How to correctly wire 2-way switch for ring main

[AnonDIYer]

Currently I have a spur from the ring main, but I'm planning on adding more sockets. I can't add a 13 amp fuse because I expect to be using more than 13 amps, therefore, I am going to convert the spur into a ring main extension, as in the following diagram:

I'd like to put in a 2 way switch so that I can isolate the ring main extension whilst I'm doing work on the extension, and as an emergency off switch. When the switch is off, A should connect to B. When it's on, A should connect to C, and D to B.

I'm planning on buying a 45 amp double pole 2-way cooker switch to use for this. This is the back of the switch:

And the instructions:

I thought about how I can wire this up. The best configuration I can think of is to connect the 4 lives inside the switch, A to L2, B to N1, C to L1, D to N2, and the 4 neutrals joined together. I believe this would be perfectly safe in the off position because the lives A and B will be connected via L2 and N1, and the neutrals C and D would not cause a problem because the circuit they are part of would be dead.

However, in the on position, lives A and C will be connected via L1 and L2, and lives B and D will be connected via N1 and N2, which is perfect, but what about the 4 neutrals? This gives the neutrals a shortcut from A to B, as A and B will always be a live circuit.. Would this not create an unbalanced circuit and be dangerous?

Can someone please let me know the correct way to wire this up?

 

[telectrix]

personally, \i think youare way outof your depth here. hire an electrician while you're still breathing.

 

[philectrical]

Normally you'd do all your wiring and then connect it up to power, you wouldn't connect it from the live and then do the work to the circuit, it's screaming out to be belted.

Agree with telectrix you should get a proper electrician in.

 

[pc1966]

This is a VERY bad idea for all sorts of reasons.

Also to extend an RFC by switching, which I repeats is a very bad idea, would require a 4PDT switch action so RFC continuity is kept.

Really, get a professional in. If you really do want a local isolator, then have a separate radial or "lollipop" circuit for whatever you are planning. Very rarely will you need more than 13A if heating is not involved, so consider carefully.

 

[UNG]

Started out by thinking the OP was trolling

On a more serious note this has the potential to be very dangerous by whatever DIY method is used by the OP, the best method I can suggest is get an electrician in to sort it so it complies with the regs and is safe for all concerned.

 

[littlespark]

How likely are you to exceed 13A? If there’s no heating load, then it’s likely never going to get near it.
13A Fused spur to radial.

 

[AnonDIYer]

Normally you'd do all your wiring and then connect it up to power, you wouldn't connect it from the live and then do the work to the circuit, it's screaming out to be belted.

That's why I want to isolate the extension with a switch. Then I can turn off power whilst doing maintenance work Also for safety reasons, as if something goes wrong within the ring main extension, I can simply turn off the switch.

personally, \i think youare way outof your depth here. hire an electrician while you're still breathing.

Agree with telectrix you should get a proper electrician in.

I can't afford to get a proper electrician in. I don't feel safe assuming there will be no dangerous overload with the existing spur I have, until I can afford a fortune for an electrician to do a complete rewire. I'd much rather do what I can to make it work safely, until I can afford the proper testing equipment, or to have a proper electrician do the testing. An extension to the ring main would supply a large enough capacity to avoid the risk of an overload. I am aware the risks of doing so incorrectly could be deadly. That's why I am doing research first and posting here first.

Also to extend an RFC by switching, which I repeats is a very bad idea, would require a 4PDT switch action so RFC continuity is kept.

What about a 4 pole rotary switch? Would this do it?

32A Rotary Isolator Switch 32amp 4 Pole 230V-415V | eBay

Rotary isolator. Smart & Colour Changing Lights. EN 60947 Compliant. Modern rotary switch technology. Rotary Switch. Insulated 4 pole AC (230V-415V). Light Colour. CE/ IEC 536 EN 60947-3.

www.ebay.co.uk

Very rarely will you need more than 13A if heating is not involved, so consider carefully.

I might be able to get away with putting a 20 amp fuse before the extended spur, however, I am aware that it should be a 13 amp fuse. I don't wish to assume overloading it will be safe and I don't expect 13 amps to be enough, so I wish to proceed carefully in extending the ring main.

 

[littlespark]

What you could do is wire it as a ring, but isolated through a 13A sw/fuse… when you are finished working on the extension, remove the sw/fuse and reconnect as an extension to the ring.

