The Lemon Fool

While shopping for double sockets, and I noticed that MK offer double sockets with switches on the outside rather than next to each other on the inside (which appears to be the norm).

Other than the (to me) obvious "so you don't accidentally turn the other switch on or off", are the there any other uses for these sockets?
Has anybody got any real life experiences with reasons why "switches on the outside" were fitted or should have been fitted?

PochiSoldi

pochisoldi wrote:While shopping for double sockets, and I noticed that MK offer double sockets with switches on the outside rather than next to each other on the inside (which appears to be the norm).

Other than the (to me) obvious "so you don't accidentally turn the other switch on or off", are the there any other uses for these sockets?
Has anybody got any real life experiences with reasons why "switches on the outside" were fitted or should have been fitted?

PochiSoldi

While technically impossible to say, the double sockets that I have linked to are VERY different electrically.

https://www.electricpoint.com/mk-logic- ... white.html
(switches on the outside, but more important a different earthing arrangement)
https://www.electricpoint.com/mk-logic- ... white.html
(switches on the inside, but a standard earthing arrangement)

It could be a simple convention so that the electrical difference can be told at a glance.

This one also has a special earthing arrangement, though different from the first.
https://www.electricpoint.com/mk-logic- ... board.html
Again, switches on the outside.

pochisoldi wrote:Other than the (to me) obvious "so you don't accidentally turn the other switch on or off", are the there any other uses for these sockets?
Has anybody got any real life experiences with reasons why "switches on the outside" were fitted or should have been fitted?

One obvious scenario is that it makes the switches much more accessible if you have something bulky plugged into both sockets, like 3-way blocks or transformers.

Hallucigenia wrote:

pochisoldi wrote:Other than the (to me) obvious "so you don't accidentally turn the other switch on or off", are the there any other uses for these sockets?
Has anybody got any real life experiences with reasons why "switches on the outside" were fitted or should have been fitted?

One obvious scenario is that it makes the switches much more accessible if you have something bulky plugged into both sockets, like 3-way blocks or transformers.

With the caveat that it makes it harder to plug bulky things in in the first place

pochisoldi wrote:While shopping for double sockets, and I noticed that MK offer double sockets with switches on the outside rather than next to each other on the inside (which appears to be the norm).

Other than the (to me) obvious "so you don't accidentally turn the other switch on or off", are the there any other uses for these sockets?
Has anybody got any real life experiences with reasons why "switches on the outside" were fitted or should have been fitted?

PochiSoldi

See Approved Document M
volume 2 at https://www.gov.uk/government/publicati ... document-m which deals with accessibility in non-residential buildings. In particular, paragraph 4.29 states in the context of design considerations for switches, outlets and controls that

It is also an advantage if individual
switches on panels and on multiple socket
outlets are well separated, or in the form of
large touch plates, to avoid the inadvertent
selection of an adjacent control by visually
impaired people and people with limited
dexterity.

Positioning the switches on a switched double socket towards the outside edge meets the "well-separated" criterion.

modellingman

Urbandreamer wrote:While technically impossible to say, the double sockets that I have linked to are VERY different electrically.

Whilst not wanting to be combative, they are not really very different electrically. They are almost the same. They just have two Earths instead of one. If you leave linked the two Earth terminals they have the same function as conventional sockets as explained here.

I may be wrong but I think only plugs with special T shaped Earth pins will fit, thus continuing the two seperate Earths through into the equipment. Happy to be corrected on this though. C.

csearle wrote:

Urbandreamer wrote:While technically impossible to say, the double sockets that I have linked to are VERY different electrically.

Whilst not wanting to be combative, they are not really very different electrically. They are almost the same. They just have two Earths instead of one. If you leave linked the two Earth terminals they have the same function as conventional sockets as explained here.

I may be wrong but I think only plugs with special T shaped Earth pins will fit, thus continuing the two seperate Earths through into the equipment. Happy to be corrected on this though. C.

OK, it's not the socket that is electrically different, but how it's intended to be used.

There are entire books upon "earthing", because the word is used to mean many different things. Replacing the word with "bonding" only clarifies if you add extra terms, which could be done with the word earthing.

On the machines built where I worked the metal work was bonded using 10mm earth wires. This was not "protective" earthing the way that a domestic socket is earthed, but as a path for high frequency, low current, noise.
The main reason for the dimensions was not the current capacity (about 70A) but the circumference. Most of the current at these frequencies is carried in/on the surface.

Two wires have double the circumference and double the cross section. Also two wires must break to cause a safety fault. Hence the two terminals on one of the sockets that I linked.

Noise can also be carried where it isn't wanted by the earth wire. Hence the concept of a clean earth. This is a separate earth path.
The final link that I provided was to a clean earth double socket, without T shaped pin.

Re your own link, the "electrical" difference in that socket consists of a T shaped pin and markings. It's the electrical use that is different.

As I'm sure that you know, this sort of arrangement is only used if absolutely necessary to equipment function.

Urbandreamer wrote:The main reason for the dimensions was not the current capacity (about 70A) but the circumference. Most of the current at these frequencies is carried in/on the surface.

