Garage fused spur - modification/repair

[JakeyBlee]

Hi all. Around a year ago I got a sparky in to 'extend my upstairs ringmain into the garage connected to the adjoining wall'. He completed the work and put in two working double sockets and light spur (fused), so to my knowledge at this time I was happy with what he had done.

Now a year on I have more electrical knowledge I see that he didn't extend the ring, but instead put in a fused spur from an upstairs socket. I've also noticed that the fuse he put in only isolated my ring camera and not the sockets themselves.. My issue is I run 2000w mitre and table saws alongside vacuums on these sockets so if it were wired up right surely the 13A fuse would be triggered?

I'm brainstorming the best way to overcome this issue and would appreciate feedback. Do i:

1. Pull another 2.5mm wire into the garage from another socket in the upstairs ring and just change the spur into a ring extension.

2. Pull another 2.5mm from another socket and have this supply the one double socket I use for the saws, and let the current spur feed everything else.

3. Fix the wiring of the fuse so it covers all the sockets and just hope that it doesn't melt it when I use the heavy power tools.

Thanks in advance!

 

[JohnW2]

Around a year ago I got a sparky in to 'extend my upstairs ringmain into the garage connected to the adjoining wall'. He completed the work and put in two working double sockets and light spur (fused), so to my knowledge at this time ..... Now a year on I have more electrical knowledge I see that he didn't extend the ring, but instead put in a fused spur from an upstairs socket. I've also noticed that the fuse he put in only isolated my ring camera and not the sockets themselves.. My issue is I run 2000w mitre and table saws alongside vacuums on these sockets so if it were wired up right surely the 13A fuse would be triggered?

Are you saying that he fed just your camera via a fused spur (which, in itself, would be fair enough) but that the two double sockets were fed as an unfused spur (which is 'all wrong')?

If so, are you asking about the situation if you corrected that situation by also feeding the sockets from the fused spur/ As you imply, if you then had two of the sort of loads you mention running simultaneously (perhaps unlikely?), the current demand would exceed 13A. If you think such loading (for significant periods of time) is 'likely', then you shouldn't really deliberately create such a situation - although, in reality is takes around 22A (about 5,000W) to blow a 13A fuse, the fuse could overheat and the cable could theoretically become overloaded.

I'm brainstorming the best way to overcome this issue and would appreciate feedback. Do i:
1. Pull another 2.5mm wire into the garage from another socket in the upstairs ring and just change the spur into a ring extension.

You are presumably talking about try to turn it into a proper 'extension of the ring'. If so, that's obviously possible (and really the ideal solution), but not quite as simple as you seem to be suggesting - so, if you wanted to pursue that approach, let us know and someone will explain.

2. Pull another 2.5mm from another socket and have this supply the one double socket I use for the saws, and let the current spur feed everything else.

You could do that. Strictly speaking, the socket supplied by the existing spur (as well as the camera) should also be fed 'via the fuse' since, a spur should not supply 'two things' (i.e. the FCU for the camera and a socket), even if one of them has a fuse. A 'fourth option' would be to leave the FCU just supplying the camera and connecting yet another 2.5mm² cable to some socket for one of the garage sockets - although that would seem a bit 'OTT'!

3. Fix the wiring of the fuse so it covers all the sockets and just hope that it doesn't melt it when I use the heavy power tools.

As above, if you consider it likely that loads greater than 13A (about 3,000W) are likely to exist for significant periods of time, that's not really 'nice'/'wise' (and certainly not 'good design practice') - although, as I've implied, you would probably 'get away with it'. However, if you feel it unlikely that there will be such loads (if it's 'just you', presumably you won't be using the two saws simultaneously?), then it would be a reasonable approach. After all, we have a bit more of a crystal ball here than a designer usually does - if he/she designs a 13A fused spur with two or more double sockets (which is perfectly 'allowed') he/she has no certain idea of what may be plugged into the sockets in the future.

Kind Regards, John

 

[JakeyBlee]

Yes so he ran a 2.5mm cable from a socket in the upstairs ring into a 13A fuse, which then exited into the camera, and a radial circuit of two double sockets and then a fused switch for the lights, but I had an earth fault about a month ago requiring me to open up all the boxes and at this point I realised only the camera was on the other and of the 13A fuse. So although he signed off the work because of the radial being on the wrong side of the fuse its not meeting regs.

