voltage at fixtures

Discussion in 'Landscape Lighting' started by johnquest, Aug 6, 2007.

  1. johnquest

    johnquest LawnSite Member
    Posts: 36

    I'm seeing something I don't understand in my voltmeter. I have 4 fixtures with 21W single contact S-8 bulbs connected at a spider splice with a 27 foot 12ga run. I have one other light (21W) on a 12ga run by itself 73 feet. This single light is connected to the 12v tap. The spider splice is on the 13v tap.

    At the transformer the 12v tap reads 11.96v. The 13v tap reads 12.87v. At the spider splice the voltage reads 12.27v, but at the fixtures (I'm measuring from the socket) the voltage reads 12.70 to 12.80v. How come the voltage is higher at the fixtures like this than at the spider splice? Each of the 4 fixtures has a 25' 16ga lead. Am I measuring the voltage at the fixtures right?

    Thanks all

    JQ
     
  2. klkanders

    klkanders LawnSite Senior Member
    from Midwest
    Posts: 848

    I am guessing you had the bulb all the way out when testing at the fixture? If possible try and test with it in.... I am thinking this will solve the problem. Let us know. Good Luck!
     
  3. johnquest

    johnquest LawnSite Member
    Posts: 36

    The fixtures are the single contact bayonet type, so not sure how to measure the voltage with the bulb in. I figured the voltage drop of 16ga cable at 25 feet and one 21w bulb and have been subtracting that from the splice voltage. The fixtures should be at around 11.90 volts. I'll try the 12 v tap too this way.
     
  4. NightScenes

    NightScenes LawnSite Silver Member
    Posts: 2,207

    Just remember, when you take the lamp out, you are removing the load from the wire therefore raising the voltage. Their are many manufactures that sell test leads that allow you to put in a lamp and still check your voltage at the fixture with a full load.
     
  5. Chris J

    Chris J LawnSite Silver Member
    Posts: 2,835

    Just check the voltage at the hub/spyder, and subtract .5 volts for the fixtures. You should be fine. If you must, you can always stick your probes (make the points really sharp) directly into the fixture wires to check the voltage. I do this on occasion, and then heat the holes to weld them shut.
     
  6. NightLightingFX

    NightLightingFX LawnSite Senior Member
    Posts: 581

    Chris,
    I like your idea of sticking your probes through the wire, and then heating up the isulation where you punctured it. I just wanted to confirm however, are you 100% confident that you won't have any wicking problems down the road? I have run into situations-trouble shooting for one, when this technique would simplify everything. I just wanted to confirm how safe this technique is? Thanks for the tip
    ~Ned:cool2:
     
  7. Pro-Scapes

    Pro-Scapes LawnSite Platinum Member
    Posts: 4,181

    forget stabbing the wires... your going to get your fingers as much as the wires themself... your checking voltage not your bloodsugar level right?

    Either make or buy the pigtails that allow you to place the bulb in a socket and check voltage on another pigtail while the whole harness is plugged into your fixture... its quick and easy and accurate.
     
  8. NightLightingFX

    NightLightingFX LawnSite Senior Member
    Posts: 581

    Billy,
    I like your idea better. Can you help me understand how to make, or buy a pigstail to check the voltage. Thinking this outloud: We need a device to plug into the fixture's socket that in turn allows you to plug in a lamp and also be able to use our probes to measure the voltage. Do I understand right? How do I make or buy this? Thanks
    ~Ned:dizzy:
     
  9. Pro-Scapes

    Pro-Scapes LawnSite Platinum Member
    Posts: 4,181

    hey ned... cast sells one for mr 16 based fixtures I think thier item is mr16test or something like that... Its basically just 2 mr 16 sockets and some pins. You insert the pins into the socket of your fixture... plug a lamp of same wattage into one of the sockets and then your voltmeter into another one.

    I been having the idea to make one where I dont have to mess around with cramming my test leads into a socket and make it just plug into my meter.

    I recall recently someone mentioned one for S8 and wedge based bulbs... i think Cast has one now or has discussed making one ? Mines rather crude... I snapped the glass off a bad 3156 bulb and soldered some wires on from a new socket to the wires inside the bulb then taped it all up. This gives me the ability to test the voltage under load. Its not pretty but it works. What would be slick is one harness that tested s8 and mr bulbs.
     
  10. NightLightingFX

    NightLightingFX LawnSite Senior Member
    Posts: 581

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