View Full Version : LED advantage

Mike M
09-14-2008, 04:16 PM
Someone with more experience than me with electrical theory please help with feedback:

Based on the CAST formula for voltage drop...

(24) LED's @ 4.5 watts, #14 WIRE, 100' run: voltage drop = 4.545

One run at tap #15 would cover this as a chain.

So, my question, could I use this formula for a single wire run for a loop, by eliminating the x (2) for the cable?

If so, I can make a 200' circular "loop" of a single #14 solid irrigation wire and get a similar voltage drop.

If I power (12) (4.5 watt) LED's, I can go 400' with my loop and get the 4.545 voltage drop. All LED's would be in the acceptable range of voltage as specified by DG LIGHTS and Kichler, using tap #15.

A simple method for wiring could be a (#12) or (#14) 2-wire landscape lighting cable run to a hub, where a splice for a loop begins using #14 solid.

I could actually run one #14 solid wire in a large circle around my home, and drive 24 LED's. The wire is so easy to conceal, I can use my grinder to open up the expansion joint in my driveway, and just run across it.

Or, I could just run two #14 loops, one for the front and one for the back.

Talk about time, labor, and copper savings. Not to mention smaller transformer size. And just one transformer, controller, less conduit. No more stuffing terminals or making flying leads. Time saved in tweaking voltage taps. And the transformer can be a fixed 15 V.

The solid wire makes such a quick and effective twist-on connection, one could just use the DBY's (the yellow twist-ons with small grease tubes) used by irrigation installers.

Heck, with such singular, long runs, an automatic trencher may actually make sense.

Service calls: one damaged wire or one failed LED, the whole circuit goes out. No problem, just use your wire tracer and fix the whole thing at your service call rate.

Am I nuts?

Chris J
09-14-2008, 05:18 PM
I don't think I'm understanding the question sufficiently. Why would you loop it if the voltage drop is going to be less than 5? As long as the difference between the first and last fixture is less than 6 or 7v drop, then daisy chain away. Why would you want to complete the loop? You would have more equal voltage to all lamps, but who cares with LED? The parameters are huge!

Mike M
09-14-2008, 05:36 PM
Even less wire and even more fixtures. I know, sounds greedy.

Chris J
09-14-2008, 09:52 PM
Not greedy, efficient. But I still don't understand the loop your speaking of. If the voltage is right at the beginning and the end of the run, then why double back with an additional wire to complete the loop?

Chris J
09-14-2008, 10:08 PM
I just completed a 50 light job day before yesterday with 29 LED deck lights. I got some pics using my sorry a## phone camera, but the job turned out really well. Tough job though. I was up to my chest in snake and gator infested swamp for 12 hours running wire under the bridge that crosses the marsh. I'm soooo sick of dealing with cotton mouth water moccasins!! Those bastards will chase you! When I get a moment, I'll try to upload the pics and see if any of them are worth posting (again, bad camera).

INTEGRA Bespoke Lighting
09-14-2008, 10:47 PM
Mike, if I understand what you are getting at with this crazy loop concept, then you will have to find yourself a DC transformer will you not? Sounds to me you are planning to run a single 14ga hardwire starting at the transformer and running to each fixture (in one side and out the other so to speak). If this is the case, you will 100% need to use a DC transformer.

KISS Mike... never forget the KISS

Chris J
09-14-2008, 11:17 PM
I forgot to add the parameters of that LED job. 250' of dock and then another 100' or so of boat house. I daisy chained the whole thing with one wire down each side of the dock and the longest run (with the most lights) had 1.4v drop from beginning to end. Amazing stuff! I used the 14v tap and had 13v at the first fixture and 11.6 at the last. Next time, I'm thinking of running a line from the tranny at my own home to the job site just to see what the result will be! :dizzy: Jeez, I still can't believe that word (daisy chain) is even in my vocabulary at this stage of the game.

INTEGRA Bespoke Lighting
09-14-2008, 11:37 PM
I just spec'd & quoted a system for a private road serving 17 properties. Not sure how long it is, but I would guess at about 3000 feet beginning to end. 145 LED lamped fixtures will do the job requiring less then 600W total. Should be interesting to see if it goes ahead.

Mike M
09-15-2008, 07:10 AM
Chris, I just spotted my first cottonmouth cutting lawns. Are there snakes down south in these swampy areas? (lol)

James, single-wire loop: DC trans? Just let the fixture be a part of the circuit.

One-wire loop:

1. Cut the one-wire run at the fixture.
2. Splice one lead from the fixture to the "hot" line coming in.
3. Splice the other lead to the wire that was cut and that will lead to the next fixture.

Design your loop to cover your zone as efficiently as possible, with the end of the one-wire returning to the transformer. This can use a lot less copper and manage electricity more efficiently.

I'm trying to "value-engineer" my systems.

Whuddaya think? I will prove it with a test run at my house. I already tested 2 halogens in a single wire loop with 50' of wire.

Anthony knows his stuff. When you use very low wattage fixtures, you can stack up a lot of lights on a run without so much worry of voltage drop. Looping just makes it better.

INTEGRA Bespoke Lighting
09-15-2008, 07:23 AM
You are riding on the edge of the frontier Dude... how does it feel? :weightlifter:

Is the edge sharp? How far is it gonna cut into your arse if things go wrong? :confused:

And I thought I was an early adopter! :laugh:

I am going to let you push the envelope on wiring techniques of LED based outdoor lighting systems while I sit here safe and sound, continuing to make the wire industry rich. :) I guess I just have too much to loose if things backfire. You have to keep that in mind Mike. If things go horribly wrong in the future you will not be able to revert to any other type of lamp/fixture option.

None the less, my hat comes off to your for your perserverance and willingness to push the envelope.

Mike M
09-15-2008, 12:54 PM

Don't get me wrong, I haven't put these out there, yet. I'm just seeing the future come up to our front doors and I want to start getting ready for new methods. I might start putting in LED's this fall, and I'm figuring the best way to wire for it. I need to play with this set at my own property and prove my ideas there first.

Since lighting is slow at the moment, I can play around. I may actually rig together a new tool idea I have, too.