Yes so when I say extend the ring I mean to route a second 2.5mm wire from the same ring as before from the next socket along the ring, and then disconnect the two sockets from each other so the ring instead travels around the garage and then back up. It wouldn't add much cable to the ring as the house is only a small floor plan.

I completely get that the fuse should be covering the sockets and the camera as the cable connecting the upstairs socket to the fuse needs all of its load protected by 13A. My only concern prompting this is that when I use my mitre saw (2000w) and my Henry hoover for dust collection (1200w) I am concerned that this along with the camera and the lights will be significant enough to melt the 13A fuse. This wouldn't have happened so far as the sockets have mistakenly bypassed that fuse. Due to this obviously something has to change so the spurred wire is protected from overheating.

Thanks for the quick reply!

 

[EFLImpudence]

I completely get that the fuse should be covering the sockets and the camera as the cable connecting the upstairs socket to the fuse needs all of its load protected by 13A.

Yes but only because the 13A fuse is the maximum that will fit in an FCU. 2.5mm² T&E can carry 27A so a 25A fuse would do if there were one - or he could have fitted a different overcurrent device - or he could have used 4mm² cable.

My only concern prompting this is that when I use my mitre saw (2000w) and my Henry hoover for dust collection (1200w) I am concerned that this along with the camera and the lights will be significant enough to melt the 13A fuse.

3200W is 13.33A (plus a little for camera and lights) so not likely - and as for exceeding the 27A of the cable....

 

[JakeyBlee]

Yes but only because the 13A fuse is the maximum that will fit in an FCU. 2.5mm² T&E can carry 27A so a 25A fuse would do if there were one - or he could have fitted a different overcurrent device - or he could have used 4mm² cable.


3200W is 13.33A (plus a little for camera and lights) so not likely - and as for exceeding the 27A of the cable....

I'm guessing the initial voltage spike of saw start up wouldn't be long enough to burn the fuse? I might just hook up the fuse and try the saws and see what the fuse does?

Thanks for the reply

 

[JohnW2]

I'm guessing the initial voltage spike of saw start up wouldn't be long enough to burn the fuse? I might just hook up the fuse and try the saws and see what the fuse does?

To be correct, it's actually a spike of current, not voltage, at startup. That start up current for a motor can be very high (10 or more times the 'running' current) but, as you surmise, the duration is far too short to blow a fuse.

It would be different for a 'standard' ('Type B') MCB. If you could get a 13A one of those (which you probably can't),it would only take about 65A to trip it immediately, which your motors might well do. There are 'special' ('Type C' and 'Type D') MCBs available for such situations.

Kind Regards, John

 

[JohnW2]

.... I realised only the camera was on the other and of the 13A fuse. So although he signed off the work because of the radial being on the wrong side of the fuse its not meeting regs.

Thanks for confirming - that's what I thought you meant.

Yes so when I say extend the ring I mean to route a second 2.5mm wire from the same ring as before from the next socket along the ring, and then disconnect the two sockets from each other so the ring instead travels around the garage and then back up. It wouldn't add much cable to the ring as the house is only a small floor plan.

Fair enough. That would, indeed, be the correct way to extend the ring. As I said, what some people might call the 'ideal' solution, but probably not really necessary in your situation - but it obviously would be more 'flexible' if your needs increased in the future..

I completely get that the fuse should be covering the sockets and the camera as the cable connecting the upstairs socket to the fuse needs all of its load protected by 13A. My only concern prompting this is that when I use my mitre saw (2000w) and my Henry hoover for dust collection (1200w) I am concerned that this along with the camera and the lights will be significant enough to melt the 13A fuse.

As EFLI has said, even one saw plus the Henry is only fractionally over 13A (and camera+lights would be negligible), so really not a problem if you changed things so that the sockets (as well as camera) were protected by the fuse. As I implied, you're presumably never going to use both saws at once.

Kind Regards, John

 

[SUNRAY]

13A mcb... no problem. Limited makes though

Eaton EMCH113 MCB SP C 13A

<p>Memshield 3 is a range of MCCB panelboards and accessories manufactured by Eaton. The range includes panelboards ranging from 25A to 800A and can be used for between 4 to 18 Triple Pole ways. There is a tin-plated busbar system throughout the range, as well as protection against contact with...

www.tradesparky.com

Miniature Circuit Breaker (MCB) B, 13A, 1-pole, 6kA - Online Shop - Schrack Technik International

Miniature Circuit Breaker (MCB) B, 13A, 1-pole, 6kA

www.schrack.com

 

[JohnW2]

13A mcb... no problem. Limited makes though

I know they exist but, for those concerned about 'type tested', I don't think they are available for many of the common makes of CU

Kind Regards, John

 

[EFLImpudence]

...unless all "type-testing" is the same.

