House to shed power cable size/type

[Judo]

Currently the shed only has a 10A RCD and from what I can see, it's been piggybacked from the nearest powerpoint in the kitchen. The shed is also the laundry with washing machine and dryer. We get by, but really it's not enough. Therefore the plan is to run new power from the house switchboard to the shed.

The cable run would be 30m and I'm thinking capable of up to 30A ideally. I could definitely live with 20A, but I figure if I'm going to the effort of running new cable, I might as well make it safe for 30A.

Calculators say 6mm2, although it looks like I might be getting close to the next size up? Thoughts?

Is stranded or solid core the way to go?

[Homestar]

6mm may do, but I would use 10mm myself. The maximum current rating of the cable isn't enough to go on. Derate factors due to length of run, what sort of cable, single or 3 phase all need to be in the calculations, as does the calculation for fault loop impedance. If your calc says 6 is close then 10 would work fine.

You won't find 6 or 10mm in a solid conductor, it will be of 7 strand construction.

[rovercare]

6mm

I doubt you'll even find solid, stranded is good, will be good for an easy 32A

[Vern]

6mm will be ample. Get it AMPle:p.
It will carry 32a a lot further than that

[Judo]

6mm will be ample. Get it AMPle:p.
It will carry 32a a lot further than that
Thanks for your qualified answer. :p (Also, thanks to the other sparkies replying!)

Sounds like 6mm it is.

Gav, I appreciate there are other factors, which is why I asked the question. Factors like 3-phase don't seem very relevant to me, and since I'll unlikely be going over about 10-20A most of the time, I'm pretty happy with 6mm. In fact I may just start with a 20A RCD in the shed anyway....

..which brings me to the next technical issue! My switchboard is full! :o

Main switchboard in the house has 4x40A RCD's, which split the switchboard in half, each side filled with CB's. One 16A CB in the house feeds 1xBR, a few power-points in the kitchen, the dishwasher and the shed 10A RCD. The house 16A CB has never tripped. The shed one does and it's because we are definitely going over 10A trying to dry clothes and weld at the same time. :p

Assuming that I'm loading the 2x40A RCD's evenly in the main switchboard, is an appropriate solution to replace the 16A CB with a 32A CB still feeding the 1xBR, a few power-points in the kitchen, the dishwasher and the shed 20A RCD via my new cable run? I.E. Effectively 2 cables/circuits being fed out of the 1 CB in the house.

[chopper]

Doesn't your electrician know ?

[Bigbjorn]

If you are planning on installing machine tools, get three phase 415 v. power installed. Used 240 v. machine tools sell at a considerable premium over three phase machines.

[Judo]

If you are planning on installing machine tools, get three phase 415 v. power installed. Used 240 v. machine tools sell at a considerable premium over three phase machines.
Scope creep! :D

Really the main requirement at the moment is to be able to run both the drier and washing machine at the same time! But instead of just changing the shed RCD from 10A to 16A - which would probably work - I'm looking a little past that and allowing for maybe a 15A outlet in the shed or just generally allowing for a bit more power if needed. But nothing really major.

[bee utey]

Main switchboard in the house has 4x40A RCD's, which split the switchboard in half, each side filled with CB's. One 16A CB in the house feeds 1xBR, a few power-points in the kitchen, the dishwasher and the shed 10A RCD. The house 16A CB has never tripped. The shed one does and it's because we are definitely going over 10A trying to dry clothes and weld at the same time. :p


A suggestion would be to replace all circuit breakers where possible with single gang RCDs which would free up a couple of spaces by removing the older style RCDs which feed multiple breakers.

[Dougal]

I have recently run underground cables to deliver up to 40A with a total cable run of about 27m.

In consultation with the sparky we buried 10mm cable. Neutral screen was cheaper than tps and we ran a 6mm earth in the same trench.

It's in use but only using a few amps. It will be some time before I need the full capacity. The sparky put a 32A breaker in at the house end as a spare holder that size was already wired. But we can upgrade to 40A later if it gets close.

