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Voltage Drop Compendium

Discussion in 'Landscape Lighting' started by INTEGRA Bespoke Lighting, Dec 11, 2007.

  1. johnh

    johnh LawnSite Member
    Messages: 34

    Sure one could argue, and probably successfully that 30V is safe. But could you argue that 15V is not safer? I guess I don't understand the need for voltages higher than 15V for our applications. I am gathering that Pete has been pretty successful designing his systems around this limitation, I know our contractors around here have also, so why fight it?
  2. johnh

    johnh LawnSite Member
    Messages: 34

    To clarify, when I said in a previous point that I agree with Pete, I was referring to this statement, not that I agree with everything Pete says or has said. No offense Pete!

  3. INTEGRA Bespoke Lighting

    INTEGRA Bespoke Lighting LawnSite Platinum Member
    Messages: 4,102

    Exactly! "Why fight it?" Is 30V safe? Yes, no, maybe... whatever the answer is, 15V is surely indisputably safer. UL and CSA certainly think that is the case.

    I have said it before and will say it again:

    1: Know your product, know your systems, understand the limitations of the code and certifications that exist for the application and build systems to meet those codes, certifications and limitations. It isn't rocket science.
    2: The public and the untrained commercial sector need to be kept safe, long after the lighting system has been installed. When have you ever encountered a caretaker, maintenance guy or home owner who didn't assume that what we do is "all 12 volts, right?"
    3: Finally, we all want this industry to flourish right? So why complicate systems with wildly ranging voltages from 11 to 22v (and hopefully not beyond)? LV lighting used to suffer from a bad reputation... why not standardize the industry so that mistakes after installation are not made. These mistakes cost us all because if the system is not standardized and other, untrained individuals start to make adjustments and changes (it does happen!) then the systems fail and ultimately this gives the whole industry a bad name. Who hasn't heard something along the lines of: "Oh I don't want that low voltage junk. I had one of those system a while ago at home and it never worked. What a waste of money."

  4. JoeyD

    JoeyD LawnSite Silver Member
    Messages: 2,933

    WOW......So wheres UL to save all the irrigators when wiring up 24v irrigtion wires in "wet locations?"
  5. irrig8r

    irrig8r LawnSite Platinum Member
    Messages: 4,553

    It's funny Joey, most of the time I read 27 or 28 V on irrigation control wires. I've gotten a little jolt now and then.. no biggee.

    And often times sprinkler controllers are located in garages and control wires go through walls without any conduit....

    In all my years I've never found a sprinkler wire get hot, although solenoids will if they are turned on with the water off....

    But this is probably the key: amperage in sprinkler system control wires is a lot less than with lighting .. Solenoids are usually no more than 0.3 to 0.4 Amps inrush, and maybe 0.2 Amps holding...
  6. pete scalia

    pete scalia LawnSite Senior Member
    Messages: 960

    Cause their is no load on sprinkler wire. it's used for switching not to handle a load.
  7. JoeyD

    JoeyD LawnSite Silver Member
    Messages: 2,933

    SO whats the danger with the 22v tap upon wiring if you have no load on it?? if I am holding a 22v tap with 3 amps on it and I put both sides togeather it is going to burn me for a second until I pull it apart. But it is not going to electricute me nor will it even come close to killing me. Funny thing is I can get the same exact sensation from holding 2 ends of a 15v tap togeather with or without any amp draw. This UL1838 is a crock and no matter how much technical stuff you may cut from magazines I am going to go with what the NEC claims as safe. Wet salty sweaty hands or not, I have been doing this for way to long for you guys to keep trying to pull the wool over the eyes of the industry to believe that 17v is dangerous yet 15v is safe. Bottom line is if we never had a Malibu system we probably would never have UL1838. It was written for complete systems and is written to protect DIY homeowners and not PROFESSIONAL lighting installers. So to each his own, you use 15v max and big wire and pull 120v all over the place and we will promote using smaller wire, higher taps to compensate the VD and more affordable efficient systems. UL1838 is a subject that is always worth debate but it is so hard to debate online. Nate is working on a VD post for the Lawnsite.com community. He will address UL concerns and will also address VD. We always will tell you though if you would like further information on this or any other subject related to installing or designing low voltage lighting then please do not ever hesitate to contact myself or Nate directly on his cell at 760-580-4980. Nate has a tremendous ammount of experience here and that is why Unique has been so succesfull. We design our products for the professional installer.

    My next post will be the results of the VD test.

    Joey D.
  8. JoeyD

    JoeyD LawnSite Silver Member
    Messages: 2,933

    So my video guy is going to take a little longer to put this video together so I figured since Nate is working on a large response to this topic I would go ahead and get the results up here so we can keep the discussion moving.

    There are going to be some that live by the fact that 15v is the maximum voltage you should use. They have their reasons, safety and UL/ETL, and if they feel they are protecting themselves from a problem then so be it. Nothing wrong with that. Then there will be some guys who will decide to use transformers that go beyond 15v for the sake of using smaller wire and traveling further distances while still ensuring 12v to each and every lamp. They are still UL/ETL approved safe and are also still well within the limitations of the NEC safety requirements for Low Voltage Lighting.

