# Forum Home Renovation Electrical  Underground electrical conduit how deep

## chrise

I am having a new large Randbuilt shed built in the back yard and I want to run power to it. The cable will be in 25mm orange conduit underground, its about a 10 metre run from the entry point of the house to the shed. Now the question is how deep does the trench have to be for conduit to go into? 300mm 500mm 600mm? I am in NSW.   I will get an electrician to wire it all up when the shed is erected etc but for now I am getting the site prepared for the slab and the trench dug and the electrical cable run in the conduit etc. (There will be a new fuse etc installed by the sparky when its all wired up for power.)  Also is there any other thing or anything special I need to do or use for NSW rules. Will normal 2.5mm standard 2 wire + earth do in the burried condiut? 
I am also thinking as I will have a bit of concrete over I will put a thin layer in the trench over the orance condiut, is this alowed or worth doing or a good thing to do or is there problems doing this.  Thank in advance  Chris

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## mydatto

600mm deep. I would go for 4mm at least for the power feed. 6mm would be better. This all depends onthe current load and length of feed cable of course.

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## deryk

Buried wiring is supposed to have 500mm cover.  
My suggestion is not to assume the cable size until you get your Electrician around and advise him what the intended load will be and let him determine the cable size. This in turn determine the conduit size. 
Depending on the owner, work sheds can have all sorts of electrical loads including welders, industrial fans for cooling in summer, heaters, bandsaws, lathes etc etc so you might want to think about that (even a future owner for resale) instead of the standard light/power subcct. 
I really doesn't cost that much more to bump up the c.s.a of the cable at this point in the project but it probably will later

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## chrise

Thanks mydatto and deryk for the info and advice. Thought it was 500mm and digging to 600 was a good idea just in case.   deryk I have already had the sparky around and as 2.5 will carry 30amps he is happy as there will be 2 cables one for light and one for power both on a separate circuit breaker each. There wont be a huge usage of power in this shed so cable size isnt an issue really but may actually use 4mm cable just in case down the track.  Again thank you for the advice.   :2thumbsup:  :Brava: hpydans:

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## applied

:Pedantic ON: 
I dont know what cereial box your sparky got his licence out of but 2.5 wont carry 30amps you cant buy 30amp breakers only 32 and you wont be able to put a sub board on anything smaller than 4mm at the bare minium. 
also if you scimp on cable now you will pay for it forever because under rated cables heat up like elements that heat costs money in wasted electricity. 
and make sure you put marker tape at 300mm.  :Pedantic OFF:

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## Pulse

might also be worth considering three phase, or at least leave room in the conduit. 
with respect to current handling twin and earth V-90 PVC/PVC is OK for 31A buried in conduit, 40A buried direct, confirmed in their catalogue and AS3008.1 table 9 (same numbers exactly) 
Question that I always had was what about the cable that is above ground, part of the same run? I'd go 4mm and have a subboard for lights and power (or three phase) 
Cheers
Pulse

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## applied

It may have a CCC 31 of but you cannot for example put it on a 32 braker that's the breakers rated working current not the point at whitch they trip they have a mean trip current of about 44Amp well above what it's rated. 
The breakers are to protect the cables that's it 20 amp breakers top out at about 28amps.

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