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RCD type for commando (blue) home charging options

Hi Tesla owners
I have a model X and am looking to get a local electrician to install a commando interlocked socket to enable me to charge at home at a practical rate/hour. Currently off the three pin plug, I get 5 miles/hour. I hope I can get about 20 miles/hour when using the commando.

I plan to use the Tesla UMC with commando adapter. I have been asked by our electrician to confirm the type of RCD to be used(Type A or Type B). I could not find this information anywhere on the net, and when asked, Tesla service couldn't give me an answer,

I would appreciate anyone on the this forum with experience in using commando sockets in the UK with the UMC to help with information and suggestions.

Thanks and regards
Type B RCDs are fairly rare.

UK wiring regulations require either Type A or Type B (your choice). Type AC (what you typically get if you don't specify) is not allowed.
Those regulations apply equally to fixed chargepoints and to commando sockets installed for EV charging purposes.

Type B are better, but significantly more expensive and it is questionable whether the problem they solve is actually likely to occur while charging a Tesla. The vast majority of UK installations for EV charging use Type A (but existing RCDs in most houses will be Type AC and so not sufficient).

People are often confused into thinking that they have a Type B where the RCD and overcurrent (MCB) functions are combined in the same device - an RCBO. These will often be marked "B32" or "B40", where the B refers to the overcurrent curve and NOT the RCD type.

RCD type is normally harder to identify - a common (but not universal) marking scheme has a rectangular box with just a sine-wave in it for Type AC, the same box with the sine wave and a row of dashes under it (representing pulsed DC) for Type A, and two boxes, one the same as Type A and the other with a horizontal line and dashes (representing continuous or pulsed DC) for TypeB.
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I have just been talking to my electrician and he asked if the 40 amp commando would do instead of the 32? The other question is what would be a good brand to buy? I quite like the model shown in the Tesla installation guide, but do not know if it is a sufficiently good quality product.

I quite like this one as being inexpensive but satisfactory quality:

Gewiss IEC 309 32A Switched Interlocked Socket 240V GW66015 | RS Electrical Supplies

Note that it has to be interlocked (per regulation).

You can also get ones like this that have space for the RCD within the same housing - but relatively expensive.

I'm not sure what to make of the 40A question - there's no such thing as a 40A commando (they come in 16A/32A/63A sizes). The 32A is the only one for which Tesla supply a 'head' for the UMC to fit it (it would make sense to support the 16A also, but they don't).

If your electrician is not familiar with EV charging, point him at section 722 in the regulations book (which applies equally to commando sockets for charging purposes). In addition to the points we've already covered about RCD and interlocked sockets, there is also earthing to consider. In many cases (but not all) the earth from the house shouldn't be used and a separate earth should be provided for the chargepoint (known as a "TT island", also common practice for garden sheds and the like). Not much extra cost/effort to do it right.

Not in the book but worth mentioning, don't penny-pinch on the cable size to the chargepoint. You might find that, under the most favourable conditions, 4mm² cable might just comply with regulations - and that would be sensible design if you were installing a commando socket for (say) a welder that uses full power only intermittently. For EV charging, you are going to be using it flat out for hours at a time, so stepping up a size to 6mm² is better - it will run cooler and so be more reliable, and the thin wire isn't cheaper in the long run as the cost difference is minimal and soon made up by the extra electricity cost in heating the cable rather than the car.

Finally, are you sure you want to go with a commando socket? All the wiring, RCD, earthing etc. is exactly the same whether you go for a Tesla WC or a Commando socket on the end of it. The Commando socket appears ~£300 cheaper, but only because you got the UMC "for free" with the car. If you intend to leave it permanently plugged in there, then that's fair enough. However, most people want to take the UMC with them for use away from home (hotels, relatives etc, usually with the 13A plug). So if you are also using it as your daily home charging solution you either:
  • Roll it up and stash it in the car before setting off every morning. Not fun as the cable inevitably gets dirty over time.
  • Take it with you only when you need it, rather than keeping it in the car. Risks forgetting it on the one occasion that you do actually need it.
  • Buy a spare UMC to keep in the car. This is actually more expensive than buying the WC for at home in the first place.
Having a dedicated chargepoint at home also means you've got the UMC to use in emergency if it breaks - whereas using the UMC every day you are in trouble if it breaks/wears out.
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Thanks Arg..Appreciate the detailed response. What we have decided so far:
  • 32 amps versus 40 amps was a miss-understanding on my part. He has clarified that we will put in a 32 amp
  • The Gewiss sockets look nice. Thanks, we probably will go for that
  • Point about the cable is noted and we shall invest in the 6mm ones
  • He has factored in an additional earth for the EV charging socket
I considered the Tesla wall charger but it is an additional £460.00. I am planning to leave the UMC plugged in at home as we rarely stay away overnight. Most of our trips end up within about 30 miles from a super charger, so we haven't had to plug in to friends or neighbours as yet. If we do go away, I will certainly have to take the UMC with me.
Fair enough. If you ever change your mind, all the wiring is the same so it will be easy to swap the commando for a WC.

Has the WC price gone up? It used to be £438 with the long cable, £398 with the short cable. I'd heard that they'd made the short cable the same price, but not that the price had gone up too.