Advice on electrical wiring for a new supply 200m run

[boban]

Ok I found this thread with a google search after I tried unsuccessfully to "do a search" : http://www.woodworkforums.ubeaut.com.au/showthread.php?t=25438

Anyway I have a similar question to Cliff's. I am about to run a new service from the boundary supply to a new meter board. All three phase.

1. The first run is 100m - this is from the supply to the meter box which will supply the following runs. I'm guessing I need 100A in total.

2. The second run is 30m - this is from the meter to the house. (50A I guess)

3. The third run is 80m - this is from the meter to the shed and office sub board. (50A I guess)

The advice I have received so far has varied from 16mm2 to 25mm2.

I was thinking of using the following

1. 25mm in the first run
2. 16mm in the second run
3. 16mm in the third run.

Another question. I was considering running the gas line at the same time. Can you put the electrical and gas in the same 450mm wide trench. It will be 600mm deep.

[DavidG]

What does your electricity supplier stipulate as required.:confused:

[boban]

Im not sure what you mean.

[DavidG]

I thought the line from the supply point to the meter box would be the supply authorities problem. The rest they should be able to recommend what is required.

Unless you are on your own supply??

ps: Are you talking 100A per phase or 33A per phase.?

[boban]

No, its my problem from the overhead supply.

Not sure that I need 300A Dave. I figure that if it were solely single phase 100A would be enough. I do want headroom in the supply though.

[Pat]

Boban, are you in Intergral or Energy Australia's franchise areas? You can ring the custmer supply sections and ask them. This info may well be in the SAA wiring rules as well. I'll ask at work tommorrow, as I work for EA, not as a sparky (A shiny pant payroll/rostering clerk).:)

[boban]

Integral Energy.

[Wood Butcher]

I thought the line from the supply point to the meter box would be the supply authorities problem.

In QLD they are only responsible up to the first pyhsical on the property, in Boban's case the boundary pole. You are then responsible for everything after that.

[Pat]

Boban give Intergral a call and hopefully they will set you on the correct path.

[Pat]

Well didn't that question open thr proverbial . . .

Asked at work and got a variety of responses, with the consense being 50mm, but and a huge but is that according to one of the inspectors, your sparky has to know the total current demand of all appliances and then follow two equations, then look up the tables in AS3008 to get the correct size cable. He did say that the two smaller runs may be able to be smaller.

May I humbly suggest getting in touch with Intergral, as you do not wish to install the cable for the inspector to deny it.

[boban]

Thanks Pat. One problem. I haven't got an hour to wait for Integral to answer the phone, then be transferred etc. I tried that this morning to no avail.

Spoke with two sparkies today and I have ordered 100m of 25mm2 for the two shorter runs. Both sparkies have said that it was more than enough. Both recommended the 25mm2 for the long run too.

You have me worried now. I've just spend $1400 on the wire (4 core and earth) and would hope that the sparkies have got it right. The way they spoke, there was no doubt in their minds.

[ajt]

25mm 4 core and earth (asuming you have a multicore cable, ie. orange circular), buried in a non-metalic wiring enclosure (conduit) is rated at 96A, without taking into account any voltage drop, which you may well need to consider depending on the maximum demand of the two sub boards.

Personally I would use something like 35mm SDI with at least V90 insulation which is rated at 125A buried in conduit from the pole to the meters, then 25mm SDI from there to each board which is rated at 105A in the same conditions.

Hope this is of some help.

[Cliff Rogers]

When you order your supply connection, they will want to know what demand you will be putting on it & they will rig a pole fuse(s) to suit.
If you then install a cable up to the pole fuse that is way too small they may ask questions.

Where you will strike problems is if you load it up too much over a long run, you won't get the full 240V at the appliance end.

You aren't going to do anything 'unsafe' if you under spec it a bit; you are just going to end up with low voltage.
If you under spec it a lot, then you may make a few things get hot.

[boban]

Thanks for that fellas.

I went through the whole exercise today. You guys would be spot on if the whole supply was going down one phase but its going down three.

I worked out that with voltage drop I'll get 74A per phase which is more than enough according to my mate and the wholesalers who employ two ex sparkies.

Cliff, I hear you. My circa 1940's (based on the age of the house) supply is doing everything now but with plenty of light dimming. The wire is so thin its laughable.

[boban]

25mm 4 core and earth (asuming you have a multicore cable, ie. orange circular), buried in a non-metalic wiring enclosure (conduit) is rated at 96A, without taking into account any voltage drop, which you may well need to consider depending on the maximum demand of the two sub boards.

Personally I would use something like 35mm SDI with at least V90 insulation which is rated at 125A buried in conduit from the pole to the meters, then 25mm SDI from there to each board which is rated at 105A in the same conditions.

Hope this is of some help.

For now Im laying the 25mm2 to the two shorter runs. I'll enquire as to the price of the 35mm2 and if its only a couple of hundred more then I'll probably do it even if I dont need it.

Thanks for that

[ajt]

Sorry I did overlook the three phase issue, if your going to have 3 phases supplied from the meters to each switchboard then 25mm is heaps.

What is your curent supply to the house and shed/office? 3 phase?

[boban]

Yes its three phase using what looks to be really thin wire, not to mention old.

[ajt]

probably 4mm, very common for older properties