UK DIY- advice on extending wiring into new shed

[swisstony]

Hi all, DIY here
First off let me just say it is advice I am after as I am fully aware that I will probably need an electrician to complete the job. My question is how much I can do myself up to a point.
So many years ago I built a shed at the top of the garden ( approx 30m away from garage). I needed power and lighting to the shed so purchased the armoured cable, fixings, outdoor sockets etc (on the advice of my sparky) and did the labour myself of digging the trench from the garage (where the feed would be ) laying the cable including tape, drainage etc. Then my sparky came in and did all the easy work Actually he was brilliant and connected up all the power, changed the fuse in the main board, added in lighting and fitted the exterior sockets for the garden. Tested and provided me with the certificate. All good.

So my next plan is to build even a bigger second shed behind the first one . During this lockdown project a man's got to have a project ! So I am building it myself over the course of the next few months. It will be positioned around 2 feet away from the first shed ( have attached a small rough diagram) . So the question at last : I would like to have power and lightning in the new shed (approx 10ftx8ft) pent roof style. So given that it will be so close to the old shed , how hard is to extend the power and lighting circuit into the new shed ? I will be using it as a small wood workshop so will need power sockets around the perimeter at worktable height. Probably about 4 double sockets. Lighting will be simple LED shop lights x 2 on the ceiling. nothing fancy.

How much could I do for the prep work ?
would it be an extension from inside the old shed across to the new shed or would it be a spur from the original feed ?
power tools are all 220V , I don't have any that are 110V

Thank you for any advice
cheers

 

[Baddegg]

What size cable and fuse/mcb are feeding the original shed mate?

 

[swisstony]

What size cable and fuse/mcb are feeding the original shed mate?

good point, I guess I could find that out by looking back at the invoice he sent me ?

 

[buzzlightyear]

given that it will be so close to the old shed , how hard is to extend the power and lighting circuit into the new shed ?

with out bursting your balloon, I would wait till this pandemic is over and get the spark back when he did the first shed.You mess up it will cost you, it is not easy until you know what you are doing.

 

[Baddegg]

good point, I guess I could find that out by looking back at the invoice he sent me ?

Possibly mate....have a look and let’s us know, you should be able to determine the protective device for the armoured by looking at your consumer unit or post up a picture

 

[swisstony]

with out bursting your balloon, I would wait till this pandemic is over and get the spark back when he did the first shed.You cock up it will cost you, it is not easy until you know what you are doing.

true. I wasn't trying to do it all myself. I was seeing how much legwork I could do myself in readiness when everything has calmed down
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What size cable and fuse/mcb are feeding the original shed mate?

can't find the original order for the SWA cable but attached is his minor works , that may help
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Possibly mate....have a look and let’s us know, you should be able to determine the protective device for the armoured by looking at your consumer unit or post up a picture

I know he had to change the fuse from 32A to 20A as it was incorrect. Think he mentioned it in his invoice
Like "
Install a 20 amp Contactum MCB in consumer unit to replace existing overated 32 amp one."

 

[Baddegg]

Looks like you’ve only got a 2.5 mm armoured cable there mate, what sort of woodworking equipment are you thinking?.....you’ve also left the sparks name and address on there mate....not cool ?

 

[westward10]

Attachment deleted. If you can obscure the contractors details you can put it back up.

 

[swisstony]

Looks like you’ve only got a 2.5 mm armoured cable there mate, what sort of woodworking equipment are you thinking?.....you’ve also left the sparks name and address on there mate....not cool ?

whoops sure he won't mind . nothing too major. I will have a chop saw, various other power tools, shop vac . Nothing that has a massive draw that I can think of and none that would be working at the same time .
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attachment edited !

 

[pc1966]

At a quick look then you should be fine if all you want to run is something that hangs off a 13A plug normally. For example a small lathe, drill, etc.

What is there in the old shed in terms of how the armoured cable is terminated? Is there a small consumer unit (fusebox) to split it between the lights and 13A socket, etc?

