DC current through a stainless steel/copper wire

[rysep]

I'm looking at suspending some low volatage (<30V) lighting with a 7x7 304 stainless steel aircraft cable. I also want to run 30V DC through the cable to power the light. So the suspension cable is also supplying the power. I will be running 4 separate cables (only 2 will be used to supply power). The closest cables will be about 2 feet apart. To keep the conductivity high I want to replace the stainless steel 1x7 core of the cable with a 1x7 copper strand. This will be used indoors in office buildings, grocery stores and the like. Will there be any corrosion issues with the copper or stainless steel wires?

 

[MikeHalloran]

I don't know how you'll get reliable electrical termination at the lamp interface.

Mike Halloran
Pembroke Pines, FL, USA

 

[zekeman]

Anodic action between the copper and stainless strands and stainless is about 1/20 of the conductivity of copper.

 

[resqcapt19]

I think you may have issues with the National Electrical Code if you do this.

 

[dpc]

If this is in the US, I think it's best to give up now. Trying to install a lighting system without UL labeling will generally result in a red tag from the local inspector.

Technically it may be feasible, but, I don't see much chance of getting it approved without spending a ton of money.

"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

 

[itsmoked]

dpc I see this type of lighting often. It's the <30V that does the trick, I suspect.

rysep; Why can't you find something off-the-shelf?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dpc]

Keith,

If it is sold as a system and has an approved LV power supply, then it might be acceptable. But I'm not aware of anyone doing it with steel conductors. But I could be wrong.

It happens a lot

"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

 

[Compositepro]

I've installed lighting like that from Home Depot. It was pricey but an interesting, modern design. The cables looked like stainless but were actually plated copper. The strands were actually very tiny but were bundled in a way that made the strands look large. I just found a piece in my desk drawer. The wires appear to have a hard temper.

 

[rysep]

I have looked into this with UL and they said as long as we use a class 2 power supply this is fine.
I have also seen similar lighting to this but it usually is something that spans from one wall to another. The lights that attach to the cable are very light weight. We are suspending much heavier lights from the ceiling and need a cable that is stronger than a tin or zinc plated copper cable. So the load is really taken by the staninless wires while the current is going through the copper wires.
My main concern is corrosion because we are running DC through copper wire in contact with stainless steel wires.

 

[MikeHalloran]

I remember working with Signal Corps wire a long time ago.
It compises a loosely twisted pair of stranded insulated wire. Four of the strands were steel, three tinned copper (or the other way round).

What I remember most is field splicing the stuff; the only approved splice is a square knot. The steel makes it pretty difficult to tie a knot in the wire; it's very stiff.

[ I got to splice it because I had borrowed a spool that was alleged to be a continuous unbroken mile. It wasn't; it had been cut in several places, and the ends knotted together, not with square knot splices, just unstripped knots, so I couldn't get a signal through it until I unrolled all of it and put it back together. )



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

Oh. Where I was going was that I don't recall corrosion being a particular concern with Signal Corps wire. I don't know if the steel was stainless, or nickel plated. I just know it was harder than the stainless lockwire I keep in my toolbox.



Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

Maybe go ask in the corrosion forum. Those guys have all this in the main corridors of their brains.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[telecomguy]

Didn't see info on the gauge of the strands. Can the center 1x7 copper 'wire' carry all the current you need? If so, why not insulate it from the stainless? Just a thought.

<tg>

 

[resqcapt19]

I have looked into this with UL and they said as long as we use a class 2 power supply this is fine.

While UL may say you are good to go, section 411.3 of the NEC requires that the lighting system be a listed system or an assembly of listed parts. This will require that your wire be listed. Without the listing most inspectors will red tag the installation. I would expect that getting the material listed would be very costly.

 

[oldfieldguy]

Mike--

The Signal Corps wire was not stainless. I've seen it rust in "legacy" installations.

It's also pure misery to unwrap a half mile of it off a tank sprocket.

old field guy

 

[itsmoked]

Keith Cress
kcress -

http://www.flaminsystems.com