The Naked Scientists

The Naked Scientists Forum

Author Topic: Why is mains electricity 240v AC?  (Read 1177 times)

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 249 times
    • View Profile
Why is mains electricity 240v AC?
« on: 21/09/2016 22:32:19 »
Quote
Why is the mains electricity supply in the UK 240V AC? Why not, for example 400V DC?
In the early days of electricity distribution, there was a vicious competition between Edison (promoting DC) and Tesla (promoting AC).

It included underhanded tricks such as Edison secretly sponsoring the development of the electric chair, provided it ran on AC. This was then used to attack the AC camp in the public mind.

In the end, Tesla's AC system won, because:
- it was easier to convert between voltages with a transformer (no moving parts)
- it was easier to transmit voltages a long way with AC (use a higher voltage)
- The copper conductors were cheaper with AC (3 wires carrying AC could carry 3 times the power of 2 wires carrying DC)

...despite the fact that the typical 30-60Hz mains frequency is in the range where human muscles are quite sensitive (airplanes traditionally used 400Hz, which allows much smaller and lighter transformers).
- In the USA, they went for safety (110V AC) - perhaps influenced by Edison's smear campaign?
- In the UK, they preferred efficiency (240V AC) - lower resistive losses

See: https://en.wikipedia.org/wiki/Three-phase_electric_power


 

Offline jerrygg38

  • Hero Member
  • *****
  • Posts: 781
  • Thanked: 27 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #1 on: 22/09/2016 14:30:32 »
When I started working for Con Edison NY in 1956, they still had 120volt DC service. The company wanted to get rid of it and gave away AC fans for free. The shock of DC is easier to handle than AC. 120 volt ac rises to a peak value of 169.7 volts. Having been shocked many times in my life this can hurt us. To go to 240 volts ac will kill us faster. I am surprized to learn they use this in the UK.
   As I read the daily teletype, people were sometimes getting killed chopping ice from their refrigerators with a knife or ice pick and hitting the wires. Other people merely destroyed their freon in the process.  Other people died by picking up series street lighting which could rise to 5000 volts when wires fell down. Thus 120 volt street lights can give you a 5000 volt shock.
   In Brooklyn Tech H.S. they had 600 volt DC switches and people put their fingers across the blades. Well stupidly I did it and found no effect. But then I said "Your have to squeeze" and then I did and I got a shock but it was more funny than bad.
 

Offline Semaphore

  • Full Member
  • ***
  • Posts: 79
  • Thanked: 2 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #2 on: 22/09/2016 15:33:13 »
When I started working for Con Edison NY in 1956, they still had 120volt DC service. The company wanted to get rid of it and gave away AC fans for free. The shock of DC is easier to handle than AC. 120 volt ac rises to a peak value of 169.7 volts. Having been shocked many times in my life this can hurt us. To go to 240 volts ac will kill us faster. I am surprized to learn they use this in the UK.
   As I read the daily teletype, people were sometimes getting killed chopping ice from their refrigerators with a knife or ice pick and hitting the wires. Other people merely destroyed their freon in the process.  Other people died by picking up series street lighting which could rise to 5000 volts when wires fell down. Thus 120 volt street lights can give you a 5000 volt shock.
   In Brooklyn Tech H.S. they had 600 volt DC switches and people put their fingers across the blades. Well stupidly I did it and found no effect. But then I said "Your have to squeeze" and then I did and I got a shock but it was more funny than bad.

Sounds like some Darwin awards have been handed out. Interesting stories, anyway.
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3823
  • Thanked: 19 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #3 on: 22/09/2016 20:29:53 »
The street lights were not 120 V but originally consisted of many arc lamps wired in series that is why such a high voltage was employed.
Although domestic supply is rated at 120 V many houses have a 2 phase supply giving 240 V for higher power loads
One of the problems with DC supplies is that arcs persist try taking a running lamp out of its socket !
 

Offline jerrygg38

  • Hero Member
  • *****
  • Posts: 781
  • Thanked: 27 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #4 on: 22/09/2016 22:00:00 »
The street lights were not 120 V but originally consisted of many arc lamps wired in series that is why such a high voltage was employed.
Although domestic supply is rated at 120 V many houses have a 2 phase supply giving 240 V for higher power loads
One of the problems with DC supplies is that arcs persist try taking a running lamp out of its socket !
   The lights I saw in New York City were quite ordinary incandescent bulbs. They were wired in series but they had a constant current transformer driving them. (An original current source). Open circuit brought the maximum voltage to the point of the open. If a bulb burnt out you could shut down the transformer and temporarily jump the bulb until a replacement has been found.
   The NY subway trains still use DC supplies for the third rail. Another problem with DC system is they help cause electrolysis which damages structures in the environment. NY had technicians and engineers whose only job was to eliminate electrolysis problem. Although I had worked for the Dept. Water Supply Gas and Electricity for 5 years after Con Edison, I was only involved with Street lightning and knew little of the electrolysis problems which also occur naturally.
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3823
  • Thanked: 19 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #5 on: 22/09/2016 22:57:03 »
One of the reasons for employing a series connection and a constant current supply was because arc lamps have a negative dynamic resistance and must be supplied from a constant current source (as I found out at the age of ten when I shorted out the feed resistor!) probably when filament lamps were installed the original wiring was retained.
 

