I want to give you guys some good, hopefully useful info. I have decided to call upon my knowledge and experience as a degreed and licensed electonics engineer....retired some 14 years now, but still in possession of a fair amount of my memory. There have been many threads where someone asks a wiring question and gets advised to use wire with as many strands as possible because current flows only near the surface of the wire. While this is true for higher frequencies, it is not true for DC circuits. The phenomena is known as the skin effect and is a design consideration for radar and microwave applications. I will spare you the math, but this is a rough representation of skin effect at DC, low frequency AC, and high frequency AC, the white area illustrates the part of the wire not used for conduction....... I grabbed this graphic off the internet, and it is not exactly correct...AC Resistance is an incorrect term. In AC circuits, it is correctly referred to as Impedance, a beast affected by frequency, inductance, and capacitance. Bottom line..using high strand count standed wire in DC circuits will not improve conductivity. There is, however, an important reason to use stranded wire in DC automotive circuits....flexibility, a characteristic not only useful when routing wires, but also due to its ability to withstand vibrations.
That is very interesting. So, DC current flows through the ENTIRE cross section of copper stranded wire. I wonder if it's possible to make hollow stranded wire for low frequencing AC and high frequencey AC since the center core of the wire does not conduct electricity? I am not an electrical whiz, but just wonder.
That is the practice, and they are called waveguides, used in Radio Frequency applications. Also, DC flows through the entire cross section of solid wire.
This is another reason the HAMB is so good. That is some stuff I was taught in the military some 45 years ago and have since forgotten since I left the field. Thanks. Us old guys need refreshers sometimes too.
Stranded is the way to go for sure in automotive. Otherwise solid will get work hardened and break. As for the high frequency AC, look up "skin effect" as that is what the phenomena is called. I see it in the high speed cabling I deal with in my job along with few other less desirable things called crosstalk and alien crosstalk ( damn martians!)
You mentioned resistance to vibration but I think there's more to say about it's importance. Here is why I never use solid wire for automotive purposes: I had 71 VW once in which someone had run a sold #12 from the battery (under the back seat) to a push button on the dash and back to the starter. The vibration of the wire against the car wore through the insulation and with the car in the driveway and me standing right there (working on the engine), it made direct contact with the body. The car was filled instantly with thick back smoke (probably toxic). If I would have had carpet or the seat in, the whole car would've gone up in flame. When I held by breath and went in with channel locks to tear the battery terminal off, all I could see though the smoke was the bare wire glowing bright red all the way from the battery up under the dash. Under the wrong circumstances, that could have been fatal... or worse if the family had been in the car.
You are absolutely correct. I am just saying that it is a waste of money to buy higher strand count (i.e. fine strand welding cable vs regular large gauge battery cable) wire thinking it will conduct better.
I have been a career electrician and electrical contractor . Larger conductors,building wire,like 1/0 are quite stiff despite being stranded.If used for starter and battery conductors,and the vehicle moves around so to speak or vibrates a lot,the stiff wire can strain the terminations and cause a failure.In this case,and in my opinion all cases,the far more flexible welding cable is better.
The Jalopy Journal
