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Discussion Starter · #1 ·
Hoping someone has some experience and can confirm my suspicions.

My installer fitted a Wallbox Pulsar. Every charge starts correctly but after approximately 2 hours the MCB trips.

The charger is on it's own circuit, protected by a 32a MCB. I've contacted Wallbox who have advised a 32a MCB should be absolutely fine.

I'm going to try dropping the amperage until I get a completed charge but I see this as a temporary workaround.

Is is common to protect an EV charger drawing 32a with a 32a MCB?

Thanks
 

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Depends where that 32 A MCB is. If it's in a main consumer unit, with other MCBs tight either side, then there is a chance that it's just getting too hot, especially in this warm weather. My personal view is that it's never a good idea to connect a charge point to the main CU for the house, unless a clear space can be left at least one side, preferably both sides, of the MCB to reduce the risk of it running a bit warm. MCBs always warm up under load, and if they get too warm they can trip, as they use heat from a bimetallic strip inside as one of the sensing mechanisms. Far better, in my view, to always connect a charge point to a separate small CU, so there's less chance of heat build up from other circuits.

There's also a possibility that the terminals on the MCB may not have been properly tightened, and that's causing additional heat build up, especially as this is a new installation, so perhaps worth getting that checked by the installer.

Nothing wrong with using a 32 A MCB to protect a 32 A circuit, although it is often OK to use a 40 A MCB/RCBO for most charge points. Changing to a 40 A one isn't really a proper fix for this issue, though, if it's caused by heat build up within the CU or terminals that are not tightened to the specified torque setting. I'd want to be 100% sure that there wasn't a potential overheating problem before just swapping over to a 40 A MCB.

Any chance of a photo showing the MCB and CU?
 

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Discussion Starter · #3 ·
Depends where that 32 A MCB is. If it's in a main consumer unit, with other MCBs tight either side, then there is a chance that it's just getting too hot, especially in this warm weather. My personal view is that it's never a good idea to connect a charge point to the main CU for the house, unless a clear space can be left at least one side, preferably both sides, of the MCB to reduce the risk of it running a bit warm. MCBs always warm up under load, and if they get too warm they can trip, as they use heat from a bimetallic strip inside as one of the sensing mechanisms. Far better, in my view, to always connect a charge point to a separate small CU, so there's less chance of heat build up from other circuits.

There's also a possibility that the terminals on the MCB may not have been properly tightened, and that's causing additional heat build up, especially as this is a new installation, so perhaps worth getting that checked by the installer.

Nothing wrong with using a 32 A MCB to protect a 32 A circuit, although it is often OK to use a 40 A MCB/RCBO for most charge points. Changing to a 40 A one isn't really a proper fix for this issue, though, if it's caused by heat build up within the CU or terminals that are not tightened to the specified torque setting. I'd want to be 100% sure that there wasn't a potential overheating problem before just swapping over to a 40 A MCB.

Any chance of a photo showing the MCB and CU?
Thanks Jeremy

It's a separate CU fed directly from a meter feed. Only has the MCB for the charger in it.

I guess the other issue could be an earth leak somewhere? Trying to get some ideas before the installer returns.

147381
 

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Best bet would be to get the installer back to check it, I think, as that's not an MCB, it's an RCBO, so could be tripping because of earth leakage. Being a C curve it's going to take a high current for a long time to get it to trip on overcurrent, and it should really be a B curve for a load like a charge point (doesn't matter too much given that the charge point cable has a much greater current rating, though). My guess is that it's either an earth leakage fault that's showing up after some time, possibly a loose or poorly made termination causing heat to build up, or may possibly even be a faulty RCBO.
 

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Discussion Starter · #5 ·
Thanks Jeremy, appreciate the advice.

They're coming on Wednesday so hopefully they sort it.
 

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The fact that it only trips after a couple of hours might make it a bit challenging to find the cause, especially if it's related to earth leakage, as it may be that something like the insulation resistance somewhere between the RCBO and the car only goes haywire after a while, perhaps as things warm up a bit. Could even be a problem with the charger (in the car) rather than the wiring or charge point. Have you tried charging with the granny lead to see what happens, by any chance? Might be worth doing that if you can, as if that also trips out the RCD on the circuit it's plugged into then that points towards an earth leakage problem at the charger, rather than the wiring or charge point.

