Electrical supply to my shed

I have a steel 9mtr by 6 mtr shed, 25 metres away from our house. I am restoring a car, and use a 150 amp mig welder, 3HP air compressor, angle grinder, and 4 fluro light tubes. I only run one tool at a time, and up to 4 fluros.

I have been using a 30 metre 15amp extension lead, with an orange electrical safety box at the shed end. The extension lead is laying on the ground.

Everything works OK.

I am not here for a whipping.

What installation would you suggest to replace what I am doing?

Your temporary requirements are being supplied okay by a 15 amp extension cord, so I would imagine you won't need it replaced by something too large in size.

I am not an electrician by trade, so take what I say with a grain of salt.

I personally would be going for 10 sq mm copper cabling run on a new circuit directly from your meter box to the shed, and a circuit breaker board in the shed to distribute power to your lights and powerpoints on different circuits off that board.

Yes, that's lot larger cable than your 15a extension lead is, but do you know what voltage drop are actually getting out there when under load ? You'd be surprised how much voltage can drop by under load on an extension cord.

One thing you can do to save yourself some money, is to do the trenching yourself from the meter box to the shed, but remember that trench needs to be a minimum of 600mm deep. Don't forget to take care of storm and waste water pipes and other electrical services running underground nearby.

Even though the extension cord is doing the job at the moment, you will do your motorised tools harm if they are running at too low a voltage. You also run the risk of accidental damage to the extension cord and longer term failure of that cord by being exposed to the elements on a ongoing basis... UV will have an effect on it over time.

When I had a similar thing done about 4 years ago, the sparky charged me $1000, and I got the trench dug, but mine was done with 16mm sq.

Could you explain why that is please?

I agree with bpratt, a sub-board with circuit breakers etc in the shed running from your main fuse-box is the way to go.
I bet you'll end up with more gear as well so get the sparky to work out what you need right now plus a bit more.
I think also that it is not so much the voltage drop that would occur using that lead ( and subsequent damage ) but more the amps those tools are pulling at startup or under load.
The 3HP compressor would be the worst. It may have a continuous rating of say 10 amps but with a half full tank of air when it kicks in again it may need 15 or more to get the air pump going.
This local woodwork forum has some good info regarding guys setting up their sheds and what they require electric wise.
http://www.woodworkforums.com/forumdisplay.php?f=245
Bear in mind that woodies usually run a compressor plus a hefty dust extractor at the same time as a table saw, linisher, lathe etc so their electrical needs may be a fair bit more than yours.
A fair few members there who are either sparkies or have a lot of electrical experience.

Stewie

qebtel, any motor that is receiving less volts than it is supposed to will run hotter and therefore fail sooner ( depending on how much lower of course ) but I think voltage drop over 30m would be minimal though so it is probably a moot point but still worth pointing out. It depends how much of master6's gear is rated at 15amp. If they are all 10 amp then no problem.
Mind you the OP said that he runs everything through a portable circuit breaker and nothing has tripped so I assume his machines are operating fine on a 15 amp lead.

Stewie

Edit : I forgot to mention that adding more circuits is fine as long as your existing power supply to your house and your meter box can handle the added load.

A standard 16 amp supply (normal power point) will be fine for what you are doing. IF using multiple devices, you just need to add up thr amps all your devices . Look on the labels and see what amps they draw. Does it add up to 16? Fluoros are negligible , 4 tubes = 72watts (0.3 amps)

Here is a brief discussion on wire sizing. Google is your friend, although I think it has been discussed here too in detail.

To save money , dig the trench 600 mm deep, lay 25mm orange conduit, buy the wire and thread it through and leave enough length at both ends to be connected to its relevant point. In a shed, I dont believe lights need to be hard wired in (check that though). In my shed have a multi powerpoint plugged into the man socket , and I just plug my fluoros into that via a 3 pin plug.


Glad to hear it.

When you are getting large current draw that's when the voltage drops as it just can't get enough through.

Compare a fire hose to a garden hose, you will get the same amount of water out of both of them, except the garden hose will take a lot more work/time to get it all through due to the size difference.

For the OP, I would recommend going up as large as possible (I said 10mm), but 6mm sq could possibly be all he needs.

