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Two Electric Cars And One Charge Point
Both cars need charging overnight and you are swapping the lead over at two in the morning.
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What's happening?
The obvious answer is a second charge point, and the obvious obstacle is the same service cutout fuse that limited the first one. Two units at 7.4kW is around 64A of charging load on a supply that is often 60A, 80A or 100A in total, so unmanaged pairs are rarely acceptable. What makes it work is load sharing: the two charge points are commissioned to know about each other and about the house, and they split whatever current is spare — both at half rate, or one at full rate while the other idles, depending on how it is set. A twin-socket single unit does the same thing in one enclosure and only needs one cable run, which is usually the cheaper answer where both cars park close together. The design decision that matters is not which unit to buy but how the available current is divided, and that has to be set at commissioning rather than assumed.
What usually causes it?
- A second electric car joining a household whose supply was assessed for one
- Two units installed separately by different firms, neither aware of the other's load
- A twin-socket unit fitted but never configured to share, so it derates unpredictably
- Parking positions too far apart for one unit and two leads to serve both cars
- A consumer unit with no spare way for a second 32A circuit
- A household that also added a heat pump, leaving far less headroom than the first survey assumed
Is it dangerous?
Two full-rate charge points on a supply that cannot carry them is the same overload risk as the first install, doubled — and it can sit hidden for months because the cars rarely draw full current at the same moment until one night they do. The failure is the service fuse going, which puts the whole house out and needs the network operator to attend. Load sharing is the safety measure, not an optimisation.
Can I fix it myself?
Work out what you actually need before adding hardware. Two cars doing modest daily mileage often charge fine on one unit at half the rate each, using the car's own schedule to take turns overnight. Check whether your existing unit is already one of a pair-capable range, and whether it supports two sockets. Note the service cutout rating again — if a heat pump or an electric shower has been added since the first install, the assessment has changed.
When should you call an EV charger installer?
Call an installer before ordering a second unit. They repeat the maximum demand assessment with both charge points in it, decide between a second unit with load sharing and a twin-socket unit, and notify the network operator of the additional load. If your two existing units were installed by different firms and are not sharing, that is a commissioning job worth doing regardless.
What will the EV charger installer actually do?
- Reassess maximum demand with two charge points and any load added since the first install
- Choose between a second wall unit with load sharing and a single twin-socket unit
- Commission the load-sharing arrangement so the pair never exceeds the supply's headroom
- Add a second circuit at the consumer unit, or uprate the board where there is no spare way
- Notify the distribution network operator of the increased load and any load-managed arrangement
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