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.

RapidTables Kilowatts to amps calculator

  • 2
    \$\begingroup\$ What is your actual line voltage? \$\endgroup\$
    – R Drast
    Aug 1, 2018 at 9:35
  • \$\begingroup\$ @RDrast Using our ChargeCheck in the EV pedestal, and then testing the voltage on the UK socket, I get 235V. I have no [safe/legal] way of measuring the 3-phase line-line voltage \$\endgroup\$
    – oobayly
    Aug 1, 2018 at 10:02
  • 1
    \$\begingroup\$ Then you need to recheck your formulas. 13000 / (sqrt(3) * 235) is 31.9 Amps. \$\endgroup\$
    – R Drast
    Aug 1, 2018 at 10:15
  • \$\begingroup\$ @RDrast But if 235 is the Line-Neutral voltage, then the Line-Line voltage is 407? Using the rapid tables calculator (link above) I get the same Amps result using either. If I flip the voltages then I get two vastly differing values... \$\endgroup\$
    – oobayly
    Aug 1, 2018 at 10:47
  • \$\begingroup\$ @RDrast That is probably a few minutes until thermal trip with the current heatwave in europe. Breaker will be warm to the touch. \$\endgroup\$
    – Jeroen3
    Aug 1, 2018 at 11:08

2 Answers 2


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...


Accelev V2 manual indicates 1 phase = 3.3kW and 2 phase of 3 = 6.6kW

enter image description here

Who specified/selected the Rolec? Can they get it modified?

  • \$\begingroup\$ The company owner. As it turns out, we spoke to our sparkies and rotated the phases on one side of each pedestal. This way two single phase cars can charge as they're drawing current through L1 & L2, not just L1. \$\endgroup\$
    – oobayly
    Sep 18, 2019 at 17:23

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