# Voltage questions



## Gaz1 (Jan 5, 2008)

I dont understand voltage, and no one (so far) has been able to make me understand... even physicists! Thought this might be a good place to ask next.

So... Voltage is "the difference of electrical potential between two points of an electrical circuit". But what does this actually mean? The UK runs on 240v, how does this fit into the above statement? 

OK, an example of my questions... I have a 12v MR16 lamp, but what makes it 12v? Why are MR16 lamps 12v? What's the advantage to this? Are those advantages still present when you've then added a pesky transformer, which appears to be pretty unreliable?

Why do some countries run on a different voltage? So the UK is 220-240, and this US is 120 - but what does this actually change? 

All info - in layman's terms(!) - about voltage greatly appreciated!

Cheers.


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## murdock (Jan 4, 2008)

the easiest way i can explain this...a long time ago i had to fix a light but i could not understand why when i put the tester across the switch i had 220 volts but when i closed the switch...the light came on but i no longer had 220 volts across the switch i couldnt figue out what was going on...it is quiet simple...were you break the circuit and have a potential difference be it a resistor...lamp...motor...or a switch you will have a voltage...when you close the circuit you will get field around the cable which can be measured using a current clamp...

we use a term called equipotential bonding the aim is to bring all exposed conductive parts to the same potential so that there is no voltage can be measured in other words no potential difference between the parts so the current can flow directly to earth.

another example my daughter complained to me about getting a shock whenever she touched the vice in my workshop i could not understand why i couldnt feel it i then i realised she was bare foot ...if i took my volt meter i would have been able to put the red lead in her hand and the black lead onto the vice i would have got a small volt reading...the solution was to connect an earth wire from the vice to an earth conductor which bought the vice to the same potential as the earth conductor...so you could no longer get a potential difference.

even static electricity which can be created by wind can generate a potetial difference between 2 points...that is why some companies which work with sensitive electronic components have earth wires for their staff to connect to a good earth and anti static mats so that there is no static electricity/potential difference between them and the components with which they are working.

the source will determine the voltage if you use a 12 volt battery then the potential difference between live and neutral will be 12 volts depending on how much you load the circuit you will get a volt drop...but basics 
watts = volts x amps or votage = current x resistance you need to understand the basics then you will understand.

i hope this helps you understand a little better.


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## frank (Feb 6, 2007)

Thinking in simple terms think of voltage as pressure. Put a feather on a set of scales and the pressure is zero ie zero volts. Put a brick on the scales and the pressure is say 10 pounds. ie 100 volts. Increase the bricks by 3 and you now have 30 brick pounds of pressure ie 300 volts. In terms of your statement in the UK there is a pressure between the two points that can be measured at 230 volts of 'pressure'.

MR16 lamps are multifaceted glass lamps. They have a halogen filament within them. The filament is designed to carry a current under low pressure

A 50 watt lamp will need 4 amps at 12 volts. The advantage is that the value of current flowing in the filament being high produces the conditions needed to give good light within the constraints of the lamp size , colour rendering etc etc etc.

The transformer is used to drop the supply voltage from 230 to 12 volts. As for reliability - should be fine unless you are using multiple lamp heads incorrectly.

And why some counties are 110 and others not. This has as much to do with history as technology. Usually its a case as in most things that whoever gets there first has the lead hand. Think Betamax and VHS recording systems etc. There are advantages to both supply systems but neither has a monopoly on benefit.

Frank


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## Trimix-leccy (Dec 4, 2007)

I have a customer down the road who has some trunking in the switch room dating back to the early 60s. Manufactured by MEM it has a sticker on it which states 'medium pressure supply'. A dosey plumber once thought it contained a water pipe...Ho-hum!
Pressure = voltage
Resistance = radiator
Current = flow rate
Battery = water tank etc etc


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## murdock (Jan 4, 2008)

you got a point there thick pipe lots of water flow... thick cable lots of current can flow.

just remeber a radiator is a cooling device...resistance creates heat.


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## Trimix-leccy (Dec 4, 2007)

Yep, fair ccomment. But whether the boiler 'furnace..?' is switched on or not ,the rad still creates an 'impedance' to the flow of the water. If you see what I mean. To be fair, if we have to analogise water with electric I think the 'functioning' of a rad is the least of his worries:whistling2:


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## brian john (Mar 11, 2007)

TRIM:

Piping adds resistance to water flow as do spikots, that reduce the pipe size allowing water to be spread out....


http://www.bcae1.com/voltages.htm

STRICTLY MY OPINION

Not sure why Europeans utilize 240 50 HZ but I assume it is because their American cousins, were using 120 VAC and they wanted to be better then us so they figured they’d double the voltage and be twice as good as us.

Americans utilize 120 VAC (the original standard in the US all other voltages types followed this) because Edison utilized 120 VDC. For Westinghouse to be able to power equipment Edison was selling and to take over Edison DC systems with his 120 VAC system, Westinghouse engineers had to have a 120 VAC equivalent that would not damage DC resistive equipment (most early loads were resistive such as lamps and heaters).
To arrive at the same heating effect as 120 VDC the peak of the sinewave needed to be 169 VAC (1.414 X 120 VAC), 120 VAC is the effective, or RMS voltage.

Advantages of AC simpler to step up and down for distribution.


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## murdock (Jan 4, 2008)

the trains in south africa still run on 3300 volt DC...why i honestly coulnt tell you.


