UK 32A or 40A breaker for 7kW EV Charger

[LawVal]

I note that in answer to another EV Charger question a member suggested a 40A breaker would be preferred to a 32A because of many hours at continuous full 7kW load. I am not an electrician but understand the reasoning.
I have a 7kW charger (which generally runs full load for a continuous 5 hours during the off-peak period) and note that the electrician has connected to a 32A type B breaker in the CU and issued his NICEIC Domestic Electrical Installation Certificate accordingly. The circuit conductors are noted as 6mm csa
I have not experienced any problem with the installation but would the general recommendation be to increase the breaker to 40A?

Thank you.

 

[Julie.]

You cannot just increase the breaker size without confirming that it will operate in the correct time.

Each breaker must operate within a set time, which equates to the circuit having a particular resistance or less. Without knowing the characteristics of the circuit you won't know if the larger breaker will still operate within the required time.

If you can confirm the actual Zs (the "loop" "resistance") as measured or calculated is less than the required Zs for the particular breaker; and the cable is of sufficient size, and is installed to the appropriate method to withstand the higher current; then it could be possible.

It isn't just a simple answer unfortunately.

 

[LawVal]

You cannot just increase the breaker size without confirming that it will operate in the correct time.

Each breaker must operate within a set time, which equates to the circuit having a particular resistance or less. Without knowing the characteristics of the circuit you won't know if the larger breaker will still operate within the required time.

If you can confirm the actual Zs (the "loop" "resistance") as measured or calculated is less than the required Zs for the particular breaker; and the cable is of sufficient size, and is installed to the appropriate method to withstand the higher current; then it could be possible.

It isn't just a simple answer unfortunately.

Thanks for the very prompt response Julie.

I attach the extract from the certificate for the existing installation so I don't know if that helps.

I am not too concerned because it has been working without any problems so far, but I can understand that the charger will be called upon to operate at max 7kW load for approx 5 hours every 1 or 2 days for many years to come and therefore its circuit/breaker will be 'challenged' more than any other in the house. So, if considered prudent, I could get an electrician to change the breaker to 40A.

The existing arrangement must be compliant so perhaps it's a 'personal preference' consideration (but of course taking into account your points if I decide to uprate).

 

[Julie.]

Thanks for the very prompt response Julie.

I attach the extract from the certificate for the existing installation so I don't know if that helps.

I am not too concerned because it has been working without any problems so far, but I can understand that the charger will be called upon to operate at max 7kW load for approx 5 hours every 1 or 2 days for many years to come and therefore its circuit/breaker will be 'challenged' more than any other in the house. So, if considered prudent, I could get an electrician to change the breaker to 40A.

The existing arrangement must be compliant so perhaps it's a 'personal preference' consideration (but of course taking into account your points if I decide to uprate).


View attachment 113510

That Zs should be fine for a 40A mcb, however it still doesn't mean it would be ok to change.

A 6mm^2 cable, depending upon the type and installation method may not be capable of carrying 40A.

I have 32A on my EVCP, no need to go to 40A.

 

[LawVal]

That Zs should be fine for a 40A mcb, however it still doesn't mean it would be ok to change.

A 6mm^2 cable, depending upon the type and installation method may not be capable of carrying 40A.

I have 32A on my EVCP, no need to go to 40A.

Thanks, Julie.

I will stick with 32A.

 

[Markyd]

You work to manufacturers instructions.......If they say 32 amp then that's what you install

 

[LawVal]

You work to manufacturers instructions.......If they say 32 amp then that's what you install

Thank you Markyd.

It was the Charger manufacturer (Ohme) that organised the electrical contractor as that is their policy, they would not sell me the charger or allow me to get my local electrician to install it. So I assumed that as it was Ohme's selected installer all would indeed be OK without the need for me to check the installation (neither am I qualified).

Following your comment, I went to the Ohme website and it states "No overcurrent protection is provided in the Ohme Home Pro, separate provision is to be provided as part of the installation. We recommend a 40A Type B MCB."

