Rings Radials RCBOs and I'm lost

[mattius]

With the impending arrival of a plug in hybrid I set myself the challenge of giving us a granny charge socket for it whilst we save up for a full charger.

I was surprised when reading the instructions ( after installing of course) of the suitably rated EV socket (just a high current standard UK plug socket ), that they recommend the installation on a radial circuit.

My understanding of a ring main is that a ring final circuit can carry a lot more load than a radial or a spur.

Anyone know why they would specify a radial?

I just extended the ring and plonked it on the outside of the garage, my logic being it's no worse than me plugging the car into my garage like the manufacturer suggests, but with the added protection of an RCBO at the socket.

[Nick Jones]

If adding to an existing circuit, Ring seems best to me as it’s fed from two directions. 
 

Do they mean that they prefer a dedicated radial circuit from the consumer unit? 

[zetecspit]

Radial circuits are often used when supplying an aplliance that has a high current draw, eg a cooker or water heater. A heavier cable is used, rated to cope with the current requirement and always exceeds the fuse or breaker rating. 

It may be the charge socket you are using has a maximum rating (no experience of one) and needs protecting with a 16A breaker? So putting it on a ring final circuit could mean the car could draw too high a current and damage the socket? No idea of your charging cable has a fuse fitted. 

 

[mattius]

https://www.electrical2go.co.uk/sync-ev-masterplug-ev-mode-2-charger-with-a-type-dp-rcbo.html

The socket in question.

My ring main is 32A ( 2.5mm T&E in a ring main ) in the garage on a 32A breaker, given this socket has a 16A RCBO feeding it, I would have thought balanced load of it being on the ring would be better.

It's kinda irrelevant unless I run a separate feed to the garage just for this from the house, as the garage is fed by a single feed from the house to power it's DB.

Edited November 25 by mattius

[PeteStupps]

Domestic wiring isn't my specialism but I reckon it's just to reduce likelihood of overloading your typical household ring circuit. Wiring Regs allow you to apply a thing called 'diversity factor' to normal electrical stuff, which accounts for the fact that you don't have all your appliances & gizmos drawing full power at once. So you might have 45amp worth of stuff hanging off your 32amp MCB but it's never all on simultaneously for long enough to overload the circuit. But EV chargers draw full power for long periods, so you're not allowed to apply 'diversity' to them when you calculate the total load.

But in your case it doesn't make much difference. Just don't try running your compressor, welder and EV charger at the same time!

[mattius]

Thanks, that's what I was thinking, the worst that could happen I trip the RCD.

[egret]

I currently charge a 1st gen leaf off a radially fed socket and it's fine, the only minor issue is that the 3 pin plug itself gets warm.  Having checked the plug and socket I'm pretty sure  this is down to the externally rated socket likely having some mild surface corrosion on the contacts causing an increased resistance.  It gets about 40-45°C, which is warmer than I'd expected, but seemingly fine.

I'd suggest double checking the terminals after a couple of months as there are anecdotes that new copper creeps, and any increase in resistance will quickly get hot.

When you upgrade to a more meaty charger, then consider getting an upgrade to a 100A fused connection from the provider if that's not already been done.  This used to be free.

[RedRooster]

Think I'd be looking at that socket if it's getting warm like that, somethings not right. 

 

[zetecspit]

2 hours ago, RedRooster said:

Think I'd be looking at that socket if it's getting warm like that, somethings not right. 

 

Sockets running at close to 13A do get warm. However, I do like a good brand if a socket is to be used for something like a heater or whatever. Fed up with some of the cheap crappy electrical stuff being sold...

[mattius]

That's why I went with an EV rated socket, it is very common for a standard socket to get warm due to the consistent power usage.

I believe the EV rated sockets just have better conductors to standard sockets and so are designed to get not get se hot.

Edited November 26 by mattius

[Sigma hurricane]

Having done lots of stuff on this over the last few years (part time eco energy consulatant for farms) i really would recomend getting one on a dedicated 16amp caveran type connnection or having a good charger that you can lower the amps or Kw output.

