# Grounding Question

Discussion in 'General Electronics Chat' started by AutoNub, Mar 14, 2012.

1. ### AutoNub Thread Starter Member

Oct 14, 2011
44
1
This thread is no longer productive. Thanks for the posts!

Last edited: Mar 15, 2012
2. ### MrChips Moderator

Oct 2, 2009
18,342
5,798
Wrong on many counts.

An "ideal" ground has zero resistance, not infinite resistance.
The voltage does not drop to zero.

You cannot use the equation V = I*R and assume that R = 0, because this would imply that V = 0.

This leads to I = V/R = 0/0 which is nonsense.

There is always a finite R not equal to 0. You also have to consider the internal R of the voltage source.

Hence we apply Ohm's law where I = V/R and R is very small. I is large but V is still finite.

"Floating ground" is a misnomer and can lead to ambiguity.

"Floating reference" or "Floating common" can be used instead but should not be associated with something "floating" on water or any other liquid.

3. ### AutoNub Thread Starter Member

Oct 14, 2011
44
1
This thread is no longer productive. Thanks for the posts!

Last edited: Mar 15, 2012
4. ### BillB3857 AAC Fanatic!

Feb 28, 2009
2,480
382
Don't confuse "ground" with dirt or water. Airplanes also have "ground" circuits. Ground, in most cases refers simply to a common point of reference. In your home (if you live in the US), your power outlets have three openings. One, the largest rectangle, is the common which carries the current returning from a properly operating device. The smaller rectangle is the hot lead, or the one that provides the power to the device. The third opening, the small D shaped opening, is a lead that ties back, ultimately to a rod driven into the earth at your service entrance. Under normal operation, this wire should carry zero current and is provided as a safety path in case something goes wrong inside a device plugged into the outlet. In most metal cased devices, the metal case is connected to a wire in the cord that connects to this pin. As oddly as it may be, the common wire and the ground wire are tied together inside the primary breaker box, which only adds to the confusion.

Check this out.......... http://answers.yahoo.com/question/index?qid=20090725101526AAWlRdW

Last edited: Mar 14, 2012
5. ### #12 Expert

Nov 30, 2010
18,076
9,680
When a high current source gets shorted to a good ground, fuses blow, or circuit breakers pop, or wires start melting. The current is usually limited by the impedance of the current source and some small resistance that is inescapable in the ground because it is so difficult to make anything be 0.00000 ohms. Instead of seeing 100,000,000 amps flow, things usually stop at a few dozen or a few hundred amps until the wires melt.

6. ### BJT_user Member

Oct 9, 2011
35
9
This is great! But you should have saved it for April 1st.

7. ### AutoNub Thread Starter Member

Oct 14, 2011
44
1
This thread is no longer productive. Thanks for the posts!

Last edited: Mar 15, 2012
8. ### shortbus AAC Fanatic!

Sep 30, 2009
6,411
3,738
@ AutoNub - may I ask where you got your BS in Electrical Engineering? As you stated you have on in one of your earlier posts.

9. ### BillB3857 AAC Fanatic!

Feb 28, 2009
2,480
382
It may depend upon exactly what BS stands for in this case!

shortbus and #12 like this.