UK DIYer Newbie - adding additional sockets

[alljohn]

Hi, Newbie here so please excuse any stupid questions. There is a single 2.5 T&E running from a dedicated connection on my "old type" fuse box (photo available if needed) in the garage to a single 2 gang 3 pin socket (approx 3 metres away) - there is no return cable. I'm wanting to add extra sockets - what options do I have?
Many thanks.

 

[pc1966]

It would be for the existing double socket (i.e. no additional sockets).

Changing from a normal socket to an RCD one here is a definite improvement in safety, but if it has a 45A fuse feeding it on 2.5mm T&E then it is a serious fire risk. Yes, the sockets are limited by 2*13A fuses, but in the event of a cable fault that fuse is unlikely to be acceptable.

If that is the case, whoever installed it in the first place has made a major and pretty fundamental mistake, and that in turn calls in to question other aspects of the installation.

 

[alljohn]

Changing from a normal socket to an RCD one here is a definite improvement in safety, but if it has a 45A fuse feeding it on 2.5mm T&E then it is a serious fire risk. Yes, the sockets are limited by 2*13A fuses, but in the event of a cable fault that fuse is unlikely to be acceptable.

If that is the case, whoever installed it in the first place has made a major and pretty fundamental mistake, and that in turn calls in to question other aspects of the installation.

I've decided to shelve the additional sockets idea until I can get this problem sorted out - I understand that the 45A fuse is not acceptable and will replace it so could you advise what size fuse I should have in there.
Many thanks

 

[Dartlec]

I've decided to shelve the additional sockets idea until I can get this problem sorted out - I understand that the 45A fuse is not acceptable and will replace it so could you advise what size fuse I should have in there.
Many thanks

It looks like someone in the past may have used the circuit designed for a cooker to run the 2.5mm to your garage socket.

The right hand fuse looks like it might be a cartridge type, rather than fuse wire (I'm not sure they made 45A fuse wire). It's possible that a different fuse was been put in. (a 15A or 20A would likely have been appropriate depending on circumstances) - Is the 45A you are quoting from the fuse itself, or the cover? I can't make out on the photo....

The issue is that the carriers are not widely available new now, and second hand replacements from ebay are not a good solution in all but the most extreme cases. Because you would now be modifying the board and circuit (even if for the better), technically it might become a notifiable job under Part P

This is the sort of job that it really is worth trying to find a local electrician, who can have a proper look at to identify the best solution forward. If you can find a small company or a one man band, an hours worth of labour would be well worth it - or some might even offer a free quote for the work.

A good electrician won't immediately just say you need a board change (although that board is now very old and if you are planning more work it may well be a good idea for many reasons), but will be able to consider the many factors involved in judging what an safe and compliant installation would be.

To your original question, had everything been in order, then a fused spur (or possibly RCD fused spur) to replace the existing socket would have allowed you to add several sockets safely.

I'm guessing there has never been an EICR (Periodic Inspection) on this property so you have no certificates to refer to?

 

[alljohn]

It looks like someone in the past may have used the circuit designed for a cooker to run the 2.5mm to your garage socket.

The right hand fuse looks like it might be a cartridge type, rather than fuse wire (I'm not sure they made 45A fuse wire). It's possible that a different fuse was been put in. (a 15A or 20A would likely have been appropriate depending on circumstances) - Is the 45A you are quoting from the fuse itself, or the cover? I can't make out on the photo....

The issue is that the carriers are not widely available new now, and second hand replacements from ebay are not a good solution in all but the most extreme cases. Because you would now be modifying the board and circuit (even if for the better), technically it might become a notifiable job under Part P

This is the sort of job that it really is worth trying to find a local electrician, who can have a proper look at to identify the best solution forward. If you can find a small company or a one man band, an hours worth of labour would be well worth it - or some might even offer a free quote for the work.

A good electrician won't immediately just say you need a board change (although that board is now very old and if you are planning more work it may well be a good idea for many reasons), but will be able to consider the many factors involved in judging what an safe and compliant installation would be.

To your original question, had everything been in order, then a fused spur (or possibly RCD fused spur) to replace the existing socket would have allowed you to add several sockets safely.

I'm guessing there has never been an EICR (Periodic Inspection) on this property so you have no certificates to refer to?