Cost me about $4k in the end, but including data cabling in the same trench, check meter, rcbo on each of four circuits, 7 outlets of different types etc.

Future proofing isn't cheap.

[Vern]

A little confused with what you have Justin, but assuming the 10a rcd feeds the shed and this is what you are replacing with the 6mm?
If so just get a 32 a CB for the main switchboard new shed supply, then get a little sub board and run a couple of circuits from that, using rcbo's to protect you final sub circuits.

[Judo]

A suggestion would be to replace all circuit breakers where possible with single gang RCDs which would free up a couple of spaces by removing the older style RCDs which feed multiple breakers.


A little confused with what you have Justin, but assuming the 10a rcd feeds the shed and this is what you are replacing with the 6mm?
If so just get a 32 a CB for the main switchboard new shed supply, then get a little sub board and run a couple of circuits from that, using rcbo's to protect you final sub circuits.

Nothing says pro more than a diagram drawn using Paint. Also, pictures say everything I want to say... ;)

https://www.aulro.com/afvb/images/imported/2014/06/577.jpg

P.S. Don't blame me for this set-up! I didn't do it!

[Vern]

Interesting job! I like the main switch in the middle there!:(

So you have two phase supply I see, and no room in the switchboard.
I'd double the two light circuits up on the left hand side (unless they have an ixl tastic on each), and use that for the new shed supply, except replace the breaker with a 32a and take it off the rcd. Then install such board in shed on new 32a supply.

[Judo]

Interesting job! I like the main switch in the middle there!:(

So you have two phase supply I see, and no room in the switchboard.
I'd double the two light circuits up on the left hand side (unless they have an ixl tastic on each), and use that for the new shed supply, except replace the breaker with a 32a and take it off the rcd. Then install such board in shed on new 32a supply.
Yes, there is a lot of interesting things around this house. Last guy was definitely DYI, but I kind of wish he wasn't!

Brilliant suggestion now I think about it. :) Reasons being:

We have 1 IXL, but I just went and checked and it's on the right hand side lights CB anyway.
The 2 light CB's on the left are only 10A+16A (rather than 16+16).
The right hand side is loaded with spa + A/C, which are both big breakers.

So shed on the left with a separate breaker seems perfect. Exactly what I was going for - I just didn't know how best to get there!

[bee utey]

A suggestion would be to replace all circuit breakers where possible with single gang RCDs which would free up a couple of spaces by removing the older style RCDs which feed multiple breakers.
After looking at your board, RCDs on each circuit would prevent nuisance tripping on all the other circuits from a shared RCD anyway. A washing machine especially deserves its own. I assume single RCDs won't cost any more than this ebay example (http://www.ebay.com.au/itm/RCD-MCB-Safety-Switch-1-Pole-10A-16A-20A-Switchboard-/200533659443?pt=AU_B_I_Electrical_Test_Equipment&hash=item2eb0bccf33).

[Vern]

Justin, when the lights are doubled up, make sure you put them on the 10A c/b.

As for those rcd's, I wouldn't trust homebrand stuff, particularly at those prices. Trust me on this one, I replace quite a few no name rcd's, buy reputable brands.

[Judo]

After looking at your board, RCDs on each circuit would prevent nuisance tripping on all the other circuits from a shared RCD anyway. A washing machine especially deserves its own. I assume single RCDs won't cost any more than this ebay example (http://www.ebay.com.au/itm/RCD-MCB-Safety-Switch-1-Pole-10A-16A-20A-Switchboard-/200533659443?pt=AU_B_I_Electrical_Test_Equipment&hash=item2eb0bccf33).
You're saying ditch the 2x 40A RCD's and just use all RCD's instead of CB's? Which would give me space for a new shed circuit too?

BTW, we've never had a CB/RCD trip at all in the house. We've been here 6 months. So I'm not overly worried about a shared RCD for that reason, but if replacing all the CB's with RCD's is an overall better solution (best practice?), then I'm happy to go in that direction.

