Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Mains Power Curiosity?

Status
Not open for further replies.

Cazzo

Member
Hello

I'm in Australia, so my mains is 240VAC 15A. It has 3 holes for the plug (but some appliances only use two of them)

My question is, what are these leads? I know the top two are power and the bottom is earth, or ground but what does this mean?

Is the top 2 "negative and positive" obviously its AC so its changing but thats where there is power. And i hear people calling these wires "live", "hot" whats does this all mean.

- What are all the wires called, and where do they go.

- What are they used for?

- And this originally lead me to this curiosity, the earth lead. there is NO power in there right? it is only earthing the appliance used yea? Why does the appliance need to be grounded. and i saw a guy connect a wrist band into this ground plug on his wall outlet, my first reaction was WTF you idiot!!!! but im not sure how it works.

Very simple question, hope you can help bro
 
I think you should start by Googling for 'domestic power supply' and similar phrases, to give you an understanding of the basics.
 
Hi Cazzo
greetings .. also from Australia :)

Hello

I'm in Australia, so my mains is 240VAC 15A. It has 3 holes for the plug (but some appliances only use two of them)
My question is, what are these leads? I know the top two are power and the bottom is earth, or ground but what does this mean?
Is the top 2 "negative and positive" obviously its AC so its changing but thats where there is power. And i hear people calling these wires "live", "hot" whats does this all mean. - What are all the wires called, and where do they go.

Rather than Negative and Positive, which is really used in DC circuits not AC circuits.

The more correct terms are Neutral and Phase The phase wire is the HOT/LIVE wire calling them the HOT or LIVE are just laymans terms. :)

In Australia and some other countries, the neutral lead is connected to the earth line at the house/building fuse/meter box. The earth wire connects to a real earth, usually a metal rod hammered into the ground, beside/under the house and relatively close to the house. The earth line then spreads out to each power point and then out to the appliances where it will connect to the metal chassis (casing) of the appliance. If for some reason the phase ( hot) wire becomes disconnected inside the appliance and it touches the metal casing it will cause a large current to flow and blow the fuse on that circuit and protect you from getting a possibly lethal electric shock.

You will find some appliances have only 2 pin plugs, neutral and phase, The applicance is designed in a way that it should be pretty much impossible for the phase wire to come into contact with the metal case. You can also google a term called "double insulated" often used in conjunction with power tools

- And this originally lead me to this curiosity, the earth lead. there is NO power in there right? it is only earthing the appliance used yea? Why does the appliance need to be grounded. and i saw a guy connect a wrist band into this ground plug on his wall outlet, my first reaction was WTF you idiot!!!! but im not sure how it works.
Very simple question, hope you can help bro

What you saw the guy doing was connecting an anti static strap and lead to the earth wire at the power point. in that case, usually there would be a also be an antistatic mat on his work bench.
They are used to static voltage that builds up on your body/clothing whilst walking across carpets etc. If he was to touch sensitive electronic circuit boards without discharging through the antistatic strap, he could zap the electronics...... surely at some time you have walked across carpet somewhere and grabbed a door knob and got a zap ?

cheers
Dave
 
Last edited:
The more correct terms are Neutral and Phase The phase wire is the HOT/LIVE wire calling them the HOT or LIVE are just laymans terms. :)

Presumably that's only in some countries?.

Live and neutral (and earth) are the correct terms in the UK, I've never heard 'hot' or 'phase' used other than on these forums.
 
Hey Dave, thanks for the info :) understand bit more now

So the earth only runs to the metal rod in the ground? that's so simple, i thought it would be complicated. So in theory, you could touch it with your fingers and you would only be touching an insulated copper connection to.......dirt lol

Also with the Phase ""HOT" wire, and the neutral, if you touch either one of these, do you die or is it only the Phase that goes through your body and into the ground??

And is 3 Phase power the exact same principle, but with much higer voltages. like 440V i think?
 
Presumably that's only in some countries?.

Live and neutral (and earth) are the correct terms in the UK, I've never heard 'hot' or 'phase' used other than on these forums.

hey Nigel :)

Ohhh really ? surely you have multi phase power in the UK ? single phase, dual phase, 3 phase systems. motors, welders etc etc
so what do you call those systems ?

Phase is pretty standard in OZ and NZ, even on power plugs and sockets you will see P, N, E by the respective pins/sockets
Some you will see L, N, E -- common on appliances imported from China etc

as I said HOT is a laymans term :)

cheers
Dave
 
Also with the Phase ""HOT" wire, and the neutral, if you touch either one of these, do you die or is it only the Phase that goes through your body and into the ground??