It is a cartridge with 45A on the sealed case so no access to the fuse wire to change it. I'll get a local electrician to look at it but in the meantime would it be better to change it to a 20A fuse either cartridge or carrier with the correct fuse wire? You're right in assuming there isn't an EICR certificate to look at.

 

[Dartlec]

It is a cartridge with 45A on the sealed case so no access to the fuse wire to change it. I'll get a local electrician to look at it but in the meantime would it be better to change it to a 20A fuse either cartridge or carrier with the correct fuse wire? You're right in assuming there isn't an EICR certificate to look at.

If all that is connected to it is currently the one double socket, and you don't plug in any large loads (say over 3kW or 13A) then it is probably not an immediate danger (it has likely been like this for some time?).

It's probably better to leave the possibilities to an electrician who can inspect personally to decide on the options. Changing it to a 20A may well be possible and would obviously be better than what is there, but if the cable runs through insulation or is not actually 2.5mm for example, then it may not.

It's also possible that the cable has been damaged by overheating if something has previously been run from it while it was fused incorrectly.

Testing that is something that can only be done by the correct tester, and I'd certainly be doing that before adding anything to the other end of it.

Changing it to a 20A fuse carrier usually involves changing the plastic shield behind as well (They are keyed so the correct colour fits with the correct fuse carrier and fuse), which can expose live parts directly and therefore is definitely not recommended to anyone without the relevant competance.

 

[alljohn]

If all that is connected to it is currently the one double socket, and you don't plug in any large loads (say over 3kW or 13A) then it is probably not an immediate danger (it has likely been like this for some time?).

It's probably better to leave the possibilities to an electrician who can inspect personally to decide on the options. Changing it to a 20A may well be possible and would obviously be better than what is there, but if the cable runs through insulation or is not actually 2.5mm for example, then it may not.

It's also possible that the cable has been damaged by overheating if something has previously been run from it while it was fused incorrectly.

Testing that is something that can only be done by the correct tester, and I'd certainly be doing that before adding anything to the other end of it.

Changing it to a 20A fuse carrier usually involves changing the plastic shield behind as well (They are keyed so the correct colour fits with the correct fuse carrier and fuse), which can expose live parts directly and therefore is definitely not recommended to anyone without the relevant competance.

Thanks for all your help.

 

[westward10]

To reduce the fuse size you need to buy a complete new carrier as a smaller BS1361, 20A fuse will not fit a 45A carrier.

 

[alljohn]

The only 20A fuse carriers I can find are on ebay (please let me know if you know where I can get a new one from). Would I be able to use something like:

Wylex Plug in Breaker B Type

Converts Wylex standard rewireable fuse holders or cartridge fuse holders to MCBs.Includes breaker and colour coded contact shield base.

www.toolstation.com

In either case would it fit straight into the 45A socket?
Thanks

 

[pc1966]

You won't get a new one for that board, they stopped making that sort decades ago.

What you have found will fit the rewirable fuses in that board, and as such is a useful improvement (safer to reset without skill, no risk of wrong fuse fire size being used, etc).

But that dangerous use of the 45A fuse for that circuit is not going to be an easy fix.

Best solution would be a new board with full RCD protection (e.g. all-RCBO, given the small number of circuits), which is definitely outside of DIY scope.

 

[alljohn]

You won't get a new one for that board, they stopped making that sort decades ago.

What you have found will fit the rewirable fuses in that board, and as such is a useful improvement (safer to reset without skill, no risk of wrong fuse fire size being used, etc).

But that dangerous use of the 45A fuse for that circuit is not going to be an easy fix.

Best solution would be a new board with full RCD protection (e.g. all-RCBO, given the small number of circuits), which is definitely outside of DIY scope.

Would there be any benefit in putting a fused connector unit before the socket? if so, what size should the fuse be?
Thanks

 

[Pete999]

Would there be any benefit in putting a fused connector unit before the socket? if so, what size should the fuse be?
Thanks

13 Amp. . .

 

[pc1966]

There comes a time when you have to step back, look at something, and take a difficult decision that might cost more money now but is going to save you a lot in the future.

If you had a car that was 10 or so years old and the garage told you it needs a grands worth of work to get it through its MOT in most cases you would call it quits and replace it, as you can see it is downhill from that point onwards.