 

[philectrical]

That's why I want to isolate the extension with a switch. Then I can turn off power whilst doing maintenance work Also for safety reasons, as if something goes wrong within the ring main extension, I can simply turn off the switch.

But you don't need to turn it off, you just do everything you need to do, then turn the power off, then make it part of the ring, then it's just part of the ring. Why would you need to be able to turn it off separately from the ring?

The easiest solution is just to make it its own ring on a different MCB if you need to control it separaterly but again i feel you need an electrician to do this.

I can't afford to get a proper electrician in. I don't feel safe assuming there will be no dangerous overload with the existing spur I have, until I can afford a fortune for an electrician to do a complete rewire. I'd much rather do what I can to make it work safely, until I can afford the proper testing equipment, or to have a proper electrician do the testing. An extension to the ring main would supply a large enough capacity to avoid the risk of an overload. I am aware the risks of doing so incorrectly could be deadly. That's why I am doing research first and posting here first.

I mean that's fair enough, i did the same thing before i got involved in the trade but i was working under guidance from a spark that i knew who i could personally ask for advice.

But you're coming up with some really strange ideas which suggest you're not competent to do the work yourself. You could literally end up putting a foot wrong and burning your house down or shocking yourself badly.

Isn't that worth just waiting until you have the money?

What about a 4 pole rotary switch? Would this do it?

https://www.ebay.co.uk/itm/400828487878?epid=1554613733&hash=item5d533d58c6:g:p~IAAOSwZvRajVf0

Those are industrial-use isolators; usually found in welding bays, factories, garages, etc..not that they couldn't be used in a domestic setting but it's certainly not standard. You'd also have to gland your cables into to do it properly and twin and earth probably isn't going to suffice.

 

[ipf]

......and some wonder why dangerous faults are found involving existing circuits when problems occur and we are asked to sort 'em out!!

Regarding DIY, I don't agree with trying to explain to those incapable of understanding danger......it just creates MORE.

 

[pc1966]

What about a 4 pole rotary switch? Would this do it?

That is a 4 pole isolator, i.e. 4PST, it would need to be a 4-pole changeover switch which are a bit rarer to find.

I might be able to get away with putting a 20 amp fuse before the extended spur, however, I am aware that it should be a 13 amp fuse. I don't wish to assume overloading it will be safe and I don't expect 13 amps to be enough, so I wish to proceed carefully in extending the ring main.

Is your goal simply to add more sockets in some extension area or similar but making use of the existing RFC?

What I am struggling with is why you need to manually isolate it. The nature of electricity is by time you find out it has gone wrong it may be too late to humanly to do anything about it! That is why for years the UK regulations have been quite strict and detailed about how to achieve fast ADS (Automatic Disconnection of the Supply) under fault conditions, and in recent decades, also on shock-level leakages via RCD/RCBO.

You mention you lack suitable test equipment and that is not a good starting point!

If doing any work on a RFC then you would be expected to have both a low-resistance meter to verify that all the end-end resistances are low (and consistent with the conductor sizes, etc) and some high voltage insulation tester to check that the cable insulation looks sound (no chewing by rodents, partial damage by nails, etc). Not just on your new work, but also to verify the safety of the circuit being modified

Usually both functions are provided by the traditional "Megger" (other brands available) but even if you look at buying that 2nd hand and learning how to sensibly use it it would probably be cheaper and safer to get a professional in.

 

[AnonDIYer]

I accidentally posted a quote, before writing my comment. I'd like to delete this comment but there's no option to delete.

 

[timhoward]

I expect to be using more than 13 amps,

Please explain this. New Kitchen? Welding? Growing interesting things?

That's why I want to isolate the extension with a switch. Then I can turn off power whilst doing maintenance work Also for safety reasons, as if something goes wrong within the ring main extension, I can simply turn off the switch.

Just no!
If "anything goes wrong" the wiring regs require disconnection (usually) in 0.4 seconds and this will happen automatically as long as it's a complete ring and you've matched the colours correctly all the way around.
There are no circumstances under which having an uncommon (specialist) switch on a ring final circuit makes anything any safer for anyone, and in fact most of use think it makes it far more dangerous.
Please abandon this idea.

What you could do is wire it as a ring, but isolated through a 13A sw/fuse… when you are finished working on the extension, remove the sw/fuse and reconnect as an extension to the ring.

