Not sure I fully agree with Wiring Matters > Years > 2025 > 107 - September 2025

Sergio Fernandez said:

However the dual pole switch shown in the example lacks a lock off/isolation mechanism. 

I hear this, but I'm not sure I fully agree there's an issue for the 'local switch' or 'local isolator' situation.

BS 7671 does not fully agree with the perspective that locking off is a requirement either, and therefore it would not be appropriate to produce a requirement from thin air when it's specifically covered in BS 7671. Specifically, there is not always a need to 'lock off' for EAWR (for example, if you are in control of the point of 'isolation' for equipment made dead throughout the work activity ... BS 7671 also acknowledges this, see Regulation 462.3 (3rd bullet example).

Of course, you can apply more than one bullet of the note of Regulation 462.3 ... and they are only examples.

Sergio Fernandez said:

If the switch conforms to another part of BS EN 60669 in addition to BS EN 60669-2-4, it will be suitable for isolation, BUT it should be marked as above.

Which in hindsight could/should have been included in the original article.  The suggested replacement SHOULD BE NO LESS SAFE THAN THE ORIGINAL.  The original had 3 functions, act as a switch, contained a fuse for safety and was a point of isolation and lock off/out.  I can understand losing one of the 3 functions/features but removing 2 is unreasonable.  

Why? See above regarding BS 7671 requirements and why this is acceptable. The article could have said a lot of things about product standards for isolators, but that wasn't the purpose of the article.

Sergio Fernandez said:

Furthermore it would probably be beneficial if this is added to BS7671 and also the OnSite guide.  Thus helping future electricians who MAY encounter this in NEW installs or in installs that are 30 plus years OLD.  The UK nominal mains voltage was officially changed from 240V to 230V in 1994 to harmonize with European standards, though in practice the supply voltage often remains closer to the old 240V standard.

Agreed regarding the On-Site Guide and other guidance ... watch this space .  I'm not sure it would be seen as "too much detail" for BS 7671, and there'd perhaps be a question as to where it goes.

I'm very aware it was common practice 'back in the day' (i.e. up to 1980s) to use a 'robust' FCU ... but those old FCUs were not made to BS 1363! BS 1363 didn't include requirements for FCUs until 1995. (Perhaps that could have been stated in the article?)

(For nostalgia's sake, there are some images of the older products on the 'on-line museum' at this web-site: https://flameport.com/electric_museum/index.cs4)

Sergio Fernandez said:

The purpose of these discussions/debates is to make the industry safer for the benefit of everyone.  In my eyes healthy debate amongst engineers is a way of making things better.  This is akin to having a peer review.

Agreed. Good discussion/debate.

mapj1 said:

Fused spurs only make sense when the supply (dedicated or shared with others), is of a higher rating - e.g a 32A ring.

Agreed!

Whilst a BS 1363 device would not be my first choice, I would not prohibit the use of one.

I do not know how efficient immersion heaters are, but given that almost all the energy is released into the tank, it should be pretty good.

Assuming a supply at 10 ºC, a thermostat setting of 60 ºC, and 100% efficiency, 3 kW for an hour will heat 220 l of water, which is enough for 2 baths, or at least 4 showers. So where does the prolonged load come from?

If the immersion is drawing current for a significant proportion of the day, the leccy bill is going to be a bit eye-watering.

BS 1363 devices may be rated at 13 A, but they are type-tested at 14.0 V ± 0.4 V with a maximum ambient temperature of 25 ºC and maximum allowable temperature rise of 52 K over 4 - 8 hours.

If the cylinder is adequately lagged, the cupboard ambient temperature should not be significantly above room temperature.

So what will a customer think?  I can plug in a 3 kW heater all day, so why not the immersion? If it says 13 A on the tin, it should be suitable for 13 A.

Well indeed, and double sockets that dont handle 2 full 3kW loads are a recurring source of surprise to hapless users- usually tumble dryer and washing machine sharing.

There is I think, an engineering argument that the passing bare minimum BS136x   13A plug/socket and 13A fused spur are all a bit under rated for modern life, what with overnight full loads such as EV charging and so on. (and modern houses are hotter to start with. )

But, rather like the car with enough petrol to put the driver into orbit stored in a single skin tin can tank a few inches off the road surface, the chance of changing the established practice now is probably almost nil.