Here you have a fuse board that is at least 30 years old, has an identifed serious risk in how it is currently connected, and quite possibly other non-obvious faults that thankfully have not yet caused an obvious problem, fatal shock, or fire.

I am advising you to get a professional electrician it to replace the board and sort out that issue at the same time. Do your homework in finding a couple of local sparks who have a good reputation, are members of a professional body, and clearly it is their main job. Get a couple of quotes and if you have any queries folk on here will be helpful.

I can't speak for any others, but I am reluctant to offer any more advice because I don't think you can safely resolve all of the possible issues here. I have nothing to gain from telling you to get someone in - I don't even do that sort of work as a commercial service - and others here are retired or not in your area, so this advice is based on a genuine concern for your safety.

 

[alljohn]

There comes a time when you have to step back, look at something, and take a difficult decision that might cost more money now but is going to save you a lot in the future.

If you had a car that was 10 or so years old and the garage told you it needs a grands worth of work to get it through its MOT in most cases you would call it quits and replace it, as you can see it is downhill from that point onwards.

Here you have a fuse board that is at least 30 years old, has an identifed serious risk in how it is currently connected, and quite possibly other non-obvious faults that thankfully have not yet caused an obvious problem, fatal shock, or fire.

I am advising you to get a professional electrician it to replace the board and sort out that issue at the same time. Do your homework in finding a couple of local sparks who have a good reputation, are members of a professional body, and clearly it is their main job. Get a couple of quotes and if you have any queries folk on here will be helpful.

I can't speak for any others, but I am reluctant to offer any more advice because I don't think you can safely resolve all of the possible issues here. I have nothing to gain from telling you to get someone in - I don't even do that sort of work as a commercial service - and others here are retired or not in your area, so this advice is based on a genuine concern for your safety.

No, that's fine - just looking for a short-term solution until finances allow for a proper resolution. Many thanks for all your help.

 

[pc1966]

No, that's fine - just looking for a short-term solution until finances allow for a proper resolution. Many thanks for all your help.

I know that finding ~£500 is not always easy or possible, but really don't touch that circuit at all - disturbing it could trigger a fault which it is not adequately protected against. Better still pull the 45A fuse and wait until it can be safely sorted.

If the circuit protection was good then no problems with advising you how to add a socket, but not when it is the electrical equivalent of an unexploded bomb.

Out of curiosity I tried to calculate what would happen if there was a L-E fault at the remote socket, making some broad assumptions on the way:

• Your supply is 230V with an impedance of 0.3 ohms, roughly split between the service live and earth (a little below the assumed worst case for TN-C-S supplies).
• You have about 30m of 2.5mm T&E with a 1.5mm earth conductor
• The fuse is a 45A one following the curves in Figure 3A1 of the 18th edition wiring regulations

This leads to the following equivalent circuit:

In the event of a fault you have a supply impedance to the end point R1 of 0.15+0.222 = 0.372 ohms, and an earth/CPC impedance R2 of 0.15+0.363 = 0.513 ohms

As a result around 260A flows and anyone touching the end "earth" would find it at 133V above the true earth potential. Assuming they have an approximate impedance of 1.875k ohm to Earth (the 50% 100V case from Wikipedia) they would get a 71mA shock, this is above the "let go threshold" so they would probably suffer it until the fuse cleared the fault.

The fuse would take around 2.25 seconds to disconnect, that puts a 71mA shock in the 5-50% probability region of causing heart fibrillation and likely resulting in death. If someone was unlucky and a bit damp, the current could be easily 50% higher and at this sort of exposure time solidly in the > 50% chance of fibrillation.

During that fault time the conductors in the T&E cable would reach about 266C, so around 100C above the short-term damage level. So even if no one is electrocuted, and no bad connections to create higher temperature hot spots, the whole circuit (and possibly any bundled with it on route) would have to be rewired.

If you re-run the calculations with 0.8 ohm supply impedance, the upper 5% or so of a TN-S supply (which yours looks a bit like from the photo), then you get around 166A flowing and a resulting disconnection time of around 35 seconds. As a result the 2.5mm T&E's CPC conductor would reach a temperature of around 623C, most likely starting a fire.