You really have two options for the cable run. Obvious and proper one is another short run of armoured cable underground between the two sheds. For that you would need more of the same 2.5mm SWA cable but make sure you leave plenty to allow easy termination at both ends by the electrician. If digging then obviously take great care not to damage the existing wire!

But given short distance span, if high enough not to be a hazard if you are doing any maintenance, and properly supported (by metal conduit or a steel wire, etc), you could run some outdoor rated cable overhead between them as an alternative to buried cable.

 

[buzzlightyear]

A minor for a new supply to a shed I don't think so.

 

[westward10]

2.5 over 30m, 20A protective device exceeds the 3% volt drop for the lighting as it stands now.

 

[swisstony]

2.5 over 30m, 20A protective device exceeds the 3% volt drop for the lighting as it stands now.

At a quick look then you should be fine if all you want to run is something that hangs off a 13A plug normally. For example a small lathe, drill, etc.

What is there in the old shed in terms of how the armoured cable is terminated? Is there a small consumer unit (fusebox) to split it between the lights and 13A socket, etc?

You really have two options for the cable run. Obvious and proper one is another short run of armoured cable underground between the two sheds. For that you would need more of the same 2.5mm SWA cable but make sure you leave plenty to allow easy termination at both ends by the electrician. If digging then obviously take great care not to damage the existing wire!

But given short distance span, if high enough not to be a hazard if you are doing any maintenance, and properly supported (by metal conduit or a steel wire, etc), you could run some outdoor rated cable overhead between them as an alternative to buried cable.

I would have to have a look but I can't recall anything.

I like the idea of the overhead run as it is such a short span and could be raised high enough to carry an outdoor rated cable . Apart from the build itself once the roof is on I doubt I will be doing any regular maintenance up there, probably guttering height and that will be it.

 

[pc1966]

2.5 over 30m, 20A protective device exceeds the 3% volt drop for the lighting as it stands now.

The measured R1+R2 of 0.21 ohm implies a 2% drop at 20A, and from some data sheet on BS5467 cable the SWA is about the same impedance as the conductors so possibly the length is only 11m? Or maybe it really was 4mm SWA cable fitted?

Something is a little odd there!
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I would have to have a look but I can't recall anything.

I like the idea of the overhead run as it is such a short span and could be raised high enough to carry an outdoor rated cable . Apart from the build itself once the roof is on I doubt I will be doing any regular maintenance up there, probably guttering height and that will be it.

At a distance of only 2 feet you could probably use a length of 3" (or whatever) plastic drainpipe between sheds (glued/sealed in place with silicone sealent) and it would be self-supporting, then simply feed a 13A extension lead through as a temporary measure.

 

[barninks]

A minor for a new supply to a shed I don't think so.

The way the OP is written it sounds like it might be an extension off another circuit? But that doesnt really make sense with the breaker change etc?

 

[swisstony]

2.5 over 30m, 20A protective device exceeds the 3% volt drop for the lighting as it stands now.

I think I over estimated the distance. It is more like 21m so extension would be 22-23m, max 24m. not sure if that makes a difference
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The way the OP is written it sounds like it might be an extension off another circuit? But that doesnt really make sense with the breaker change etc?

consumer unit is in house which feeds the garage which is where the extension was carried out from. Hope that helps

 

[barninks]

consumer unit is in house which feeds the garage which is where the extension was carried out from. Hope that helps
[/QUOTE]
yes - ok that makes more sense - as i thought. In which case you need to think about the loading in the garage as well.

 

[westward10]

Volt drop is measured from the origin so you have to include the part from the consumer unit to the garage.

 

[barninks]

Was the armoured cable run in a duct at all? or just buried in the ground?

 

[swisstony]

Volt drop is measured from the origin so you have to include the part from the consumer unit to the garage.

That does make sense. I am getting the feeling here that given the below

consumer unit is in house which feeds the garage which is where the extension was carried out from. Hope that helps

yes - ok that makes more sense - as i thought. In which case you need to think about the loading in the garage as well.
[/QUOTE]

That does make sense. I am getting the feeling here that given the above comments a) the distance b) potential voltage drop and c) potential load in new shed, I may need to consider a separate unit in one of the sheds.