As he's said, he's restoring a car so chances are is that he'll end up using a lot more power tools, and no doubt he'll get help from time to time so chances are is that multiple tools will be at use at the same time. Going too light on the cabling will be a big mistake and will cost him a lot more to rectify at a later day, and that's if you can feed the larger cable down the (suggested) 25mm conduit that is now buried.




Get that going at the same time he's welding some thick plate together, that'll suck that extension cord dry I don't know the formula for working out voltage drop, but I'm sure it'd cause him big problems, definately in the long term.


Far better to bite the bullet and get it done properly the first time round, even though it will really hit the hip pocket nerve hard.

I wouldn't rely on a 16 amp circuit for a large 9 x 6 metre workshop shed. More like a 32+ amp circuit from the main switchboard to the garage, with multiple circuit breakers on the board in the garage, i.e. CB for lights, and 2 CB's for different power circuits.




The OP is going to pay the bucks to get underground power to the workshop, he'd be mad not to hardwire in his flouro's, where he can have a wall switch near the door to turn them on and off. I think the OP is trying to get away from the shambles of extension cords laying all over the place.

Running 25mm conduit underground for a cable size you are unsure of would be a mistake. 10mm cable would be a tight squeeze to thread through, and if he ran through 2.5mm cable and then upgraded to 6mm or 10mm later on, I doubt he'd be able to pull it through past the elbows. He could easily get 2.5mm TPS through the 25mm, just trying to replace it with something larger when the 2.5mm didn't work out would be a huge problem, perhaps even having to re-dig the trench.

I certainly would not go any smaller than 4mm cable for a 16 amp circuit over that distance, which might end up being longer depending upon the location of the main board and the shed. For all we know the main board might be 35m away from the shed, at least the way the cable might need to be run, even though the shed is 25m from the house.

bpratt seems to be pretty well on the money.
I wouldn't run anything less than 6mm cable to the shed.
The size of the mains to the house and current max demand should also be considered.
No point in paying for a cable that can carry 40 amps if the mains into the house can only carry another 20 amps.


My build: viewtopic.php?t=62001

Good point, not much point in being able to run 60 amps out to the shed if all you have is 80 amps or even just 63 amps coming in to the house.

All that considered, there may be times when there might be a 'need' to allocate more to a workshop shed than they have in the rest of the house, and knowing their limitations, they simply don't run anything much in the house when working in the shed. I dare most sparkies won't let you do this, because should the house be sold the next owner won't have any idea of how things are configured.

The electrical infrastructure needed in a shed is a function of the power demand, not the size of the shed.

If you read the OP's first post properly, it is not a large workshop, but a shed that is going to run one tool at a time in the pursuit of restoring a vehicle. I feel qualified to comment on this because I do the exact same thing ie a 6 x 9 shed in which I restore cars. I run a 2.5 hp compressor, and a 130 amp mig, and 4 fluoros (exactly what the OP is doing) and I can assure you 16 amps going to one power outlet is sufficient. Note the OP is currently doing it all successfully thru an extension cord.


Would be overkill and a wast of money. For what he is doing, it is just the same as having another power point added to one of the existing power ccts in his house. Cct breakers are on the main board, you dont need more again in a home based shed.


I have that setup in my shed and I know Im not mad. The fluoros are hard-mounted, the wiring all clipped to the purlins, and I run it all through a std mounted wall switch next to the door, which runs a 3 pin plug to a multi powerboard. IT all works very well, and is neat, just like a hard wired setup. No shambles, no cords laying about, the point being I did it myself, and did not pay a leccy to do it , because legally I didnt have to.


You size things correctly at the time, not to include possible upgrades later. So if he "thinks" more power is required later, he should be allowing for that now. It seems the OPs current needs is all he wants.
2.5mm or 4mm cable will fit quite comfortably inside 25mm conduit. You thread it through before laying the conduit, thus elbows are not an issue.

Yes the total cable length needs to be known. 2.5mm would do the job even on a 40m run (Voltage drop of less than 5%) , check yourself https://www.tlc-direct.co.uk/Technical/ ... eDrop.html
I used the following Power:3900Watts, Voltage:240, Length:40m

The relevant Standard is AS3000

Again, not relevant to the situation of a home handyman essentially using an additional socket.

I don't really care what you run in your shed, I was offering my suggestions to the OP based upon what I had done in the old shed we had.

