Adding a 7 kW EV charger to an existing 60 A single-phase house supply

Do the arithmetic first. The charger draws 7 000 / 220 ≈ 31.8 A, call it 32 A. Against a 60 A main fuse, with an existing recorded maximum demand of 47 A, the total is 47 + 32 = 79 A before any new base load is added. That is a 32% overload of the supply. The main fuse will not blow immediately - fuses are thermal and take time - but sustained overload at that level will cause it to fail, and the utility will not treat repeated fuse failures as a coincidence. It is not acceptable.

Diversity does not solve this. The 47 A peak already includes the shower and the air-conditioner. Adding a load that runs continuously for hours at 32 A on top of an evening peak that is already at 78% of the supply capacity leaves no margin. A charger is a long-duration load, not an intermittent appliance, so the usual diversified maximum-demand approach is the wrong tool.

Options:

1. Load management. Fit a dynamic load-management device with a current transformer on the supply tails that continuously reduces the charger's output so total demand stays below a set threshold (say 55 A). This is the lowest-cost option and allows overnight charging at full rate in practice, because the shower and air-conditioner are usually off then. It must be a listed system compatible with the charger, not an improvised contactor.
2. Apply for a supply upgrade to a larger single-phase or a three-phase service, and design the installation for the upgraded capacity.
3. Reduce the charger rating to 3.5 kW (16 A). This alone gives 47 + 16 = 63 A, still marginal, so it needs load management as well.
4. Interlock the charger with the shower so the two cannot run together. This works technically but is unpopular with the occupier and easy to defeat, so it is the last choice.

I would present options 1 and 2 to the owner, with option 1 as the practical solution and option 2 where the owner expects full-rate charging at any time.

The RCD type matters because of what the vehicle does to the residual current.

A vehicle charger is not a resistive appliance. The onboard charger rectifies the AC supply, and a fault in the vehicle can produce a smooth or pulsating DC residual current. A Type AC RCD is designed only for sinusoidal AC residual current and can be blinded by DC - the core saturates and the device fails to operate at its rated residual current, even though the test button still works. A Type A device handles pulsating DC but not smooth DC above about 6 mA.

The compliant arrangements are:

• A Type B RCD, which detects DC, pulsating DC and AC residual current; or
• A Type A RCD used together with a residual direct current detecting device (RDC-DD) built into or installed with the charger that disconnects the supply if the DC residual current exceeds 6 mA, as required by the EV charging product standard.

In addition, the final circuit requires 30 mA additional protection for the socket outlet or the charging point, and the device must be selected and installed in accordance with the charger manufacturer's instructions - which often specify the type and rating precisely.

Practical points:

• A 40 A MCB or RCBO with the correct characteristic and a Type A + 6 mA DC detection arrangement is a typical solution where the charger has built-in DC detection.
• Test the RCD with an instrument capable of the appropriate residual current waveform; a standard AC test does not prove a Type A or Type B device will operate on a DC-offset fault.
• Do not rely on the charger's own self-test as the only verification - record the trip times on the certificate.

A Type AC device here would be a false economy: it would pass a push-button test and fail in the only situation that matters.

Cable sizing. The charger is a continuous load of 32 A, so the cable must carry 32 A after every correction factor is applied - there is no diversity to lean on.

• A 6 mm² PVC-insulated conductor in conduit has a tabulated capacity around 32 A, which is exactly at the limit with no margin for a warm wall, grouping with other circuits in the conduit, or a slightly higher ambient. That is not a sound selection for a continuous load.
• A 10 mm² conductor gives roughly 43 A in the same method, a sensible margin.
• Volt drop confirms it: for 6 mm² at 7.3 mV/A/m, Vd = (7.3 × 32 × 30) / 1000 ≈ 7.0 V, or 3.2% of 220 V - inside the 4% limit but using most of it. For 10 mm² at 4.4 mV/A/m, Vd ≈ 4.2 V, or 1.9%, leaving room for any additional drop within the installation.

I would specify 10 mm² and protect it with a 40 A device, confirming the selected device rating against the tabulated capacity for the actual installation method.

TN-C-S earthing. With a combined neutral and earth, a broken PEN conductor on the overhead line can raise the earth potential at the charging point, and the vehicle body is connected to that earth while a person standing on the ground may be touching it. The charging equipment therefore needs one of:

• a protective conductor disconnection device that monitors the voltage between line, neutral and earth and disconnects both line and neutral if the PEN is lost and the voltage moves outside the permitted window; or
• conversion of the charging point to a TT arrangement with its own earth electrode and a 30 mA RCD, which is the usual fallback where the equipment does not provide PEN fault detection.

The metal water pipe already bonded to the main earthing terminal must stay bonded, and the charger's earth conductor must run back to the consumer unit - never to a local rod combined with the PME earth. Record the earth loop impedance and the RCD trip times at the charging point before handover.