So is the consensus that once we start getting back to normal that as temp measure I could run a outdoor rated 13A extension lead through some ducting to the new shed. That way I could have some power, albeit temporary and just have a work light in there until my spark can return ?
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Was the armoured cable run in a duct at all? or just buried in the ground?

buried in the ground

 

[barninks]

I wouldn't necessarily go to all the effort of running a duct from one shed to the other if you end up taking another supply from the house/garage to the new shed, especially as the existing cable is buried and so you cannot easily draw another cable through.

You really need to first ascertain the volt. drop to the existing shed.

 

[pc1966]

@swisstony Is the shed fed from a dedicated breaker in your house?
As it it only feeds the shed and not anything else in your home. Just wondering what it was used for before the electrician changed from 32A to 20A.

Edited to add: Just realised it feeds your garage!
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Before going to the effort and expense of running another SWA cable you need to be realistic about what you plan on using in the sheds & garage to determine the load, and from there you can decide if the existing circuit and cable is acceptable or not.

Assuming the measured value of 0.21 is at the garage, and your cable is 22m long, then I estimate the resistance at around 0.63 ohms. That gives a 3% drop on 230V for around 11A.

The regs have 3% for lighting circuits due to the annoying flicker you see with filament bulbs which as quite voltage-sensitive, with LED lights you won't see as much effect. For other power circuits it is 5% drop, which would be 18A max.

So think about:

• What do you have in the garage using power?
• What do you plan for old shed?
• What do you plan for new shed?

Realistically if it is DIY style workshop with only you using stuff it will be one machine at a time, plus lighting, plus any electric heating (which might be the biggest load as 2kW is around 9A).

 

[swisstony]

@swisstony Is the shed fed from a dedicated breaker in your house?
As it it only feeds the shed and not anything else in your home. Just wondering what it was used for before the electrician changed from 32A to 20A.

Edited to add: Just realised it feeds your garage!
[automerge]1585906289[/automerge]
Before going to the effort and expense of running another SWA cable you need to be realistic about what you plan on using in the sheds & garage to determine the load, and from there you can decide if the existing circuit and cable is acceptable or not.

Assuming the measured value of 0.21 is at the garage, and your cable is 22m long, then I estimate the resistance at around 0.63 ohms. That gives a 3% drop on 230V for around 11A.

The regs have 3% for lighting circuits due to the annoying flicker you see with filament bulbs which as quite voltage-sensitive, with LED lights you won't see as much effect. For other power circuits it is 5% drop, which would be 18A max.

So think about:

• What do you have in the garage using power?
• What do you plan for old shed?
• What do you plan for new shed?

Realistically if it is DIY style workshop with only you using stuff it will be one machine at a time, plus lighting, plus any electric heating (which might be the biggest load as 2kW is around 9A).

You called it . It will be 2 x LED shop lights on the ceiling with maybe a desk light on the bench for close up work. Power wise, yes it is going to be a small workshop where I do wood working. Eventually I will have a table saw, then everything else will be one at a time + lighting. Think the only time two units would be on at the same time is when I am using the shop vac (dust extraction) to any of the power tools. for example mitre saw, sander, table saw, circular saw etc.

Old shed will be converted into storage for wood. Garage currently has the tumble dryer in there ( not on all the time but if I let my wife have free rein it would !!! ) , two LED strip lights and occasionally an extension lead plugged in to work in garden or on car. oh and currently that is where the power tool battery chargers are , 3 of them.

 

[Mike Johnson]

If your proposed table saw has an induction motor that could change things, you will have to think about the surge current on start up to prevent nuisance tripping.

 

[pc1966]

If your proposed table saw has an induction motor that could change things, you will have to think about the surge current on start up to prevent nuisance tripping.

That is a good point. If needed he could have a C or even D curve 20A breaker for this and probably still meet the disconnection times (also has RCD protection so would meet it for L-E fault anyway). That might be enough for surge effects.

If the tumble dryer is used a lot along with electric heating in the shed and the tools then it might be too much, but that is for later consideration. Rather than replacing (or adding) the SWA cable he could have a separate circuit put in from main CU to the garage just for the SWA (assuming a spare location in the CU) to remove the tumble dryer from the equation.

