# “Hyper Ground System” Huh? (automobile question) **URL:** \ **Category:** Factual Questions\ **Created:** [August 17, 2004, 4:13am UTC](https://boards.straightdope.com/t/hyper-ground-system-huh-automobile-question/260197 "2004-08-17T04:13:44Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [August 17, 2004, 8:59pm UTC](https://boards.straightdope.com/t/hyper-ground-system-huh-automobile-question/260197/21 "2004-08-17T20:59:58Z")
_A single strand of copper wire could show zero ohms resistance…_ > [@Q.E.D.](#): > > No, it would not. It would read quite a lot more than zero ohms, though an inexpensive multimeter might not be able to resolve it. What’s “quite a lot more?” With a Fluke 88 set at Low Ohms/High Resolution I get 0.13 ohms on an 8" stretch. A 2" stretch reads 0.00 ohms (I did say it **could** show zero ohms). ---
**Author:** ![Finagle](https://avatars.discourse-cdn.com/v4/letter/f/b19c9b/32.png) [@Finagle](https://boards.straightdope.com/u/Finagle)\ **Post date:** [August 17, 2004, 9:18pm UTC](https://boards.straightdope.com/t/hyper-ground-system-huh-automobile-question/260197/22 "2004-08-17T21:18:35Z")
> [@Gary T](#): > > _A single strand of copper wire could show zero ohms resistance…_ > > What’s “quite a lot more?” With a Fluke 88 set at Low Ohms/High Resolution I get 0.13 ohms on an 8" stretch. A 2" stretch reads 0.00 ohms (I did say it **could** show zero ohms). According to the handy table [here](http://www.epanorama.net/documents/wiring/wire_resistance.html), a 2" 28 AWG wire (pretty darn thin) would have a resistance about 0.02 ohms. Your wire seems a bit thinner, based on its 8" length, so maybe a 0.03? A foot of 10 AWG (closer to what you’d find in a battery cable) looks like it would have a resistance of 0.002 ohms. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 17, 2004, 9:35pm UTC](https://boards.straightdope.com/t/hyper-ground-system-huh-automobile-question/260197/23 "2004-08-17T21:35:36Z")
> [@Gary T](#): > > _A single strand of copper wire could show zero ohms resistance…_ > > > [@Q.E.D.](#): > > > > No, it would not. It would read quite a lot more than zero ohms, though an inexpensive multimeter might not be able to resolve it. > > What’s “quite a lot more?” With a Fluke 88 set at Low Ohms/High Resolution I get 0.13 ohms on an 8" stretch. A 2" stretch reads 0.00 ohms (I did say it **could** show zero ohms). I have to agree with **Gary T** here. Using any commonly acceptable measuring tools in the automotive trade (Fluke 75, 78, 87, 88) a single strand of copper wire **will** measure 0 ohms or so close to zero as to assumed to lead resistance. Voltage drop is the only way to accurately measure very small resistances. Let’s do a very simple ohms law calculation Starter draw = 100A (low for some cars BTW) Acceptable voltage drop for starter circuit 0.20V R=V/A R=12.6/100 R= .126 ohms 1/10 of an ohm is not likely to be read accurately by someone in a shop. FTR, I once had a car that came in for a checkout. Started the car and it cranked a little “funny” Not entirely sure at first, but it didn’t sound like most Volvos do when they start. Drove the car, and it steered “funny”. Put the car on the rack, and got the shock of my life. On this model the battery cables ran from right to left across the front of the cross fame member. The driver of this car had hit something and shorted the positive cable to the main negative cable. The main negative cable was burned in half totally. The positive cable was still intact sort of. Most of the cable had burned away in about a 1/2" gap leaving exactly 12 count them 12 strands of copper connecting the 2 ends. :eek: Since I had no main battery ground, I started looking and finally figured out that the battery was still grounded to the body, and the radio suppression ground from the body to the engine was still in place, and that was my ground path. Any the very first thing I did was measure the resistance of the positive cable. You got it zero ohms. I kept that cable for many years and used it in teaching the need for doing voltage drop. 😃 Oh, Kudos to **Gary T** most technicians are either do lazy or not bright enough to do voltage drops. Further proof (as if any was needed) that Gary is the man. 🙂 ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 18, 2004, 4:15am UTC](https://boards.straightdope.com/t/hyper-ground-system-huh-automobile-question/260197/24 "2004-08-18T04:15:59Z")
> [@Crafter\_Man](#): > > But I’m confident **Q.E.D.** already knows copper has a PTC, and didn’t want to complicate the discussion any more than necessary. Indeed. In fact, when I worked at EWC, we used the temperature coefficient of copper to calculate the winding temperature rise inside some transformers by taking DC resistance measurements before and after. **Gary T**. .013 ohms is infinitely more than zero. 😉 I’ll grant you that using voltage drop measurements will do better on a low-res meter than resistance measurements will, however. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [August 18, 2004, 1:51pm UTC](https://boards.straightdope.com/t/hyper-ground-system-huh-automobile-question/260197/25 "2004-08-18T13:51:57Z")
> [@Rick](#): > > Voltage drop is the only way to accurately measure very small resistances. Actually, the only way to accurately measure small resistances is to use the “4-wire” method. The uncertainly can be further lowered by using current reversal techniques to cancel the thermoelectric voltages. > [@Rick](#): > > Let’s do a very simple ohms law calculation > Starter draw = 100A (low for some cars BTW) > Acceptable voltage drop for starter circuit 0.20V > R=V/A > R=12.6/100 > R= .126 ohms One of the things you’ve left out is the battery’s “equivalent source impedance.” This is important, because when the starter is powered the battery will no longer be at 12.6 V; it will be lower. As an example, if the battery voltage goes to 11 V when the starter is powered, and 100 amps is flowing through the starter, then R = 0.11 ohms. It should also be noted that this is the combined (additive) resistance of the starter and the two starter cables. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 18, 2004, 4:55pm UTC](https://boards.straightdope.com/t/hyper-ground-system-huh-automobile-question/260197/26 "2004-08-18T16:55:12Z")
> [@Crafter\_Man](#): > > > [@Rick](#): > > > > Voltage drop is the only way to accurately measure very small resistances. > > Actually, the only way to accurately measure small resistances is to use the “4-wire” method. The uncertainly can be further lowered by using current reversal techniques to cancel the thermoelectric voltages. I meant in a field / shop setting with commonly available automotive repair tools. I stand by my statement. [Previous page](https://boards.straightdope.com/t/hyper-ground-system-huh-automobile-question/260197.md?page=1)