Thread: Proposed electrical for new shop project

Hello Scott, I am not a sparky, so I will avoid any specific electrical answers, but will go from my experience planning and roughing in my shed.

It was cheaper for my sparky mate to purchase all the bits and bobs at trade prices and quantities, then pass them onto to me to rough in to an agreed schematics. I think the only stuff I brought was the hard and flex conduit from the big green store, as I had a ute at the time. This also meant that everything was to code.
All gpo's are at 1400mm from the floor for easy access. My bench heights are about 900mm.
All wires are ran external in solid or flex conduit attached to the white melamine boards on the walls for easy access, if I ever need to.

I have 5 circuits in my 8x4 shed, 2 10amp circuits, one of which lives the beer fridge, 1 very short run for a 20amp circuit for my lathe, a light circuit and a 15 amp circuit. Is this enough for me. Yes. The most I use is a tool, be it the lathe on it's own circuit and the DC on the west side circuit or the Bandsaw/Spindle Moulder/Thicky on the 15amp circuit and the DC. The beer fridge is on the east circuit.

Im not a sparky but here is what I did in my shed which is similar size to yours (42 m^2)
- used a combined breaker/RCP units instead of separate units
- use a single 10A breaker for a single light circuit
- used 16A breakers for the 10A GPOs . I reckon you have gone OTT with the number of 10A GPO breakers. I have ~20 double 10A GPOs and have these on 3 x 16A breaker circuits. I run a lot of things at the same time and have never had a breaker trip due to loa
- 3 of my smaller 15A machines are on 16A breakers, and two of the HD 15A machines (welder and compressor) on 20A breakers - you can always swap them out later.

If you remove the unnecessary 10A breakers this will leave some space in the breaker box for other things like more 3P or 15A breakers if you need them.

I would suggest looking at RCBO’s rather than separate RCD’s.
Looks a bit overkill for a home workshop, how many tools will be running at the same time? I think you can reduce the total number of circuits.

Sparky here SWR - I would say complete overkill & old way of doing things, akin to when RCD's were expensive.
Price of RCBO's has become so cheap, I would be surprised if any sparky would say that it's cheaper for you to purchase and install yourself.

Originally Posted by pintek

. . . . . I would be surprised if any sparky would say that it's cheaper for you to purchase and install yourself.

It might be a sparky's way of avoiding any redress. Something goes pear shaped he might just blame the products you ought?

Originally Posted by pintek

Sparky here SWR - I would say complete overkill & old way of doing things, akin to when RCD's were expensive.
Price of RCBO's has become so cheap, I would be surprised if any sparky would say that it's cheaper for you to purchase and install yourself.

Thanks for this advice by all.

I have revised my board based on this advice

I get that the first cut was overboard so I have simplified the board with less breakers and it is a fair bit cheaper.

Des this look better?

Originally Posted by SWR

Thanks for this advice by all.

I have revised my board based on this advice

I get that the first cut was overboard so I have simplified the board with less breakers and it is a fair bit cheaper.

Des this look better?

I still suggest you look at RCBO's. It saves space and eliminates multiple circuits being affected due to residual current trip.

G'day SWR,

You can drop the rating of your 3P RCBO to 32A and do away with the redundant downstream CB - the RCBO provides overcurrent protection as well as as earth leakage detection.

Not sure if cost is the main driver for your layout having one RCBO feeding multiple MCBs, but by the same token you could do away with the other three 1P RCBOs if you swap all your 16A & 20A MCBs for RCBOs. Remember, most devices will have a 'normal' amount of earth leakage. The more circuits you put on a single RCD the more likely you are to get nuiscance tripping

You should be able to drop your DB size down to a single 18 way and still have plenty of space for expansion if you ever need it.

Originally Posted by caillan

G'day SWR,

You can drop the rating of your 3P RCBO to 32A and do away with the redundant downstream CB - the RCBO provides overcurrent protection as well as as earth leakage detection.

Not sure if cost is the main driver for your layout having one RCBO feeding multiple MCBs, but by the same token you could do away with the other three 1P RCBOs if you swap all your 16A & 20A MCBs for RCBOs. Remember, most devices will have a 'normal' amount of earth leakage. The more circuits you put on a single RCD the more likely you are to get nuiscance tripping

You should be able to drop your DB size down to a single 18 way and still have plenty of space for expansion if you ever need it.

Thank you for your advice Caillan - it is very appreciated and It will help me enormously.

Starting to look more reasonable.

3ph RCBO are not 4 pole - don't mistake the current rating on a 3ph RCD as being a circuit breaker rating.
Get your sparky to wire your board. There are still plenty of things wrong with your diagram.

IMO the biggest mistake you are making is that you are designing the system yourself and I would question the suitability of your “ electrician” for the project for entertaining the idea in the first place.
This is basic bread and butter type work for a tradie who is well versed in day to day domestic electrical work. I suspect at a guess that your electrician whilst having the appropriate accreditation is not in the game as such?
By all means do all the hack work of running cabling and conduit work if that takes your fancy but being involved in the design process as you can see by the comments to date can easily be false economy

Not trying to have a go at you but I see this all the time with DIY and owner builders who think they are saving money but through their lack of knowledge and experience ultimately spend more than getting professional assistance.

I am just seeing it again in the last few weeks with an owner builder down the road, he hasn’t even poured a footing yet and I can see he has spend at least $30,000 too much in how he has gone about his earthworks, not to mention the extra weeks lost in the process. Of course he will probably never realise that and is thinking how much he has saved by arranging it all himself direct with the contractors.

You don’t know what you don’t know.

I would consider changing some or all of the 15amp outlets to 20amp, my 3 large tools ( table saw, bandsaw , planer/thicknesser ) all have 20amp plugs and appropriate cable fitted as specced by the manufacturers. You can always plug a 15 or 10amp into a 20amp flat pin socket.