Charger tripping

[user 3172]

Did consider that. Given that there's no obvious indication of anything wrong in the car or the charger, I did consider whether the circuit breaker itself may be iffy.

It's a fairly new house (1991) and everything else looks sound.

I might try putting a new 32amp in place when I get chance just to see if it performs any better.

 

[jadnashuanh]

FWIW, in the USA, there's a reason why they specify use of a 40A CB on a 32A EVSE. NOw, you can build them with different curves, but even then, pulling nearly max over time is just not reliable. Most require a constant overload for a period of time before they'll trip. They'll trip nearly instantaneously only if the load is exceeded, often by a considerable amount. Each of those factors can be tailored for specific applications, but again, essentially a 32A load on a 32A protection device IMHO, SHOULD trip after an extended time, especially as there are slight voltage variations, the load won't be able to react instantly, and the actual current draw could fluctuate slightly. Most meters probably wouldn't be able to show that as their sample rates aren't that fast, but if the CB was on the edge, it could just be enough to cause it to trip when one happens.

Typically what will happen as the wire heats up is that its resistance will rise, which will drop the voltage at the load. Dropping the voltage will drop the power available, even at the same amperage draw. Since power = volts * amps, you'll charge at a slightly lower rate, even as the amps stays the same. It is the pilot signal output of the EVSE that the car reads to determine the maximum current draw it can apply to the EVSE. If that is stable, the current level the car pulls should remain stable, and as voltage changes, the actual power delivered will change.

 

[user 3172]

Given I watched or more accurately listened to the charge process today, it seems to me most likely that the constant level of draw is the problem.

The CB has never tripped in response to surge (switching on / off etc and no sign of arcing) and as you point out, the surge level is typically 3+ times the nominal current rating of the CB with a very quick response time. There is no evidence that the charger is suddenly drawing that much extra current. Specs online for the CB show that a small excess current will trip the CB but only after a much longer time. It took about 20 minutes of 7.4kw draw to throw the switch earlier today. When it did, there was no evidence of excess current in the circuit, no warm cables, components etc.

I ran the circuit with the 40amp CB for well over an hour and nothing happened any differently except that the CB didn't trip. No more heat in the circuit than previously. A sudden surge from a fault in the car / charger would almost certainly have tripped the 40amp CB if it had been the cause of the 32amp one tripping.

Will keep a close eye on things for now.

 

[jadnashuanh]

A slight voltage spike may be all it would take since the car may not respond fast enough to lower its draw. As I've said, IMHO, a 32A breaker on a device pulling 32A is just asking for problems. Most CB's work via heat...and, depending on where and how it is installed, the ambient temp, insulation of the case, and air flow, if it can't dissipate the heat, it can make it look like the current is higher if it gets even a little bit hotter, tripping it. That's why the USA has that 80% rule so you don't get nuisance tripping.

 

[user 3172]

Well, it charged perfectly fine last night without any trips or falls!

Here's hoping for the second time.... :roll:

 

[KJHXXX]

Hi, one thing to consider is maybe you actually have an earth fault? The RCBO might be tripping due to over current OR ground fault?

 

[KJHXXX]

Reading the thread again, to confirm, was the new circuit breaker a D40 or D32? You need the D40. You never fit a 32A RCBO for a device pulling very close to a constant 32A. This is asking for trouble!

 

[user 3172]

Just to clarify, the RCBO on the charger has never tripped. It's the circuit breaker on the main consumer unit that's been tripping.

The RCBO on the consumer unit has not tripped ever either so it's not earth fault related. It's current related.

The new RCBO unit they've fitted in the charger is the D40 but made no difference.

It's been charging for a few nights now with no repeat. Either it's a dodgy circuit breaker or 32amp was just too close for comfort.

 

[cdnji]

As jadnashuanh pointed out, the fault is probably on the circuit supplying the EVSE.

You mentioned that it's the circuit breaker on the main consumer unit that's tripping. That confirms what jadnashuanh's been saying - that it could be the circuit itself. That's also why replacing the built-in RCBO with a D40 is not going to fix the issue.

Assuming that the circuit was laid with a 32A circuit breaker in the MCU in mind, then fixing it is not a simple matter of replacing the 32A CB in the MCU with a 40A CB. The whole circuit must be replaced to support a 40A load - new CB, new cabling.

Either that, or if you got the optional Amp-Selector Keyswitch for your Rolec EVSE, you can set the EVSE to 16A instead of 32A.

 

[jadnashuanh]

It all depends on the gauge of the wiring feeding the EVSE as to whether you can put in a larger CB. In the USA, for a 40A breaker, you'd have to have at least 8g wire feeding the branch circuit. If you do, then there should be no reason you couldn't change the breaker, but if not, then, as stated, it's a wiring upgrade that's needed as well as the CB. The USA has an 80% rule on this type of circuit, so 40A*80%=32A maximum constant load. While internal protection protects the device, a main panel CB is designed to protect the wiring, it really doesn't care about the device itself.

 

[user 3172]

fixing it is not a simple matter of replacing the 32A CB in the MCU with a 40A CB. The whole circuit must be replaced to support a 40A load - new CB, new cabling.

Agreed, I am not going to just put a 40amp CB on a circuit not designed for 40amps but when installing a 32amp charger, no self respecting electrician is going to install a cable which is only just capable of handling 32amps continuous and protecting it with a 32amp CB just in case. That's a recipe for a meltdown disaster.

The cable is armoured 3 core 6mm2 which as far as I can trace from the relevant spec sheet is capable of handing

• Clipped direct 49Amps
  Cable tray 53Amps

PS If anyone thinks this is incorrect data please shout!!!

Since it's clipped and only 5m in length, that's a 49amp current capacity. But as I say, the charger is nominal 32amp anyway, it is never going to continuously draw much more than 32amps other than due to catastrophic component or wiring failure, in which case either of the 40amp CB or RCBO units should trip well before any cable starts to get remotely warm.

BTW, everything is working perfectly normally now. No problems charging, no CB trips and no warm cabling. Here's hoping that the problem is resolved for good.