Long wire run

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stephendv
stephendv Solar Expert Posts: 1,571 ✭✭
in Solar Beginners Corner #1
Hi all,

We've finally got permission from the town hall to build a wooden cabin on our piece of land and it's time to get the power distribution and solar installation setup. We eventually plan to build a proper house and I sited my existing stationary diesel gen and power shed close to where the real house will be. But I'd like to build the cabin quite a bit further away and am not sure which size cable to run from the power shed to the cabin. The total run will be 1300 feet.

I already have a cable in the ground from the power shed to a distance of 540 feet. This is AWG 7 copper cable, power is 240V AC (Spain). So I need additional cable section for a distance of 760 ft. I've tried some of the online calculators and they require the load to be entered. Now since this is a well behaved off-grid house, I expect it will be drawing less than 400W most of the time, but occasional peaks of 3kW when my wife turns her hairdryer on. Which value should I use for the load then? I don't want to waste money on too much copper, when I'll only very rarely be using that 3kW.

The cable will be rubber or PVC sleeved and laid in a PVC conduit which is 1inch diameter. Conduit and cable will then be buried.

Any ideas on the most economical cable size?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
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    Re: Long wire run
    Which value should I use for the load then? I don't want to waste money on too much copper, when I'll only very rarely be using that 3kW.

    I just pulled #6 wire, 3 ea, thru a 1" condouit for 900'. If I was doing it again, I woudl use 1.5" condouit, it will pull much easier.

    If you want the hair dryer to run, you must enter it's wattage into the caculator, otherwise, it may only go half speed, and your wire heat up and melt. Caculate the hairdryer, and a couple of lights on at the same time.

    For 900' of #6, alumunium wire [same as #8 copper] (with the proper splice joints and anti-ox goop) I am allowed a 300W load :( I suspect you will need to be # 4 or #2 wire. Or you may have to use a pair of step up-step down transformers to 480 VAC.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #3
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    Re: Long wire run

    With a 3500W load and 6AWG, there's an 18V drop (about 8%). I don't mind losing a bit of power in the cable during these extreme peak events as long as the cable doesn't melt!
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #4
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    Re: Long wire run

    If it's only 18V over 900', I guess you are not going to get too warm.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
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    Re: Long wire run

    you should go at least with #4 imho. not so much for your wife, but any future loads and circumstances that may arise. using the hair dryer the #4 would put it at roughly a 5% drop for about 12v being dropped or roughly a 33% improvement. it is true that for 5 or 10 minutes of using the hair dryer that there should not be a problem with using #6 though and would be up to you.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #6
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    Re: Long wire run

    Thanks guys. Compromised and went for #5. That's a h*ll lota coppa.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,749 ✭✭✭✭✭✭
    #7
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    Re: Long wire run

    Stephen,
    I really, really dislike power sheds in hot climates! They will kill your batteries sooner! I discourage it as much as I can. 1300 feet is a long way though. When do you have to do this? I ask because there may be options in the near future that could put your electronics and battery at the house where they belong?
    I am doing something very similar for a client right now and am going to wait until the end of September for the wire run! Either way, Buenas Suerte!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #8
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    Re: Long wire run

    Need to start pouring foundations next week, so will need a cable from the existing generator to job site quite urgently. I built my powershed specifically to keep batteries happy, it's half buried and I've thrown about 30cm of earth on top which helps with the heat a lot.
    In total there is about 80cm2 of incoming ventilation holes and a 30cm2 extract hole in the roof with a fan fitted. This is mostly for the benefit of the generator. Once solar is in place, the generator should in theory only be used in winter, never summer. In winter the temps can drop to -5C.

    Some pics (but I've since covered the entire thing in earth):
    http://www.casanogaldelasbrujas.com/blog/2009/05/17/generator-exhaust-expansion-chamber/

    There are some added complications in that I currently have a 300m wire run from the powershed to a well pump, so even if I can site the panels+inverter+battery in the most optimal position (between well pump and cabin), I'd still need to lay about 150m of cabling.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,749 ✭✭✭✭✭✭
    #9
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    Re: Long wire run

    Nice! It will be good exercise walking, and since there will never be snow or ice to slip on. I just like to have the gear where someone can attend it. Maybe run some wire or wireless indication to tell you when a pump is running since you won't hear it for instance. Failure mode always is nice to plan for offgrid!

    In your climate/location and with enough solar I bet that within 5 years of completion you will not need the generator! Good Luck!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • BilljustBill
    BilljustBill Solar Expert Posts: 219 ✭✭✭
    #10
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    Re: Long wire run
    stephendv wrote: »

    Some pics (but I've since covered the entire thing in earth):
    http://www.casanogaldelasbrujas.com/blog/2009/05/17/generator-exhaust-expansion-chamber/
    .

    Your pictures are great. That is a very nice place to store batteries or even as a storm cellar!!

    May I ask what would something that size cost to build?

    Thanks,
    Bill
    Bill
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #11
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    Re: Long wire run

    Thanks :D Not sure the costs will be useful as I'm based in Spain... and I sort of lost track halfway through the project. Used a contractor for the excavation, foundation and half the walls then took over myself. Think the contractors bill was about 3k Euro.

    The idea behind it was to have a battery friendly storage in our climate but more importantly to have something that would deaden the generator sound. It's a 1500rpm single cylinder and makes a lot of noise. The underground shed takes care of the clattering and other generator noises and the undergound exhaust silencer takes care of the deep bass boom. Can't even hear it when standing on the other side of the shed.

    Mistakes I made:
    - Too little ventilation for the generator. Since I don't have the solar or batteries yet, I've been running it in summer and it got far too hot when running for more than an hour. Had to knock a hole in the roof and mount a fan, also cut some holes in the door for additional ventilation. Might be able to close some of this off in winter and when I buy some batteris, so it won't run as often.

    - Drainage too shallow. Have had the damn thing flooded a few times after torrential rains. Had to dig an additional french drain system which so far seems to have sorted it out. If it floods again, I'll get a small and cheap DC pump to take care of surplus water.

    - The first underground exhaust system was a failure as it just acted as an amplifier for the bass sounds: http://www.casanogaldelasbrujas.com/blog/2009/05/17/generator-exhaust-expansion-chamber/
    Version 2 is virtually silent: http://www.casanogaldelasbrujas.com/blog/2010/01/26/exhaust-silencer-version-2-0/
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