I will take it up with Ohme but I guess they may just say that; 40A is "recommended" and as the 32A is working fine then all is OK. We will see.

Thanks for your input Markyd & Julie. This is my first posting and I must say I am very impressed, this forum is by far the best I have come across.

 

[littlespark]

Not related to the 32/40 amp question, but i have recently been to 2 repairs where the charge point people had arranged their own installer, and in both cases it was a loose connection where these installers had connected to an SWA that the customers own spark had put in for them.

(customer gets their own electrician to run in the power to an IP rated box.... Charge point installer simply connects to this box)

They're obviously on a price per point, and must rush through the installs without checking.

 

[Bsharp]

Has this charger been installed to an existing split load board??
I.e. one which contains 2 RCDs protected half (ish) the circuits each??

 

[Bsharp]

Also fyi the cable type installed is ‘F’ so swa (steel wire armoured) with an installation method C (clipped direct) so therefore cable capable in this situation of safely pulling 53amps. So 40 amp breaker would be fine

 

[Julie.]

Also fyi the cable type installed is ‘F’ so swa (steel wire armoured) with an installation method C (clipped direct) so therefore cable capable in this situation of safely pulling 53amps. So 40 amp breaker would be fine

I don't quite trust reports or EIs with installation methods, it's virtually impossible for the same method to be used all the way through the installation of a particular circuit.

It's usually a combination of clipped direct over most of it, a bit through duct/conduit and a bit behind insulation (thermal) etc - only the installer truly knows if the C is true in it's entirely, or just mostly true (and what the non-true bits are).

 

[LawVal]

Has this charger been installed to an existing split load board??
I.e. one which contains 2 RCDs protected half (ish) the circuits each??

Hello Bsharp thanks for the info and yes it is a newish (10 years) split board.
The circuit chart is as follows reading from the main switch on the right-hand side of CU.
100A mains switch
63A RCD 30mA
40A MCB, electric cooker
32A MCB, lounge, bedroom & hall wall sockets.
32A MCB, not used
32A MCB, not used
6A MCB, all internal lights
63A RCD 30mA
32A MCB, kitchen wall sockets + washing machine, oil-fired boiler
16A MCB, external lamp post
32A MCB, external car charging point
6A MCB, not used
6A MCB, not used.

 

[pc1966]

I don't quite trust reports or EIs with installation methods, it's virtually impossible for the same method to be used all the way through the installation of a particular circuit.

Indeed, in my own flat the RFC is on 20A because that is what it was on the original fuses. It ought to be OK for 32A but I did not put it in so have no knowledge of just how/where the cable runs.

It was probably done that way due to a high Ze originally, but I never had the chance to measure before the original cutout and MICC feed was replaced.

 

[Bsharp]

I don't quite trust reports or EIs with installation methods, it's virtually impossible for the same method to be used all the way through the installation of a particular circuit.

It's usually a combination of clipped direct over most of it, a bit through duct/conduit and a bit behind insulation (thermal) etc - only the installer truly knows if the C is true in it's entirely, or just mostly true (and what the non-true bits are).

Fair point, but you have to trust the installer at some point. My bet would be cable cleated externally from CU to EV charger in this case. But again without seeing the install you have to trust the installers reasoning.

 

[Bsharp]

Hello Bsharp thanks for the info and yes it is a newish (10 years) split board.
The circuit chart is as follows reading from the main switch on the right-hand side of CU.
100A mains switch
63A RCD 30mA
40A MCB, electric cooker
32A MCB, lounge, bedroom & hall wall sockets.
32A MCB, not used
32A MCB, not used
6A MCB, all internal lights
63A RCD 30mA
32A MCB, kitchen wall sockets + washing machine, oil-fired boiler
16A MCB, external lamp post
32A MCB, external car charging point
6A MCB, not used
6A MCB, not used.

