# Plus, minus and ground...

Hello, not quite sure thats the right category to write in, but I reently got confused with the electricity.

In my home, the contacts provide 220V 3-5A, and have 2 holes and one small plate. The holes are for plus and minus voltage and the plate is for ground.
Now the questions:

1. Why are there +, - and GND;
2. What is the difference between ground and minus;
3. And why the arduino has only GND and +?

!! There is no + and - in your wall outlet. There is 220V alternating current (AC)

The UK calls the line / neutral. No such in EU plug.
The Ground oin is earthe ground. It is there for safety reasons

Single phase AC supply has live and neutral - neutral is typically near ground in voltage, but
not the same. With multiple phases supplies there may not be neutral, just the 2 or 3 phases,
which are all live. You don't use + and - talking about ac mains, its not meaningful.

With DC, + and - indicate the polarity of a supply. Often one side of the supply is taken to be
the reference, called 0V, or "ground' or "signal ground".

Some DC supplies are two supplies with a common ground, usually + and - 15V or similar,
for analog electronics. Digital devices usually just have one supply, +5V or +3.3V, and ground
is the negative terminal of the supply. Usuallly.

In your house the neutral should be connected to earth ground at the breaker box. With no current flowing there is no voltage on the neutral (relative to ground). When current is flowing the slight resistance in the wire can create a slight voltage drop across the wires, and the neutral may not measure exactly "zero".

The current flows through a "complete circuit" through the hot & neutral wires and through the load. Under normal conditions, no current flows through the ground wire. If you "break the circuit" but turning off a switch, unplugging an appliance, or if you cut/disconnect either the hot or neutral, no current flows.

Voltage is always present at the power outlet (assume no associates wall-switch) but current only flows when something is connected when something is powered-on. Power (Watts) is the product of voltage & current (Volts x Amps).

The AC (alternating current) follows a sine wave from zero up to the positive peak, back through zero to a negative peak, and then back to zero again. Assuming you have 50Hz were you live, that cycle repeats 50 times per second. ...The AC voltage is positive half the time and negative half the time. And of course, the direction of current flow also alternates at 50Hz (or 60 Hz here in North America).

The Arduino ground is usually just a reference and "ground" is a "concept". For example, if your Arduino is battery powered the battery's negative terminal would be connected to the Arduino's ground, but there may be no connection to earth ground. In this case, current does flow through the ground wire.

If your Arduino is connected to USB and you have a desktop/tower computer, the Arduino's ground will be connected through USB, through the computer, and finally to the wall socket's earth ground.

The Arduino can be damaged by negative voltages (relative to it's ground) but sometimes (often with op-amps) you need a dual power supply (positive and negative voltages). If you connect a 2nd battery with it's positive terminal to ground, the negative terminal of the battery becomes your negative power supply.

JMD1:
Hello, not quite sure thats the right category to write in, but I reently got confused with the electricity.

In my home, the contacts provide 220V 3-5A, and have 2 holes and one small plate. The holes are for plus and minus voltage and the plate is for ground.
Now the questions:

1. Why are there +, - and GND;
2. What is the difference between ground and minus;
3. And why the arduino has only GND and +?

Show a photo of the actual system where it says 'plus', 'minus' and 'ground'.
Also would be good to see whether the situation is AC, or DC.

Anyway.... in general, if you have a power source for powering a circuit, then the power source must be within a loop of the circuit, so that current leaves the power source, and is able to return to the source. So the power source requires 2 terminals....... ie. a DC battery source has 2 terminals. 'Ground' is just an arbitrary reference point in your circuit, such as a node in your circuit. The reference point in a circuit is often a point that is linked to one end of a power source (usually a voltage source). You can arbitrarily assign any voltage you like to that reference point..... such as 1000000 Volt, or 1 Volt, or 0 Volt. Assigning 0 V is often convenient. This reference voltage is used for circuit analysis - such as for cases where you want to calculate voltages at other points in your circuit (relative to that arbitrarily chosen reference voltage). Even though a 'voltage' is arbitrarily assigned to the reference node, we might NOT know 'exactly' what the actual voltage of that reference really is (with respect to some OTHER reference point).

Some systems having a 3rd wire (EARTH) involves wires that are electrically connected to the 'earth'.... yes, our planet..... a big electrical stake driven into the ground outside your home (somewhere) that connects to the 'salty/conductive' earth in the soil or ground. The reference voltage of this earth is also arbitrary, and it can be arbitrarily assigned to zero Volt. When you connect the EARTH to the original reference point in your circuit, then the original reference point can then be considered 'earthed', which allows many other circuits to have the same 'earth' voltage (eg. 0 V). That's if you want other circuits with a point that has the same 'earth' voltage (eg. 0 V).

For AC house power systems, the reference voltage is typically the 'neutral'. And the 'earth' pin may be connected to (for example) the metal outer chassis (case) of a home appliance, for protecting people. Some details of how it achieves this protection...

https://www.howequipmentworks.com/electrical_safety/

that connects to the 'salty/conductive' earth in the soil

I knew the sea was salty but I didn't know the soil was.

Grumpy_Mike:
I knew the sea was salty but I didn't know the soil was.

Me too hehehe. I think maybe..... but need to check up on it.... a long long time ago, in a land ... here... it was underwater, salt-water! Or could be moisture and impurities, ions etc... in the ground. Some guys from the power industry measure resistance between stakes ....after they drive the conductive stakes deep into the ground at various locations. Fairly dry ground isn't going to be good for earthing. They need at least some moisture in the ground. Our home garden soil is probably going to have relatively low concentrations of salt, or else our plants/lawn-grass would have problems growing. Although, I have heard about people sinking bores in the ground to get bore water..... and the water can be too salty.

DVDdoug:
In your house the neutral should be connected to earth ground at the breaker box.

Depends on the earthing arrangement and what country your in. The UK have 3 domestic systems.

TN-C-S (PME) - Earth and Neautral are connected until after the Cut out fuse and then the CPC is seperate

TN-S - Earth is not connected to Neutral but uses a seperate earth path, usually the Armour in SWA and is commoned at the supply transformer

and TT - there is no earth supplied by the DNO and is provided by earth rods in the ground

I did make an earth when I did a lot of short wave listening as a kid. Basically a large biscuit tin filled with coke ( the type of coal not the drink ) and buried. Then it was watered in like a plant. Living in Manchester England ensured it didn't dry out. This had a lot less hum than the mains earth. I was even able to experiment with ground communications by feeding the output of an amplifier between to earths and picking it up at the end of the garden with two dining forks connected directly to a pair of high impedance headphones.

Weren't there attempts at something like this for trench comms in WWI ?
Tried it myself in the '60s - not very good results. And that was with a 10W (valve) amplifier driving the electrodes .

Allan

Weren't there attempts at something like this for trench comms in WWI ?

Yes they actually used it successfully.
Yes it was the 60s when I did it. Their was an article in Practical Wireless that set me off. I was only using a passive receiver but got about 30 yards range with an old gramophone player valve amplifier. Maybe it is the damp Manchester soil.

They are still playing with ground transmission, but it is a one way thing since it requires ELF waves and massive amounts of power, along with the really long antenna. Data transmission is extremely slow, as expected. They basically invented dial-up internet in the ground....

I lived in Huntingdonshire - lowest rainfall in the country - about 20"..

Perhaps that's why I didn't have much success.

Devices such as the 'Fullerphone' were used for morse, I think - I had one of the buzzers for Morse practise. It had a high voltage output winding , presumably for ground signalling..

Allan