It is not normally the plug side that the issue as youll find a few other countries using our G type plug actually use 16amp plug fuses such as hong kong.
 

As you say its often down to the poor sockets or wiring within and cheap plugs sometimes.
It tends to be less of an issue for hybrids in the past as they only had 10Kwh batteries but now more and more have larger batteries the prolonger charge time results in heating up and therefore increased resistance and so on and so on ect. 
 

The reason for the dedicated curcuit is with the long 13amp charge time you really hamper your diversificaiton on the ring circuit. If for example you pluged in a oil rad or similar that would have you nearing your 32amp limit. (plus bear in mind with increased resistance you have increasing  voltage drop therefore increasing amperage to meet the required charge/ heating rate.)

[Sigma hurricane]

Also on the EV socket front its now a bs 1363-2 requirement since 2020 off memory. It requires the socket to be tested for an inductive load not just a resistive load. (Basically held to higher standards)

Hopefully you dont also have an electric shower as that would tecnially risk putting you over the DNO notification requirments as it would still clasify as a EV charge point to my understanding.

[mattius]

It's technically just an outside socket and well within DNO requirements as it's only ever gonna trickle charge.

No electric shower, and handily already got a 100A main fuse.

Handy because I'm not friends with the DNO, they put a requirement through the door to inspect the lines going into our property due to age. Then threatened to break into our property if we weren't available during Monday - Friday 9-5. We work for a living thanks very much...

 

[Escadrille Ecosse]

On 11/26/2024 at 8:28 PM, Sigma hurricane said:

Hopefully you dont also have an electric shower as that would tecnially risk putting you over the DNO notification requirments as it would still clasify as a EV charge point to my understanding.

Love this. The croft in the Highlands has an overhead uninsulated 3-wire supply to the old style ceramic insulators on the chimney. Installed in 1959/60.

The connection from the chimney to the 100A company fuse at the (now modern) consumer unit in the house is the original rubber insulated 3 core flex. Flex not SWA, that is attched to the rhones (guttering) with the old style metal clips. The house is a couple of hundred years old so this is just above head height. I can reach up and clean the rhones standing on the ground.

Run the cooker or the electric shower and the voltage at the board drops from about 230V to about 200V and if you hold the incommer it is slightly warm to touch.

When we replaced the old wire fuse box a few years ago the 'man' came out to pull the company fuse and make sure we fitted the regulation double insulated tails. These are each the size of the incomer. When I commented on this all he did was check that MY earthing was adequate. FUD.

 

Edited November 27 by Escadrille Ecosse

[Sigma hurricane]

Oh cable sizing when you look at the dno side of things is mental. The silly thing is sometimes I have had farms move their meter from the building to a box next to the transformer and magically with no changes other than that they are allowed to import and export more Kw. It all comes down to if it stays within their limits at the cut out of +10% -6%. 
The issue is these days everything was sized based on diversity across the whole street or even 1/4 the village off the same transformer. The odds that people are turning their electric kettles and electric showers all on at the same time is low. However with ev chargers being on for several hours it becomes a problem. 
 

To be fair during our EV charging cheap hours we often pull the fuse rating for a couple of hours between the house battery charging the ev charging the Ground source heat pump heating up the hot water tank and a buffer. Plus sometimes the washing dishwasher and a few other bits all on at same time. I log all the voltages ect on my incoming supply I think my record low is around 195V and high about 262v 

[mattius]

When I used to work in power stations I was talking to the national grid big guys, they said that if everyone had an electric car and everyone charged at the same time, the actual grid could not handle it. The voltage drop would be too great.

Other tid bit from those days I thought was cool, the HV cabling (11kw and 33kw) is oil cooled, this has a secondary benefit as they can see where it's damaged by the pressure drop, clever.

[RedRooster]

12 hours ago, Escadrille Ecosse said:

FUD.

 

Brilliant