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.

 

[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?