To get a shock you need to complete a circuit - so touching both live and neutral will give you a shock, as will live and earth (because neutral is normally connected to earth as well). You can get a shock off the single live wire because you tend to have an earth connection via your body.

And is 3 Phase power the exact same principle, but with much higer voltages. like 440V i think?

Same voltage - 3 phase is simply three different lives, separated by 120 degrees - the 440V comes from the difference between two of the lives, all are still 240V from neutral.
 
You're welcome :)

Hey Dave, thanks for the info :) understand bit more now
So the earth only runs to the metal rod in the ground? that's so simple, i thought it would be complicated. So in theory, you could touch it with your fingers and you would only be touching an insulated copper connection to.......dirt lol

yup :) it goes from the power point to a Buss bar at the meter/fuse board then down to the earth rod

Also with the Phase ""HOT" wire, and the neutral, if you touch either one of these, do you die or is it only the Phase that goes through your body and into the ground??

The Phase ( Hot/Live) is where lurketh your possible demise. have a reread of my first post.... The neutral is connected to the earth on that same bussbar .

And is 3 Phase power the exact same principle, but with much higer voltages. like 440V i think?

yup in the 3 phase system you have 240V between any one phase and the neutral and 440 V between any 2 of the phase lines

cheers
Dave
 
Ohhk i understand everything now, thanks guys

Except the 3 phase part...

So you have the same Voltage, 240VAC, but what do you mean between any one phase? by phase do you mean one of the wires. and where is the 440V from? i thought it would be if you connected to wires together, but you get 480V?????
 
hey Nigel :)

Ohhh really ? surely you have multi phase power in the UK ? single phase, dual phase, 3 phase systems. motors, welders etc etc
so what do you call those systems ?

We have three phase, domestic premises receive neutral and just one of the lives, with alternate homes connected to alternate phase.

So, N, L1, L2 and L3 (and earth again).
 
Back in this thread I posted a few drawings of US Mains distribution which may or may not be of some help.

Nigel I have a question for you. In the UK does the power enter a residence as 240 volts or similar to the US as 440 (or so) split phase? Similar to the US but higher voltage. I have wondered about that.

Ron
 
Distribution from the sub-station is three phase, 240V per phase.

Each house is provided neutral and just one phase - as simple as that, no need for anything more unless you're an industrial user and need three phase.

By alternating phases to different houses the current in the neutral wire is greatly reduced (in theory and perfect balance there would be none) so the neutral wire can be a much thinner (and cheaper) cable.
 
The advantage of having a split-phase 240V with a center-tap ground, as used in the US for high power appliances such as dryers or electric stoves, is safety of course. If you touch either of the hot leads you are only across 120V to ground, not 240V.
 
Thanks Nigel as that makes sense and was something I was curious about. Thanks also Carl for the added information.

Ron
 
The advantage of having a split-phase 240V with a center-tap ground, as used in the US for high power appliances such as dryers or electric stoves, is safety of course. If you touch either of the hot leads you are only across 120V to ground, not 240V.

As I understand it the numbers of deaths in the USA from electrical shock is not appreciably lower than the EU?.
 
As I understand it the numbers of deaths in the USA from electrical shock is not appreciably lower than the EU?.
Could be true. It's counter-intuitive but I have read no data on that.

Perhaps us Yanks are more careless and touch the hot lead more often(?).;)
 
I think it's more a case of 240V not being terribly dangerous - you have to work pretty hard (or be majorly unlucky) to get killed by 240V.
I know that 120V can kill you if you are also touching a solid ground, especially if it also involves water, but I guess if you are connected to a solid ground then you are fried either way and if not, then you will likely survive. The in-between situation where you have a sufficient ground resistance to kill you with 240V but not with 120V is probable rare.

I do like the idea of 240V for house wiring since it obviously reduces the amount of copper required by half for a given power. Do you know what the standard wire gauge is used for house wiring in the UK?
 
Nigel:

Is all of the 3 phase power available in the uk is all Delta wired?

Do you have the wierd 277 V that the US has for lighting?

The US distributes 3 phase Y and 3 phase (HI Delta). Because of that industril might have 240 3 phase, 208 3 phase, 240 single phase, 208 single phase and 120 single phase. Then there are other varients such as 460 and 480 VAC for higher power loads.
 
Nigel:

Is all of the 3 phase power available in the uk is all Delta wired?

Do you have the wierd 277 V that the US has for lighting?

The US distributes 3 phase Y and 3 phase (HI Delta). Because of that industril might have 240 3 phase, 208 3 phase, 240 single phase, 208 single phase and 120 single phase. Then there are other varients such as 460 and 480 VAC for higher power loads.

My plant uses 3 phase 480 delta. However all the lighting is 120 in my buildings. Gotta love it. :)

Ron
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top