Cable track lighting systems are elegant, only good for 300 Watts
12V LED lamps save an overloaded track lighting system
I recently encountered a fine mechanical installation of a cable track low voltage lighting system that was electrically overloaded. The cable track cable is good for 300W. That’s six (6) 50W lamps. Many installations will benefit from new high-efficiency LED lamps that provide similar light levels with improved optics at only 10W each. So if you have 40 linear feet of cable track zig-zagging over a public gathering area, you easily position 3 or even 6 lamps per 10′ section, whereas with 50W halogen lamps, each 10′ section would get only one or two lamps every 10′ section.
Another issue with this installation was that the low voltage wiring from the transformer was on #12 cable just good for 300W at 12V (25A). NEC Code requires that wire be loaded to only 80% of its capacity, and the results of this installation show a good reason to maintain this margin for safety. Fortunately, Arch St. Lighting was right there for me, and had good advice, and a replacement canopy and track feed device for me from their catalogs.
Due to overload and/or poor termination, the leads between a 12V fixture canopy and the suspended cable track system heated up enough to burn through and loose of the fixture canopy.
This tiny lamp consumes a lot of power, and at only 12V draws a lot of current to do so — 50W / 12V = 4.1A per lamp!
If the light quality is good, then 400 lumens from an MR-16 form factor is excellent.
When overload is a concern for low-voltage lighting systems, LED lamps look increasingly attractive as a solution for immediate design issues as well as an investment in energy conservation and labor-savings over the long life of the lamp.
Cable track feeds typically involve slack cable running out of a recessed wiring enclosure, through grommets in a decorative canopy, and clamping to the electrical-mechanical combined support and power system. Because the system operates at <30 volts, people will not be shocked by touching the two poles of the feed.
Track and conventional lighting provide welcoming variety in an entrance hall
Suspended cable lighting systems offer flexibility in mounting and lend themselves to odd angles or zig-zags. This high-end system uses pulleys at anchor points to help keep the system taut.
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Cable track systems typically use a braided steel cable that is probably about the #8 guage you say you found. The cable is both mechanical support for the lampholder and an electrical conductor. I do not recommend using anything other than the steel cable provided with a fixture kit, or by the manufacturer of the fixture kit. A good lighting supplier, such as Arch Street Lighting, in Philadelphia (I believe they will ship anywhere), can get you replacement cable for most low voltage cable track lighting systems.
http://www.archstreetlighting.com/
Andrew writes:
Subject: source for 12 gauge bare track wire for diy led lighting system
“I came across your informative website while looking for bare wire
cable for a couple of led lighting tracks I want to install in our new
home. I set up a 25′ bare wire system in our previous home using 8
gauge bare wire that I happened to find. I live in the Boston area.
“I’d appreciate any suggestions.”
In answer to an email query about low voltage/DC wiring principles for architectural lighting design:
Different nations, or even states/provinces, will have different codes on low voltage wiring. The question isn’t DC or AC: it’s whether the voltage is 48V or below (for the U.S.). The voltage that can break human skin is about 80V for women and 100V for men, so 48V is a pretty safe voltage for human contact.
AC low voltage will typically be more inherently safe than DC, since the AC low voltage power supply is going to be a transformer with limited current capacity, and therefore limited power delivered to the wires, even if they get shorted to each other.
In DC (with the plus and minus wires you mentioned), voltages are typically very low since each battery cell only generates about 1.5V and most batteries are 12V or 24V or 36V or 48V. These voltages won’t shock a person, but a 12V automotive battery can deliver huge amounts of current into a short-circuit, and would probably start a fire or destroy the battery or both, if a conductor (any piece of metal) shorted across the plus and minus wires, or the wires themselves somehow crossed each other.
In either DC or AC, a short circuit can destroy the power supply (whether battery or transformer).
So, your main design concern should be to make sure voltage can never exceed 48V, and that conductive parts are not likely to cross the two wires. Also, some sort of power limit if using a DC power supply such as a battery.
There are many existing bare-wire and moldable-track lighting systems out there, so I’d recommend doing a good bit of research in lighting manufacturer catalogs before investing too much energy ‘re-inventing the wheel’.
The LED lamp shown mounted on the cable track gimbal lampholder is a Phillips AmbientLED model available at Home Depot.
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