Equally if you invented it now it would probably not get approval. I suspect the "13A' would not either, and might end up being nearer 10A .

The  European 16a Shucko plug fares no better, and also cooks with a long term load but is equally too long established, and I guess there is no appetite for inventing a peak current 20A domestic type thing that is utterly incompatible.

(Ignoring the fact that actually the ever interesting Brazilians did just that back in 2007, and their 'new standard' (NBR 14136) plugs  allow 20A on 4.8mm dia pins or 10A on  4mm dia pins, in a socket that may be supplied by either 110v, or 220v or 110-0-110 split phase, depending on where in the country you are. They also seem to have quite a few cooked looking sockets and a light sprinkling of every flavour of connector imaginable, so let's not copy that, shall we.)

Mike.

Are you suggesting that BS136x possibly needs an update or a revision 2?

mapj1 said:

13A fused spur are all a bit under rated for modern life, what with overnight full loads such as EV charging and so on. (and modern houses are hotter to start with.

Maybe a new product standard is needed?

Should we consider making the average UK domestic dwelling be now run in 4mm2 CSA rather than the standard 2.5mm2 CSA T&E?  Some people say a domestic Ring/Ring Final or Radial should be 2.5mm2 CSA because it has always been that way.  However the cost of a drum of 2.5 vs 4mm T&E will be a limiting factor

While this is fine for an Electrician to isolate at the CU what would a Plumber or Heating engineer make of it?  Are they competent to Lock Off and isolate at the consumer unit?  Should a plumber or heating engineer even touch the customers consumer unit?

Alan B said:

On the suggestion of a rotary isolator I think it just looks out of place inside a home and I would only use one if essential for safety requirements.

Rotary isolators do look industrial and the average person in a dwelling will find them unsightly

mapj1 said:

tumble dryer and washing machine sharing

Kettle and toaster every morning. :-)

In my opinion the set of BS136x standards need thoroughly revising to introduce a greater factor of safety in the design of plugs, sockets, accessories to ensure they are fit for purpose across the full range of domestic applications, backed up by a more rigorous set of tests to ensure the devices being placed on the market meet those standards, not just when brand new and shiny, but after some surface oxidation/corrosion/wear-and-tear, to prove they are robust across their likely operating life.

In 2025 we should not be having to discuss topics like whether a 13A load can be used with a 13A accessory in a common household application, it should just work and work safely. But this is just one example of a broader problem, similar issues occur with long-duration loads on 13A sockets where it has become almost accepted belief that typical 13A plug/socket combinations are not suitable for supplying 13A for any significant length of time, hence the anxiety about using EV granny chargers or using high powered plug in heaters for any duration. 

More significantly, why do we still have house fires, injuries and even fatalities from overloaded multiway socket/plug adapters, when electrical protection devices are now both readily available and cheap, capable of ensuring these devices are always safe regardless of how they are used or abused? 

Sergio Fernandez said:

Personally I think Rotary Isolator would be far better than 20 amp Double-pole switch shown Fig 2 as this allows for isolation and LockOff/LockOut

Should we also replace light switches with rotary isolators?  I have replaced many lamps over the years, but have never yet needed to change the immersion heater.

mapj1 said:

Brazilians

Here are a couple of Brasilian electrical adapters which just happen to live in a desk drawer.

As you can see, the larger one, which can accommodate three different types of plug (but not all at the same time), is rated at 20 A/250 V for the largest pins, so what have we got to worry about?

TurboGen said:

In 2025 we should not be having to discuss topics like whether a 13A load can be used with a 13A accessory in a common household application, it should just work and work safely.

I entirely agree.

TurboGen said:

In my opinion the set of BS136x standards need thoroughly revising to introduce a greater factor of safety in the design of plugs, sockets, accessories

Now I don't agree.

As with all standards, BS 1363 specifies a set of limits. So if a plug (etc.) experiences a greater temperature rise than 52 K, it has failed the type test.

I suspect that the better quality BS 1363 devices will barely get warm.

As Graham has pointed out, the fuse itself will heat up, but the pins have a considerably higher CSA. Granted the conductivity of brass is only about half of that of copper, but I cannot see their contributing much to any warming.

It seems to me that the fuse holder is probably the weakest link on the basis that the metal is relatively thin, it relies on spring pressure alone, and oxidization could increase the resistance.