a 16A MCB in the house.

It may be possible to change to house MCB to a 20A or 25A, although at 30m long voltage drop will be a consideration, assuming you want to comply with the 3% limit.

A Type C MCB is only required for certain loads with a high inrush current, such things won't normally be found in a domestic property.

 

[SUNRAY]

Loop impedance my preclude a type C

 

[ericmark]

To be within the volt drop for lighting your just over the limit for a 16 amp supply on 2.5 mm². However the first problem with EV charging is the type of RCD. I am not sure what is required if type F or type B but likely existing is type AC or type A.

So step one can you get a suitable RCD for the house? I really don't know the answer, but I have watched the U-tube demo and know the EV charger can cause the RCD not to trip with a fault, so it may be easy to correct, or it may be a problem.

An electrified car's battery capacity is measured in kilowatt hours (kWh). As an example, the Tesla Model S 75D has a 75kWh battery. It has a real-world range of around 230 miles, meaning you use (on average) 32.6kWh of electricity per hundred miles.

so if we think about 12 hours on charge that is around 44 kWh so around 100 miles limit to be recharged by next day.

So before going ahead with setting it all up, is 100 miles enough? For me yes it would be, but if your going to need to pay out to up-grade, then question one is if worth it?

And over 16 amp then looking at power to house, mine has a 60 amp supply, so that could cause a problem.

I am sure it can be done, but as to if worth doing is another question, our houses were never designed for electric vehicles, and at the moment where I live we have one charging point in the village which is used about one day a week where one guy visits his mother, the point is in the railway station so there is a potential for heavy use, so three cars and there is a problem.

 

[Rookieoftheyear]

To be within the volt drop for lighting your just over the limit for a 16 amp supply on 2.5 mm². However the first problem with EV charging is the type of RCD. I am not sure what is required if type F or type B but likely existing is type AC or type A.

So step one can you get a suitable RCD for the house? I really don't know the answer, but I have watched the U-tube demo and know the EV charger can cause the RCD not to trip with a fault, so it may be easy to correct, or it may be a problem.

so if we think about 12 hours on charge that is around 44 kWh so around 100 miles limit to be recharged by next day.

So before going ahead with setting it all up, is 100 miles enough? For me yes it would be, but if your going to need to pay out to up-grade, then question one is if worth it?

And over 16 amp then looking at power to house, mine has a 60 amp supply, so that could cause a problem.

I am sure it can be done, but as to if worth doing is another question, our houses were never designed for electric vehicles, and at the moment where I live we have one charging point in the village which is used about one day a week where one guy visits his mother, the point is in the railway station so there is a potential for heavy use, so three cars and there is a problem.

Thanks for the detailed helpful reply.

I have done the maths on charge rate and distance travelled for commuting. Also considering I live in rural Wales - and like yourself have a 60A main fuse - I have concluded 3-3.7KW charging is perfectly acceptable. I have a 35 mile each way commute, I’m also looking at charging options in work as well.

You mention voltage drop for lights. I’ve used a heat gun in the garage before and on full heat the lights flicker - I assume this voltage drop on the 2.5mm in play?

I also have an outbuilding near to where the car can be parked, there’s a borehole in here and this also I think is fed from 2.5mm from the house. But it is less distance than the garage so voltage drop possibly less of a factor.

Ref RCD - I’ve recently had the house RCD replaced. A lot of chargers do have RCDs or RCBOs built in I believe?

My options as I see it are:

• Standard three pin 13a charging at 3kW
• Install a 16A commando socket for charging
• Install a 16A bona fide EV charger eg ROLEC or Pod Point

I’m just trying to satisfy myself that options two or three would be safe given the 2.5mm wiring.

 

[flameport]

Standard three pin 13a charging at 3kW

Intended for temporary / emergency use only, and even then will require an outlet designed for EV charging, and it's more like 2.3kW.

Install a 16A commando socket for charging

That style of socket is not permitted for household use due to the lack of shutters. Interlocked types might be suitable, however both this and the previous item will very likely require a Type B RCD installing, will have no control over when the vehicle is charged or at what rate, and are entirely unsatisfactory and unsuitable choices.

Install a 16A bona fide EV charger eg ROLEC or Pod Point

The only sensible option, provided it contains all of the required protective devices within the unit, and it's not a Rolec effort.

 

[ericmark]

I think it likely volt drop does not really matter, the lights may dip, but likely the charger will auto compensate for volt drop.

RCD should be marked

type AC or

type A or

type F or

type B when I got my RCBO's it said type B on the package but it turned out they were type AC I think type F or B required for EV chargers, but in the main in our house we have type A or AC, More can be found here you need to check what is required for your charger, and what is fitted already.

 

[Rookieoftheyear]

Intended for temporary / emergency use only, and even then will require an outlet designed for EV charging, and it's more like 2.3kW.


That style of socket is not permitted for household use due to the lack of shutters. Interlocked types might be suitable, however both this and the previous item will very likely require a Type B RCD installing, will have no control over when the vehicle is charged or at what rate, and are entirely unsatisfactory and unsuitable choices.

The only sensible option, provided it contains all of the required protective devices within the unit, and it's not a Rolec effort.

Thanks, understood

I think it likely volt drop does not really matter, the lights may dip, but likely the charger will auto compensate for volt drop.

