Guidance for plug in solar for Electricians

The Department for Energy Security and Net Zero (2026) have produced a product specification (Plug-in Solar Device Interim Product Specification Version 2.0, July 2026) which outlines the requirements for the PV panels and the respective electrical installation. It's probably a good starting place to have a review of that document.

https://assets.publishing.service.gov.uk/media/6a60a03c47af652afa0c89f5/plug-in-solar-final-_interim-product-specification.pdf for those that haven't stumbled on it already.

   - Andy.

 Page 25: Anti-islanding and termination of power supply
An external resistance of greater than 2000 Ω must be applied across the plug pins of the
mains plug within 40 s after disconnection - this delay allows the inverter to detect loss of
mains supply. 

Is that really 40 seconds, or should it be 40ms?

That does not make sense. Why a resistor? Surely with a loss of supply the anti islanding should kick in and turn off the inverter? 

JP

When I was at college doing the C&G2360 Part Two we had a workshop lecturer who did his apprenticeship in a carpet factory and then worked for the MEB and the companies that took over as the local DNO until he retired and was persuaded to come and teach us practical skills in the college workshop.

He advised us that having carried out the safe isolation procedures to prove an installation or circuit “dead” that we should then put our insulated long nose pliers or something similar across the terminals as a final test, as to quote him “it's better to sacrifice your long nose pliers than your fingers”.

The resistor in the plug in PV to prove dead is a test as simple and as unsophisticated as shoving your long nose pliers across the pins of the plug in PV 13-amp plug when you pull it out of the socket, it should not be necessary, but it’s a very good idea as it may stop you or someone else getting injured.

Forty seconds.

assets.publishing.service.gov.uk/.../plug-in-solar-final-_interim-product-specification.pdf

Yes, that's the document I quoted from. Where did 40 seconds come from? It seems an awfully long time when we typically think of disconnection within 5 seconds.

But , reading it again, it requires the resistor to be in place 40 s AFTER disconnection. So it will disconnect, then within 40 s a resistor will bridge the terminals so there is no chance of any charged components backfeeding the plug.

Yes, that's the document I quoted from. Where did 40 seconds come from? It seems an awfully long time when we typically think of disconnection within 5 seconds.

But , reading it again, it requires the resistor to be in place 40 s AFTER disconnection. So it will disconnect, then within 40 s a resistor will bridge the terminals so there is no chance of any charged components backfeeding the plug.