[proddick]

Often new members have questions about charging and the attached document from BEAMA is quite good at explaining the options, sockets, cables, etc.

We see regular discussions on using only the portable EVSE (aka Granny) and the document contains following -

Ideally, all Mode 2 charging should be done using a dedicated circuit (i.e. any charging done at home). For new installations, when installing a socket outlet for EV charging, section 722 of the wiring regulations requires that a separate dedicated circuit is installed.

Info on BEAMA below

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www.beama.org.uk

 

[Geoff_S]

Ideally, all Mode 2 charging should be done using a dedicated circuit (i.e. any charging done at home). For new installations, when installing a socket outlet for EV charging, section 722 of the wiring regulations requires that a separate dedicated circuit is installed.

Genuine question. Why is it ideal? What are the issues for just plugging into an existing, properly installed, properly protected 3 pin socket in a garage? As I have done for the last 9 months.

What would be the potential problem be if I had a double socket on a dedicated circuit, my EV plugged into one socket and my polisher on the other?

Ta 😊

 

[cDy]

It's not what is ideal about the dedicated circuit, it's what is not ideal about a normal UK 13A socket installation. In the UK, 13A sockets are usually installed on a 'ring', with all the sockets daisy chained back to the consumer unit in a loop. Current can flow either way round the loop, so if there is a loose connection at any point in the loop everything keeps on working - you don't know there is a point of high resistance at one of the connections. That's why it's important to have your ring mains impedance checked periodically. Typically 2.5mm2 (or 4mm2) cable is used, which can support 18A (or 25A) on each side of the loop, if the cable runs through insulation. And ring mains circuits are sized assuming that diversity applies - that is, a 13A device isn't plugged into every 13A socket and switched on at the same time.

If you put in a dedicated circuit for an EV, with a 13A or commando socket on the end, you can use 4mm2 cable direct from the consumer unit and it is never shared with any other device and is easy to check for faults - just a connection at each end and no daisy chain. I would put in 6mm2 cable (or even 10mm2, ready for 2 EVs!) so that an EVSE could be located at the same location at a later date.

Edit in italics, thanks to @Hilltop Dave for noting my mistake.

 

[Hilltop Dave]

Typically 4mm2 cable is used, which can support 25A on each side of the loop, if the cable runs through insulation.

For many installations 2.5mm2 cable can be used.

 

[Boxbrownie]

And of course the granny chargers are only drawing 10 amps maximum, our i3 has been happily charged every day on the granny charger for three and a half years now, the plug never gets even warm to the touch and the contacts within the sockets (checked yearly as part of the holiday annexe agreement) and the plug look like new.

Just don’t plug anything of high load into a mid 20th century untested and original domestic mains circuit, Ive been in cottages were the kettle would blow the fuse if it took too long to boil!

 

[WonkoTheSaneUK]

you don't know there is a point of high resistance at one of the connections.

Until the magic smoke gets out!

 

[Geoff_S]

It's not what is ideal about the dedicated circuit, it's what is not ideal about a normal UK 13A socket installation. In the UK, 13A sockets are usually installed on a 'ring', with all the sockets daisy chained back to the consumer unit in a loop. Current can flow either way round the loop, so if there is a loose connection at any point in the loop everything keeps on working - you don't know there is a point of high resistance at one of the connections. That's why it's important to have your ring mains impedance checked periodically. Typically 4mm2 cable is used, which can support 25A on each side of the loop, if the cable runs through insulation. And ring mains circuits are sized assuming that diversity applies - that is, a 13A device isn't plugged into every 13A socket and switched on at the same time.

If you put in a dedicated circuit for an EV, with a 13A or commando socket on the end, you can use 4mm2 cable direct from the consumer unit and it is never shared with any other device and is easy to check for faults - just a connection at each end and no daisy chain. I would put in 6mm2 cable (or even 10mm2, ready for 2 EVs!) so that an EVSE could be located at the same location at a later date.
[/QUOTE

It's not what is ideal about the dedicated circuit, it's what is not ideal about a normal UK 13A socket installation. In the UK, 13A sockets are usually installed on a 'ring', with all the sockets daisy chained back to the consumer unit in a loop. Current can flow either way round the loop, so if there is a loose connection at any point in the loop everything keeps on working - you don't know there is a point of high resistance at one of the connections. That's why it's important to have your ring mains impedance checked periodically. Typically 4mm2 cable is used, which can support 25A on each side of the loop, if the cable runs through insulation. And ring mains circuits are sized assuming that diversity applies - that is, a 13A device isn't plugged into every 13A socket and switched on at the same time.

If you put in a dedicated circuit for an EV, with a 13A or commando socket on the end, you can use 4mm2 cable direct from the consumer unit and it is never shared with any other device and is easy to check for faults - just a connection at each end and no daisy chain. I would put in 6mm2 cable (or even 10mm2, ready for 2 EVs!) so that an EVSE could be located at the same location at a later date.

So are ring mains by their very nature potentially dangerous? Would a system of dedicated cables for each individual socket be better?

 

[mikegs]

Would a system of dedicated cables for each individual socket be better?

Technically, yes. That is called a radial circuit. But in a typical house you'd need about 20 of them as against 2 rings.

So 'better' depends on what factors you include - just Google "best car" and you'll find there are many depending on what kind of car you want.

Ring mains are a compromise of power delivery and cost because 2 breakers and maybe 30m of cable is cheaper than 20 breakers and perhaps 200m of cable for radials (and a massive consumer unit).

 

[proddick]

So are ring mains by their very nature potentially dangerous? Would a system of dedicated cables for each individual socket be better?

I think UK is one of few countries that installs rings. In USA and Spain we have a few sockets per breaker but are all radial.

I particularly like how wiring is done in modern houses is Spain with trunking and junction boxes everywhere as makes adding circuits so much easier. Some people don't like aesthetics of junction boxes, but worth it IMO.