I understand your point but don't think this approach is wise as FCU's can easily confuse people - I've found one before now where Supply and Load were connected to incoming and outgoing ring and the appliance was live 24/7!

 

[AnonDIYer]

But you're coming up with some really strange ideas which suggest you're not competent to do the work yourself. You could literally end up putting a foot wrong and burning your house down or shocking yourself badly.

Isn't that worth just waiting until you have the money?

In an ideal world yes. The reality is, if I wait I won't just have to pay a fortune to change the circuit late, considering it would be a lot harder to change then, than now, but I'd be taking a much bigger risk. The spur off the ring main should not be more than 13 amps, and hoping there's no dangerous overload until I can afford to hire an electrician is surely not a smart move.

What's wrong with learning how to do things properly? Everyone has to start somewhere, and I don't believe even the best electricians could be 100% safe and competent before they learned how to be.

I don't consider any work I have done to be complete, until I have tested for faults, surely this is especially true with testing for ring main faults.

But you don't need to turn it off, you just do everything you need to do, then turn the power off, then make it part of the ring, then it's just part of the ring. Why would you need to be able to turn it off separately from the ring?

Because simply putting in a 32 amp or more 4 pole double throw switch would solve the problem. I'm giving up with the idea of trying to make do with less than 4 poles because of the neutral problem. The problem now is I'm not finding very good results when I search for a suitable switch. Most switches don't even state how many throws they have, meaning I have to spend time considering switches that may not be suitable. A lot of switches that would work, have an off position in the middle. This would mean, every time I change over, there'd be a temporary break in the ring main.

Those are industrial-use isolators; usually found in welding bays, factories, garages, etc..not that they couldn't be used in a domestic setting but it's certainly not standard. You'd also have to gland your cables into to do it properly and twin and earth probably isn't going to suffice.

What about this switch (the 32 amp one)? LW42 20/25/32A 4Pole Rotary Selector Universal Rotary Changeover Switch Isolator | eBay - https://www.ebay.co.uk/itm/363422468983?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D237334%26meid%3D0335e5c0502e49d38a40b2ad4f530fe3%26pid%3D101195%26rk%3D9%26rkt%3D12%26sd%3D144256490302%26itm%3D363422468983%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv9PairwiseWebMskuAspectsV202110NoVariantSeed%26brand%3DUnbranded&_trksid=p2047675.c101195.m1851&amdata=cksum%3A3634224689830335e5c0502e49d38a40b2ad4f530fe3%7Cenc%3AAQAGAAACMKy7vEOvBI8Auv8QpEnxmxLXZS4es8rMPqHXyNkGqLRd5oFGCqYoxmH%252FqjQpK%252FWirOlnB9WVZFMpP6mhJ1kymU1M8jq5VvMoo31uLspbmeLeWT%252BfvsZpO2ahpxyDvgjOcdQx0iWHkpUoufOD4JjzKJbU98t748WYITGs2%252BeHRSELeuBy%252FyCI7u9eoSg%252FyNXo6qpQ%252B9wRFeo6UyaXdJYDwV94mYw4QgnSmE1bx5KdINZkADZypdDrGs8yaDZhodCpmI4TXp3TQzGjrnPsl2IpifElkTLwDh4fpTCNn3sDPMUCNeWxkDyRKqGusVtcmGpEIvNovGHxFfG%252BR%252Fl3y0pwOD32S8sd0wUgtbt3xNmvYAtu1v1w6uIJwip7VAS6rCrOwDOhjV0%252FLwSQgcql6aq1bC9vV5xsq2VoeOPSCntndugYChkHKZiTOPvv30ceZBWp7lOPmbbwUWNZx2K9FpNHuutKbseOQ9d%252FEquPHxfkl%252FfdUDv6Iqa2h4MKN7KRpovWk47BLFPnx%252BkgNEDWsVIqnyOd7U94q9H%252BRXO%252FbTuFYREJjBoleUS3kjX8VsQsQBrbERTVnyQpFogFkGfmVL0u6WRY3EM%252FO5n5QCVoHVswC90ypxmvKQbcNo94%252Fud4b%252F%252BdycUV8LXOtmbnSmhYdRVE6ydArc5uKZyrnObyPmv%252BAygPVREKKKG7mF%252BBlevH%252BLkO7hOR%252FQvQXI27l%252BThCaU8vw65s5r2YGpG7lFOkf%252Fj5cN4%7Campid%3APL_CLK%7Cclp%3A2047675

It looks like the cables will fit into it without being glanded. Could it be any more dangerous than connecting the cables via wago connectors in a junction box?