[rovercare]

After looking at your board, RCDs on each circuit would prevent nuisance tripping on all the other circuits from a shared RCD anyway. A washing machine especially deserves its own. I assume single RCDs won't cost any more than this ebay example (http://www.ebay.com.au/itm/RCD-MCB-Safety-Switch-1-Pole-10A-16A-20A-Switchboard-/200533659443?pt=AU_B_I_Electrical_Test_Equipment&hash=item2eb0bccf33).

Single pole decent RCBO's are $30-$35 each +GST, similar to 2 pole, but you need lots more

As said, just join 2 light cct's and bang in 32A CB

You don't need 10mm unless you are pulling some SERIOUS amps(or long distance), over and above what almost anyone would do in a home workshop

Stop overthinking it:D

Oh, ebay RCBO's, push the test button under load and the smoke comes out, there is a sparky from Moe, that advertises in the local rag, fitting them everywhere....absolute rubbish

[bee utey]

You're saying ditch the 2x 40A RCD's and just use all RCD's instead of CB's? Which would give me space for a new shed circuit too?

That's what the sparkie who wired my solar in 2008 told me, except he couldn't get them cheap at the time.



BTW, we've never had a CB/RCD trip at all in the house. We've been here 6 months. So I'm not overly worried about a shared RCD for that reason, but if replacing all the CB's with RCD's is an overall better solution (best practice?), then I'm happy to go in that direction.

I've lived in the same house for 19 years (had it 90% rewired when we moved in) and the RCD's have tripped perhaps 10 times. But when they did they didn't cause other appliances to go out with them. Example: wife puts on the washing machine, the drain pump leaks, trips the RCD but the fridge, freezer and entertainment stay on. I've currently got 4 RCDs with a max of 3 breakers on each, would go all RCDs if I redid the system. The two work sheds especially have their own.

[Vern]

You're saying ditch the 2x 40A RCD's and just use all RCD's instead of CB's? Which would give me space for a new shed circuit too?

BTW, we've never had a CB/RCD trip at all in the house. We've been here 6 months. So I'm not overly worried about a shared RCD for that reason, but if replacing all the CB's with RCD's is an overall better solution (best practice?), then I'm happy to go in that direction.

If it ain't broke, don't fix it! My switchboards at home are set up like yours, works fine, never have a drama, I can't see the point in changing mine, and I'm a Sparky.:)

[Judo]

Cheers Damien, bee_utey and all.

Once I build some motivation to try pull the new cable through the conduit under the backyard (fingers crossed that works!), I'll join the 2 light circuits on a 10A CB, replace the spare CB for a brand name 32A RCD (bypassing shared RCD).

:)

[rovercare]

Cheers Damien, bee_utey and all.

Once I build some motivation to try pull the new cable through the conduit under the backyard (fingers crossed that works!), I'll join the 2 light circuits on a 10A CB, replace the spare CB for a brand name 32A RCD (bypassing shared RCD).

:)

32A CB, put RCD at sub board in shed

If conduit is 20mm being cheap install it may be, then you will not pull 6mm TPS through, you can however just strip it back to be single insulated and pull it through the conduit, so long as there is no single insulated stuff left exposed anywhere when the job is done

[Judo]

The good news is the conduit is 25mm. phew! That makes me happy!

What's the reason for only using a CB in the house then RCD in the shed? If I do it the other way around, I'm protecting more of the circuit. Is it convenience in case it is tripped while in the shed? Why not run RCD at both main and shed boards? (How mine is now).

Regarding earthing, I'm assuming I don't have an earth pole at the shed (can't see one). Is it standard practice to just use the house earth? Why/when would I have a separate earth pole in the shed?

:)

[Vern]

Use the earth that comes in the 6mm cable. Pain in the backside having to go to the house to reset the rcd, its a sub main feeding a sub board, not necessary to have an rcd protecting the submain. But can never over protect so won't hurt.
Good luck pulling the cable through, will be a two person job, one at either end:)

[Judo]

I have informed SWMBO. :D