Shed power... yet another question.

[Yonnee]

I'm doing all the tedious work for setting up power for my "New shed" (now 2 years old), and along with dramas about getting an electrician to come out in the first place, I'm now being told that the 6mm main supply cable I ran from the house meter box might be too small. I ran similar in my previous shed with a similar distance from the meter box (approx 50M) without any problems. Upon recommendation 2 yrs ago I purchased 6mm cable again.

The cable is run from above the meter box, along the side of the house in the roof, down the back wall and out near the bottom into conduit, down to 700mm out to the shed and up inside the shed wall straight under where I want the breaker box. From this point I've run 2.5mm cable around 1 half of the shed for 5 x 10A DGPO's and another up over the roof and round the other half for another 5 x 10A DGPO's. I want a 15A GPO next to the breaker box, and I've run another 6mm cable over the roof for another 15A GPO on the opposite side. I'd also like to be able to run up to a dozen double fluro's as general lighting and specific area lighting such as over benches, etc.

Phew...

OK, my question is;
Is the 6mm supply cable too small or am I somehow going to have to replace it with 10mm cable? The house bit doesn't worry me, it's trying to feed it back through the conduit under the ground!! Apart from the extra expense of the 10mm cable after I already bought 100M of 6mm!

I'M NOT WIRING IT UP MYSELF, JUST RUNNING EVERYTHING READY.

Please help!

Yonnee.

[chrisp]

Yonnee,

It is one of those "it depends" situations - what is it you are intending to run?

6mm2, again it depends in how the cable is ran, is good for about 38~40A (it will be less if it is ran in insulation or it is hot where it is laid), but about 40A will be right in most cases.

It then becomes a question of whether 40A is enough for what you want to run at any one time. You can go through a "maximum demand" calculation to determine the cable size, but it is probably easier and better to determine what machinery you want to run at any one time and tally up the current demands of each machine. If it is under 40A (see above proviso) you should be fine.

If the electrian thinks it is too small, get them to explain why - it may simply be a matter of re-routing parts of the cable run.

[thatirwinfella]

i don't have my reg book with me right now so i can't check, but you may just be in the minimum size for parallel conductors. if it's too small the sparky should be able to run a second [or a third] run of 6mm.

you've already bought the 6mm, and if it's cut you'll have a hard time getting a return on it.

however, there are strict regs covering cables in parallel, and it's not something you should be doing.

[cross]

i don't have my reg book with me right now so i can't check, but you may just be in the minimum size for parallel conductors. if it's too small the sparky should be able to run a second [or a third] run of 6mm.

you've already bought the 6mm, and if it's cut you'll have a hard time getting a return on it.

however, there are strict regs covering cables in parallel, and it's not something you should be doing.

Checked the regs, min size for parallel conductors is 4mm.

The cable is run from above the meter box, along the side of the house in the roof, down the back wall and out near the bottom into conduit, down to 700mm out to the shed and up inside the shed wall straight under where I want the breaker box. From this point I've run 2.5mm cable around 1 half of the shed for 5 x 10A DGPO's and another up over the roof and round the other half for another 5 x 10A DGPO's. I want a 15A GPO next to the breaker box, and I've run another 6mm cable over the roof for another 15A GPO on the opposite side. I'd also like to be able to run up to a dozen double fluro's as general lighting and specific area lighting such as over benches, etc.

From the points you listed a max demand calculation works out to be approx 23A. Obviously you will get a much more accurate number if you calculate each load has mentioned by chrisp.

I would definetly ask the electrician why he feels the 6mm is to small, perhaps he is trying to sell you some extra cable, or he is seeing something you havnt listed?

[Yonnee]

Thanks for the help so far.
I do repairs, modifications and manufacture of all things trailable so my MIG welder is a given as is my Ingersol-Rand 17cfm compressor. This along with my fridge, radio, battery chargers and a few lights, I just might have to look into replacing the 6mm with 10mm... Bugger!! Going to be a bit of a pain but I think I'd rather deal with it now than find out later after it's all hooked up that it's too small.

Anyone got a 50M roll of 10mm twin & earth cable they'd like to sell...???

[NCArcher]

6mm sounds ok to me for the uses you've listed.
Ask the sparkie to justify the extra expense.

[Yonnee]

6mm sounds ok to me for the uses you've listed.
Ask the sparkie to justify the extra expense.

It's not my sparky, my neighbour over the road is starting a similar all-be-it smaller shed, and the Sparky he spoke to said he wanted to see 10mm cable simply for the voltage drop over that length.

Bearing in mind the stuff I'm running at the moment might not be the same gear I run in 5 - 10 years. I wouldn't mind looking into a dust extractor system in the future.

As has been said before, the extra expense now will be forgotten in 6 months...