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Can I use an extension lead with plug-in solar?
No. Plug the kit directly into a fixed wall socket: no extension leads, cable reels or adaptors of any kind. Check your setup against the rules, then see what the kit’s own cable does.
- extension leads, reels or adaptors allowed
- 0
- current from an 800 W inverter at 230 V
- 3.48 A
- G98 over-voltage trip, stage 1
- 262.2 V
Kit cable into a wall socket
This is how a plug-in kit must connect
The kit’s moulded plug goes straight into a fixed wall socket on a socket circuit. Outdoors, the socket must be rated IP55 or better.
the plug supplied ... shall conform to British Standard (BS) 1363-1, and is plugged directly into a fixed BS 1363-2 socket
Explanatory Memorandum to SI 2026/848, para 5.1The device is designed to be connected to a UK mains socket solely by the manufacturer-supplied standard plug.
DESNZ Interim Product Specification §1
The physics of this cable
- Current
- 3.33 A
- Cord rated 10 A (33% used)
- Voltage rise
- 0.68 V
- 0.3% of the socket voltage
- Inverter sees
- 240.7 V
- 21.5 V below its 262.2 V trip
- Lost as heat
- 2.3 W
- 0.3% of output, about 2 kWh a year
The cable carries the current well within its rating. The voltage rise is small.
Resistance of flexible copper conductors at 30 °C, out on live and back on neutral. Physics only: it doesn’t make a connection allowed.
The rules
What you can plug the kit into
From the DESNZ Interim Product Specification, which the law (SI 2026/848) makes the legal test for plug-in solar in Great Britain.
6 of the 8 connections are ruled out. The socket itself must be a fixed BS 1363-2 socket on a socket circuit (not a lighting circuit, or a spur feeding a cooker or boiler), rated IP55 or better outdoors. See sockets and wiring.
The physics
Voltage rise in the kit’s cable at 800 W
How many volts the cable adds between the socket (we assume 245 V, within the legal range of up to 253 V) and the inverter, and the heat it wastes. This is physics only, to help you judge a cable the kit’s maker offers. It doesn’t make an extension lead allowed.
| Conductor | 2 m | 5 m | 10 m | 20 m |
|---|---|---|---|---|
| 0.75 mm² rated 6 A | +0.35 V1.2 W as heat | +0.88 V2.9 W as heat | +1.76 V5.8 W as heat | +3.53 V11.5 W as heat |
| 1 mm² rated 10 A | +0.26 V0.9 W as heat | +0.66 V2.2 W as heat | +1.32 V4.3 W as heat | +2.65 V8.6 W as heat |
| 1.5 mm² rated 16 A | +0.18 V0.6 W as heat | +0.45 V1.5 W as heat | +0.90 V2.9 W as heat | +1.81 V5.9 W as heat |
| 2.5 mm² rated 25 A | +0.11 V0.4 W as heat | +0.27 V0.9 W as heat | +0.54 V1.8 W as heat | +1.08 V3.5 W as heat |
Current is the easy part. 800 W is about 3.48 A, within the rating of every cord size here. The rise is what matters: at 1.0 mm², every 16.3 m of cable adds about 1% to the voltage the inverter sees. If your socket already runs high, a long cable can take the inverter to its 262.2 V over-voltage setting, and it switches off.
Ratings are for a two-core flexible cord in free air. Cable wound on a reel or bundled up can’t shed its heat and carries less. Resistances are the maximum for flexible copper conductors at 20 °C, raised to 30 °C. The voltage figures assume the inverter puts out its full 800 W.
Extension leads and plug-in solar: questions
Can I use an extension lead with plug-in solar?
No. Plug the kit directly into a fixed wall socket. The DESNZ product specification says kit instructions must “clearly state that the use of extension cables, multi-way adaptors, RCD adaptors and travel adaptors are not permitted”, and the law describes the plug going “directly into a fixed BS 1363-2 socket”. Electricity North West and Electrical Safety First say the same, and it applies to outdoor and heavy-duty leads and cable reels too.
My socket is too far from where the panels go. What can I do?
Move the kit closer to a socket, use a longer connection cable that the kit’s maker sells or approves, or have a registered electrician fit a new socket (IP55 or better if it’s outdoors). Fitting a socket is electrical installation work, not part of the plug-in rules.
Can I plug the kit into a double socket with something else in the other half?
Yes. A double wall socket is two fixed sockets. The rule is about plug-in adaptors and gang extension leads, not about using the other half of a fixed double socket.
Is 800 W a lot of current for a cable?
No. 800 W at 230 V is about 3.48 A, well within the rating of the cords kits are sold with. The issue with extension leads isn’t mainly current: the rules ban them outright, and a long, thin cable also raises the voltage the inverter sees and wastes a little power as heat.
Why would the inverter switch off with a long cable?
An exporting inverter has to push its voltage slightly above the socket’s to send current back. The cable’s resistance adds to that. On a 245 V socket, 10 m of 1.0 mm² cable adds about 1.3 V. If the voltage at the inverter reaches its over-voltage setting (262.2 V for G98 stage 1), it disconnects to protect the network.
Can I use a plug-in RCD with plug-in solar?
No. Plug-in RCD adaptors are banned by the specification. It asks you to check your consumer unit has modern residual current protection (RCBOs), and to have an electrician check and upgrade older installations.
Sources
- DESNZ Plug-in Solar Device Interim Product Specification, v2.0 (July 2026): §1, §6.1, §6.2.3, §8.3.2
- Explanatory Memorandum to SI 2026/848, para 5.1
- SI 2026/848: Plugs and Sockets etc. (Safety) Regulations 1994 and ESQCR 2002 (Amendment) Regulations 2026
- Electrical Safety First: plug-in solar panels
- Electricity North West: plug-in solar (“the use of extension cables is not permitted”)
- BS 7671:2018+A4:2026, Appendix 4, Table 4F3A: current ratings of flexible cords (BSI/IET, paywalled)
- IEC 60228:2023, maximum resistance of class 5 flexible copper conductors (paywalled; public preview)
- EREC G98 Table 2: stage 1 over-voltage 262.2 V for 1.0 s (Distribution Code consultation pack, DCRP/MP/26/02)
- ESQCR 2002 regulation 27: supply voltage 230 V, +10% / −6%
Free tools
Plan the rest of your setup
- Compliance checkerIs this kit on the ENA register?
- Compatibility checkerPanels, inverter and plug against the rules
- DNO finderYour network operator, by postcode or MPAN
- Real-world yieldsWhat owners’ kits actually make
- Report your yieldShare what your kit really makes
- CalculatorOutput, savings and payback for your home