 

[AnonDIYer]

If "anything goes wrong" the wiring regs require disconnection (usually) in 0.4 seconds and this will happen automatically as long as it's a complete ring and you've matched the colours correctly all the way around.
There are no circumstances under which having an uncommon (specialist) switch on a ring final circuit makes anything any safer for anyone, and in fact most of use think it makes it far more dangerous.

But it would be a complete ring. The difficulty I have is finding the right switch, a changeover switch that completes the ring main without the extension in the off position, and completes the ring main with the extension in the on position. If I do this correctly, will I not be able to rely on my 32 amp MCB cutting out power should something go wrong. It certainly cuts out in a lot less time than 0.4 seconds.

 

[philectrical]

In an ideal world yes. The reality is, if I wait I won't just have to pay a fortune to change the circuit late, considering it would be a lot harder to change then, than now, but I'd be taking a much bigger risk. The spur off the ring main should not be more than 13 amps, and hoping there's no dangerous overload until I can afford to hire an electrician is surely not a smart move.

What's wrong with learning how to do things properly? Everyone has to start somewhere, and I don't believe even the best electricians could be 100% safe and competent before they learned how to be.

I don't consider any work I have done to be complete, until I have tested for faults, surely this is especially true with testing for ring main faults.



Because simply putting in a 32 amp or more 4 pole double throw switch would solve the problem. I'm giving up with the idea of trying to make do with less than 4 poles because of the neutral problem. The problem now is I'm not finding very good results when I search for a suitable switch. Most switches don't even state how many throws they have, meaning I have to spend time considering switches that may not be suitable. A lot of switches that would work, have an off position in the middle. This would mean, every time I change over, there'd be a temporary break in the ring main.

What risk? What exactly is it you're trying to achieve and why? If it's just an extension that you want to be a ring and not a radial, you just put it on its own ring with its own MCB at the consumer unit. In houses we usually find a ring for the kitchen, a ring for the rest of the downstairs and a ring for upstairs. Why can't you just add a ring for your extension and then you won't have to turn off the other ring at all.

What about this switch (the 32 amp one)? LW42 20/25/32A 4Pole Rotary Selector Universal Rotary Changeover Switch Isolator | eBay - https://www.ebay.co.uk/itm/363422468983?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D237334%26meid%3D0335e5c0502e49d38a40b2ad4f530fe3%26pid%3D101195%26rk%3D9%26rkt%3D12%26sd%3D144256490302%26itm%3D363422468983%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv9PairwiseWebMskuAspectsV202110NoVariantSeed%26brand%3DUnbranded&_trksid=p2047675.c101195.m1851&amdata=cksum%3A3634224689830335e5c0502e49d38a40b2ad4f530fe3%7Cenc%3AAQAGAAACMKy7vEOvBI8Auv8QpEnxmxLXZS4es8rMPqHXyNkGqLRd5oFGCqYoxmH%252FqjQpK%252FWirOlnB9WVZFMpP6mhJ1kymU1M8jq5VvMoo31uLspbmeLeWT%252BfvsZpO2ahpxyDvgjOcdQx0iWHkpUoufOD4JjzKJbU98t748WYITGs2%252BeHRSELeuBy%252FyCI7u9eoSg%252FyNXo6qpQ%252B9wRFeo6UyaXdJYDwV94mYw4QgnSmE1bx5KdINZkADZypdDrGs8yaDZhodCpmI4TXp3TQzGjrnPsl2IpifElkTLwDh4fpTCNn3sDPMUCNeWxkDyRKqGusVtcmGpEIvNovGHxFfG%252BR%252Fl3y0pwOD32S8sd0wUgtbt3xNmvYAtu1v1w6uIJwip7VAS6rCrOwDOhjV0%252FLwSQgcql6aq1bC9vV5xsq2VoeOPSCntndugYChkHKZiTOPvv30ceZBWp7lOPmbbwUWNZx2K9FpNHuutKbseOQ9d%252FEquPHxfkl%252FfdUDv6Iqa2h4MKN7KRpovWk47BLFPnx%252BkgNEDWsVIqnyOd7U94q9H%252BRXO%252FbTuFYREJjBoleUS3kjX8VsQsQBrbERTVnyQpFogFkGfmVL0u6WRY3EM%252FO5n5QCVoHVswC90ypxmvKQbcNo94%252Fud4b%252F%252BdycUV8LXOtmbnSmhYdRVE6ydArc5uKZyrnObyPmv%252BAygPVREKKKG7mF%252BBlevH%252BLkO7hOR%252FQvQXI27l%252BThCaU8vw65s5r2YGpG7lFOkf%252Fj5cN4%7Campid%3APL_CLK%7Cclp%3A2047675