Finally it raises a useful point, he might want to fit some sort of emergency lighting so if the power fails for any reason he is not in a dark and dangerous workshop trying to get out past various cutting tools!

Not too expensive and potentially a great feature, for example:

2W LED Non Maintained Emergency Bulkhead White

High quality polycarbonate construction with long life LED

www.cef.co.uk

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Just looked, a 20A C breaker has Zs max as 0.87 ohm which is probably met, but a 20A D is 0.44 ohms for 0.4s disconnection which is not likely to be met.

 

[swisstony]

If your proposed table saw has an induction motor that could change things, you will have to think about the surge current on start up to prevent nuisance tripping.

Dewalt 745 so I think that is induction motor with soft start
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That is a good point. If needed he could have a C or even D curve 20A breaker for this and probably still meet the disconnection times (also has RCD protection so would meet it for L-E fault anyway). That might be enough for surge effects.

If the tumble dryer is used a lot along with electric heating in the shed and the tools then it might be too much, but that is for later consideration. Rather than replacing (or adding) the SWA cable he could have a separate circuit put in from main CU to the garage just for the SWA (assuming a spare location in the CU) to remove the tumble dryer from the equation.

Finally it raises a useful point, he might want to fit some sort of emergency lighting so if the power fails for any reason he is not in a dark and dangerous workshop trying to get out past various cutting tools!

Not too expensive and potentially a great feature, for example:

2W LED Non Maintained Emergency Bulkhead White

High quality polycarbonate construction with long life LED

www.cef.co.uk

[automerge]1585909776[/automerge]
Just looked, a 20A C breaker has Zs max as 0.87 ohm which is probably met, but a 20A D is 0.44 ohms for 0.4s disconnection which is not likely to be met.

great comments and very useful. You have pointed out many things I hadn't considered
I will perhaps send over some of these to spark for consideration. In the meantime I have gleaned some useful tips on a temp measure .

 

[Mike Johnson]

Bit off subject, but do you really need a site saw? What are you going to be cutting?

 

[Baddegg]

Of course he does he a man!

 

[pc1966]

Not just a man, but a man with two sheds!
We all bow down humbly in awe...

 

[Mike Johnson]

The reason for asking is that my table saw gets very little use since buying a track saw.

I will see your two sheds and raise you four sheds, two barns and a piggery.

 

[Baddegg]

Not just a man, but a man with two sheds!
We all bow down humbly in awe...

That’s the dream right there!....

 

[Mike Johnson]

DeWalt 745 does not have an induction motor, so will be very noisy comparatively, big consideration in a small shed.
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That’s the dream right there!....

Are you Susan Boyle under that disguise.

 

[swisstony]

Bit off subject, but do you really need a site saw? What are you going to be cutting?

I think the guys said it, but yes man needs tools especially power tools Wood working is a hobby , love making and building stuff for around the house and on my wish list is a table saw as with that I can make so many alterations for rip cutting ( cross cutting is covered by mitre saw)
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The reason for asking is that my table saw gets very little use since buying a track saw.

I will see your two sheds and raise you four sheds, two barns and a piggery.

I can't beat that ! lucky ------- . I am subtly building and converting the top of the garden into man caves but don't tell the missus, she hasn't twigged yet So far up there is summer house , 1 shed, 1 gazebo which is my temp workshop then the space for the new shed. Once I clear the site up goes the new shed and then she can have the space back where the gazebo was for the spa . Though she might not like all the saw dust I have left ..whoops !

 

[radiohead]

Just looked, a 20A C breaker has Zs max as 0.87 ohm which is probably met, but a 20A D is 0.44 ohms for 0.4s disconnection which is not likely to be met.

It is covered by a 30ma RCD, the maximum permitted Zs is 1667 ohms, the maximum for the overcurrent device is irrelevant.
Also the posted MW records a TT earthing system with a remarkably low recorded Zs, something doesn't add up, unless it is getting it via the bonding.

 

[Timbo]

What size cable is actually feeding the garage where the shed is fed from?