I’d be slightly more concerned about the type of RCD present in the consumer unit.
If as you say it’s 10 years old then the RCD is more than likely going to be a type AC. Bs7671 requires a type A RCD to be installed for reasons which I won’t confuse with at this point.
Worth checking.

 

[Bsharp]

I don't quite trust reports or EIs with installation methods, it's virtually impossible for the same method to be used all the way through the installation of a particular circuit.

It's usually a combination of clipped direct over most of it, a bit through duct/conduit and a bit behind insulation (thermal) etc - only the installer truly knows if the C is true in it's entirely, or just mostly true (and what the non-true bits are).

What do you put regarding installation method on your reports or certs? I presume you trust these only joking I know what you mean though. Engineering judgment is needed if only running a couple of metres through thermal insulation wouldn’t make any difference tbf if the rest of install was say free air for the remains 25ms.

 

[westward10]

I’d be slightly more concerned about the type of RCD present in the consumer unit.
If as you say it’s 10 years old then the RCD is more than likely going to be a type AC. Bs7671 requires a type A RCD to be installed for reasons which I won’t confuse with at this point.
Worth checking.

Strictly speaking BS7671 does not require type A, type AC are still acceptable given the correct circumstances however in this case they probably are not.

 

[Bsharp]

Strictly speaking BS7671 does not require type A, type AC are still acceptable given the correct circumstances however in this case they probably are not.

Agreed. . I always install separate EV board spd and type A just my preference and I’m in no way claiming to be the any better than any other. Also just out of interest (maybe your not ) but I notice on the EIC posted by the OP the r1+r2 of the said EV circuit is 0.67ohms. 6mm2 swa with 6mm2 line and cpc as stated on cert would me the run is around 110m’s plus!! Big house that!!

 

[LawVal]

I’d be slightly more concerned about the type of RCD present in the consumer unit.
If as you say it’s 10 years old then the RCD is more than likely going to be a type AC. Bs7671 requires a type A RCD to be installed for reasons which I won’t confuse with at this point.
Worth checking.

Thanks Bsharp. Just checked and interestingly the two RCD's are different in terms of "numbers" ie.
The one next to the incoming switch is a BG CUR 6330 with IEC/EN 61008-1.
The one that does the car charger side is a BG CUR 6330A with IEC/EN 61008.

Perhaps the car charger electrician also changed the RCD on that side.

Whilst I was in there I tested the RCD's and I am pleased to say both tripped and reset!

 

[Bsharp]

Thanks Bsharp. Just checked and interestingly the two RCD's are different in terms of "numbers" ie.
The one next to the incoming switch is a BG CUR 6330 with IEC/EN 61008-1.
The one that does the car charger side is a BG CUR 6330A with IEC/EN 61008.

Perhaps the car charger electrician also changed the RCD on that side.

Whilst I was in there I tested the RCD's and I am pleased to say both tripped and reset!

He has swapped The RCD out for a type A so no issue there. Sorry for rambling on a bit but RE you actual op the EV will be fine on the 32 amp.

 

[LawVal]

He has swapped The RCD out for a type A so no issue there. Sorry for rambling on a bit but RE you actual op the EV will be fine on the 32 amp.

Thanks Bsharp. I find this all very interesting so not rambling on at all. Thanks to all for the input.

 

[Risteard]

You work to manufacturers instructions.......If they say 32 amp then that's what you install

I'm not aware of any manufacturer that advises it. They typically state 20A for 16A, or 40A for 32A.

Not sure why a circuit breaker was used for this installation - typically a double pole switching RCBO should be used. What make/model of chargepoint is installed?

EDIT: It appears to be on a shared RCCB. An EVSE should be protected by its own dedicated RCD. Typically this means an RCBO, although it could be an RCCB supplying only one circuit.

 

[LawVal]

I'm not aware of any manufacturer that advises it. They typically state 20A for 16A, or 40A for 32A.

Not sure why a circuit breaker was used for this installation - typically a double pole switching RCBO should be used. What make/model of chargepoint is installed?