It looks like the cables will fit into it without being glanded. Could it be any more dangerous than connecting the cables via wago connectors in a junction box?

That's basically the same thing, it's a switch meant for industrial usage. Last time i connected some of these up it was for 3 phase machinery in a metalworking shop. They're not meant for domestic usage.

I don't know what idea you have in mind or what you're trying to do that you won't tell us about but you should abandon the idea. 'Starting somewhere' usually entails learning the basic science and principles, learning about how cable rating and mcb's work together, about how to terminate correctly, etc, etc. Learning how to do electrics doesn't start with coming up with odd configurations to suit weird problems, especially when there's a very easy solution to the problem of 'needing to turn the supplies on and off separately'.

Sounds to me like you've got a grow on tbh that you need to be able to disconnect from your supply if suspicions get raised, and it's probably why you won't get a spark in. Forgive me if i'm wrong and just being cynical.

 

[AJB Temple]

I am a DIYer too. In my case I have invested in modern test equipment, appropriate tools, safe isolation testers and read both regs and testing manuals. Therefore, I do understand that DIY people need to do things for themselves at times, and I am not judgemental about that.

My reaction when I read your suggestion was:

It’s potentially dangerous
It’s illogical
It’s over complicated, especially as you are avoiding explaining the need to isolate the ring extension.

If you are capable of safely installing the sockets and correct sized wiring for the ring extension, then it is difficult to see why you don’t simply do that. Then, cut the power and prove dead on the existing ring final circuit. Then, when certain it is safe, connect the extension.

If you do not have test equipment then you are taking a risk and I suppose that is a matter for you, but I would not expose my family (or anyone else) to using circuits where I had not done continuity, resistance, CPC, ramp tests etc.

I can’t for the life of me see any logic in fitting some kind of switching system to isolate and make dead part of a ring final circuit, whilst leaving the original circuit live. It made me wonder if you realise that current flows both ways around a ring final circuit. If it were me doing this and I had a load that exceeded the capability of a regs compliant spur, I would simply install a new radial with appropriately sized and suitably protected cable. I could switch that out at the CU. Simple and safe.

I also wondered from your post if you are clear what the purpose of the fuse is. You anticipate a load exceeding 13 amps in that section (suggesting some sort of large element or start capacitor perhaps) and your solution seems to be install a larger fuse. Even as a DIY person this seems to me to defeat logic: you need the correct sized cable for the job in hand, and a suitable trip device such as an RCBO rated to protect the cable from overload currents. I can’t see how some complex manual switching arrangement to isolate your ring extension is a sensible solution.

Anyway. I hope you arrive at a safe solution and a means of testing that you have installed it correctly.

 

[AnonDIYer]

'Starting somewhere' usually entails learning the basic science and principles, learning about how cable rating and mcb's work together, about how to terminate correctly, etc, etc. Learning how to do electrics doesn't start with coming up with odd configurations to suit weird problems, especially when there's a very easy solution to the problem of 'needing to turn the supplies on and off separately'.

Of course it does, and that's what I have been doing. There's always more to learn, but so I'd like my main focus on being learning everything I need to know to be safe at the task in hand. I'm aware that 2.5mm twin and earth is only rated for 17 - 27 amps depending on whether it's clipped into the wall or not, but in a non faulty ring main it's capacity is doubled so that it exceeds the maximum 32 amps the MCB will allow. I had a faulty kettle trip the MCB every time it was switched on so I don't believe it's wise to assume appliances always use the amps they are supposed to use.

It seems like fitting a 32 amp 4 pole double throw switch should be a simple task, and perfectly reasonable for maintenance and safety. Going from a faulty ring main to a safe ring main at the flick of a switch, certainly seems like a good idea to me. The problem is I've found no switches that state clearly they are 32 amp 4 pole double throw for single phase, no tutorials from fully qualified electricians about how to fit them. That's why the solutions I've thought of are "odd configurations to suit weird problems". It's also, why I am posting. It's better to make mistakes in the planning stage and correct those mistakes, than to follow through and learn the hard way. It seems to me that if the worst comes to the worst and there is a fault, being able to isolate the fault can only be a good thing.

Sounds to me like you've got a grow on tbh that you need to be able to disconnect from your supply if suspicions get raised, and it's probably why you won't get a spark in. Forgive me if i'm wrong and just being cynical.

A simply workshop but with power tools that will almost certainly exceed the 13 amp limit for a spur. A faulty power tool or accidentally running too much at once, no problem if the breaker trips, hence the need for a correctly setup ring main extension. 32 amps for the entire ring main is more than enough but I'd rather allow for it just in case. I'd rather have extra capacity that I don't need, than not enough capacity that I do need, or worse exceeding the safe capacity and risking a dangerous overload. When testing the ring main, if it fails, I'll still need to use the original ring main without the extension until I've fixed the fault. I can't do that without a cutoff switch. I wouldn't even be able to use the lights whilst I fix the fault.

 

[DPG]

Of course it does, and that's what I have been doing. There's always more to learn, but so I'd like my main focus on being learning everything I need to know to be safe at the task in hand. I'm aware that 2.5mm twin and earth is only rated for 17 - 27 amps depending on whether it's clipped into the wall or not, but in a non faulty ring main it's capacity is doubled so that it exceeds the maximum 32 amps the MCB will allow. I had a faulty kettle trip the MCB every time it was switched on so I don't believe it's wise to assume appliances always use the amps they are supposed to use.

It seems like fitting a 32 amp 4 pole double throw switch should be a simple task, and perfectly reasonable for maintenance and safety. Going from a faulty ring main to a safe ring main at the flick of a switch, certainly seems like a good idea to me. The problem is I've found no switches that state clearly they are 32 amp 4 pole double throw for single phase, no tutorials from fully qualified electricians about how to fit them. That's why the solutions I've thought of are "odd configurations to suit weird problems". It's also, why I am posting. It's better to make mistakes in the planning stage and correct those mistakes, than to follow through and learn the hard way. It seems to me that if the worst comes to the worst and there is a fault, being able to isolate the fault can only be a good thing.



A simply workshop but with power tools that will almost certainly exceed the 13 amp limit for a spur. A faulty power tool or accidentally running too much at once, no problem if the breaker trips, hence the need for a correctly setup ring main extension. 32 amps for the entire ring main is more than enough but I'd rather allow for it just in case. I'd rather have extra capacity that I don't need, than not enough capacity that I do need, or worse exceeding the safe capacity and risking a dangerous overload. When testing the ring main, if it fails, I'll still need to use the original ring main without the extension until I've fixed the fault. I can't do that without a cutoff switch. I wouldn't even be able to use the lights whilst I fix the fault.

A properly designed circuit does not need a section of it to be isolated. Please take the advice you have been given. Your idea is not a good one

 

[timhoward]

I'm aware that 2.5mm twin and earth is only rated for 17 - 27 amps depending on whether it's clipped into the wall or not, but in a non faulty ring main it's capacity is doubled so that it exceeds the maximum 32 amps the MCB will allow. I had a faulty kettle trip the MCB every time it was switched on so I don't believe it's wise to assume appliances always use the amps they are supposed to use

Going from a faulty ring main to a safe ring main at the flick of a switch, certainly seems like a good idea to me

Just having a switch is dangerous. I wouldn't trust about a 1/3rd of sparks out there to wire such a switch up safely, and while you seem to understand many concepts you are also clearly blind to other ones.
It's also a bad idea having something so unusual in your house.

If you think through the scenarios you have mentioned...
In the case of faulty equipment consuming too much current - either fuse goes in plug, or over current protective device operates to protect wiring.
The wiring stays safe without a switch. You reset the circuit breaker and crack on.
A lighting circuit would not be affected by an over-current fault on the sockets circuit unless there was an earth leakage issue, and even then you just unplug things until until the RCD stops tripping.

If you are hell-bent on having isolation for this area, the right way to do it is a separate circuit, Some sparks would let you first fix to keep costs down.