Why did the UK change from round pin to square pin plugs?

People stacking round pin adaptors was not unusual at all. The results were gross overload & gross misfusing. Hence square adaptors were specifically designed to not stack. Power strips did not exist wheb BS1363 was drawn up in 47.

I've not experienced dc mains, but there was plenty of it about with appliances to suit. DC motors tend to be less reliable. Universal motors run on either. Live chassis radios run on either. DC does require beefier switches than ac, as arcs don't self extinguish.

I still don't know what you mean by 'designed not to stack'. The typical 13A adapter had outlets at the front and on each side. There was nothing to prevent a second adapter being inserted at the front making five outlets or even a third adapter, making seven outlets.

I know power strips did not exist then but exist now. Hence my comment that the question is now academic.

Heating is normally regarded as a fixed load and wired separately. Same as the UK. If you tried to heat an entire house with fan heaters plugged into a ring, you'd be in trouble too.

But just why would you want to?

Much as I think the UK system OK, I'd not dream of using it in a French (etc) house. For obvious reasons.

It's interesting that the panel is often situated in a very easy to get at place. Suggesting trips are commonplace.

In fact trips are not commonplace in the USA or Canada.

If you play with them you'll learn something.

There are various arrangements of three-socket adapters: some have the outlets on the sides and the rear (opposite side to pins), while some have outlets on the sides and the top or bottom, or the rear, top and one side. With a mixture of the two types, you can stack them almost indefinitely - I think: I'd need to try it!

I didn't know that square-pin adapters were explictly designed *not* to stack, though I can fully understand why you wouldn't want to stack them if it meant overloading the wall socket. If I use an adaptor, it tends to be because I'm too lazy to go get an socket bar from my cupboard of cables. And I only use extension bars/adapters for the plethora of low-power devices such as bedside lamps (LED, so low power), wall-warts, Alexas, laptop PSU/charger etc.

Anything high-powered (electric fire, hair-drier, washing machine, dishwasher) always goes in a wall socket of its own, without an extension bar.

I have a few wall sockets in one of our bedrooms that are covered by fitted bookshelves. I ran long cables with socket bars on the end, brought out to the edge of the shelves. I'm particularly careful not to overload those, because if the fuse in the plug that powers those socket bars fails, it's a

You live there, then? Aren't you Wodney under yet another alias?

Just why would you stick a breaker panel in the middle of a living room wall if you rarely needed to access it?

at least you halfway admit you don't know

it overloads the socket physically as well as sometimes electrically

Don't need to. We have this funky system called usenet where we can ask others in different countries about how often they see stuff like that happening.

Why do you believe that that is common there ? Have you lived there ?

What was fundamentally different about round-pin adapters compared with the variety of topologies of square-pin adapters which allowed stacking of round-pin adapters?

I've got a CE-marked (*) three-way square-pin adapter in front of me which has its sockets on the rear, top and left faces. I could in theory stack those indefinitely, plugging one adapter into the rear face of the one in front. I'd have two free sockets per adapter. OK, the lead coming out of the bottom of one plug might foul the top of the corresponding plug on the next adapter, but a thin twin-core lighting flex would be flexible enough to allow it. I haven't got another of the same type, but with a different one as the second adapter it's *just* possible with a thin lead:

(*) So *presumably* not a non-standards-compliant Asian clone. Maybe I'm wrong...

See the picture here:

A designer will decide how many sockets to provision on each circuit. If the anticipated load is high, then they may do more circuits with fewer sockets per circuit. In more commercial style installations it is not uncommon to make radials quite restricted in purpose for better discrimination (i.e. a fault in one only has limited and localised effects)

A design aim of a radial is that the circuit protective device provides both overload and fault protection for the whole circuit, and the current carrying capacity of the cable is equal or higher than that of the protective device trip current. So regardless of use or loading it will remain safe.

However it does have less flexibility and it is more likely that you will get nuisance trips due to overloading.

A spur is not the same thing as a radial - it usually implies an extension to a socket circuit where the extension is cabled such that it has a lower current handling capacity.

The term is usually used for ring circuits where you take a single cable branch away from the ring. For one socket (single or double) no additional fusing is required since the limitation of one socket prevents overload, and the circuit protective device will still handle fault protection (i.e. short circuit protection) for the single cable. If you need more than one socket, the the spur must be fused to protect the spur cable from overload.

You can also have a spur from a radial - although this is less common arrangement and typically applies only where using a "backbone" style of wiring - say running a core of 4mm^2 T&E protected by a 32A MCB along a route, and taking spurs from it in 2.5mm^2 cable for each socket. The MCB will provide overload and fault protection for the backbone, but only fault protection for the spurs.

Even if you only have one ring per storey, that gives enough capacity for 14kW of heating in many properties - which is a fair bit... (and more than some CH boilers)

Some were designed such that the new sockets were only on the top and sides of the adaptor, and the size of the adaptor's case was such that it would hit the wall if you tried to plug another of the same design into one of those side sockets.

Get back to us once you've played with a pile of them.

Yes, *some*. But not all. Unless the only truly standards-compliant ones are those that don't have a socket on the rear, opposite the pins, and all the rest are non-compliant (despite being CE-marked, as in the photo of the one that I posted earlier this evening).

For the avoidance of doubt, just because adaptors *can* be stacked, that doesn't mean they *should* be - even with all the loads being low-power wall-warts or bedside lamps (and so electrically OK) they will still exert a lot of twisting motion on the pins of the various adaptors and so could easily become partially unplugged - though with shrouded pins as all modern plugs should have, that's not a problem for little fingers touching the pins.

There is one really stupid place where I have to use an adaptor. We have a double-socket which has been placed very close to a decorative panel on top of a worktop. An ordinary plug has enough clearance for the cable not to foul the panel, but the wall-wart for our Alexa extends downwards (ie below the live and neutral pins) too far. So we have to use an adaptor as a stand-off so it is far enough away from the panel. Without this, the wall wart doesn't insert fully and there is a slight gap on the live/neutral pins. The electrician who fitted that socket (for the previous owners of the house) probably never envisaged huge wall-warts. I wonder what the limits are on the overhang of a wall-wart around the sides, given that they usually have a larger profile than a simple plug.