Supply to outbuilding....

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JT1

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I'm a new member...hello.

The project is the installation of a supply to a workshop / shed & a second shed in the back garden of a residential property. The property is a ground floor maisonette with solid concrete floors.

I have made a sketch of the site but I believe I cannot add it at this stage, so I will describe it:

The consumer unit is located in a cupboard in the middle of the property: single phase with equipotential bonding, metal cased c/u. The route of the internal cable, runs from the cupboard to the bathroom, under the bath, through to a bedroom to the point out of the external wall to the back garden. I have dug a trench to the shed for the SWA cable. The length of the internal wiring to the point it exits the property is a total of 11m approx. The length of the trench to the workshop / shed is 12 metres. I plan to install a garage / builders RCD unit in the shed to provide for 2 plug sockets, 4 inside lights & 4 outside lights & then back out to another trench 1.5 metres long to the second shed which requires 4 plug sockets & 4 inside lights.

The first shed is primarily used as a workshop for using woodworking small wood tools...the biggest being a 1600 Watt sliding cross cut mitre saw, I have several small saws & drills but only one will be used at a time. There will be no lathe! I will need to run a laptop at the same time as a tool sometimes & the lights will need to be on, I will use low energy leds. The second shed is for a model train set with a small load. I want to be able to turn on the outside lights located at the shed, from the house.

As a reference I am reading: " Electrical installation work 2nd edition" by Brian Scadden. I am trying to understand but am struggling with working out the size of the cable I need, there is a lot of information to take in - I understand the concern about voltage drop with longer cable runs & I would prefer to upscale the size of the cable to ensure it is big enough. Where I am struggling more is working out the size of the load? I have looked at "Doncaster cable" website which has a cable size calc & also TLC direct which has one too. I first thought I would need 2.5mm SWA cable, then 4mm but now thinking bigger? The SWA will sit in the trench on a bed of sand & will be covered by warning tape. However, I need to run a type of conduit too, to allow for a cable to the light switch at the house?

Other information: Ambient temperature assumed at under 30 degrees. T&E 3C cable from the property c/u to the outside wall to be the same size as the SWA cable to the shed. The connections within the IP rated junction box will be earth continued ( if that's the way to say it!?). At the shed the SWA cable will be finished in a junction box & the cable to the RCD unit will be fed through the back of the box. Inside the shed I am assuming I need metal clad boxes/fittings with metal conduit? 

I will try to answer any questions asked to provide an accurate picture.

Thank you.

 
I 'm guessing you'er an apprentice  by the way you write and references you make .    No problem anyway .  

 You need to to decide what the "Design load" is  and the length  then work out your cable size .     We can help with that .  

This extra conduit for a light  ?Why swithed from the house ?    Extra work.     Put a board  in the shed and feed everything from there , don't run extra cables back for lights etc. 

You refer to steel conduit in the sheds ....  PVC conduit  would be fine ,  steel probably OTT  .  

Don't go mad with the cable size ....doubtful all the machines will be used at the same time  , specially if theres only one person in there. 

 
Run a CAT6 cable for data and install a switch and WiFi unit in your main workshop, have all the lighting you require to be operated by smart switches.

 
Last edited by a moderator:
I 'm guessing you'er an apprentice  by the way you write and references you make .    No problem anyway .  

 You need to to decide what the "Design load" is  and the length  then work out your cable size .     We can help with that .  

This extra conduit for a light  ?Why swithed from the house ?    Extra work.     Put a board  in the shed and feed everything from there , don't run extra cables back for lights etc. 

You refer to steel conduit in the sheds ....  PVC conduit  would be fine ,  steel probably OTT  .  

Don't go mad with the cable size ....doubtful all the machines will be used at the same time  , specially if theres only one person in there. 
Thanks for the reply. I will try to work out the design load - as I said in my original post, my tools will be used one at a time. In order to work it out I need to calculate the total wattage for all the tools? 

The length?...I have already given the length of the cable run - what length do you mean?

The reason for the switch at the house is so my wife can walk down the garden after dark. I don't mind the extra work but it will be much more convenient for us to be able to turn the lights on at the house. For example, if we leave the lights on by accident, then we would need to walk down to the shed to turn the lights off & then walk back in the dark. This can be tricky when you have dogs & they don't mind where they do it!!

If PVC conduit is good enough, then I will go with that, thanks. I will defo use conduit because I find the cable itself ugly when on show.

 
Run a CAT6 cable for data and install a switch and WiFi unit in your main workshop, have all the lighting you require to be operated by smart switches.
Thanks for the reply. This is really a grey area for me. What you are suggesting sounds great - convenient but I will need to have a better understanding of these types of system. I will do some research.

I have wifi in the property, is a wifi unit in the shed possible without cable, as an extension? I think I have a signal booster gadget somewhere?

 
Thanks for the reply. This is really a grey area for me. What you are suggesting sounds great - convenient but I will need to have a better understanding of these types of system. I will do some research.

I have wifi in the property, is a wifi unit in the shed possible without cable, as an extension? I think I have a signal booster gadget somewhere?
......oh OK, it's the naming of the cable was unfamiliar to me. I understand now, thank you & yes it's a good idea - Iv'e already dug the trench so could lay that cable too. However, I assume it is an extension of the line coming in from the supplier & unfortunately this is in an awkward position the other end of the property. I will experiment with trying the existing set up first.

 
Your workshop may need heating in winter?   A 3kW fan heater or similar may be your biggest single load. I have a similar workshop setup with a hand-wash basin and instant water heater which whilst very intermittent is another significant load. 

 
Your workshop may need heating in winter?   A 3kW fan heater or similar may be your biggest single load. I have a similar workshop setup with a hand-wash basin and instant water heater which whilst very intermittent is another significant load. 
Thanks for the reply.

Good thought,  it has been insulated, I think it will be manageable as is. 

 
Thanks for the reply. This is really a grey area for me. What you are suggesting sounds great - convenient but I will need to have a better understanding of these types of system. I will do some research.

I have wifi in the property, is a wifi unit in the shed possible without cable, as an extension? I think I have a signal booster gadget somewhere?
You can get WiFi units that will cover the distance but these are quite expensive, running a cable and using a second WiFi unit with the same network ID and password as your main one will allow seamless transfer between the two.

Smart switching is becoming more popular as it is a lot easier than you think and adds a lot of options and convenience at low cost.

 
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