Another thing your could do is feel the temperature at the front of the RCBO when it trips. It will be slightly warm when running normally at a 32 A load, but it shouldn't feel uncomfortable if you touch the front of it with the back of a finger. If it does feel hot, then tell the installer, as that may be a clue as to what's causing the problem.

The installer will check the insulation resistance, as that's an obvious possible cause if it's tripping because of earth leakage, but it might also be worth getting him to actually measure the earth leakage current in the CPC to the charge point (easy to do, just clip a leakage current tester around the CPC). Chargers do often have a very small normal leakage to earth, ones I've measured have typically been around 2mA to 5mA when the charger is running at full current. This leakage comes from the interference suppression components I think, and often seems to contain high frequency, pulsed, components. The RCBO fitted to your box can deal with pulses OK, but may possibly be a bit sensitive to high frequency noise. ERIS is not a brand I've ever fitted, so I've no experience of problems with them.

With luck, the fault may be obvious, and the installer will be able to fix it easily. Be useful if you could let us know the cause when it's found, as it's always handy to know why these things may happen.
 

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Discussion Starter · #7 ·
I'm charging overnight so asleep when it happens, may try an evening charge to see if anything does occur.

Don't have a granny lead, but did go to a campsite which had a 7kwh (non smart) charger and that worked overnight both times without issue, so suspicion is that it's not the car, but can't rule anything out.

I'll update when I find out more.
 

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Just done a test charge, lasted about 30 mins before the fuse tripped.

Fuse didn't feel warm when this happened.

That will help the installer when he/she comes back, I'm sure, as it points to it most likely being an earth leakage fault, I think. If it was an over-current trip after 30 minutes of being charging the RCBO would almost certainly have been pretty warm.

If you can also try the granny lead, using an outlet that's in good condition, and as long as you have RCD protection on the socket circuits (if in doubt, post a photo of the main consumer unit and one of us can confirm this) then if that doesn't trip that would pretty much rule out a fault with the charger in the car, and give another bit of useful information for the installer.
 

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Discussion Starter · #10 ·
I don't have a granny charger so can't test that, but the fact I've did two successful charges in a row on another home charger suggests to me that the car is unlikely to be at fault -though happy to stand corrected.

I've reduced the amps by about 20% and restarted the charge to see if that does anything .
 

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Sounds like the problem is most likely to be with your charge point/wiring, then. Could be as simple as a faulty RCBO, perhaps, or something visibly awry that's creating an earth leakage fault. Be interesting to see if reducing the charge current setting makes any difference. It might not be directly related to charge current though, although it might just seem that way of the RCBO is a bit overly sensitive to high frequency earth leakage, as reducing the current might reduce that as well. It could also be that there's an earth leakage path somewhere that's very temperature sensitive perhaps, so that reducing the current might reduce the small temperature rise associated with current flow and so drop it below the trip threshold.
 

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I have read that MCBs shouldn't be used at thier maximum capacity for long periods. The general recommendation is 80%.

Having said that, I have been able to take my Hager RCBO a few amps above its rating, without tripping immediately. This was done gradually by changing the max amperage on my EV Charger. I suppose that if a sudden spike had occurred, it would trip much faster.
Of course doing this is not recommended, and I did it just for a few minutes to test, checking each time to make sure it wasn't too hot (it got pretty hot before tripping).

During normal use I keep the EVSE at a lower rating than the RCBOs max rating, just to keep it safe.
 

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There are time/current curves for MCBs/RCBOs. All are rated to work OK at their maximum current rating indefinitely within their operational ambient temperature range. They don't actually trip until the current exceeds their rating for a period of time that's dependent on the extent of the overload. For example, a B curve MCB/RCBO trips near instantly at between 3 and 5 times it's rated current, so up to 160 A for a 32 A rated device.
 

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Discussion Starter · #14 ·
So been holding off replying until I was sure the issue was fixed.

The installer came back, disconnected the feed and tested everything, said they couldn't see a problem. Got on the phone to Wallbox support who said a firmware update was needed....

Since then, no issues whatsoever. Whether it was the update, or reconnecting the feed I'll never know.

Either way, it's sorted.
 
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