We have found that our two EVs are tripping the 32A MCBs in our Consumer Unit, but from my basic knowledge the 2*6.6kW chargers on UK 3-phase should only draw about 19A.
I've measured the power consumption by timing the meter disk1 and each car draws about 6kW (the two at the same time on two different circuits draw a total of 13kW).
\$ I = \frac {P} {3 \times V_{LN}}
= \frac {P} {\sqrt{3} \times V_{LL}}
= \frac {13kW} {3 \times 230V}
= \frac {13kW} {\sqrt{3} \times 400V}
= 18.8A \$
I can't believe that EV charging has a power factor of 0.59, but another question – MCB of desired rating – alluded to MCBs having low tolerances (20A MCB tripping between 18A to 25A). Is this correct?
The charging posts we have are two 2x22kW Rolec Autocharge posts. Our director likes to buy big (futureproofing being his motto)… but because of lack of total capacity into our building our electricians limited the supply to the posts to 22kW each (using a 32A MCB). Still, our current 13kW usage falls well short.
1 Meter is 60 revs / kWh. Measure time for 5 revolutions with no EV charging load, and use that as our base usage (5 rev in 20s = 15kW). Then attach one EV, wait for load to settle (5 rev in 14s = 21kW). Difference is 6kW.
Best Answer
So, it turns out that one of the cars only charges on single phase. I checked the IEC 62196 Type 2 cable and it only has 5 of the 7 pins present (most importantly it's missing L2 & L3).
My interpretation of this is: The car is drawing 6.6kW over a single 230V phase, or 29A. Which means that when it's combined with another vehicle, the L1 pole of the 3-phase MCB easily exceeds 32A, causing it to trip.
Please feel free to correct any invalid assumptions...