Landscape Lights and Voltage Drop

[Mike The Mute]

The question at hand is; When running my wire in a loop to prevent voltage drop a total distance of 500' (out and back) with approx. 720w load spaced out through a majority of the run, will there be enough power to each light? Lights will be 18w ea. and hoping to find trans. w/boost or multi-tap (12,15,22v).
I'm trying to find a single 900w transformer with only one set of posts. Seems they are all broken down into 300w increments nowadays.
All wiring was planned to be done with standard UG LV stranded wire in 10awg.
As per usual, the customer is beyond penny pinching. I say, if it can't be done right, stick solar lights in the ground.
Also, anyone know of a manufacturer of 900w single post, multi-volt transformers?

 

[hbiss]

Even though you are doing a ring it will not prevent voltage drop. The lights will still get progressively less voltage as you approach the center of the string with the center the least.

The recommended method of running landscape wiring is a star configuration with the transformer as close to the center of the layout as possible. That is why you only find transformers with multiple outputs. You would run 120v to that location and choose a tap to compensate for that voltage drop. Your LV wiring should be equal and short to minimize differences in voltage and brightness. Many times one transformer isn't going to do it.

-Hal

 

[Mike The Mute]

More to do about ...

More to do about ...

I catch what you're saying. Understandably, the center would have less than at the terminal. Still, far less drop and further total distance than single run. Star pattern may be useful, I'd like to run 110v to key points anyway. I'd like the multi-tap so I can select the voltage I need to keep all fixtures within spec.
Any thoughts on wire size and loop distance if I could find the 900w 12-22v trans.?
I did it this way about 4 years ago. Had 56 fixtures in all. 2 fixtures and LV rope around a dock (small lake, no boats) were in the back. The rest were hanging from the trees, pointing up @ the trees, @ the house and along the landscaping. 4 trans. on dimmers. Sick set up. I DID pipe and pull to approved boxes for low and line voltage (seperate pipe and boxes) before running "landscape" wire. She wasn't concerned with cost. Material was over $4000. No problems. Lots of "Ooh"s and "Aah"s.
This lady is a different story.

 

[winnie]

One approach is to balance the voltage drop of the system, so that each bulb sees the same voltage. You can do this if you feed the string of bulbs from opposite ends. You can do this with a three conductor circuit.

One conductor feeds directly to the lamps. The other conductor feeds to the end of the string, and supplies the third conductor. The third conductor then feeds the lamps again.

------------------------------
     |     |     |     |     |
     O     O     O     O     O
     |     |     |     |     |
     -------------------------
                             |
------------------------------

This uses an extra conductor, and it makes the voltage drop the same as if all of the loads were at the end of the line, meaning much _more_ over-all drop. But all of the lights will have the same voltage drop.

However, 720W at 12V is 60A. 10ga is not suitable for this for ampacity reasons. If we limit the circuit to 20A (1/3 of the total load), and have a string length of 250 feet, then you will be dropping some 12V in the wires, as much as being used in the lamps.

-Jon

 

[stickboy1375]

Try this out...
http://www.cast-lighting.com/volt-calc.html

 

[Dennis Alwon]

Kim lighting makes a 900 watt trans but it is 3 circuit 300 each. They also recommend if your distance one way is 250 feet then the maximum watts is 100watts with an 8-2 cable. I used their recommendations and had no problems. #8-2 UG wire is expensive but it worked well.

You can also go to http://www.kimlighting.com/ and go to low voltage lights-- page 90 has the chart on the pdf screen

 

[iwire]

When running my wire in a loop to prevent voltage drop a total distance of 500'

Wouldn't that be a 310.4 violation?

hoping to find trans. w/boost or multi-tap (12,15,22v).

You do not want to do that as when lamps start burning out the voltage will increase and you will burn more lamps out.

I'm trying to find a single 900w transformer with only one set of posts. Seems they are all broken down into 300w increments nowadays.

The NEC limits LV lighting circuits to 300 watts which results in 25 amps of current on a 12 volt system.

If you had a 'single post' 900 watt transformer you would have a 75 amp circuit and would need 4 AWG minimum.

IMO you will not have satisfactory results with 10 AWG, at least 8 AWG, 6 AWG would be better.

 

[petersonra]

Wouldn't that be a 310.4 violation?

It certainly appears that way, even though this seems like a safe solution to a non-trivial problem.

 

[iwire]

even though this seems like a safe solution

I agree with you.

 

[Mike The Mute]

I don't get it. 310.4 leaves you assuming that it's only OK to run in parallel with 1/0 or larger. Until you read the exception 620.12(a)(1). Is it because of the nature of the beast (low voltage lighting) that this doesn't work for me? Maybe I'm reading it wrong.
The intention of using the higher tap to acheive 12v @ the sockets was to be read on an average down the run to center and with no bulbs installed to prevent the jump with each burnt bulb. Sound more like it?

 

[Mike The Mute]

Sticky and Winnie, Thank You!!!! Thanks to everyone. But especially the links you two gave. This site has always been a major help when I needed it. I'm telling the homeowner to pay up for the extra transformers and while I'll still be running in parallel, it will be done in 300w increments in a clover shape. I'll be sure to do the proper calcs. this time too! Thanks again, Mike

 

[iwire]

I don't get it. 310.4 leaves you assuming that it's only OK to run in parallel with 1/0 or larger. Until you read the exception 620.12(a)(1).

620.12?

The intention of using the higher tap to acheive 12v @ the sockets was to be read on an average down the run to center and with no bulbs installed to prevent the jump with each burnt bulb. Sound more like it?

If you have no bulbs installed there will be no voltage drop at all.

So if you where to connect the bulb less circuit to a 15 volt tap you will read 15 volts anywhere on the circuit.

Once you start installing lamps the the voltage will drop.

It is also important to remember that with a 12 volt system a change of 3 volts is 25 %

So if you where to run a 12 volt lamp at 15 volts it would be the same as running a 120 volt lamp at 150 volts. It would not last long.

 

[petersonra]

maybe some enterprising electrician should send in a suggested change to the code to allow parallel wiring for the purpose of reduction in voltage drop.

 

[petersonra]

Until you read the exception 620.12(a)(1)

Article 620 does not apply to landscape lighting.

 

[iwire]

maybe some enterprising electrician should send in a suggested change to the code to allow parallel wiring for the purpose of reduction in voltage drop.

The answer is easy, run larger conductors.:grin:

Also the NEC does allow the paralleling of small conductors for control wiring.

 

[petersonra]

The answer is easy, run larger conductors.:grin:

Big Orange only sells a couple sizes of landscape wire. If God had intended that larger wires be run, Big Orange would stock them.

 

[iwire]

Big Orange only sells a couple sizes of landscape wire. If God had intended that larger wires be run, Big Orange would stock them.

LMAO

Can't argue with that.

 

[brian john]

http://www.acmepowerdist.com/products.asp?PAGE=prod_landing.html

 

[coulter]

So how about runing LV lighting like airport lighting. 6A constant current, series string, one wire loop around the runway/taxiway?

carl

 

[brian john]

A little info from GE regarding voltage levels and lamp life.


http://www.gelighting.com/au/lighting_applications/downloads/ps_precise_cc.pdf