Plug & play solar module from the Netherlands.

[Oliver90owner]

Of course, there is little problem if your house is wired radially rather than a ring main power circuit. The residual voltage problem, after removing a plug, can still occur.

UK wiring regulations try to be idiot-proof - because there are lots of them about!

Lots of houses on the continent are apparently wired radially?

[Stinsy]

The UK is unique in using ring final circuits. For the time period (1940s) they were perfect. They are economical on use of copper and foresaw the proliferation of electronic devices. Ring final circuits have a LOT of downsides, some of which are overcome by the fuse in the BS1363 plug and wiring regs that are far "stricter" than other countries. However none of this overcomes the primary weakness of ring final circuits: You have wiring rated at 20A protected by a 32A overcurrent protective device, in the (very common) event that a break in the ring occurs, the user would see no symptoms but the wiring would be overheating and you could not expect the MCB to trip. A solar generator connected to such a circuit would grossly aggravate an already sub-optimal situation and (probably) burn your house down.

Hence you are not permitted to connect a solar generator to an existing final circuit (ring or radial) unless you also comply with a whole bunch of other requirements, one of which is that the solar generator cannot be connected by a plug.

There is no reason for ring final circuits to be installed in new installations other than "tradition". But new builds and extensions up and down the country being built today are having ring final circuits installed as we speak. While I support the IET in its reluctance to proscribe things completely and rather suggest what is required if you are to do something, they really should add wording along the lines of radial circuits being the first choice.

[Oliver90owner]

Thanks for that, Stinsy.

However I’m not sure how a radial circuit is wired - like do these radials, which have multiple outlets along their length (I should really check this out on a decent website), use progressively thinner conductors further from the consumer unit?

My house has power ring circuits and I can clearly see how it could be overloaded by adding extra power beyond the circuit breaker, so that is all I really need to understand for safely.

Adding a few extra Watts (like one of those panels) would unlikely cause a fire - but the regs have to cover any and every scenario.

Presumably any solar on a radial circuit connected at the end of that radial line should be safe? Unless someone adds a large array!

[Stinsy]

A radial circuit is simply wired from one socket to the next, each intermediate socket having a "loop in" and "loop out, with an "end of line" having only a "loop in". Typically the same wire is used for the entire circuit, but a thicker wire might be used to the first socket if it is a very long run to keep the voltage drop under control, but the calcs get complicated if you do that. Typically a sockets radial would be 20A wired in 2.5 T+E or 32A wired in 4mm T+E if it is for a kitchen/utility room.

Adding solar to a radial isn't "safe" but it is safer than adding to a ring final because a ring final could already be dangerously overloaded due to an undiagnosed broken ring. The regs make no distinction between ring and radial where adding solar to an existing circuit is concerned, the same rules apply. However radials being common on the continent and rings being common in the UK might be the reason they're allowed to plug micro solar devices in and we aren't.

The regs make no differentiation but 1A (230W) makes little difference to anything whereas 10A (2300W) could be the difference between burning your house down or not.

However unless there is a very compelling reason, you should just use a dedicated circuit to the solar...