 

[JohnW2]

...unless all "type-testing" is the same.

However, what we do know is that not all devices are (without 'violent modification') mechanically compatible with all CUs, so there are certainly some issues. I'm far less convinced about the relevance of possible 'electrical compatibility'.

Kind Regards, John

 

[SUNRAY]

Hi all. Around a year ago I got a sparky in to 'extend my upstairs ringmain into the garage connected to the adjoining wall'. He completed the work and put in two working double sockets and light spur (fused), so to my knowledge at this time I was happy with what he had done.

Now a year on I have more electrical knowledge I see that he didn't extend the ring, but instead put in a fused spur from an upstairs socket. I've also noticed that the fuse he put in only isolated my ring camera and not the sockets themselves.. My issue is I run 2000w mitre and table saws alongside vacuums on these sockets so if it were wired up right surely the 13A fuse would be triggered?

I'm brainstorming the best way to overcome this issue and would appreciate feedback. Do i:

1. Pull another 2.5mm wire into the garage from another socket in the upstairs ring and just change the spur into a ring extension.

2. Pull another 2.5mm from another socket and have this supply the one double socket I use for the saws, and let the current spur feed everything else.

3. Fix the wiring of the fuse so it covers all the sockets and just hope that it doesn't melt it when I use the heavy power tools.

Thanks in advance!

Number one point... Don't panic.

As I understand it you currently have this:

The existing house ring at the top and garage at bottom.



In my view the useage of your garage warrants improving the supply. The current set-up does not conform to regs. However I wouldn't be panicking to make changes.

2 suggestions:

Run a cable from another socket as you have already offered and make part of the existing ring redundant.

Run a cable to the existing source of the spur and add a connector in the backbox if there is space

I'm not sure from your description how the lights come into this.

Other peoples suggestions are also valid.

With the useage of the garage, my personal preference would be a new circuit from the consumer circuit to reduce the chances of something in the garage tripping the house circuit, or for that matter something in the house plunging the garage into darkness with rotating machinery still turning.

 

[JakeyBlee]

Fantastic, thanks for all the replies!

I think ill just trial connecting the fuse up properly and seeing if the saws melt the fuse. I want to add a socket on the other side of the garage but for low wattage stuff, so itl look like this:

If this fails and the fuse blows then ill extend the ring. Im just concerned how ill identify which of the wires in the upstairs sockets is the redundant one to remove... But ill cross that bridge when i come to it. The extended ring will look as follows:

Again, thanks for all the replies and discussion

 

[JohnW2]

Number one point... Don't panic.

I agree - and hope that view has been apparent from all I have written

In my view the useage of your garage warrants improving the supply. The current set-up does not conform to regs.

Indeed not, and the OP obviously understood that it was non-conformant with regs - hence his questions about options for remedying that..

2 suggestions:
(1) Run a cable from another socket as you have already offered and make part of the existing ring redundant.
(2) Run a cable to the existing source of the spur and add a connector in the backbox if there is space

Yep, both good suggestions and both conformant.

However, as I've implied, given that the OP's currently foreseeable total load is only fractionally in excess of 13A (and even that presumably only for very brief durations) to merely move the garage sockets onto the load side of the FCU would, in reality be quite adequate. One can debate/argue about what may happen 'in the future', but that's always the case when one installs a fused spur with multiple sockets, since the designer and installer can never know for sure what loads may be 'plugged in' in the future.

With the useage of the garage, my personal preference would be a new circuit from the consumer circuit to reduce the chances of something in the garage tripping the house circuit, or for that matter something in the house plunging the garage into darkness with rotating machinery still turning.

Both theoretically valid issues. However, I would say that the first is pretty trivial (rare, and easily rectified). As for the second, I would point out (as I always do when people fuss about 'division of circuits' between RCDs) that what you suggest would do nothing to prevent "... plunging the garage into darkness with rotating machinery still turning" if that happening was due to a power cut, so I would (and do) personally always address that possibility by having emergency lighting installed wherever significant fixed 'rotating machinery' is installed/used.

Kind Regards, John

 

[EFLImpudence]