Using a existing smaller guage wire in new system?

Discussion in 'Landscape Lighting' started by kolipo1, Aug 7, 2019.

  1. kolipo1

    kolipo1 LawnSite Member
    Messages: 27

    Total Noob questions. First lighting install. Using Light the Nite 150w transformer.

    I'm installing a new system with a long run in back and short run in front. I will use a T connection to separate the front and back.
    My question is, there is a 50' section of 14/2 wire already buried. If I connect the transformer (60' 10/2) to the existing (50' 14/2) and run another (60' 10/2) will that minimize the resistance from using the bigger wire on either side? Or will I have to calculate the whole thing on 14/2 wire?
    Also for the front being tied into the back system, I still calculate the total runs of wire front and back right?
     
  2. starry night

    starry night LawnSite Gold Member
    Messages: 3,734

    I won't give you a direct answer to your question because I never use anyone else's existing wire. But I will ask why you would use someone else's 14 gauge and then think you needed to use 10 gauge for your own?
     
    knox gsl likes this.
  3. knox gsl

    knox gsl LawnSite Fanatic
    Messages: 7,096

    My question is how much load are you putting on it? Personally I'd put in new wire with the confidence that you know it's done right.
     
    starry night likes this.
  4. OP
    OP
    kolipo1

    kolipo1 LawnSite Member
    Messages: 27

    My main goal here is to understand how the ohm/ voltage drop works. The way I understand it is, The smaller wire the more ohms/ resistance in that wire and length. If I step up the wire size after the smaller wire that section would be less drop back in that wire size length and resistance and math. In other words it would be worth stepping up the size after the smaller wire so that section can go further than using the original existing wire size.
     
  5. hal

    hal LawnSite Bronze Member
    from Georgia
    Messages: 1,545

    Where you splice in newer bigger wire is only benefit from that point forward. All the voltage drop to that point is the beginning of the new voltage drop. Why not replace the whole wire with bigger than splice new with old?
     
    kolipo1 likes this.
  6. OP
    OP
    kolipo1

    kolipo1 LawnSite Member
    Messages: 27

    Trying to save client money. Retrofitting and adaptability is a good thing. cost benefit analysis stuff. The old wire was very shiny on the inside so why not use it if I can. Anyway system works perfect and I still have room for expansion. I'm just learning to fully understand how all this works. Its pretty simple now that I have more of a grasp on it. Its pretty much like irrigation and pressure loss.
     
  7. OP
    OP
    kolipo1

    kolipo1 LawnSite Member
    Messages: 27

    Your name looks familiar. Were you on GTX forum way back?
     
  8. hal

    hal LawnSite Bronze Member
    from Georgia
    Messages: 1,545

    You want to be 10 - 10.5 volts minimum on the end bulb to get a good illumination. (On a 12 volt system)
     
    kolipo1 likes this.
  9. knox gsl

    knox gsl LawnSite Fanatic
    Messages: 7,096

    Not me, I had to look that one up.
     
  10. Viewpoint

    Viewpoint LawnSite Member
    Messages: 83

    Your assumption is correct, and on paper, bumping up to a larger (less restrictive) wire after the 14/2 will allow you to stretch that circuit further than sticking to 14/2 the whole way.

    There are a whole list of reasons why I personally wouldn't do it in practice, but that's not what you asked.

    What these other "noobs" ;) aren't picking up on is that the 150w Lite the Night is a DC driver, not a transformer. Therefore typical AC voltage drop calculators don't work.

    DC VD calculations are similar, but the drop is reduced by half, theoretically. I think. DC is new to the LV lighting world and I don't deal with it except for the rare tape-light installation where I can put the driver close enough to the product that VD isn't an issue.

    If you're wanting to learn more and get beyond the "noob" stage, look into the Certified Low Voltage Lighting Technician (CLVLT) offered by the AOLP (Lite the Nite is an AOLP member). www.AOLPonline.org
     
    kolipo1 likes this.

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