    For this test I took what I would consider a very common situation in lighting. So here is the scenario: 200ft 12/2 run with 4x35w Par 36 lamps= 140watts.

    Materials Used
    1-Unique 840 I Force (118v at Primary Plug, 11.6-8v @ 12v Tap)
    4-35w F225 Well Lights w/ 25ft 16/2 leads= 140watts
    200FT of 12/2 Low Voltage Direct Burial Cable
    Wired up in a Hub style format using 2 red wire nuts

    Method 1

    2(ac) x 12(wire value) x 200(12/2 run) x 11.67(amps on run) / 6530 (Circular Mills)
    = 8.578 Volts of Drop

    Method 2

    200(12/2 run) x 140watts / 7500 (Cable Constant)
    = 3.733 Volts of Drop

    Method 3

    11.67(amps on run) x .00162(12/2 wire resistance) x 200(12/2 run) x 2(ac)
    = 7.562 Volts of Drop


    After I wired the run up, 4 35w fixtures in a Hub style wiring method I set the home run to 12v first to see what my VD would be. My Hub (first point of connection) measured at 5.9v and 6v fluctuating back and forth. So we can say that our VD is 6v. So that put Method 1 off by Positive 2.578volts, and put Method 2 off by Negative 2.267volts and Method 3 being off by Positive 1.562volts. But that can’t be the end of the test; you need to get the amperage up on the lamps before being able to really determine your VD. At the 12v tap I was only drawing 8amps on a run that should be pulling 11.67 amps.
    So if I do my VD calculation, my VD was 6 volts so that would mean ideally that I would need to step my TF up to the 18v tap, which my TF has. So I bump it up to 18v and I am still only burning at 10.4volts at my Hub and only pulling about 10amps. So I then bump my run up to my 20v tap(19.8v @ 20v Tap) where I then was burning at 11.6-8v at my Hub, putting my lamps at 11.1-3v and my amperage at 11.5amps.

    So what does this mean?

    What it means is that my VD was actually 8.5volts and that is exactly what Method 1 calculated which means method 1 is actually the most accurate. Method 2 was off by negative 4.767 (almost 5 volts) which makes it the worst, and method 3 was off by negative .938 volt which puts it in second place and makes it pretty darn accurate.

    So I ask Nate, why do we tell guys that Method 3 is the best to use when you have Method 1 in your book and it is much closer, practically perfect? His reason is that Method 1 although being so accurate is harder to remember. You can find resistance values for all sizes of wire where finding Circular Mills and Wire Values is not as easy to acquire for all sizes of wire. He then followed up and explained that the bottom line is the best method to use is by utilizing your volt meter when wiring your system. The VD methods should only be used for ball parking a job and for determining the size TF you will need and what voltage taps you will require. He then pulled another VD method out on me which he calls his own and is right on. He says when using a 35w lamp you will have a 1volt drop for every 100ft of 12/2 cable. That means with 4 35w lamps and 200ft of 12/2 cable that puts your VD at 8volts. Pretty darn accurate.

    So again, once I get the video done I will post here and on my website. If you guys have another method you want to test just give it to me and I will utilize the same stuff for the same test, I have all the materials including exact TF and lights set aside to run any other test you guys would like.

    Let me know what you guys think.

    Joey D.

    I attached section 5 from Nate's book that address's VD.

    Attached Files:

  9. pete scalia

    pete scalia LawnSite Senior Member
    Messages: 960

    SO whats the danger with the 22v tap upon wiring if you have no load on it?? if I am holding a 22v tap with 3 amps on it and I put both sides togeather it is going to burn me for a second until I pull it apart. But it is not going to electricute me nor will it even come close to killing me. Funny thing is I can get the same exact sensation from holding 2 ends of a 15v tap togeather with or without any amp draw.

    Maybe no danger to you because you are young and healthy. Take an elderly person with a heart condition and it may be a different story. Call me crazy but getting burned is not fun and very painful. The day UL cerifies a transformer over 15 volts is the day I use em. Until then I'll stick to 15 volts. I have no trouble bringing 12v to the lamp and have no desire to prematurely burn lamps out lamps with a 22volt tap when I lose a bulb or two on that cable run.
  10. pete scalia

    pete scalia LawnSite Senior Member
    Messages: 960

    You can't believe that your investigation was anywhere thorough . To make such a claim that no one has ever been seriously injured by less than 30 volts is ludicrous based upon your peripheral investigation. 15 volts was not just plucked from the air by UL. I have seen case after case where higher than 15v transformers dessimate lamps powered by higher volt taps. Not everyone changes a bulb immediately after it blows like they should. it's a domino effect and it's not pretty. even halogens don't last long when operating over 12 volts. Set aside safety and that alone is a real problem

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