Why woven grounding strap?

sphanna

sphanna

Well-known member
I have pondered for a long time just why the ground straps usually are woven flat copper. I for fear of showing my ignorance have never gotten around to asking about this. So there, I've swallowed my pride. Can anyone enlighten me?
 
A flat metal bracket or bar would eventually crack from vibration.
A braided ground strap would minimize that. Also provide flexibility for ease of routing and mounting.

The original Ford Model A ground strap was a stack of flat copper sheets. I suppose they could individually crack but you would still have the remaining strips.

Richard
Anaheim CA
 
I don't have a points car so I went with a piece of double ought ( 00 ) welding cable. In my opinion it was a very smart move. Starts better and lights are brighter.
 
That is a good question to ponder. Ford was not alone in using braided ground straps after the model A, they were very common until the ground cable started to be attached further from the battery, and could possibly come in contact with other wires and chaff them, and then the insulated ground cable became popular. The woven ground strap was in my opinion an improvement over the multi layer copper strap the model A came with, as it flexes better.
 
Correct me if I am wrong but I belive that electrons flow on the outside of a wire so a woven wire would have more surface area to increase current flow.
Dave
 
Extra flex cable "woven wire " has very high current carrying capacity, and meets requirements for removal and installation of battery. Electrons move like water in a pipe, all moving, voltage is water pressure, current is water flow, then there is impedance, we can go on and on,
 
The real reason the grounding strap is woven of many fine conductors, is due to the electrical property of high frequency current to travel on the surface of conductors. this is known as the "skin effect" and was well known in the '20s and before. It is important to shunt high frequency electrical noise to ground that is generated by the spark ignition process and generator brush arcing. All electrical sparks are oscillatory and create profuse electrical emissions that were particularly troublesome during the primitive early days of AM radio. The DC current leaving the battery is by and large pure DC, BUT, this becomes "hashed by the ignition system and the generator brushes...The braided strap provides a low A/C impedance to ground for these spurious signals...

http://en.wikipedia.org/wiki/Skin_effect
 
1crosscut said:
Correct me if I am wrong but I belive that electrons flow on the outside of a wire so a woven wire would have more surface area to increase current flow.
Dave
Click to expand...
From my memory a long time ago, I think this is true for AC, and also the higher the frequency, the more towards the outer of each strand the current flows. I don't think it applies to DC, but I'm sure someone else will comment on this.
 
1crosscut said:
Correct me if I am wrong but I belive that electrons flow on the outside of a wire so a woven wire would have more surface area to increase current flow.
Dave
Click to expand...


Electrons in a DC circuit flow through the wire, like a hose. or in the case of the woven type, through the individual wires.

In the case of RF (radio frequency), the electrons flow over the conductor surface. This is called "skin effect". That is why adding insulation on bare conductors changes the velocity factor of the wire in RF uses.
 
My take is the flat wire has more wire in it then the regular say 0 gauge and the woven part keeps the wires tight..........plus all the electrical theories add to it also :).
 
The skin effect is with AC currents and is due to eddie currents canceling the current in the more central parts of the wire. The high tension wires are commonly tubing to keep them lighter.


Skin Effect
 
The comments above are correct. Electrons move on the surface of a conductor so a conductor with more surface area, more wires, will move the energy with less loss of potential, (voltage). The weaving process creats flexibility that will allow the cable to last a long time and we all know that Model A's are flexible ! By weaving a huge # of very small wires you get the best of both worlds.
 
springerpete said:
The comments above are correct. Electrons move on the surface of a conductor so a conductor with more surface area, more wires, will move the energy with less loss of potential, (voltage). The weaving process creats flexibility that will allow the cable to last a long time and we all know that Model A's are flexible ! By weaving a huge # of very small wires you get the best of both worlds.
Click to expand...


Unfortunatly springerpete is wrong.

As others have said the skin effect only happens with AC and I *think* it has to be fairly high frequency. DC has absolutely no skin effect.
 
I guess from this discussion, I have the original strap in my early 30. It is many sheets of copper straps layered on my Fordor. Also on my coupe, I have just a battery cable as the ground. This seems to work just fine too. That is what got me thinking on this. Thanks for your replies.
 
Flat woven ground cables: The electron flow skin efect is what makes our automobile's old aluminum/wax paper condensers work so well. The stored electrons on the aluminum foil is enough to make you flinch when you touch the terminal whle holding the condenser. The Vandegraf generator stores its electrons on the surface of it polished aluminum sphere. The stored electrons on its surface can light up a florecent light bulb when you hold the bulb in your hand and pont it towards the sphere. These only work with DC current. So the theory of "DC doesn't flow on the surface" doesn't apply here? Please explain.
 
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