Low voltage cable lighting ... through a house's structural cables

[toadspittle]

I'm building a house. It's partially a post-and-beam design, with a cathedral ceiling in the living room. Normally, there would be a large cross-beam spanning the room (which traditionally keeps the walls from pulling away from each other and falling down), but my builder is not normal. :) He sent me a crazed, inspired e-mail yesterday (he'd been working on the drawings) and wondered if we might considered replacing those beams with tensioned steel cables (which would do the job just as well).

I may not go for it. Mainly for aesthetic reasons; although much of the house is contemporary enough to stand up to the look of those cables, my wife and I still like a little bit of rusticity (hence the beams) and I'm also rather concerned that the high ceiling will look WAY too high without the thick beams cutting across the space.

BUT ... I'm still intrigued by the related engineering question he brought up:

Since we were originally going to mount lights on the beams (some aimed up at the ceiling, some aimed down), without beams we'd need to mount them somewhere else. He had the nutty idea of replacing each beam (there were two planned, originally, to cut the room into thirds) with a pair of cables, mounting low-voltage halogen lights on them, and running the 12V straight through the structural cables.

[ For anyone not familiar with cable lighting, it's just like track lighting, but with suspended bare wires; see some examples here (http://www.grandlight.com/products_lowvolt_kablelite.htm?src=LFTH) and here (http://www.ccl-light.com/docs/track/adjustable.html). ]


I love the economy of the solution (even if I'm not going to use it). So my question: is this possible to do? Or am I risking

(a) electrocution
(b) fire
(c) trying to pump the wrong amount of current through the wrong gauge of wire (since the structural cables will likely be MUCH thicker than standard lighting cables)
(d) some other debacle?

[GaryM]

a) Don't touch the cables! Although for practical purposes it's difficult, if not impossible, to electrocute yourself with 12 volts.
b) Don't see a problem. it's related to c)
c) Current flow will be controlled by the total resitance in the lighting circuit. Although keep in mind that steel is not as good a conductor as copper.
d) Need a good method to insulate the tensioned cables from the other surfaces to which they are attached. Although with only 12 volt potential there might not be any issues. The cable attachment to the structure should terminate in insulators. And at 12 volts most non metallic materials might be OK.

[herman_and_bill]

I imagine you will be using a transformer to get the 12 volts, and when the transformer shorts out you will be getting the 120 volts, correct?

[Q.E.D.]

Originally posted by herman_and_bill
I imagine you will be using a transformer to get the 12 volts, and when the transformer shorts out you will be getting the 120 volts, correct? No, most transformers have pretty good isolation between the 120 VAC primary and the low-voltage secondary. In most cases, it would take an unusual failure for that isolation to fail. The most common failure mode for small transformers is winding overheating and fusing deep inside where the temperature rise is the highest.

[gotpasswords]

Has your architecht been sniffing the diazo fluid again?

I can see a couple problems:

The structural cables are probably bigger than what the "trolley" fixtures are capable of attaching to. They usualy mount to something approximately 3/16" which is probably not strong enough to hold up a house.

Moisture in the wood at either end of the cables will cause some "leakage" current and excess power consumption. It's probably a trivial amount, but it probably is measurable. Also, you'll need to watch out for any reinforcing washers or plates at the ends of the cables, so there's not a short-circuit.

[trabi]

There's no danger of fire or electrocution or - as far as I can tell - detectable leakage.

If the wood's properly seasoned then it should be dry enough to insulate for 12 volts. If it had enough water in it to cause enough of a drain to even register on your electricity meter, especially with a 12-volt supply, then within a year or so your beams will be so warped from the drying process that your house will look like a corkscrew and lighting will be the least of your problems.

Also, I doubt if the thickness of the wires is an insurmountable problem. The current should flow through it fine, but you might have to adapt the mounting clips, that's all.

Sounds like a fun idea. The only question is whether it appeals to you esthetically.

[kanicbird]

Big problem - galvanic corsion. The 2 dissimular metals (copper wire from transformer to steal cables & from steal to copper lights) will eventually cause corsion on the join. This may not rust through your steal supports but will cause poor contacts and ugly rust spots.

[trabi]

galvanic corsion

I think you mean corosion. The same thing happens with the wires attached to car batteries. The way to cure it is to grease the joints.

[Desmostylus]

Originally posted by trabi
I think you mean corosion. Maybe even "corrosion". ;)

[trabi]

Maybe even "corrosion".

DOH! :smack:

[kanicbird]

one of the 3