Why you must not backfeed a house from a socket (myth-busting safety)

The shortcut people reach for — and why it kills

The tempting idea is a lead with a plug on both ends: one end into the generator or V2L adapter, the other into a socket in the house, to 'push' power back through the ring or radial into the rest of the board. It is widely called a 'suicide cable', and the name is earned. There is no safe version of it.

• Exposed live pins. While one end is energised, the pins at the *other* end are live and exposed — a direct contact, electrocution and fire hazard the moment a person or pet reaches the open plug.
• No changeover, so it can back-feed the grid. A socket feed has nothing to disconnect the mains. If the source can reach the incoming supply, it energises the network outside the house — including conductors a linesman may be working on believing the line is dead.
• No earth reference. A floating V2L output fed this way has no neutral-earth bond, so there is nothing for an RCD to operate against. It can pass a plug-in socket tester and still leave the installation unprotected — the dangerous 'looks fine' case.
• Gross overload risk. The plug, the socket and the final-circuit cable are sized to *take* power from the board, not to carry the whole installation's load back through one 13 A accessory.

Beyond BS 7671, the network operator's own connection rules (the ENA Engineering Recommendations, e.g. G98/G99 for small generators) prohibit connecting a source to the public network without the proper protection and agreement. The exact recommendation locators are referenced here in principle only.

Why a 'socket tester says it's fine' is a trap

A plug-in socket tester checks that line, neutral and earth are present and in the right places. It does not confirm that the earth has a low-impedance return path, nor that an RCD has a reference to operate. A floating V2L output — no internal neutral-earth bond — can light a socket tester's 'correct' pattern while offering no fault protection at all. The protection only exists once a single neutral-earth bond is made at the source, and that is a designed, tested arrangement, not something a socket lead provides.

It is also notifiable work — not a DIY job

The lawful way to feed a house from a backup source involves fixed wiring: an inlet, a changeover and usually a consumer-unit alteration. In England that is notifiable under Part P of the Building Regulations, which means it must be designed, installed, tested and either certified by a registered competent person or signed off by building control. A plug-to-plug lead is an attempt to avoid exactly that — and avoids the protection it provides.

Vehicle manufacturers reinforce the point from the other direction: they warn against back-feeding fixed wiring from a V2L outlet and do not sanction wiring the output into a home's fixed installation. Treat the V2L socket as an outlet for appliances, not as a feed-in point for the house.

The correct route instead

If you want a backup or load-shifting feed from a generator or an EV's V2L output, the source connects through a fixed inlet — a proper inlet socket on the building, wired as a circuit — into a break-before-make interlocked changeover. The changeover guarantees the house is connected to *either* the grid *or* the source, never both, so it cannot back-feed the network or parallel the supply. The floating output is then given exactly one earth reference — by making it TT in a separate outbuilding, or by an isolation transformer inside the dwelling — so an RCD has something to operate against.

A break-before-make changeover also keeps most domestic V2L out of the paralleling regime — there is never a moment when both sources are connected together.

The full power-and-control and earthing design — interlocked contactors, the TT-outbuilding route and the indoor isolation-transformer route — is covered in the cornerstone guide and the changeover and earthing pages. The single rule for this page is simpler: the source never reaches the house through a socket.