Wait, wait, what? I thought all current was carried in the fields around the wire. Enlighten me , please.

genou wrote:

Urbandreamer wrote:The main reason for the dimensions was not the current capacity (about 70A) but the circumference. Most of the current at these frequencies is carried in/on the surface.

Wait, wait, what? I thought all current was carried in the fields around the wire. Enlighten me , please.

At DC frequencies, current flows through the bulk of the conductor. As the frequency increases conductivity tends towards the surface.
https://www.britannica.com/science/skin-effect

This phenomenon restricts the current to a small part of the total cross-sectional area and so has the effect of increasing the resistance of the conductor.

50Hz is quite a low frequency. Motor control these days is usually in the KHz range.

Since you are obviously interested, here is some advise to reduce pitting in bearings etc caused by induced sparking.
https://www.est-aegis.com/wp-content/up ... _Paper.pdf

genou wrote:

Urbandreamer wrote:The main reason for the dimensions was not the current capacity (about 70A) but the circumference. Most of the current at these frequencies is carried in/on the surface.

Wait, wait, what? I thought all current was carried in the fields around the wire. Enlighten me , please.

It's energy that is carried in the fields around the wire. Energy flux is the Poynting vector.

In a vacuum the current is entirely inside the wire. Current requires charge carriers such as electrons and there are none in a vacuum. In practice there are few relevant charge carriers in any surrounding air or insulators, almost all the current will be in the wire. The restriction of the current to the surface of the wire is the skin effect.

(References to Wiki because they will almost certainly be more extensive and comprehensible than I could be in a reasonable time.)

9873210 wrote:

genou wrote:
Wait, wait, what? I thought all current was carried in the fields around the wire. Enlighten me , please.

It's energy that is carried in the fields around the wire.

That's the one. My bad.

Urbandreamer wrote: current flows through the bulk of the conductor.

This is where my brain hurts. I was brought up on the "water in a pipe" analogy, so "current flowing" takes me back to that. I later learned of its limitations. But other than electron drift, I have no mental picture of what is happening in the conductor.

I suspect I will never get to grips with this stuff without an OU effort, which I fear will not happen.

But thanks both. I do claim some points ( or make apologies ) for size of thread drift.

genou wrote:This is where my brain hurts. I was brought up on the "water in a pipe" analogy, so "current flowing" takes me back to that. I later learned of its limitations. But other than electron drift, I have no mental picture of what is happening in the conductor.

Perhaps you can imagine ripples on the top of the water - that's a physical surface effect, a frequency of transmission that is superimposed on the main

When you look at an electrical circuit or schematic you can see what it will do at DC (or in a perfect physical representation).

Once you get to the shortcomings and compromises of "real life" you start to experience all sorts of "unexpected" things as frequency gets considered
Examples I see often would be cables removing top end ( working as low pass filters) because of capacitive coupling with the shield, and CM Chokes or beads being compromised on a circuit because of a ground plane beneath them
- and that fact that just about everything works as a RF transmitter or receiver (depending on where you are looking at it from )

pochisoldi wrote:Has anybody got any real life experiences with reasons why "switches on the outside" were fitted or should have been fitted?

Simple answer in my case, I have double sockets with USB charging sockets built in at the centre. Thus there is no room for switches on the inside. https://www.amazon.co.uk/BG-ELECTRICAL- ... r=8-5&th=1

That said, I have seen same set up with switches on the inside with USB charging sockets below the switches,
https://www.amazon.co.uk/MK-ELECTRIC-MB ... =8-16&th=1.

So I'm guessing the answer is purely aesthetics.

pochisoldi wrote:Has anybody got any real life experiences with reasons why "switches on the outside" were fitted or should have been fitted?

They are also known as Hospital sockets and are used in any location where it is important you don't accidentally turn the wrong thing on or off, like turning the life support off instead of the bedside lamp.
I'm pretty sure the science labs at my old school had them.

I guess they are also considered uglier than the normal arrangement.

You could have a switch to the right of each socket, but then people might still think the switch in the middle was for the right hand socket.

Thanks for everyone's replies.
The subtle "clean earth"/"high integrity earth" aspect wasn't obvious until you looked at the back of the sockets, and took me down a google worm hole.

As I suspected it seems to come down to "don't turn off the wrong socket" - something common to hospitals and data centres, with the latter requiring additional bonding due to higher overall earth leakage currents. (all those suppression capacitors connected to earth), so it would make sense to add the ability to split the protective earth function (contact with exposed metalwork that becomes live) and the functional earth connection which is used by the transient and noise filters fitted on the inputs of virtually every computing and networking device.

PochiSoldi

genou wrote:I suspect I will never get to grips with this stuff without an OU effort, which I fear will not happen.

You never get to grips with everything. The more you know the more you know you don't know. On to a PhD, post doc, ... . At some point string theory will show up and strangle you.

9873210 wrote:

genou wrote:I suspect I will never get to grips with this stuff without an OU effort, which I fear will not happen.

You never get to grips with everything. The more you know the more you know you don't know. On to a PhD, post doc, ... . At some point string theory will show up and strangle you.

Indeed not. My father worked for PO Telecoms/ BT, and I am quite confident with domestic issues just by seeing/doing, but my theoretical understanding is appalling. But as Mr Clarke said Any sufficiently advanced technology is indistinguishable from magic.