UK Advice about PHEV car charging.

[Indyisme]

We have 2 PHEV vehicles in the family which we charge overnight in the garage, each car plugs into a normal 3 pin household socket. There is a small garage Hager consumer unit in the garage which has a 16A MCB protecting all the wall sockets which are wired with 2.5mm cable. The car chargers are 2.4kw with a current max rating of 10A. One night the 16A MCB tripped but we're unsure why.
My question is: Could the reason be that with both cars charging at the same time on the same circuit that it was being overloaded? If so could I safely replace the 16A MCB with a 20A or 32A MCB without causing any other problems.
Also the cable which supplies the power to the garage from the house is protected with 16A MCB, would I need to upgrade that also?

 

[littlespark]

The circuit breakers are there to protect the cable it supplies. So you can’t just go uprating the breakers without checking the size of cable.

The way cable is run is also a factor. Clipped direct in free air can take more amps than buried in insulation, and the circuit breaker size will be determined from that.

Rule of thumb, 2.4kW / 240V is 10A each… so if both decided to charge at same time, that’s 20A pushing the 16A breaker.

At 2.5mm cable, you might be able to use a 20A breaker, but not 32, as that would be above the capacity of the cable. (Unless the sockets are wired in a ring, but there’s no info on that)

What size is the cable feeding the garage board?
A 16A supply suggests not very big.

 

[PS Electrics]

We have 2 PHEV vehicles in the family which we charge overnight in the garage, each car plugs into a normal 3 pin household socket. There is a small garage Hager consumer unit in the garage which has a 16A MCB protecting all the wall sockets which are wired with 2.5mm cable. The car chargers are 2.4kw with a current max rating of 10A. One night the 16A MCB tripped but we're unsure why.
My question is: Could the reason be that with both cars charging at the same time on the same circuit that it was being overloaded? If so could I safely replace the 16A MCB with a 20A or 32A MCB without causing any other problems.
Also the cable which supplies the power to the garage from the house is protected with 16A MCB, would I need to upgrade that also?

Any spare ways in the Garage Consumer Unit?

I suspect you have a radial but whatever you could create two 16A radial circuits (providing you have a spare way)

As littlespark said you can't just upgrade the MCB to 20A for a number of reasons as well as it not being enough anyway.

I suspect the 2 cars would be plugged in on different sides of the garage so arrange the radials in that configuration. You don't want to inadvertently plug 2 in on the same radial.

You will also need to upgrade the cable and MCB supplying the garage to 32A.

You don't have selectivity in your current set up anyway with a 16A MCB backing up a 16A MCB.

Cable sizes for this would be dependant on length and installation method and volt drop. Also some consideration to the existing installation.

If you don't have a spare way then you could either get a larger consumer unit or upgrade the garage supply to 40A so you can have one 25A Ring. If your garage is wired as a radial with 2.5mm you would need to convert it to a ring or rewire in 4mm as 25A is right on the edge for 2.5mm as a radial. Best case scenario it can take 27A but that is dependant on a number of factors.

The above is a rough guidance on what you could do it would obviously depend on your current set up what would be best.

Another consideration is that normal 13A sockets don't do well having high loads connected for long periods, there are now dedicated ev charging sockets for this.

 

[Indyisme]

The circuit breakers are there to protect the cable it supplies. So you can’t just go uprating the breakers without checking the size of cable.

The way cable is run is also a factor. Clipped direct in free air can take more amps than buried in insulation, and the circuit breaker size will be determined from that.

Rule of thumb, 2.4kW / 240V is 10A each… so if both decided to charge at same time, that’s 20A pushing the 16A breaker.

At 2.5mm cable, you might be able to use a 20A breaker, but not 32, as that would be above the capacity of the cable. (Unless the sockets are wired in a ring, but there’s no info on that)

What size is the cable feeding the garage board?
A 16A supply suggests not very big.

Hi littlespark,
All the sockets in the garage are wired from the same 16A MCB, not sure if that means it's wired in a ring?
The cable feeding the garage board goes underground from the house to the detached garage. All I can say about that is that it's a very thick black armoured cable. There's no information on the cable itself that tells me what the specs of the cable are.

 

[Indyisme]

Any spare ways in the Garage Consumer Unit?

I suspect you have a radial but whatever you could create two 16A radial circuits (providing you have a spare way)

As littlespark said you can't just upgrade the MCB to 20A for a number of reasons as well as it not being enough anyway.

I suspect the 2 cars would be plugged in on different sides of the garage so arrange the radials in that configuration. You don't want to inadvertently plug 2 in on the same radial.

You will also need to upgrade the cable and MCB supplying the garage to 32A.

You don't have selectivity in your current set up anyway with a 16A MCB backing up a 16A MCB.

Cable sizes for this would be dependant on length and installation method and volt drop. Also some consideration to the existing installation.

If you don't have a spare way then you could either get a larger consumer unit or upgrade the garage supply to 40A so you can have one 25A Ring. If your garage is wired as a radial with 2.5mm you would need to convert it to a ring or rewire in 4mm as 25A is right on the edge for 2.5mm as a radial. Best case scenario it can take 27A but that is dependant on a number of factors.

The above is a rough guidance on what you could do it would obviously depend on your current set up what would be best.

Another consideration is that normal 13A sockets don't do well having high loads connected for long periods, there are now dedicated ev charging sockets for this.

Yes the 2 cars are plugged in on different sides of the garage. When you talk about a spare way I assume you're asking if there's a space in the consumer unit for another 16A MCB? If so, unfortunately there isn't.

 

[PS Electrics]

Yes the 2 cars are plugged in on different sides of the garage.

I would have thought so but you never know!

When you talk about a spare way I assume you're asking if there's a space in the consumer unit for another 16A MCB? If so, unfortunately there isn't.

Yes that is exactly what I meant it isn't a problem it just changes your available options.

 

[littlespark]

Can you post a photo showing the big thick black armoured cable and the garage board?
We could maybe judge the size from visuals only.
Armoured usually has the size moulded into the plastic at regular distances… ie “3G2.5” would be a 3 core, 2.5mm

If it’s possible to uprate the breaker supplying the garage, it would give some more options.