View Full Version : Homeowner with line drop

06-11-2008, 10:31 PM
I just installed some lights round my parents pool and the last two path light have alot of voltage drop. What I did was install twelve 20-35 watt lights on about 70 feet of heavy outdoor lighting wire. I used a double tap 600 watt transformer with 12 13 14 15 volt taps. I used the 13 volt tap (i don't know why I picked that one). Do I need to use a different tap or should I have ran more than one wire? Sorry for my ignorace any help is appreciated.

06-11-2008, 11:31 PM
this is why theres proffesionals to do this...how many lights? you should only have a few fixtures per run. it sounds like you daisy chained em..

Chris J
06-11-2008, 11:41 PM
Depending on how many of these 12 lights were 35w, you have probably overloaded your transformer. Most 600w trannys are actually two 300w circuits. You should see at least two common terminals. That means that if more than a few of these lights are 35w, you have more than 300w on one circuit. There are other a whole bunch of other things I could criticize about your goofy install, but I need to send this message to you very quickly so you can somehow un-plug this system before you burn your parent's house down!!!!!!!
I hope you live close to them so you can go do this right now!
After you unplug the system, and call a qualified lighting contractor, could you please tell me what your main profession is? I will anxiously await that response.

06-11-2008, 11:54 PM

Thanks Chris! Very entertaining!

06-12-2008, 01:07 AM
Least Chris held his tounge from more coulorful metaphors.

Im willing to bet even with all 20 w lights they are somehow on 12ga and over loaded

Burning down the house is playing in my head right now.

06-12-2008, 01:12 AM
Ignoring that it appears that ALL 20 of the lights are on the same circuit, doesn't 20x35 equal 700? Even if you wired it properly it sounds like you've overloaded the transformer.

06-12-2008, 01:23 AM
dont ignore anything. He said 12 lights at 20-35 w Re Read it.

06-12-2008, 01:35 AM
dont ignore anything. He said 12 lights at 20-35 w Re Read it.

AHA! Perhaps I've been staring at lawnsite for too long... ;)

Chris J
06-12-2008, 01:37 AM
Don't you guys know that it's 1:30 AM? I thought I was the only one who didn't sleep at night!

David Gretzmier
06-12-2008, 01:39 AM
To answer the question- If you are going to do this yourself, run 4 wires of at least 12 guage, 10 guage preferable. the first wire does the first 3 lights, the 2nd does the next three, and so on. each side of the trans should have 2 wires to a common. use a volt meter to check each run at the connections to the lights, and use the tap for that group of lights that gives you a reading range of 10.5-11.5 volts. good luck.

now all you guys can throw rocks at me for helping someone.

Chris J
06-12-2008, 01:49 AM
You helped no one David. If they put that many lights on the same run originally, do you really think they will understand your explaination? :laugh:

David Gretzmier
06-12-2008, 02:12 AM
probably so. but I tried. gnite.

06-12-2008, 09:02 AM
I understood his explanation. I'm taking off the last three or four lights and running another wire, I wasn't using my head when I put that many lights on just one tap. I guess that's why I don't get paid to do this.

06-12-2008, 09:43 AM
Scott... taking off the last 3 or 4 and leaving 8 or 9 chained is not a solution... its a slight improvement but try running 2 more wires minimum and using a volt and amp meter this time.

06-12-2008, 09:54 AM
yeh your going to need atleast 3 runs. 4 is best. thats the only way to do it.

The Lighting Geek
06-12-2008, 11:17 AM
Scott you really need to pay attention to what we are trying to tell you here. Not trying to scold you, but the risks associated with overloaded wires, transformers, and not to mention bad connections are serious. You could do some serious damage.

Chris J
06-12-2008, 06:24 PM
Scott, I didn't mean to bust on you so hard, but I just wanted you to get the message. Even low voltage can create big fires. Please just do some more reading and ask some more questions before trying this again. I'm always willing to help if you say the magic word, but I just don't react too well when someone shoots first and asks questions later. This is normally when I take out my invoice book.

06-12-2008, 11:51 PM
If I use this formula for VD I can run all the lights I have with three wire runs since I am running 12g wire and use 7500 for the cable constant.

Voltage Drop = (Total Watts x Length of Run) / Cable Constant

Does this sound right? I'll still check it with a meter when I am done.


David Gretzmier
06-13-2008, 12:55 AM
uh, in a decade of doing landscape lighting I have never heard of the 7500 cable constant. so if I want to light a 20 watt bulb 1000 feet away

20 x 1000 = 20000 / 7500 cable constant = 2.66 voltage drop.

sweet. I can now put that pathlight at the end of that crazy long driveway. all I need is a 14 volt tap.

this formula may work in other instances however. I've just never heard of it. anyone else?

06-13-2008, 09:47 AM
thats the worst VD method ever...........double that number and your right on!

Bill S
06-13-2008, 02:34 PM
The number according to Nightscapings formulat is actually 7490 as a constant.

Joey, what makes that the worst method ever? It appears as though it is good enough for Nightscaping, one of the original manufacturers of LV lighting...

06-13-2008, 04:38 PM
well do the method then run a test and you find that the method is actually off by double. In an AC system with that method you have to multiply by 2. The electricity travels there and back.

I have no idea why they use that method. I have done the tests in house to prove that it is not accurate. You can do a search on here.

most accurate method is: VD=2 x Wire Value x Length of wire to first fixture x Amps / Circular Mills