Upgrading later is an expensive option for any one, and size of the shed comes down to what the owner could be putting in there at some time in the future, i.e. fridge, freezer, other heavy duty power tools.

Plug in flouro lights instead of hard wired flouros with light switches at the door could possibly be of some convenience to the OP, even if you find such things frivelous/wasteful/whatever.

No good telling my my suggestions are 'bad', they are there to provide the OP with suggestions/options. But I strongly suggest the OP would be foolish to simply run 2.5mm TPS that far underground, and try to 'save money' by getting 20mm orange conduit (which 2.5 TPS would fit in). If the OP wants to take up your suggestion, which he is free to do, I would recommend he gets 32mm orange conduit so that he could feed 6mm or 10mm down there if he finds he needs to upgrade.

You should care cos if you were paying attention you'd have read that what I & master6 are doing is identical.
Yes but you are clearly did more in that shed in terms of electrical demand than master6 is doing, so your advice is overkill. Part of the reason I am on this forum is to save people money, and I assume thats why most people are here, to get the right advice to assist in that. My observation is that people more often than not spend more than they should have.
You again miss the point, hopefully master6 got it though. Point being its another way to save money. Not everyone has oodles of cash to spend on tradies.
I can assure you there is nothing foolish about it. It is just simple physics; you have to run a substantial length of wire to drop more than 5% voltage, and for 2.5mm thats about 40 - 50metres. Also no one said anything about 20mm conduit.

Agreed, it is never a bad idea to slightly oversize underground conduits. The cost between 25mm /32mm over 25 metres would be less than $25 I think. Furthermore, if master6 wanted to run 4mm (32 A) cable its probably going to cost no more than $2 /m more than 2.5mm. The only advantage that will give him is allow him to run his compressor and welder simultaneously, which as he has said, he wont.

So if he wanted to spend an extra $100-$150 for a possible increase in electrical demand from his shed in the future sure, but if not, why bother.

What if he decided to put in a tv? Or air conditioner? What if he took up wood work?
If you were going to spend money to do this correctly, why would you limit yourself in the future?
$200 more now is a decent insurance premium than deciding in 4 or 5 years time that you want to upgrade.
Selling purposes? I have a powered shed, but don't go plugging in a heat gun and have the lights on at the same time!!

The 5% volt drop you mention is over the entire installation, beginning with the consumer mains. You're assuming that they are less than 1%.
A typical 10mm2 cable carrying 40amps over 10m is 0.75%. Now if that run goes over 10m as a lot of older properties would, or if that house draws more than 40amps, you'll quickly find yourself over that 1%.

It's pretty easy to run 40m!
It's not measured as the crow flies. It's the cable. Up the cavity from the switchboard. Through the roof the cable needs to be properly clipped or at least installed in inaccessible areas. That won't be a straight line.
Down the cavity, underground, back up into the shed, across a wall. Want another Power point? It may need to go back up and across, down. You'll have at least that 40m used in no time!

The cheapest option isn't always the best or safest option.
Not many electricians out there are going to recommend running a 2.5mm cable to a shed. That's not because they want to charge more, it's because they have to sign off their name to the job, and they sure as hell don't want to be losing their license because the client was too tight to pay an extra $200 to have it done properly.



My build: viewtopic.php?t=62001

That's the point I was trying to get across, don't short change yourself now, plan for what might just happen down the track.

No sparky will put 2.5mm across 25m to a shed, because it's bound to be a lot further than 25m, in fact at the minimum I reckon he'd be a lot closer to 35 - 40 metres with the up's and down's that are more than likely involved.

In fact I dare say that any self respecting sparky (read: not wanting to risk his licence), will not do it on anything less than 6mm cable. He'd say here's my quote, and if you get someone who's silly enough to run 2.5mm to the shed, here's my card to call me back when you are forced to upgrade.

Here's some prices from Rexel for orange conduit :-

20mm $4.21
25mm $2.90
32mm $8.42
40mm $13.09

All are 4m in length, and strangely enough 20mm is a lot more expensive than 25mm !

So if he goes for 32mm conduit, he's paying nearly 3 times as much as 25mm, but if he ends up going for thicker cable at a later, it won't go through 25mm once the conduit is laid in the ground.

I think enough has been posted here for the OP to work with, however I will continue to make corrections where I see fallacious comments being made.

