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M3 tripping MCB just before end of charge

GBUK

Member
Jul 7, 2021
15
18
UK
Moderator comment - thread renamed for clarity "RCD" to "MCB"

A couple of times now my m3 has tripped my 32a breaker, the associated 40a rccb is unaffected. Always happens at 78% soc when I’ve set a 80% maximum.

I push the breaker lever back up almost straight away and charge continues and completes without issue (so I’m guessing it’s not heat related).

Before I call in a sparky, anyone seen this behaviour and could it be the cars firmware version?
 
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VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,732
6,301
Surrey, UK
A bit of confusion over what exactly it tripping?

Title says RCD, text says 32A breaker, but not the RCCB.

Is it a 32A MCB (over current) or a RCD rated at max 32A (but not overcurrent protection)? Does what is tripping have a 'test' button is normally a big clue?

Exactly what is tripping will make a big difference to the type of fault.
 

GBUK

Member
Jul 7, 2021
15
18
UK
A bit of confusion over what exactly it tripping?

Title says RCD, text says 32A breaker, but not the RCCB.

Is it a 32A MCB (over current) or a RCD rated at max 32A (but not overcurrent protection)? Does what is tripping have a 'test' button is normally a big clue?

Exactly what is tripping will make a big difference to the type of fault.
Sorry my lack of knowledge on the terminology. The ‘breaker’ that’s tripping doesn’t have the test button (that’s on the 40a one which is fine). The 32a breaker just has C32 /DLS6 written on it, doesn’t state mcb or rcd unfortunately.
 
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Jason71

Active Member
May 8, 2019
3,196
3,269
Shropshire
Sorry my lack of knowledge on the terminology. The ‘breaker’ that’s tripping doesn’t have the test button (that’s on the 40a one which is fine). The 32a breaker just has C32 /DLS6 written on it, doesn’t state mcb or rcd unfortunately.
A picture of the fuse box would help plus deltails of the charger you are using.
 

GBUK

Member
Jul 7, 2021
15
18
UK
A picture of the fuse box would help plus deltails of the charger you are using.
8F2B768E-0114-44A4-8937-818484678F7C.jpeg

I’ve got an old school British Gas/Polar charger from my 2017 Zoe days!
 

VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,732
6,301
Surrey, UK
Thats an MCB tripping, so over current detected.

I would get a sparky involved - once they have checked the connections/wiring, it wouldn't surprise me if they suggested swapping out the MCB - if it was me I would be happy with that second step as its a transient fault - MCB's are pretty inexpensive and a swap out would be cheaper than them spending more money/time to fault find. The fact that its the tail end of the charge shows that its not an obvious fault. Also, if it is, as it sounds to be not new, its possible that things just need a bit of a check to see if its still performing as expected, so a new MCB might not be a bad thing as its will have been running at its limit for extended periods of time - they may even suggest upping it to 40A, wiring permitting.

A couple of other things that you can do ahead of the sparky to give them more info is to use something like TeslaFi (if you don't already have it they do a free trial for a couple of weeks) to log the charge voltage and current every minute. Also, reduce the charge rate from I assume 32A down to say 28A and see if it does the same.

If it continues to do it after all this, then maybe look at what the car is up to.
 

GBUK

Member
Jul 7, 2021
15
18
UK
Thats an MCB tripping, so over current detected.

I would get a sparky involved - once they have checked the connections/wiring, it wouldn't surprise me if they suggested swapping out the MCB - if it was me I would be happy with that second step as its a transient fault - MCB's are pretty inexpensive and a swap out would be cheaper than them spending more money/time to fault find. The fact that its the tail end of the charge shows that its not an obvious fault. Also, if it is, as it sounds to be not new, its possible that things just need a bit of a check to see if its still performing as expected, so a new MCB might not be a bad thing as its will have been running at its limit for extended periods of time - they may even suggest upping it to 40A, wiring permitting.

A couple of other things that you can do ahead of the sparky to give them more info is to use something like TeslaFi (if you don't already have it they do a free trial for a couple of weeks) to log the charge voltage and current every minute. Also, reduce the charge rate from I assume 32A down to say 28A and see if it does the same.

If it continues to do it after all this, then maybe look at what the car is up to.
Thank you for providing such a thorough response, appreciate it.
I’ll do as you suggest and fingers crossed a fresh mcb will do the trick. Ill also reduce the charge rate down a touch in the mean time to see if that makes a difference.
 
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SpareHeadOne

Member
Oct 27, 2020
403
281
UK
Yes, sparky required.

My old charge point did that a couple of times not long before I had it replaced (planned). The sparky told me that the cable for my 32A point is only rated at 36A and found charring on the internal terminals.

He theory was that the whole setup was getting too warm when my car is drawing full load for lots of hours, so we limited the new charge point to 26A. That means something like an extra hour to fully charge but in practice I don't really notice.

He said they would normally fit a 40A cable for that setup so that it's well within tolerance; I agreed with him that it wasn't worth paying the money to upgrade the cable just to save the charge time once or twice a year - if I'm in that much of a hurry I do a preliminary charge at one of the local rapids.
 

Adopado

Active Member
Aug 19, 2019
4,533
3,422
Scotland
Thank you for providing such a thorough response, appreciate it.
I’ll do as you suggest and fingers crossed a fresh mcb will do the trick. Ill also reduce the charge rate down a touch in the mean time to see if that makes a difference.

It's always interesting to know the outcome on these issues so do come back and let us know the full story once you are happy it has been properly sorted out.
 

davyjohns

Member
Nov 18, 2019
79
39
newcastle under lyme
After 18mths of perfect charging my breaker tripped part way through a charge overnight. On one occasion it tripped after 8 mins. I reduced the charge current on the car screen to 20 amps and the charge was perfect. 20 amps would give me adequate time overnight but I had a 32 amp unit installed. Installer paid a visit and said that the early charge points supplied at 28/29 amps and that there had recently been an update on the charge point to set this at 31 amps. The breaker is a 32 amp and he will fit a 40 amp breaker. Looking back on Teslfi the charge rate in June was 29 amps and is now 31 amps so this does look like the problem.
 

Adopado

Active Member
Aug 19, 2019
4,533
3,422
Scotland
After 18mths of perfect charging my breaker tripped part way through a charge overnight. On one occasion it tripped after 8 mins. I reduced the charge current on the car screen to 20 amps and the charge was perfect. 20 amps would give me adequate time overnight but I had a 32 amp unit installed. Installer paid a visit and said that the early charge points supplied at 28/29 amps and that there had recently been an update on the charge point to set this at 31 amps. The breaker is a 32 amp and he will fit a 40 amp breaker. Looking back on Teslfi the charge rate in June was 29 amps and is now 31 amps so this does look like the problem.

However, the issue must have been that the original 32amp breaker was faulty. The slight increase in the charge rate was the straw that broke the camel's back. 40amp gives even more headroom ... and is also a common value for charge points, so nothing to lose, but that original 32amp shouldn't have tripped unless it had acquired a fault. (32 amp breakers don't trip at 32 amps)
 

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