EDIT: It appears to be on a shared RCCB. An EVSE should be protected by its own dedicated RCD. Typically this means an RCBO, although it could be an RCCB supplying only one circuit.

Hello Risteard. In answer to what make:

The charger is an Ohme Home Pro 7kW and extracts from the website product manual are;
• Ohme units have PEN fault detection
• The RCD inside the unit is Type A and 6mA DC
*The RCD in the unit is certified as a RCD-DD, conforming to IEC62955.
*No overcurrent protection is provided in the Ohme Home Pro, separate provision is to be provided as part of the installation. We recommend a 40A Type B MCB.
*The Ohme Home Pro has a dynamic load balancing feature. A current sensor (CT) clamp is provided to measure the electrical demand of the property, or sub-board

I have sent an email to Ohme querying the 32A breaker installed by their appointed electrician whilst they recommend 40A in the manual albeit by feedback here the 32A seems to be OK (and is working fine)

 

[Bsharp]

Hello Risteard. In answer to what make:

The charger is an Ohme Home Pro 7kW and extracts from the website product manual are;
• Ohme units have PEN fault detection
• The RCD inside the unit is Type A and 6mA DC
*The RCD in the unit is certified as a RCD-DD, conforming to IEC62955.
*No overcurrent protection is provided in the Ohme Home Pro, separate provision is to be provided as part of the installation. We recommend a 40A Type B MCB.
*The Ohme Home Pro has a dynamic load balancing feature. A current sensor (CT) clamp is provided to measure the electrical demand of the property, or sub-board

I have sent an email to Ohme querying the 32A breaker installed by their appointed electrician whilst they recommend 40A in the manual albeit by feedback here the 32A seems to be OK (and is working fine)

I just had a read of their literature and as you say it “advises” 40amp.
So I wouldn’t worry.

 

[Risteard]

Hello Risteard. In answer to what make:

The charger is an Ohme Home Pro 7kW and extracts from the website product manual are;
• Ohme units have PEN fault detection
• The RCD inside the unit is Type A and 6mA DC
*The RCD in the unit is certified as a RCD-DD, conforming to IEC62955.
*No overcurrent protection is provided in the Ohme Home Pro, separate provision is to be provided as part of the installation. We recommend a 40A Type B MCB.
*The Ohme Home Pro has a dynamic load balancing feature. A current sensor (CT) clamp is provided to measure the electrical demand of the property, or sub-board

I have sent an email to Ohme querying the 32A breaker installed by their appointed electrician whilst they recommend 40A in the manual albeit by feedback here the 32A seems to be OK (and is working fine)

OK, when you refer to the RCD within the unit deriving from an RDC-DD (not RCD-DD) within the unit, then I am surmising that this is an electronic device within the unit and not actually an RCD complying with BS EN 61008 or BS EN 61009. As such, personally I do not feel that it is compliant to supply this without a dedicated double pole switching RCD upstream (realistically this being achieved with an RCBO which switches both poles). This should be of at least Type A. A Type B is not necessary due to the RDC-DD.

 

[LawVal]

OK, when you refer to the RCD within the unit deriving from an RDC-DD (not RCD-DD) within the unit, then I am surmising that this is an electronic device within the unit and not actually an RCD complying with BS EN 61008 or BS EN 61009. As such, personally I do not feel that it is compliant to supply this without a dedicated double pole switching RCD upstream (realistically this being achieved with an RCBO which switches both poles). This should be of at least Type A. A Type B is not necessary due to the RDC-DD.

I don't know the "technical" but the asterisk points in my above post are copied and pasted from the manufacturer's manual and I would have thought the manufacturer would have specified what was appropriate and compliant ie for overload protection they state "We recommend a 40A Type B MCB."
I don't know if the internal RCD is an electronic device or otherwise, they just say it is;
• The RCD inside the unit is Type A and 6mA DC
*The RCD in the unit is certified as a RCD-DD, conforming to IEC62955.

Do you think I should change the MCB for a RCBO?