In a nutshell, Master6 may choose any of the following if he wishes AND his electrician calculates the voltage presented at his power outlet is within spec.

1. Run 2.5mm (15A) to the shed , perfectly adequate for what you intend (depending on run length)
2. Run 4.0mm (32A) to the shed , perfectly adequate for what you intend and allows significanty more devices to be used (depending on run length)
3. Run 6.0mm (45A) ................. etc keep going bigger as much as you like if you want to spend the money if you like. As i have said, I agree with upgrading now if you suspect possible future use may dictate it.


But sometime it is. Going for bigger wiring doesnt make it safer if you never use the extra current you can draw. This is for the OP to work out in tandem with his leccy.

That is nonsense. The leccy is responsible for sizing it appropriately and making an installation compliant to wiring rules, nothing more. 2.5mm cable could well be approriate , if that is all the master6 ever wants.

Again, without the run length you have no way of knowing that, and I have given you the calculations to show it is possible. Nevertheless, you seem intent on pushing misinformation.

For those who wish to continue to disagree , Ive included the relevant sections of AS3000.
1.6.2(c) Voltage and voltage tolerances.
NOTE: The nominal voltage and tolerances for low voltage supply systems and electrical installations are—
(a) for Australia, 230/400 V +10% to −6% (in accordance with AS 60038);

1.6.4 Utilization voltage
The electrical installation shall be designed and installed to ensure that the voltage at the terminals of electrical appliances and equipment is suitable for the nominal operating voltage of electrical appliances and equipment to be supplied.
NOTES:
1 Clause 3.6 contains requirements relating to voltage drop.
2 A stand-alone system designed to provide a low voltage supply should be designed to maintain the voltage at the point of supply within the range noted in Clause 1.6.2(c) under normal full-load conditions.

3.6 VOLTAGE DROP
3.6.1 General
Under normal service conditions, the voltage at the terminals of any power-consuming electrical equipment shall be not less than the lower limit specified in the relevant electrical equipment Standard. Where the electrical equipment concerned is not covered by a Standard, the voltage at the terminals shall be such as not to impair the safe functioning of the electrical equipment

3.6.2 Value
The cross-sectional area of every current-carrying conductor shall be such that the voltage drop between the point of supply for the low voltage electrical installation and any point in that electrical installation does not exceed 5% of the nominal voltage at the point of supply.

I am an electrician, I'm well aware of what the standards are.
The OP stated the shed was 25m away from the house. I am assuming this isn't the switchboard. So it's more than likely going to be a substantial amount greater.

The nominal voltages and tolerances are correct. But this still needs to be within 5% volt drop!
You're previous post implied that as long as the shed circuit alone was within 5% it was ok. That's wrong.

You list the current ratings for these cables.
Are you aware of AS 3008?

4mm cable is only carrying 32amps if it's not in contact with any insulation. Chances are it will be in the roof space. It's now de-rated to 24amps!

Of course you can put that 2.5mm cable in. You can draw about 10amps on it perhaps. But for a powered shed that's pretty silly.

I'd install a 10amp circuit breaker to the circuit to ensure that you can't pull any more than 2400W because if you were to go over 13 you are most likely(assuming, as we don't know the run length other than GREATER than 25m) exceeding your 5% voltage drop.

I guess you're the kind of person who doesn't buy things in bulk, simply because, although you're getting more for your $, you don't want to pay the little extra, because you don't need that little bit more just yet!

I'm giving my advice as somebody who has done the 4 years of training and another 5 years of working in the industry.
I think you would be crazy to install a 2.5mm cable to a shed that's clearly a great distance from the switchboard, when for about $150 more you can well and truly cover yourself.


My build: viewtopic.php?t=62001

+1 to that.

There's no way I'd shortchange myself on running 2.5mm to anywhere but internal power points, particulary to a 9 x 6 shed more than 25 metres away from the house, let alone the meter box.

I am pleased to have the input from a qualified person who does know what they are talking about.

ok I think the discuss has reached a good conclusion. Given that a few seemed to have now decided to argue the point. it's time for this thread to be closed. Thank you to those qualified people who were kind enough to add information as well as those with experience in similar hobbies who could well imagine requirements changing.
This thread will no longer be open for posting.

I hope the OP is able to come to a good arrangement with a local sparky now he has some idea of potential requirements.


kexkez
Homeone Forum Support Team Member