How to correctly wire 2-way switch for ring main

[Anon]

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?

Edit

It seems clear that it's the wrong switch, and there would be no safe way to wire it up to use for my ring main extension. I could do with some assistance in choosing the correct switch though. What about a 4 pole changeover or 4 pole rotary isolater switch?

 

[Terry - Somerset]

I'm not an electrician but my initial concerns would be:

• the MCB protecting the existing ring is probably 32A. You need to be carful how much power your enlarged ring would use - particularly as you want to use a 45A switch
• what size cable is used in the existing ring main - could be 2.5 or 4.0mm - may be impacted by power consumption
• using a switch for a purpose for which it is clearly not intended seems wrong - there may be a more appropriate bit of kit
• personally I would seek some professional advice and consider wiring in a supply direct from the consumer unit

 

[Anon]

The existing ring is 32A. I'm planning on doing this with a cooker switch because it's very hard to find a 32A 2-way switch. Most are for lighting with a much lower amp rating. I don't expect to exceed 32A, but I want to be sure the current is balanced so that if somehow I do cause an accidentally overload, the MCB will trip, instead of my house burning down.

There may be a more appropriate bit of kit but I don't know what that is. I have no problem using a switch for a purpose that it's not intended for, provided it's safe to do so. I've already got a 20A switch to isolate the spur. If I can use the 2-way cooker switch I've found on eBay, it would mean I can simply swap the front plate of the switch, which would make my life much easier and save a lot of money I can't afford to spend.

I am seeking professional advice. I am on a tight budget, so I certainly can't phone a qualified electrician. Just gotta do my research online and ask for help on forums.

 

[Bingy man]

The existing ring is 32A. I'm planning on doing this with a cooker switch because it's very hard to find a 32A 2-way switch. Most are for lighting with a much lower amp rating. I don't expect to exceed 32A, but I want to be sure the current is balanced so that if somehow I do cause an accidentally overload, the MCB will trip, instead of my house burning down.

There may be a more appropriate bit of kit but I don't know what that is. I have no problem using a switch for a purpose that it's not intended for, provided it's safe to do so. I've already got a 20A switch to isolate the spur. If I can use the 2-way cooker switch I've found on eBay, it would mean I can simply swap the front plate of the switch, which would make my life much easier and save a lot of money I can't afford to spend.

I am seeking professional advice. I am on a tight budget, so I certainly can't phone a qualified electrician. Just gotta do my research online and ask for help on forums.

I am not a qualified electrician - I’m a gas engineer of 30+ years but what you are planning does not sound safe . I believe you can run a spur point off the ring main to a single or double power socket, but you can’t run multiple sockets from this spur even if you can isolate it via a cooker switch . Imho you would need to contact a qualified electrician to assess what your planning - it starts at your consumer box which will have a max rating that you can’t exceed, I’ve seen many unsafe installations over the years causing pipe work to become live, appliances that once isolated are still live ( confirming safe isolation) boilers connected via a 3 pin plug but when removing the plug the pin is live as it’s being fed from another source ( it’s not dead until you have proved it’s dead ) . Your life and that of your family is I’m sure far more important than your budget to get the work done. Also god forbid as you said in your post “you don’t want to burn the house down” if you carry out work on your electrics that’s unsafe your home insurance may be invalid. So please get a professional electrician, tell him what you want and ask if it can be achieved safely. I once found a double socket had been fitted into the wall by the homeowner in a child’s bedroom-kid was always sick and unwell and the parents didn’t know why . I was there to service the gas fire and the socket in question had been cut into the flue for gas fire . Hence the kid was being poisoned by carbon monoxide…when I explained to the kids dad what he’d done he broke down and cried , his wife was hysterical. Stay safe!!!!

 

[Fergie 307]

This is a bad idea, what you will have is effectively an extension lead, which won't even have a suitable fuse. Depending on how many sockets it already serves, and how many more you need, you could just extend the ring main. This is only really viable if there are only going to be a small number of sockets altogether. If this is for a workshop or similar you should really run a new supply with its own protection. More complicated than what you are proposing, less complicated than explaining the possible consequences to the boss/insurance company.

