Why do we have 240 volt electrics in our homes

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ioweddie

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Woke up in the night...for some reason I thought why do we have 240 volt electrics in our homes....our cars work on a 12volt system...I'm pretty sure if you have a caravan...the fridge...etc are 12volt...I know you can get 12 volt TV's...most LED lighting will work with low volts...phones etc...am I being stupid...or have I got something here....Could save lots of money in the future...Over to you guys...
 
I think its something to do with power transmission. If the voltage was lower then the conductors would need to be bigger to deliver the same power. Years since I did physics but I'm sure some clever sort on here will be along soon to explain. FWIW overhead power to trains in the UK is 25KV, delivers massive current and uses a relatively small conductor.
 
Try running an electric cooker from 12 V

A 1Kw element would draw approximately 83 Amps.

The higher the voltage transmitted the lower the losses. The National grid runs at 400,000 V or 275,000 V then down to 132,000 V for regional distribution and then stepped down until it reaches homes etc.
 
Try running an electric cooker from 12 V

A 1Kw element would draw approximately 83 Amps.

The higher the voltage transmitted the lower the losses. The National grid runs at 400,000 V or 275,000 V then down to 132,000 V for regional distribution and then stepped down until it reaches homes etc.
There are gas cookers
 
We used to have 240v nominal but brought it down to 230v nominal to match other countries. Some of those had 220v and took it up to 230v.

Easy way to think is think about the power cables coming into streets etc.
If they were low(er) voltage they would be massive cables.

A higher voltage allows for easier distribution.
 
It’s partly to do with efficiency. Higher voltage and lower current can be equal to lower voltage and higher current.

Eg an electric kettle draws about 12.5A (3KW) with 240v. To get the same amount of watts you’d need 250A with 12V, which would need huge cables and is less efficient. Or if you stuck with 12.5A with 12V you’d be waiting all day for a cup of tea! ;)

The US and some other countries run about half as many volts as the UK and other countries, it’s a compromise as less efficient vs. marginally safer (electric shock risk)

The UK ring main distribution for electric cables in the home is quite clever - by creating a ring the load is shared on both sides of the cable, so they can be smaller. Copper cable isn’t cheap when wiring millions of homes :)
 
All of the above, plus it is AC which has massively lower losses than DC when transmitted over large distances - to the point where you would almost need a power station on every street if we were on DC.
 
One aspect of why it's 240 volts is because it's one phase of a 3 phase 415 volt supply and 3 phase is how electricity is generated and distributed.

High voltage DC transmission is being looked at again and some already exist over long distances. They avoid some of the capacitance effects which are substantial at high AC voltages; long cables being effectively huge capacitors. In the distant past I've done manual switching on 11KV distribution systems and even at that relatively low voltage, the capacitance effect is quite apparent when a cable is switched.

DC was until recently more difficult to transform from one voltage to another, which would originally have been one of the main reasons for adopting AC as the means pf transmission. That and the fact that electricity is generated as AC.
 
Woke up in the night...for some reason I thought why do we have 240 volt electrics in our homes....
I didn’t get beyond your first sentence before I fell over my Zimmer frame in hysterics 😂
 
Construction sites use 110volts because it’s safer.
Why don’t we use this in our homes?
Short answer is it’s a trade off between safety and efficiency.

Construction sites also carry greater shock hazards - outdoors working (moisture/rain), trailing cables, cutting hand tools etc. This isn’t as common as in the home with cables buried in walls or conduit etc.
 
Short answer is it’s a trade off between safety and efficiency.

Construction sites also carry greater shock hazards - outdoors working (moisture/rain), trailing cables, cutting hand tools etc. This isn’t as common as in the home with cables buried in walls or conduit etc.
Safety I can understand but efficiency ?
 
Safety I can understand but efficiency ?
Short answer is it’s more energy efficient to transmit electricity at higher voltages.

Ever felt the cables of an appliance drawing a high load? They tend to get warm, this is wasted energy.

As mentioned already, power in watts is voltage x current - so at 110v you’ll need more amps, hence needing larger cables for the same power rating. This is also another reason - copper cabling etc isn’t cheap.
 
Short answer is it’s more energy efficient to transmit electricity at higher voltages.

Ever felt the cables of an appliance drawing a high load? They tend to get warm, this is wasted energy.

As mentioned already, power in watts is voltage x current - so at 110v you’ll need more amps, hence needing larger cables for the same power rating. This is also another reason - copper cabling etc isn’t cheap.
Thanks for that.
I know nothing about electrics even though I work for one of the biggest M&E companies in Britain.
 
As already hinted at, it's to do with transmission power loss. The power dissipated (lost) in a resistor is proportional to the square of the current flowing through it. Double the current, four times the power dissipated. The grid cables do have resistance, so the lower the current flowing through them the lower the power lost.

Power in Watts is also Voltage multiplied by Current (all basic Ohms Law stuff), so the higher the voltage for a given power (the national grid load) the lower the current and hence the lower the power loss. The National Grid uses either 275,000V AC or 400,000V AC to distribute power around the country, AC because that's what transformers require to work.

We use 240V because historically it was considered a good optimum to deliver to homes. The USA use 110V because that's what Edison decided was best for his incandescent lamps. He originally wanted the supply to be DC, but because of transmission losses (and the difficulty and inefficiency of changing DC to a different voltage) AC sensibly won.
 
Woke up in the night...for some reason I thought why do we have 240 volt electrics in our homes....our cars work on a 12volt system...I'm pretty sure if you have a caravan...the fridge...etc are 12volt...I know you can get 12 volt TV's...most LED lighting will work with low volts...phones etc...am I being stupid...or have I got something here....Could save lots of money in the future...Over to you guys...
It is to do with distribution .

What you need is POWER . Essentially Power is Volts x Amps ( leaving some detail aside ) .

To reduce current , and the amount of cable required to carry it ; generator output is transformed up to high voltage . This has its own hazards .

When it nears its destination , the power is transformed down to lower voltages , and after local distribution, to 240V for end use .

In countries where ac voltage is 120 , appliances use twice the current and equivalent cables carry half the power .

At 12V it would be much less .
 
Interestingly, I can remember when, certainly parts of Bristol, ran on 210v and the electricity board issued alto transformers to boost up to 240v. There is also buried underground some old DC cables which I think was for trams.
 
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The trade off for safety is not as simple as purely voltage. Lower voltage = higher current = much higher fire risk... this is one reason why Part "P" building regulations specifically addressed low voltage down-lights. Fatal fires have been caused by incorrectly installed extra-low voltage lights.

The 110v supply on building sites is "centre earthed" so has 55 volts plus 55 volts- it is only by contact with both live conductors that a shock of 110 volts can be received.

In the UK much more emphasis is made on Earthing (and Earth Bonding) and Residual Current Devices... the intention being that the power is cut BEFORE anyone receives a - potentially fatal - electric shock. I wouldn't want to go to the US standard... wires twisted and capped to join them, unsheathed plug blades. single layers of insulation on flexible cords. IMHO our system is much safer.
 

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