Low voltage deck lighting - need straight answer.

Old 10-11-03, 08:45 AM
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Low voltage deck lighting - need straight answer.

I can't seem to get a straight answer to my question from anyone I ask.

I have a 300 watt power transformer for some decking/patio lighing that is to be installed. The code, from what I've read, as well as the instruction with the pack say NOT to install the FIRST fixture within 10 feet of the pack.

Soooo... does that mean the the last (or next to last, etc.) CAN be within 10 feet? Or in other words, can their be ANY fixture within 10 feet of the pack? or does the pack need to be 10 feet away from ANY fixture.

I can not get a straight answer from anyone.


Old 10-11-03, 08:58 AM
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Location: welland ontario
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It could be so the light sensor doesn't sense the light from the lights and turn off. It would sit there going on & off if that was the reason. That would mean no light first or last should be near the transformer.
Old 10-11-03, 09:03 AM
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There is no light sensor involved in this application.

NEC mentions nothing of light sensor.

Pretty sure that's not it.
Old 10-11-03, 09:48 PM
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Can you give us more specifics?

What code article are you referencing?
What voltage is your lighting system?
Are the lights series or parallel wired?
Who is the manufacturer?
Old 10-11-03, 10:01 PM
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Hopefully this helps.

From Intermatic's FAQ section

"You must have at least 10 feet of cable between the first fixture and the power pack to avoid premature bulb burn-out. The cable may be buried, coiling is not recommended"

I attempted to pull up some specs. for your 300 Watt transformer, but intermatics documentation is apparantly written by trained chimps.

Just a hunch, but you are running 12 V lights, the transformer is rated for a maximum cable distance of 100Ft. In order to accomplish that, the secondary voltage of the transformer is set higher than 12 volts (actually higher than 13.6, as most 12V lights will function fine up to that point.) This is done to mitigate the effects of voltage drop. Within 10 feet of the trans pack, the voltage is higher than the lamp rating. An overvoltage to a lamp will cause premature failure of the lamp.

Based on that, the key is to not have a fixture within 10 cable feet of the transformer. You could place a light on top of the transformer if you so desired, as long as the cable length is at least ten feet. Therefore, putting the last light in the run closer than ten physical feet away is no problem.
Old 10-12-03, 06:26 AM
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1. 12V System
2. Pack by Intermatic (Malibu "ML300RTW)
3. Fixtures are assorted 12V fixtures (i.e. Kichler, etc.)
4. NEC (Do not know exact code -- it is in where they mention "low voltage lighting systems")
5. I belive parallel is the only way you can hook up 12V systems...
(Wire travels along "route" and fixtures are "tapped" into wire.) Route can be split via "Split the load" method, "Tee Method" or "Split Tee" method
6. The run with 300W must be done with 12 gauge, this allows for a max run of 200 feet (?).

CSelectric, I think you're right -- I think that is the only reason for the "10 foot" rule...

Where did you see 100 feet as max? I'm seeing 200 feet with 12ga... what did I miss?

Thanks for the help!
Old 10-12-03, 07:53 AM
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I pulled the 100ft number off of Intermatics site. It may well have been the rating for 14 or 16 guage cable, as Intermatic sells both.

I can almost guarntee you the 10ft ruling (remember that's cable length not physical distance.) is due to the transformer secondary coming out high. The voltage should be stated somewhere on the transformer, but with Intermatic one never knows. (don't misunderstand that, they make a good product that will work fine and last a long time. It's just that their product documentation, technical supoport and web site are a bit lacking in this, admittadly very picky, electricians view of things.)

As far a parallell connections, yes that is the only way to hook up lighting to a 12V transformer. However, you can hook 12V. lighting to a 120V system in series (10 12V lights in series = 120V.) It is the rare lighting system that works in this manner, but I have seen it before.
Old 10-12-03, 04:57 PM
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Thanks CS!

I really appreciate all the help.


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