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3 pin plug and extension lead

When I had my M3 delivered the guy told me not to use an extension lead on the 3 pin plug. I’m heading down to Cornwall in a few weeks and was planning on charging the car overnight using a 3-pin because it’s a cottage on a farm. Looks like I will need an extension lead to do so so I have two questions..

1. Can I use an extension lead?
2. Does it have to be a certain amp/waterproof etc?

Thanks.
 
13A weatherproof extension lead (compatible with all EVs)

Get an inline RCD and the 3 pin socket tester - different product page

Be wary, the plug/flying lead on the Tesla UMC is a big old thing and does not fit many weatherproof enclosures or being so rigid, may rock itself loose over the course of a charge. The one linked above will work just fine and is well made and very flexible.

You will probably want to keep the UMC itself out of persistent water contact. Couple of bricks and bucket or leaving it beneath car if its not going to puddle.
 

WannabeOwner

Well-Known Member
Nov 2, 2015
7,261
4,015
Suffolk, UK
When I had my M3 delivered the guy told me not to use an extension lead on the 3 pin plug

Yeah, that's the Party Line. Here's my 2p-worth:

Get a good quality extension, like the one @VanillaAir_UK links to, not an El Cheapo from Screwfix / Homebase, nor your mate's frayed lawn mower extension!!. Something with have H07RN-F rubber cable rather than some nasty PVC stuff, so that it can withstand a fair amount of abuse scraping on tarmac etc. and continues performs well in sub-zero temperatures (blue "Arctic" PVC extension cable is rubbish ...) and a rubberised plug / socket. I bought mine "one cable size up" so that combination of extension and UMC doesn't stress anything (but Tough Leads blurb on extension leads says that is not necessary, and it bulks up the cable weight, and increases the price)

You can waterproof the connection to UMC with bucket and two bricks - connection on top of a brick to keep it dry, upturned bucked with brick on top to stop it blowing away ... and better still buy something with a more robust solution for socket-end (they won't be waterproof though, only splash-proof, so you might still want Bucket+2-bricks :) )

Feel the plug (at 13-AMP socket end) for any warmth after a hour or so, and before going to bed. Be prepared that M3 may trip the whole house breaker ...

If any warmth dial down the AMPs on the car dashboard, or try a different socket.

Decide if you need RCD on the plug end (circuit may well be modern / well protected ... but others in future might not?)

Don't precondition on 13AMP (until final few minutes). 13AMP isn't enough to do that and charge as well

Tesla UMC is a robust cable (capable of 3-Phase), other "granny leads" are much thinner. I've not had any problem using an extension (and by the nature of it connection time has been all-weekend continuous running)
 
Thanks for the in depth info, I’m only planning to use it once for the week just to top up overnight, there is an instavolt near by but I would be relying on them being available and working which feels like a risk so I need a back up.

I don’t mind splashing the cash as per VanillaAir_UK info if I’m doing it right, I guess it being a purpose built cottage on a farm I should be wary about tripping everything as it’s likely not going to be wired up like your conventional house.

I haven’t looked yet because of the persistent rain but how long is the cable provided?
 
Whole house tripping can be attributed to cumulative earth leakage and/or over sensitive RCD. So it may be caused by other loads in a house rather than dodgy wiring. Some powered devices leak a small amount of current to earth. On their own, its not an issue, but when all combined, the cumulative effect may exceed the RCD trip limit, typically 30mA but, may be less if the RCD is over sensitive. The Tesla UMC seems to introduce around 3mA which is within spec, but if you are already close to limit, it can tip things over the limit.

We suffered this and was initially very confusing. We tried different permutations of circuits and a different UMC and even car. When we turned off some circuits we could charge, but whole house on, bang.

In the end I got my multimeter out which thankfully seemed to be pretty good at reading the leakage. IIRC our house was just over 20mA, so theoretically another 3 should not have triggered the RCD. But it seemed that when charge first initiated, the leakage would briefly spike, tripping the RCD - this could be proven by starting charge with one house circuit off, then successfully reintroducing the circuit.

In the end, I called in my friendly electrician to re purpose a circuit in another consumer unit. Problem solved, but we do have to use that specific 16A circuit to charge the car. Another plan to fix the problem was to swap a few circuits around in the main consumer unit and put the whole garage on its own dedicated RCBO, but on opening up the consumer unit, there was no room to fit the taller RCBO. We didn't swap the RCD over as there was no guarantee it was going to behave any different and risk it may have caused problems, and by that time, we had a working solution. Cost, 1-1/2 hours labour plus MCB, so under £100.
 
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WannabeOwner

Well-Known Member
Nov 2, 2015
7,261
4,015
Suffolk, UK
it seemed that when charge first initiated, the leakage would briefly spike, tripping the RCD - this could be proven by starting charge with one house circuit off, then successfully reintroducing the circuit.

I've done just that ... we turned most stuff off (using breakers), started the car charging and then turned everything else back on. (Dunno what would happen with the "top off every hour" that M3 seems to do sometimes ...)

I told my hosts their electrics was a deathtrap :rolleyes: ... hopefully that will cause them to get it fixed before I visit next :)
 
No chance of a Commando socket there? You'd just need a 16AMP / 32AMP (or maybe even 3-Phase) Commando Adaptor fr the UMC (about £30 I think). That would give you a faster charge than 13 AMP, and avoid the extension lead, assuming you can park near it

I’m not sure there is but I will drop them an email this week and find out, I’m sure they have a camping area but not sure it’s set up for caravans to pull up and plug in.
 
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