Discuss DIY- advice on extending wiring into new shed in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

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.
 
@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).
 
Last edited:
@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.
 
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.
 
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:
[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.
 
Last edited:
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
[automerge]1585909978[/automerge]
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:
[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 .
 
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. ;)
 
DeWalt 745 does not have an induction motor, so will be very noisy comparatively, big consideration in a small shed.
[automerge]1585921647[/automerge]
That’s the dream right there!....

Are you Susan Boyle under that disguise.
 
Last edited:
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)
[automerge]1585985525[/automerge]
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 !
 
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.
 
What size cable is actually feeding the garage where the shed is fed from?
 

Reply to DIY- advice on extending wiring into new shed in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock