Need some advice on wire gauge

Discussion in 'Landscape Lighting' started by hadfield43, Aug 5, 2013.

  1. hadfield43

    hadfield43 LawnSite Member
    from wyoming
    Messages: 50

    I posted this in the home owners forum but didn't get much response. They recommended I post over here, so please don't kick this message back down there. I am hoping very much someone would be kind enough to guide me.

    Here is my situation, I am in a bit of a time crunch as I am coming up on my irrigation installation and I don't want to later retrench to put in wiring for lighting.

    I have not done tons of research on placement of lights, but I looked at a lot of houses in my neighborhood. Generally each tree has one spot light of some kind and then there are some driveway lights/lamps. I think this look is fine and would look lovely at my house once I put my trees in (next year). I realize there is more to this than meets the eye, but I figure for now I just need to get wiring to each tree and along the driveway, then I can study and figure out placement, brand, etc.

    I am making an assumption that I will go with LED. The reason for this assumption is that I have 11 lights on one line that runs about 350 feet, the other has about 4 that is shorter. If I go with higher wattage halogen lights I am guessing I will be over 300W. With LED I am pretty sure for 11 lights I would be easily under 150W. I could balance these but that means digging a mole under the driveway and that will cost me $375 (I know because I had to do this on the other side of my driveway (I have a circular) for my sprinkler and a wiring run)

    My main question is this. For a run that will be 350 feet or so, carrying 150W from a 15AMP socket, what gauge of wire should I use (12 or 10 or higher)?

    Any help on this would be extremely appreciated, I need to order some now so I have it in time for my sprinkler installation.
  2. hadfield43

    hadfield43 LawnSite Member
    from wyoming
    Messages: 50

  3. hadfield43

    hadfield43 LawnSite Member
    from wyoming
    Messages: 50

    One other question, can someone recommend a good brand of light - I know I don't need this now, but it would be good to have an idea. I do not need anything super premium, but I am guessing that the Malibu stuff at Home Depot is low quality, maybe something middle of the road? Ideally under 50 bucks per fixture?
  4. hadfield43

    hadfield43 LawnSite Member
    from wyoming
    Messages: 50

    Well based on this, seems like at 150W I should split into two runs?

    Multiply the Total Wattage x Total Length of cable. Do this separately for each wire run from the transformer.

    If the total is 10,000 or less: Use 12 gauge cable
    If the total is 10,001 to 15,000: Use 10 gauge cable
    If the total is 15,001 to 25,000: Use 8 gauge cable
    If the total exceeds 25,000: split the run into 2 runs and recalculate.

    Mine would be 52,500 at 150W
  5. hadfield43

    hadfield43 LawnSite Member
    from wyoming
    Messages: 50

    So based on this, the best answer would be to have the run on the left stop at the center west bed

    Then dig under the driveway (ugh) and have the run on the right do the the north west bed and everything to the right and below of it.

    Even at this, the suggestion would be to use 8 gauge cable.

    Is it me or am I totally misunderstanding this, seems really excessive 8 gauge is massive!
  6. hadfield43

    hadfield43 LawnSite Member
    from wyoming
    Messages: 50

    okay well I think I am slowly answering my questions. Basically assuming the advice given above is correct I need to split my lights into 4 separate runs. Here are my calcs:

    Run 1:150 FEET (MAX LENGTH) x 15WATTS = 2250 (12 Gauge and lots of capacity to spare)
    Run 2:220 FEET (MAX LENGTH) x 28WATTS = 6160 (12 Gauge and capacity to spare)
    Run 3:150 FEET (MAX LENGTH) x 23WATTS = 3450 (12 Gauge and lots of capacity to spare)
    Run 4:240 FEET (MAX LENGTH) x 26WATTS = 6240 (12 Gauge and capacity to spare)
    Run 4 Alternative (using existing hole under drive way): 380 FEET (MAX LENGTH) x 26WATTS = 9880 (12 Gauge - No room to spare) BUT SAVES $375 on boring/moling next year under second circular driveway.

    If my length runs and sum(LED Bulbs) is correct can someone confirm this logic is correct?

    11W for Large Lumen Spot lights (e.g. for trees)
    2W for pathway lighting.
  7. Joey waid

    Joey waid LawnSite Member
    Messages: 109

    There's a lot on google about amp draw and per length of run. It that it takes a lot of amps to push 12 volts any distance. The lower the volts the bigger the wire per given amps.
  8. S&MLL

    S&MLL LawnSite Senior Member
    Messages: 751

    I don't post here often and not a big fan of free advice but you have wasted so much of your time trying to figure this out I feel bad for you.

    Run 1-12gauge wire from your transformer and daisy chain your lights and call it a day.

    10 gauge is good for way more watts then you will be drawing.
  9. hadfield43

    hadfield43 LawnSite Member
    from wyoming
    Messages: 50

    Thank you for your reply - sounds like good advice (free or otherwise).
  10. starry night

    starry night LawnSite Gold Member
    Messages: 3,312

    Whoever posted using S&M's username: Where is he and what have you done with him? This helpful answer is obviously not from him. If you are going to use his name, you should learn some sarcasm and derision.

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