Wiring Question

[MEforKids]

Hey there,

I am working on fixing up a practical that has very thin unmarked zipcord attached to set pieces with 5w 12v lamps, running off a 12v battery contained in the set unit. All the wiring needs to be replaced and I have some 18 awg speaker wire on hand but am concerned if the jacketing is protective enough and because it is the half copper half aluminium wire if I will run into problems.
Trying to make this safer all around, I have learned from poking around so far that most people would use this wire in a car but not in most other applications which leads me to think that because it is low voltage it should be okay...but better safe than sorry. Thanks.

 

[JD]

but am concerned if the jacketing is protective enough and because it is the half copper half aluminium wire if I will run into problems.

If it is clear plastic and one conductor looks copper and the other is silver looking, it is because the silver looking conductor is tinned copper. Haven't run into any aluminum zip cord yet.

Another thing to keep in mind, just because it's low voltage doesn't mean it's low current. Wire gauge is based on the amount of current flowing through it. Even a small 12 volt battery pack is capable of causing wire to burn up and thus be a fire hazard.

 

[WayfarerAM]

Voltage is important for determining the jacket type/thickness needed for insulation of the conductors. With the low voltage (12v) speaker wire shouldn't be an issue.

Like JD said what you have to worry about is current (amperage). In this case you would have to worry about the distance from the battery and the number or lights. Look for an ampacity chart with 18 gauge wire and go from there based on your distance and the current. Based on you info each bulb is 5w/12a= ~.42a per lamp.

 

[MikeJ]

like posted above, speaker wire is all copper. How many lamps do you have total? Use ohms law to calculate the power requirements of the cable. I think you will probably be fine with the zip cord though, but always do the calculations if there is any doubt.
For any load, the lower the voltage the higher the current will be, requireing thicher cable. One of the benefits of running things at higher voltages is the reduced current given the same application.

 

[techieman33]

like posted above, speaker wire is all copper. How many lamps do you have total? Use ohms law to calculate the power requirements of the cable. I think you will probably be fine with the zip cord though, but always do the calculations if there is any doubt.
For any load, the lower the voltage the higher the current will be, requireing thicher cable. One of the benefits of running things at higher voltages is the reduced current given the same application.

Speaker wire is not all copper. I've run into plenty of speaker wire that was copper clad aluminum.

 

[JD]

Speaker wire is not all copper. I've run into plenty of speaker wire that was copper clad aluminum.

Wild. The expansion coefficient is so radically different between the metals.You would think the aluminum would burst through the copper.

 

[Colin]

Speaker wire, coax, voice coils, and residential wiring is sometimes copper clad aluminum. The weight savings is the supposed attraction for voice coils, and the cost difference gets significant in a building.

Copper clad was the solution devised when it became clear that aluminum was setting people's houses on fire. It still has to be sized up 2AWG compared to copper, but is deemed safe once you do that (which pure aluminum is not, as building wiring at least).

At higher frequencies, most current passes through the outermost section of a conductor, so in something like data transfer the aluminum core is sort of filler and the copper skin does what copper does best.

 

[MikeJ]

True, It could be CCA, though more uncommon, but in any case both sides of the wire will be made from the same material.

 

[MEforKids]

Thanks for all your replies. The wire is definitely aluminum because the bit of label I have says that. My uses will probably only have about 45-50W going at once which is only 3.75A, and a max distance of 10 feet. Looking at the charts it seems like that should be fine. My only concern now is the aluminum.

 

[Colin]

Thanks for all your replies. The wire is definitely aluminum because the bit of label I have says that. My uses will probably only have about 45-50W going at once which is only 3.75A, and a max distance of 10 feet. Looking at the charts it seems like that should be fine. My only concern now is the aluminum.

Aside from your local authority's unknown opinion on anything homemade, you should be okay given how oversized the wire is for the application. I guess you could fuse the circuit to be sure you can't get a huge fault current (if an auto/marine battery capable of delivering). The main issue left is the temperature rating, which is probably only 60C for your speaker wire. Just keep it away from heat sources and keep current within spec. Properly sized aluminum gets unsafe due to the expansion coefficient mentioned above, especially when mismatched with terminals meant for copper, causing the wire to work itself loose at connections, plus aluminum oxide allowed to form in a loose connection makes for even more resistance and heat. The expansion/contraction issue is more with solid wire. Good termination is the key. There are methods for terminating aluminum that clean and inhibit oxidation, and hold the connection tight, but I think these are more a big deal for permanent in-wall situations. I wouldn't loose sleep over your application as long as the connections are sound and the temperature is safe.

 

[n1ist]

I guess you could fuse the circuit

Always fuse the circuit, right at the battery. Instantaneous fault current from most lead-acid, NiMH or Li batteries can easily set things on fire.
/mike

 

[Colin]

Always fuse the circuit, right at the battery. Instantaneous fault current from most lead-acid, NiMH or Li batteries can easily set things on fire.
/mike

Yeah I don't know why I made it sound optional. I recall a house fire in NH a few years back that was started by a 9V kicking around in someone's junk drawer getting shorted by a paper clip.