RCD should be marked

type AC or

type A or

type F or

type B when I got my RCBO's it said type B on the package but it turned out they were type AC I think type F or B required for EV chargers, but in the main in our house we have type A or AC, More can be found here you need to check what is required for your charger, and what is fitted already.

Thanks again ericmark

It's a Type A RCD 30mA and that protects the whole house. Looking into chargers, something like the POD Point has, since Jan 2019, got inbuilt protection and only a Type A RCD is needed at source.

Further reading has got me thinking about the MCBs in series and MCB discrimination. I guess the MCB in the main CU would need to be upgraded from 16A? Otherwise there would be two 16A MCBs in series.

 

[ericmark]

Thanks for link, it would seem the POD Point can have extra protection built in I would assume on a fault it auto disconnects but this

As of the 1st January 2019 either a Type B RCD must be used or a Type A with 6mA DC protection included in the Pod-Point (see detail on packaging to determine what protection is required),

From January 2019 new Pod-Point’s will include 6mA DC vehicle fault protection and only Type A RCD/RCBO’s are required at source, if the Pod-Point was built earlier than this Type B RCD protection should be fitted at source, the symbols printed on the RCD in figure 1 can be used to identify the type of RCD protection.

In one part it says Type B and another part that Type A is OK, reading between the lines it would seem the "6mA DC vehicle fault protection" is a trip fitted inside the Pod Point so if there is disabling DC it will trip so stopping the DC from affecting the rest of house.

However I would fit a 20 amp type A RCBO in the house as belt and bracer's so if the 6mA DC vehicle fault protection fails it will not affect rest of house, if a high integrity board is fitted to the house, which would also mean a garage fault would not cause house to trip.

Transformers
If a galvanically isolated transformer is required, it should be placed upstream of the EVSE. The Neutral output feed of the transformer shall be connected to EVSE earth (creating a TN-S system). the PE taken before any RCD and MCB (if 2 pole MCB is used), resistance measured between the EVSE PE and this Earth must be less than 100 ohms. Do not connect the output earth/neutral of the transformer to a PME earthed system. Upstream transformer RCD protection maybe of Type AC (if fitted), downstream RCD protection is still required.Transformers should be rated for 100% duty cycle at 10% above rated charge current and should be located in a dry well ventilated area. Direct EVSE connection to an IT system is prohibited.

I am not sure on rules here, I suspect since inside a garage no isolation transformer is required? But you need to talk to some one who has been on the courses for fitting charging points.

To be frank even as an electrical engineer I would not fit my own charging point, mainly as I could not claim the money back, but also because I understand the dangers but not all the rules, it for example talks about an earth rod at least 100Ω and I don't have a meter to measure that, so would need to hire one.

This forum is called DIY and really this is well over what should be done as DIY.

 

[Rookieoftheyear]

Thanks ericmark. You're correct this is way beyond DIY and not something I will be doing myself. I just think it's useful to understand the requirements myself.

I gave you slightly wrong information before, the house has a Type AC RCD (the most common), not Type A.

So I suppose a new question I have is to build my understanding of RCD compatibility vertically/up/downstream of each other, since most EVSE's require a Type B or Type A-EV RCD.

Is it possible to install a Type B RCD downstream of the Type AC on the whole house?

 

[SimonH2]

The problem you've not grasped is that putting certain loads through the RCD in the house can prevent it tripping due to a fault in other circuits. So there's the potential for DC (or other non "50 Hz AC") currents from the charger preventing the house RCD tripping if there's a fault in the house and someone touches something live. Having "the right RCD" at the garage end/in the charger supply pod won't fix that. For that reason, the garage should not be on the house RCD - either fit an RCBO that isn't fed by the RCD, or fit an MCB (also not fed by the RCD) and fit an RCD in the garage, the latter being dependent on cable type and routing being suitable for not being RCD protected.
As suggested, there's probably little point changing the MCB at the house end - if there's a fault, both a 16A MCB in the garage and a 20A MCB upstream (in the house) are likely to trip. It's not a case fo the current reaching 16A and the MCB trips - under fault conditions the current will reach "many times" 16A, and by the time the 16A MCB trips, the 20A MCB will also be irrevocably into it's tripping cycle (i.e. the mechanical bits are already moving).

The regs are indeed complicated for EVs - and it's mostly around the "lost neutral in the street" problem.
These days the standard is for a supply called TN-C-S - the key feature being that neutral and earth share the same conductor (known as a PEN, Protective Earth & Neutral conductor) between the local transformer and your house. If this breaks, not only do you lose your earth, but loads in yours and other houses will now try and apply 240V to your house "earth". Inside the house that isn't a problem as bonding will prevent (e.g.) the taps being earthed via a metal water pipe while a broken PEN means that the toaster is now at 240V. But outside, you don't want your car being at 240V while you're stood on a wet ground
So to avoid that danger, there either needs to be a good local earth, or the charger outlet needs to disconnect the DNO supplied earth from the car. It's actually more complicated than that, and why there are now charging points that will do all the isolation stuff in a factory wired box.
As an aside, AFAIK this is the only situation where it's allowed to put a switch in an earth conductor.

A Type C MCB is only required for certain loads with a high inrush current, such things won't normally be found in a domestic property.

We had to have the RCBO for mum's garage changed to a C curve - when my brothers were doing some work before she moved in, they couldn't start a hand held circular saw without the B curve tripping. Fortunately the loop impedance allowed for a C curve.