 

[Bsharp]

OK, when you refer to the RCD within the unit deriving from an RDC-DD (not RCD-DD) within the unit, then I am surmising that this is an electronic device within the unit and not actually an RCD complying with BS EN 61008 or BS EN 61009. As such, personally I do not feel that it is compliant to supply this without a dedicated double pole switching RCD upstream (realistically this being achieved with an RCBO which switches both poles). This should be of at least Type A. A Type B is not necessary due to the RDC-DD.

I’m sure the op said that the electrician installed a new type A RCD in existing consumer unit, also as you say the Ohme charger does have integral RCD type A 30ma and
DC 6ma RCD biilt in. And as the method of installation was via swa then the charge point could arguably be connected via MCB. Although not the way I would as no real way of user testing the internal RCD in the ohme unit (I think)
As I said earlier I always supply sub board SPD type A RCD and that’s the way I’ll always fit as that’s what I feel comfortable doing.

 

[Risteard]

Although not the way I would as no real way of user testing the internal RCD in the ohme unit (I think)

Yes, and in my opinion strictly speaking does not comply with BS 7671 as the RCD-style functionality of the device is not actually achieved by the presence of an RCD complying with one of the listed Standards.

 

[Bsharp]

Yes, and in my opinion strictly speaking does not comply with BS 7671 as the RCD-style functionality of the device is not actually achieved by the presence of an RCD complying with one of the listed Standards.

Definitely, this is why I stick to the same install procedure every time.

 

[Miguel Esteban-Perez]

I note that in answer to another EV Charger question a member suggested a 40A breaker would be preferred to a 32A because of many hours at continuous full 7kW load. I am not an electrician but understand the reasoning.
I have a 7kW charger (which generally runs full load for a continuous 5 hours during the off-peak period) and note that the electrician has connected to a 32A type B breaker in the CU and issued his NICEIC Domestic Electrical Installation Certificate accordingly. The circuit conductors are noted as 6mm csa
I have not experienced any problem with the installation but would the general recommendation be to increase the breaker to 40A?

Thank you.

32 A for 6 mm2 its ok. By the way , cable insulation is PVC or XLPE?

 

[LawVal]

32 A for 6 mm2 its ok. By the way , cable insulation is PVC or XLPE?

One of the previous helpers advised me that the cable type installed is ‘F’ so swa (steel wire armoured) with an installation method C (clipped direct). This is extracted from the installation certificate.

 

[Miguel Esteban-Perez]

Well, taking a look at BS 7671:2018 seems that for PVC , with Methods A,B,C ranges go from 32 to 47 A. Of course an isolated cable supports more , I think that in your country with less temperature and some more humidity and with your mass systems it could also work for 40 A, but as said, keep it up in 32 A for 6 mm2.

 

[brianmoooore]

Surely this can be considered to be a fixed load, or at least a fixed maximum load of 32A.

 

[Julie.]

Surely this can be considered to be a fixed load, or at least a fixed maximum load of 32A.

Unfortunately not.

It's for an EVCP which is basically a fancy socket outlet.

The EVCP tells the vehicle that it has a maximum current of 32A.

The charger within the vehicle then (if working correctly) will charge at the 32A rate - or a reduced current if the in-vehicle charger has a maximum of say 28A.

However there is nothing inherently limiting this current, if the in-vehicle charger goes faulty, it could take much more than it should.


A fixed load is only where it is not possible to take more than rated as an overload, other than for fault type conditions.

An immersion heater for example is limited by its internal resistance, it wouldn't be able to overload, only suffer a fault.

 

[brianmoooore]

An immersion heater for example is limited by its internal resistance, it wouldn't be able to overload, only suffer a fault.

I won't mention the one I came across once, then. The outer sheath of the element had dissolved and the element spiral had shorted to the sheath part way along. It enjoyed a significant, but brief life, as a 6kW immersion, before failing completely. No RCD in the circuit, of course, and TNC-S (or PME as it was then.)