 

[Rich C]

You can't make the switch shown do what you want. To make a correct ring extension you would need to switch both lives and neutrals, but you're well short of both connections and the right changeover pattern for that.

Your best bet is a separate ring for the extension, or failing that an unswitched extension to the current ring.

 

[Sideways]

Do you drive without insurance and do your own gas fitting too ?
You don't know what you are doing. Don't seem to care. And will make yourself liable for the consequences. If you can't do it safely, don't do it at all.

You expected someone to say this so there you go.

 

[deema]

A) What Sideways said
B) have you thought about bomb disposal by asking questions on a forum? About the same level of lethality if you get it wrong.
C) what your proposing is just wrong, don’t do it.

 

[Bingy man]

It’s an accident waiting to happen,I’m sure many of the members on this site have a basic understanding of electricity, but apart from electricians, electronic engineers etc how many know how to safely isolate and prove safe isolation and take the necessary steps to prevent the supply being accidentally turned back on with deadly consequences. There is not much you can do these days due to 16/17 Ed regs in your own home . Most jobs other than changing a light bulb or replacing a 3 pin plug have to be certified and tested by a suitable electrician and documented and notified to your local building control . Just the same for gas appliances and installations. It’s also likely if you don’t have the necessary testing equipment then how would the installation be tested-turn it on , no rcds tripping, no fuses blowing-so it must be ok ???

 

[Spectric]

This is a change in design and therefore becomes notifiable to building control and will need certification from a qualified electrician. Ring mains are historic and can cause many issues especially when modified by the unqualified, main issues are either broken ring or bridged ring. You cannot switch a ring on/off , you need to undertake testing on the current wiring to find the impedances in order to perform a re design, but extending a ring is ok provided all the initial testing has been done and the area served is less than 100 square metres there is no limit on sockets but there is a limit on the number of spurs taken from a ring.

This has always been an issue with rings because you can end up in a situation where there are so many loads that you have an overload where the current on the ring is excessive but not high enough to operate the protective device and you can end up with a thermal event.

The protective device should be 32 amp and this can only function as a protective device if the ring is intact and is why testing is important so it can be certified SAFE ! You also need to look at energy let through, another important factor in electrical design.

If this is for an external workshop then your situation becomes more difficult, or is it just adding more sockets in your house, either way dump that switch.

 

[Craig22]

What others have said. Don't. Get a qualified electrician (using Checkatrade or similar) who is certified in this 18th Edition resources - Electrical . You'll have to wait, because these folks are usually really busy. But they will do the right job, certify it, and that covers your house insurance too.

Alternatively faff about, and burn the house down. And lose everything. Remember Cutty Sark, Windsor Castle and the two fires at Glasgow Museum of Art? All electrical fires associated with restoration work - so ultimately down to someone who was not qualified rigging lights and heating up inappropriately

 

[Jacob]

This is a change in design and therefore becomes notifiable to building control and will need certification from a qualified electrician. Ring mains are historic and can cause many issues especially when modified by the unqualified, main issues are either broken ring or bridged ring. You cannot switch a ring on/off , you need to undertake testing on the current wiring to find the impedances in order to perform a re design, but extending a ring is ok provided all the initial testing has been done and the area served is less than 100 square metres there is no limit on sockets but there is a limit on the number of spurs taken from a ring.

This has always been an issue with rings because you can end up in a situation where there are so many loads that you have an overload where the current on the ring is excessive but not high enough to operate the protective device and you can end up with a thermal event.

The protective device should be 32 amp and this can only function as a protective device if the ring is intact and is why testing is important so it can be certified SAFE ! You also need to look at energy let through, another important factor in electrical design.

If this is for an external workshop then your situation becomes more difficult, or is it just adding more sockets in your house, either way dump that switch.

