Question for electrical engineer types

While everyone agrees copper wire is best for spark plug wire, I had a thought while trying to locate some in my stash for my 730 JD. Why wouldn't RG 59 or RG 6 cable television wire work. It has a solid copper core and is insulated. Any thoughts besides not being original looking?

Is the insulation good for 25k to 50k volts?

In addition to the high voltage, there is the shielding braid to deal with. Many center insulators are foam type, and I wouldn"t be sure that the insulation would be able to stand up to the voltages, without sparks jumping to the sheild braid. Some of the center conductors in those cables aren"t made for constant flexing and vibration either.

Perhaps magneto ignitions should stay with copper (silver is a better conductor!). But stainless steel ignition wire is available and should last longer since it does not corrode. It might be a good choice for battery ignitions.
Plug wire

the foam insulation used in most coax cable will melt at very low temp allowing the center conductor to contact the shield.

it will work for a short term temp fix if you can keep it cool, but won't last.

RG-59 and similar coaxial cables are intended for carrying low voltage, high frequency signals with minimum loss. They do this by maintaining a very constant capacitance over the length of the cable. They are not intended to be used at more than a few hundred volts, certainly not the tens of thousands of volts produced by an ignition system. The insulation is not up to the task, and the shielding provides a handy ground path for the ignition pulse when it overcomes the insulation.

There are shielded ignition wires used in aircraft, but these are totally different from coax.

As far as "everyone agrees copper wire is best", I have to take exception with that statement. If it were true, all the cars running down the road would have copper cored wires. Although 1000 ohms per foot sounds like a lot, the current through an ignition wire is very small, so that the voltage drop across the length of a resistance wire is only a few volts; insignificant compared to the peak spark voltage. The purpose of the resistance is to provide damping so that the current through the ignition wire doesn't "ring" and generate excessive RF energy. As long as it is in good condition, a resistance plug wire is just as good as a copper one. The only real problem with resistance wires is that they are likely to degrade over time; when the resistance gets high enough the spark will short through the insulation instead of going through the plug gap.

Of course, it doesn't make any difference on a tractor that doesn't have a radio. But your wife and neighbors might like to listen to their radios as you drive by.

I'm not sure everyone would agree that copper wires are the best. They are on old equipment because that is what they had back in the day. As resistance is increased (up to a point) the spark is intensified, plus the rf noise is high with either stainless or copper. I've run lots of graphite core wires with no problems that I am aware of. Dave

Would it make a difference if the spark did go to the braid as it would or could be terminated at the end you put on the wire? I'll put the regular spark plug wire on when I find mine back but just curious.

I dont know if it would work,but like you say you could hook the shielding cable to it too.Also I remember from my days many years ago as a TV repairman that one single wrap of black tape is good for 500 volts maybe more.If it arced through the insulation about 10 or 20 wraps with black tape might fix it.Dont know how long it would last.Might work.It might work to remove the shielding cable and wrap it a few times with black tape or slide the wire with the insulation through some vacuum line,that might work.

RG59 and RG6 don't have a conductor anywhere near the size used in something like Packard 440 spark plug wire. RG-59 uses a 22 to 25 gauge steel wire with a thin copper coat, and RG-6 uses an 18 - 20 gauge wire - again steel, copper clad. Good spark plug wire is silver or tin plated copper, usually 14 - 16 gauge with a 40,000 volt rated insulator. I doubt the foam used in coax works very well as a high-voltage insulator.

You can get copper core wires at Napa Auto Parts. They come in 4 and 8 cylinder I get the 8 and it makes two sets for a lot less money.
Walt

the reasons given are enough. I like Magnetic suppression wires>they have a low resistance real stainless conductor wrapped around a kevlar core. The wires conduct with effectively no resistance, while keeping radio static in check. The material is also better in the Silicon rubber insulation. JimN

Try it and you will know. How do you think Edison figured stuff out? Black tape or not, you will have sparks jumping all over the place. One big problem on old TVs was what is called corona, which is a discharge that ionizes the air, creating a smell and a glow. You could spray, insulate all you want, always took a new high voltage lead to stop it. Right wire for right job. If any of this is not what you find, come back and tell me.

While you think you are right,try it yourself.I bet it works well enough to run.Heres why,if the wire is not close enough to anything to arc,it wont.If you can run the wires away from anything metal an inch or more,it probably wont arc.How do I know?I once saw a motor that ran with baling wire for spark plug wires.If you can get it on there,far enough away from each other and metal to just spark the spark plug,it will run.

For all the current in spark plug wires. It's makes zero difference if it's stranded silver, copper, aluminum,gold or steel.
Pulsed high voltage (10-50KV) DC is funny stuff. A circuit that may measure a couple of ohms with a low voltage ohmmeter. May have hundreds or thousands of ohms resistance due to inductive impedance. Particularly at a sharp bend.

Walt In Pa. I have herd that solid core wire on highway vehicles is ilegal due to the fact that it messes up there radar

Radar? Probably not. But it certainly raises heck with AM radio. Interfering with any radio communications device is a federal offense.