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## goose134 (Nov 12, 2007)

I've heard that the reason for the US 60Hz decision was that clocks would run better. True? I mean it doesn't really make a lot of sense, but...


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## Heatsink (Jan 7, 2008)

GENERALLY,

More people are able to work on low voltage systems since the risk of death from electric shock is less (but remember it's the current that kills, not the voltage). That's why many lights, computers etc run on low voltage, low current (low power) supplies.

High voltage is useful for transporting power over a long distance since it minimises the current, the resistance and thus the power loss.

Most small appliances like computers, lights etc these days can run on low power, (these have those plug in transformers for your mobile phone charger etc) so why do we still have 240/120V? Because we still have airconditioning, Heating, Vacuum Cleaners, Kettles, Fridges, Ovens etc that draw large amounts of power and convention has stuck causing the voltages to remain.

Here's one that I don't understand too well though... Why is it that we use high voltage AC for transmission over land; but deep sea cables use high voltage DC???


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## frank (Feb 6, 2007)

I seem to remember that Canada and parts of the USA were 25 Hz at one time. I seem to remember also from college days motive equipment and energy transmission is improved by lower frequencies. So why go from 25 to 60 -- who knows? Here in the UK we had DC systems until as late as 1960 and 550 volts 3 phase as a common utility supply until the 1970's. In fact there were all sorts of weird combinations in place until harmonisation began some time after WW2. By the way. Was much mid state USA domestic equipment designed for 38 volts?

Frank


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## brian john (Mar 11, 2007)

> More people are able to work on low voltage systems since the risk of death from electric shock is less (but remember it's the current that kills, not the voltage). That's why many lights, computers etc run on low voltage, low current (low power) supplies.


More people are killed with 120 VAC than any other voltage class in the USA



> High voltage is useful for transporting power over a long distance since it minimises the current, the resistance and thus the power loss.


Resistance is resistance (impedance) and does not change with the voltage, excluding skin effect



> Most small appliances like computers, lights etc these days can run on low power, (these have those plug in transformers for your mobile phone charger etc) so why do we still have 240/120V? Because we still have air conditioning, Heating, Vacuum Cleaners, Kettles, Fridges, Ovens etc that draw large amounts of power and convention has stuck causing the voltages to remain.


The advantage of having separate transformers/power supplies (from what I am told) is cheaper and easier to have certified by listing agencies. Also keeps the product smaller.



> Here's one that I don't understand too well though... Why is it that we use high voltage AC for transmission over land; but deep sea cables use high voltage DC???


Which deep sea cables?

The power cables I know of are across lakes and rivers.
But if cables go from country to country with different frequency it may have to do with the converters utilized at either end to convert voltage and frequency.


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## brian john (Mar 11, 2007)

Frank I do believe you are right at one time it was 25 HZ, but I think among many reasons (FLICKER being one) it was decided to change the frequency the Europeans doubled our voltage to one up us so we doubled the Hertz realized you were at 50 HZ so we added 10 to beat you guys.....I have been told NYC had DC systems in place until a few ago.

Philadelphia still has some Two Phase 5 wire systems in use, 4 ungrounded/energized conductors and one grounded conductor/neutral.

What do you call the grounded/neutral conductor in the UK and what do you call the hot/energized/phase conductor?


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## Heatsink (Jan 7, 2008)

brian john said:


> More people are killed with 120 VAC than any other voltage class in the USA


That's exactly right- avoid that nasty stuff; but very few people get killed by static electric discharges where the shock can be in the range of 20000V (http://wolfsonelectrostatics.com/news/news-item12.asp). This is because the current is small and only delivered over a very small period of time. This draws us back to the parallel between Voltage and water pressure. Voltage is like the head of water pressure, but if there is not much water there, you will not get very wet. 

So Voltage is definitly a part of the stored or potential Energy of Electricity, but to complete the picture, knowledge of the total charge is required. The analogy is that Voltage is the height that the bucket of water is held above the ground, whereas the energy of the electricity is like the height of the bucket of water filled with a known amount of water. So, 1 drip of water at 30000 feet (V) would have little effect but 1 Gallon at 30000feet would be a whole lot worse.





brian john said:


> Which deep sea cables?
> 
> The power cables I know of are across lakes and rivers.
> But if cables go from country to country with different frequency it may have to do with the converters utilized at either end to convert voltage and frequency.


I know of a power cable that runs across the Tasman Sea between the Australian mainland and Tasmania. This is a HVDC cable.

Also, I found this study et.al.

http://search.abb.com/library/ABBLi...LanguageCode=en&DocumentPartID=&Action=Launch


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## Trimix-leccy (Dec 4, 2007)

Reply to Brian John

UK

99% intallations have 
Earth
Neutral
Liive

Neutral and earth are seperate throughout the entire installation

Recently they have decided to mees things about
So now, Live = Phase [Hot]

Also to alleviate the boredom all the colours have changed so

old live was red now it is brown
old neut was black now it is blue

Then we get onto 3 phase [my favourite]

phase L1 was red now brown
phase L2 was yellow now black
phase L3 was blue now grey
neutral was black now blue or something like that 

so what was a phase col is now a neutral col and what was a neut colour is now a phase colour.. you just put a little sticker on it and everything is wonderful

So now,all you have to remember is

red to brown, black to blue, and blown to f?ck!!


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