What is a "bridged" ring main and why would it be a hazard? Just wondered, as an amateur electrician!
PS does it mean one ring main joined to another? I can see why that would be bad.

 

[Woody2Shoes]

What is a "bridged" ring main and why would it be a hazard? Just wondered, as an amateur electrician!
PS does it mean one ring main joined to another? I can see why that would be bad.

I take this to mean a 'figure-of-eight' on one circuit. Depending on how it's been done, it may or may not be dangerous. However, as a non-standard circuit configuration, it's impossible to prove that it's safe using standard testing procedures (and associated, often semi-automated, test gear).

I think that the mere fact that the OP is asking questions like this means that they are not qualified to do this work - which I believe would be 'notifiable' work - and they are certainly unable to test the resulting circuit to prove that it's safe.

As for 'being on a budget' - we all are, to some degree or other. What price safety?

 

[Spectric]

Hi

If you imagine an intact ring as a loop, a bridged ring is where any part of the ring has another part in parallel. Ring mains could give big headaches on testing and is why I only used radials and avoided domestic, industrial so much more control.

The above is how to link for testing, the equivalent circuit then becomes this:

Effectively putting all Live and Neutral impedances in parallel so that at any point on the circuit X impedance will equal Y impedance so long as there is no bridging.


For completion this is how to link for ensuring an unbroken ring:

Then measure the impedance between live and neutral at all sockets, should be within 0.5 ohms.

Hope this helps.

 

[Woody2Shoes]

An interesting discussion here:

https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid= 61114
Interesting quote right at the bottom of that thread which echoes a comment upthread here:

"... Very low usage so I doubt that the layout is dangerous but if it were a workshop or the like I think it would be different. ..."

 

[Woody2Shoes]

This guy - a very competent individual - has an interesting point of view on ring final circuits:

 

[Spectric]

Just avoid them, they have no benefits or advantages and originated from a copper shortage after WW2.

Must be twenty plus years since I installed a ring, after that Radials all the way. 20 amp protective device for 2.5mm CSA circuits and 32 amp protective device for 4mm CSA circuits.

In a workshop you just daisy chain the sockets and stop at the end, nothing back to board.

 

[Anon]

I believe you can run a spur point off the ring main to a single or double power socket, but you can’t run multiple sockets from this spur even if you can isolate it via a cooker switch

Exactly, I can't run multiple sockets off a spur, that's why I need to convert it to a ring main extension.

So please get a professional electrician, tell him what you want and ask if it can be achieved safely.

I have absolutely no means to pay for a professional electrician. This would mean making do with too many sockets from a spur in the meantime, which I know is unsafe.

 

[Myfordman]

You will need a 4 pole changeover switch to do this. In the "off" position it will have to close the existing ring and isolate both ends of the new one and the "on" position it will have to open the existing ring and connect to each end of the new ring. There is no domestic type switch to do a function like this and almost certainly it will have to be an industrial drum type switch in a suitable enclosure possibly with stranded cable to get it all in the box without breaking.
Sounds like you are way out of your depth in asking this question as well as not being able to afford professional advice. In any case I don't see a Part P sparky being prepared to do this as he can earn a low risk living doing conventional work.

 

[Anon]

This is a bad idea, what you will have is effectively an extension lead, which won't even have a suitable fuse.

This is what it's like like currently, and I'm aware it's a bad idea.

Depending on how many sockets it already serves, and how many more you need, you could just extend the ring main.

This is precisely what I'm going to do. At the moment, I have a 20 amp switch to isolate the spur. Obviously, I can't use that switch to isolate the ring main extension. To isolate, I'd need to toggle between a complete ring main without the extension, and a complete ring main with the extension. I was thinking a double pole 2-way switch that can handle 32 amps would do for that, hence why I am considering using the 45 amp cooker switch. It seems like it won't do though because I can't think of a safe configuration, as the neutrals would need to be connected safely.