Electrical wiring regulations – tricky to digest?

Mike Buchanan ,
26 Jul 2019

Mike Buchanan from Cambusmore Estate in Perthshire, takes us through some recent changes to electrical requirements. 

A new 18th edition of the electrical wiring regulations, known as BS 7671:2018, came into force in January 2019. Several revisions will affect members. There are around 5,000 house fires each year in Scotland and around 10% of these are due to the electric installation so there is a good case for continuing to raise standards. 

However I am disappointed that the regulations are full of acronyms which are unintelligible to non-electricians.  Some of the acronyms are even shortened versions of Latin words!  If you have not already, you will soon start to see recommendations appearing on electrical inspection certificates which are written in acronym soup. Hopefully the following will make it easier for Scottish Land & Estate members to digest this soup.

RCDs (Residual Current Devices)

RCDs are devices that compare the current going out on the live and the current returning on the neutral to see if they match. If not, the device will trip out. All new wiring should be fitted with RCDs from January this year (except for the exceptions of course!). Although retrofitting is not required by the wiring regulations, the new repairing standards for letting houses will require comprehensive RCD protection by 2024.  Why owner occupiers will still be allowed to electrocute themselves is a mystery to me!

Commonly a single RCD can be used to protect several circuits or individual RCBOs (simply RCDs and MCBs combined) can be used for each circuit. Modern residual current devices will usually trip out if they detect more than 30milliamps of inbalance for more than 30milliseconds.

SPDs (Surge Protection Devices)

An SPD is a device designed to protect the electrical installation against surges or spikes from either lightning or noisy machinery. Although not strictly compulsory, the latest regulations are worded in such a way that it is easier to fit one than to justify not fitting one in commercial premises. Nor are they compulsory in domestic premises but they are advised if there is a lot of valuable electrical equipment. 

Most SPDs provide a bypass path from live to neutral if there is an overly high incoming voltage. There are three classes of SPD;

Class 1 - used at the point of entry to a house if it is fed by overhead cables with a higher risk of lightning strikes.

Class 2 - used if fed by an underground cable. Commercial premises may need multiple SPDs protecting different zones.

Class 3 – surge protection which is built in to many multiway extension leads.

AFDDs (Arc Fault Detection Devices)

AFDDs are devices that look for the “stuttering” current that might arise from a faulty connection or some sorts of short circuit and tripp out before anything bursts into flames. They should not respond to arcing that may occur in power drills and some other devices.  

AFDDs are not compulsory but the regulations are written in such a way that it is perhaps as easy to fit them in new wiring as to risk assess why they should not be fitted. There is no requirement to retrofit them. AFDDs are fitted to individual circuits as opposed to CFDs which will usually be fitted to whole consumer units.  Unfortunately AFDDs are still quite expensive and having to fit them to every circuit makes this exercise very expensive.

Consumer Units

Consumer units must be made of non-flammable material such as steel. This requirement does not need to be retrofitted to existing installations so old PVC (Polyvinyl chloride aka plastic) boxes may be retained at least for now.

Consumer units have always been required to have no holes in their walls big enough to allow inquisitive fingers to get inside. The standard is IP2X (or no 12mm holes) on the bottom or sides and for the top surface  IP4X (no 1mm holes).

Interlocked sockets

The round blue sockets typically used for caravans or outside machinery now require to be “interlocked” so that they cannot become live until a plug is fully in place. Again, this requirement is not retrospective.  

Halogen bulbs

Since September 2018, a Euro regulation has prohibited the import or manufacture of old low efficiency Tungsten and Halogen bulbs, but existing stocks can still be sold and fitted. Modern LEDs both consume less power and are much safer as they don’t run so hot. 

Smoke alarms

It is now acceptable for smoke alarms to be battery powered so long as they are tamper proof to prevent tenants removing batteries (tenants often do not like the warning beeps when the battery is running low).   Also smoke alarms had to be interlinked with hard wires but this can now be achieved wirelessly. Carbon Monoxide (CO) alarms have never required interlinking, but are required in every room containing a combustion device or through which a flue passes.

There’s lots to digest with these new regulations but hopefully this blog has made the acronym soup more palatable.


If SL&E Members could fit mains 'smoke' alarms fitted with NiCad batteries, it means that the batteries never need to be changed.

Once the NiCad batteries are fully charged, the 'smoke' alarms remain fully functional for 18 months after the mains electricity supply has been switched off.

By 'smoke' alarms, I mean heat and Carbon Monoxide detectors as well.