underground service drop


  #1  
Old 11-18-14, 08:47 AM
J
Member
Thread Starter
Join Date: Nov 2014
Posts: 3
Upvotes: 0
Received 0 Upvotes on 0 Posts
underground service drop

i need to bring AC to my house on a large acreage, all private land to the road.
thats about 1800 feet/600mts. i dont want to look at power poles and have thought that if i run the wire in a HDPE tube of adequate diameter to accept the cable, then bury the tube at an average of 12 inches depth, i should be ok. first because the tube will be a continual length, no splices. second, its my land, under my control etc. its also very dry and steeply inclined towards the road. im not worried about moisture. but i do plan on using aluminium, not so much for the cost factor as for the theft potential of copper. the house itself is wired with copper.
where i seek help is in wire sizing and "correctness" of the installation. i kinda doubt if the plan is totally legal but i still want it to be safe.
i cant say professionaly how many amps i need, control panel has ten amp breakers and that works fine with the generator system we now use. biggest load is probably hair dryer or the tv, the rest is lighting. no refrigerator, no heat, no air conditioner, and its 220 volts 50 hz.
thoughts welcome, thanks
 
  #2  
Old 11-18-14, 08:51 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 64,569
Received 3,877 Upvotes on 3,475 Posts
Welcome to the forums.

Our help to you will be limited as we are primarily a North American based website. Our codes don't pertain to your installation.

I can tell you one thing.... 1800' is too long for a single pull. You will probably need splice boxes every 500' or so.

Where are you located ?
 
  #3  
Old 11-18-14, 09:10 AM
J
Member
Thread Starter
Join Date: Nov 2014
Posts: 3
Upvotes: 0
Received 0 Upvotes on 0 Posts
located in chile, sa., i prefer to use and think in us code terms as they are well proven but not overboard like europeans.
chile is kinda down the middle but very little control of existing instalations. lots of illegal taps on power lines etc.
why do you say 1800 is too long if i can buy a roll of wire up to 1km? i didnt figure on splicing the wires as aluminum is stupid for splices.
thks
 
  #4  
Old 11-18-14, 09:34 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 9,785
Upvotes: 0
Received 45 Upvotes on 43 Posts
The 1800' run would be really tough to pull without power equipment and tradesman who know how to use it correctly. The problem is that if the pull is done incorrectly the wire insulation will be damaged which will lead to water corrosion in the aluminum. Worst case would be the cable stretches and snaps and it's all ruined.

Common practice in this case would be to put in ground quazite boxes every few hundred feet to pull and splice from. A brand name Polaris makes good connectors for aluminum which can be used in underground boxes. Of course the other good possibility is to do an open trench and use direct burial cable which could be done in one length.

US code would require depth of 18" minimum for conduit, 24" for direct burial cable. Also by US code, minimum service size is 100A @ 240V -- you'd have to investigate how your local power company will handle that. Assuming the 100A service you would need 3x600kcmil per phase aluminum cable in 3" minimum pipe if you did conduit.

You also might want to investigate getting a higher voltage service from the power company and running that up to a pad-mounted transformer near the house. You would save a lot of money in cable. That all depends on what the power company can deliver at the road.

An additional thought would be to add up the wattage of your appliances to get a better estimate of the service size you need, assuming Chile doesn't have a minimum size.
 

Last edited by ibpooks; 11-18-14 at 11:58 AM. Reason: Fixed spelling and added some clarity
  #5  
Old 11-18-14, 11:02 AM
J
Member
Thread Starter
Join Date: Nov 2014
Posts: 3
Upvotes: 0
Received 0 Upvotes on 0 Posts
the method i had in mind was to put the cable in HDPE tubing then bury it as it was laid. the house is on high hill and road service is at about 280 meters below, or an almost 1000 foot drop. hence i figured with lubrication it would not be too dificult to put cable in tube. planned to try to put in pull line first of all but gravity should do most of the work with a little help.
but that was before you convinced me that i need to run 4/0 cable, times two!
wholly makeral!
gotta rethink all of this looks like, i was thinking of 5/8 to 1" tubing which is pretty easy to handle.
from what you say, id need nearly a 4inch tube to run the two lines. is that right?
if so, short runs to inspection wells would be the only way to run it. that i can also do, its just a lot more work and a lot more cost. but still think overhead is unacceptable. and even if i did overhead, why would that be less wire size?
i calculated my needs again and came up with 4.4 kw if that helps.
 
  #6  
Old 11-18-14, 11:56 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 9,785
Upvotes: 0
Received 45 Upvotes on 43 Posts
I was figuring wire size based on the minimum service allowed service in the US of 24kW. If you aren't going to use nearly that much power we could decrease the wire size quite a bit, but it's still going to be a huge cost.

Overhead wires can be smaller because the air current keeps it cool. When it is underground the heat will build up so a bigger wire is needed. Also a bigger wire is needed when the distance from the transformer is increased.

Is there any way to get higher voltage from the power company? 1800 feet is such a long distance for 220V. If you can't get the power company to cooperate, I would probably locate the main service on a post down by the road and install a step-up transformer to as high of voltage as you can readily get direct burial cable, transformers and switchgear for, then install a step-down transformer at the house to get back to 220V. For example if you can go to 1000V, the cable size is #2AWG; 2,200V the cable size is #8AWG. You might need to hire some local tradesman who has experience working with medium voltage systems but my guess is that price is offset by the huge cost of cable otherwise.

Any way I figure it is at least $20k USD just in aluminum cable if the whole distance is run at 220V.
 
  #7  
Old 11-18-14, 12:56 PM
M
Member
Join Date: Mar 2014
Location: Canada
Posts: 63
Upvotes: 0
Received 0 Upvotes on 0 Posts
Why not go with ACWU? No cable pulling, just dig a trench and lay it in. I get 2% voltage drop on 220V - 1800ft run, 15 amps using 4/0 ACWU.
The transformer idea sounds good, but it is expensive (at least when I looked into it), and I always wondered about the vampire load of transformers?

In Canada, I can source 600m of 4/0 ACWU for about $12/m...
I would consider bringing in fill to bury it deeper though...or concrete the shallow sections.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: