Thread: Electric ground

I often time see only an input voltage and a ground to power various electronic components. What about the negative terminal on your power source? I thought that current would not flow unless this end was connected to the positive end. Do they actually only use the positive end and ignore the negative? or is ground another way to say negative end? Just a little confused about this.

You can ground any point of an electrical circuit, or have no ground at all. As an example an automobile battery is typically grounded on the negative side but some cars used to have positive ground. In the case of a power supply with a negeative and positive voltage, that just means the circuit is grounded in the middle.

They must have written the schematic wrong....

They drew a component that I was looking at as having a positive input, one data output, and a ground. There are only 3 pins, so the ground must actually be the negative terminal.

Originally Posted by Cold Fusion

They must have written the schematic wrong....

They drew a component that I was looking at as having a positive input, one data output, and a ground. There are only 3 pins, so the ground must actually be the negative terminal.

That is done often. Even some large commercial gas fired HVAC (heating ventilation air-conditioning) RTU's (roof top units) will have their low voltage control wiring being fed through the chassis. I do not like it. But I do not have much say in it.
If you do not know this and you try to start them you cannot get them started until you supply the board with common, secondary transformer power, from the chassis.

An interesting thing that is happening with the electronic controls of gas fired heating and cooling systems is. That the control boards if the system is 110 volts. In some cases has to have the hot or typically black wire connected to the power terminal, and what they call the common has to be connected to the neutral. This wire is usually tied together at the primary box with the ground. But not at a secondary box or sub panel.

In the city where you have a lot of old BX, you cannot tell which wire is the hot and which wire is the neutral because the wires are the same color. Often there are splice boxes in the drop ceilings or basement. That can cause a cross over.

When you go to fire up the unit, you get a blinking Morse code like, error code from the board that states the neutral or common is hot. It is getting pretty weird.

Because if an electrician was to do a simple outlet installation and moves the wiring for the HVAC system, he could leave the system in a disabled state. If he does not put the wires back exactly.
The elctrician should put them back as they were anyway. However normally any other device would function. And the wires are often not color coded.



Another one that we just came across on an electric furnace with an AC evaporator coil, is that if you switch the two wires that come from the breaker that feeds the electric coils. That you get a feedback in the unit, that is capable of powering the fan, without low voltage initiation.
Even if the other leg that feeds the fan is disconnected. We add in a set of low amp fuses to isolate the heaters and the blower and control board.

So if you cross the wiring while wiring in these fuses it creates a wild effect that should not take place in my opinion. But again I have no say.



Sincerely,


William McCormick

Originally Posted by Cold Fusion

I often time see only an input voltage and a ground to power various electronic components. What about the negative terminal on your power source? I thought that current would not flow unless this end was connected to the positive end. Do they actually only use the positive end and ignore the negative? or is ground another way to say negative end? Just a little confused about this.

Hi Cold Fusion,
Everyone was I think. In cars the battery was grounded to the cars body. A thick cable was screwed
to it. It connects the batterys negative terminal to the cars body. The spot where it was fixed to was
called ground. It's easier now to screw minus cables to the car directly than to run them' back to the
battery all the time, I guess.

Steve

Originally Posted by Steve Miller

Originally Posted by Cold Fusion

I often time see only an input voltage and a ground to power various electronic components. What about the negative terminal on your power source? I thought that current would not flow unless this end was connected to the positive end. Do they actually only use the positive end and ignore the negative? or is ground another way to say negative end? Just a little confused about this.

Hi Cold Fusion,
Everyone was I think. In cars the battery was grounded to the cars body. A thick cable was screwed
to it. It connects the batterys negative terminal to the cars body. The spot where it was fixed to was
called ground. It's easier now to screw minus cables to the car directly than to run them' back to the
battery all the time, I guess.

Steve

It saves on copper.

Most individuals do not know. But electricity flows from the currently marked (-) terminal in the battery. The terminal of the battery that gets tied to ground. That terminal is really abundant with Electromotive force.

So the electrons actually flow from the chassis to the device and then back to the battery on the (+) terminal completing the loop.

Benjamin Franklin had it labeled the other way. He felt that the terminal with the pressure of electrons was to be called the positive terminal. In this country at one time it was called the positive terminal. And many books were written about it.

The cathode ray tube really confused a lot of honest individuals that just did not have the time to go and build and test one in the early 1900's.

Sincerely,


William McCormick

The actual polarity is not that relevant as "grounds" also apply to AC, audio and RF circuits. Its may be more instructive to consider a "ground" as just being a common connection.

The historical use of "ground" might have originated from lightening rods connected by heavy wire to the physical earth. This allowed lightening strikes to dissipate energy through this copper wire connection with a safe, low voltage potential from the top of the house to the bottom (ground). Otherwise the discharge might flow through the occupants instead!

In RF circuits the "grounds" are sometimes multiple; for example we may have a "chassis ground", a "Power Supply Ground", an "Analog Ground" and a "Digital Ground". These will all be at the same DC potential but may have small unwanted noise (AC) voltages between each other. These small unwanted noise voltages can then be avoided by using differential signals as in LVDS approaches for example, or by using transformers (Audio, RF) or by differential OpAmps (with CMRR) for DC measurements.

In mixed signal design, "grounding issues" are crucial and this is not a trivial subject by any means. Also some people disagree on particular strategies.

In any system the overall and final ground is probably "chassis ground" i.e. the metal box around the electronics as this represents the final barrier between unwanted radio interference getting out or in! However a metal box, by itself, may not provide any shielding if its connection to the internal circuit grounds is poorly planned. A good example can be found in the humble computer - for example place a medium wave or shortwave radio next and you will probably find a lot of interference. Although the case may be metal the cables going in and out may be "floating" relative to this ground and radiate. Also, each plug in card may have a DC connection but the long path length from PC ground to chassis ground could be over 100 nH - i.e. 100 ohms at 150 MHz. Given that many PC's clock at 2 GHz these days, we can expect the shielding effectiveness to be poor - the PCB design per se is the only available measure available to reduce Electro Magnetic Interference (EMI) and susceptibility.

Anyway sorry for the long explanations but I hope they are of interest :-D

Originally Posted by Vaedrah

The actual polarity is not that relevant as "grounds" also apply to AC, audio and RF circuits. Its may be more instructive to consider a "ground" as just being a common connection.

The historical use of "ground" might have originated from lightening rods connected by heavy wire to the physical earth. This allowed lightening strikes to dissipate energy through this copper wire connection with a safe, low voltage potential from the top of the house to the bottom (ground). Otherwise the discharge might flow through the occupants instead!

In RF circuits the "grounds" are sometimes multiple; for example we may have a "chassis ground", a "Power Supply Ground", an "Analog Ground" and a "Digital Ground". These will all be at the same DC potential but may have small unwanted noise (AC) voltages between each other. These small unwanted noise voltages can then be avoided by using differential signals as in LVDS approaches for example, or by using transformers (Audio, RF) or by differential OpAmps (with CMRR) for DC measurements.

In mixed signal design, "grounding issues" are crucial and this is not a trivial subject by any means. Also some people disagree on particular strategies.

In any system the overall and final ground is probably "chassis ground" i.e. the metal box around the electronics as this represents the final barrier between unwanted radio interference getting out or in! However a metal box, by itself, may not provide any shielding if its connection to the internal circuit grounds is poorly planned. A good example can be found in the humble computer - for example place a medium wave or shortwave radio next and you will probably find a lot of interference. Although the case may be metal the cables going in and out may be "floating" relative to this ground and radiate. Also, each plug in card may have a DC connection but the long path length from PC ground to chassis ground could be over 100 nH - i.e. 100 ohms at 150 MHz. Given that many PC's clock at 2 GHz these days, we can expect the shielding effectiveness to be poor - the PCB design per se is the only available measure available to reduce Electro Magnetic Interference (EMI) and susceptibility.

Anyway sorry for the long explanations but I hope they are of interest :-D

The use of the grounding rod for lightning, was to have the lightning strike at the house, only to find that because of the ground rod, holding down the voltage of either a wire on the roof under the shingles, or actual brass rod antennas, from raising in voltage. That the surface of the objects would liquefy.

As the lightning would come to strike the house with a ground rod. Because the voltage would not change, quickly enough, materials about to be struck would liquefy at the surface repelling the actual conducting bolt of lightning. The materials create an ARC ray, just like lightning. Because everyone knows the only way to stop electricity is with more electricity.

Insulators actually raise in voltage faster then silver. That is why they stop electricity. Because on the inside of the insulator of a wire, it matches the wires voltage. It would on the outside too if the voltage was not drained off. Silver is actually the slowest to conduct. But conducts the most amperage.

In a vacuum you can see an insulator will in fact conduct electricity just in small quantities. Or low amperage.

Tar shingles have a bit of radio active material in them, this can also cause the lightning to look elsewhere to strike. As lightning nears the house, the shingles get excited, and emit an ARC ray. Causing the lightning to look elsewhere. Slate as well probably has a similar effect. Ceramics too.

But if you do not ground ceramics or slate, they will raise in voltage and can even detonate. That is why the ground rod is there. Plumbing, electrical neutrals and grounds help too.

Near misses of lightning bolts, can cause havoc to any system. During a near miss, all the rules of standard electricity are off. Rays from a near miss can detonate sheet rock inside the house. Even though the outside of the house is not damaged. These effects can be very dangerous. And a grounding rod may not protect the house. Or the inhabitants.



Sincerely,


William McCormick

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