Offline jerrygg38

  • Hero Member
  • *****
  • Posts: 781
  • Thanked: 27 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #6 on: 23/09/2016 00:40:12 »
One of the reasons for employing a series connection and a constant current supply was because arc lamps have a negative dynamic resistance and must be supplied from a constant current source (as I found out at the age of ten when I shorted out the feed resistor!) probably when filament lamps were installed the original wiring was retained.
  One other very interesting series circuit that Con Edison employed was a series capacitor circuit so that the power went through a capacitor first and then the copper wiring. This was a high voltage circuit at least 4KV or even higher. Hard to believe they would do such things. Why? The answer is that it was a dedicated line going to a high current spike welding company. Parallel capacitors did not work but the series capacitor did the job. This brings me back to when I started work at 17.5 years and went to college at night.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8669
  • Thanked: 42 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #7 on: 24/09/2016 12:54:31 »
I am surprized to learn they use this in the UK.
 

It's less surprising when you recognise that we generally have more sense than  to connect ourselves to the electricity supply which makes the voltage less important. I guess the same is true of our friends in the rest of Europe and also China, India, Australia, New Zealand, much of Africa, and- well essentially everywhere outside the US (and, curiuosly, Japan)
https://en.wikipedia.org/wiki/Mains_electricity_by_country

Also. many homes  + businesses in the US also have 240 V supplies.
« Last Edit: 24/09/2016 13:03:07 by Bored chemist »
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4726
  • Thanked: 155 times
  • life is too short to drink instant coffee
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #8 on: 24/09/2016 13:57:41 »
Quote
I am surprized to learn they use this in the UK.

Alas, no longer! You can still get 240V rms single-phase in Australia,  but the UK standard was dropped some years ago to conform to the EU requirement. The rest of Europe uses 220V but cheats:

from Schneider - Electric UK Ltd

Quote
For many years, mainland Western Europe has used a mains electricity supply rated at nominally 220VAC 50Hz. The UK used 240VAC 50Hz.
 
Currently, ALL Western European supplies are classified 230VAC. In reality there is no 230VAC supply unless you create one locally. 230VAC was a “standard” created during European "harmonisation" to give a single voltage standard across Western Europe, including UK and Irish Republic.
 
Although the ideal would have been to have a single voltage there were too many political, financial and technical obstacles to reduce UK voltage to European levels or to increase European voltage to UK levels, so a new standard was created to cover both. This was achieved by changing the tolerances of previously existing supply standards. UK voltage  to 240VAC + 6% and - 10% and European to 220VAC +10% and -6%  (thereby creating a manageable overlap) and we would call these two combined 230VAC, despite the fact that nobody was intentionally generating at 230VAC!
 
Depending on the voltage sensitivity of the product and the variance from nominal of the actual supplied voltage, it may not be advisable to use a 220VAC specific device in the UK or a 240VAC specific device in Mainland Europe etc. For instance a 240VAC supply can rise to as high as 254.4VAC and still be within tolerance, but the maximum rated voltage for a 220VAC product is only 242VAC. A 220VAC supply can drop as low as 206.8 within tolerance but the minimum rated voltage for correct operation of a 240VAC product is 216VAC It may work perfectly well either way but it could be, technically, outside the specification of the equipment with obvious implications. A 230VAC product must be compatible with all voltages across this range
 
If a product is to be used in the UK a 240VAC rated device is ideal but either 240VAC or 230VAC products can be used with confidence.
 
If a product is to be used in mainland Europe or Irish Republic a 220VAC rated device is ideal but either 220VAC or 230VAC products can be used with confidence.

Problem is  that if you use a 240V motor at the minimum  permitted "230V" supply voltage (220V - 6%) it will only deliver 75% of its rated power. This has caused me serious problems trying to cool an MRI machine on the hottest summer days. Patients were turned away and invited to vote for Brexit.   
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8669
  • Thanked: 42 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #9 on: 24/09/2016 14:11:22 »

 
Problem is  that if you use a 240V motor at the minimum  permitted "230V" supply voltage (220V - 6%) it will only deliver 75% of its rated power. This has caused me serious problems trying to cool an MRI machine on the hottest summer days. Patients were turned away and invited to vote for Brexit.

So, let me get this straight-because a machine didn't comply with our national standards (which happen to coincide with EU ones) requiring satisfactory operation across a range of voltages, you suggested to patients that they should vote for the UK to refuse to take part in the specification of the EU standards (which the manufacturers will still have to meet if they want to sell in their biggest market- the EU)

How does refusing to take  part in the setting of standards improve them?
Are you saying the the UK's contribution to the EU standards was so stupid that the standards will be better without us?

That seems a rather harsh judgement.
 

Offline vhfpmr

  • Jr. Member
  • **
  • Posts: 46
  • Thanked: 3 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #10 on: 25/09/2016 00:29:34 »
Problem is  that if you use a 240V motor at the minimum  permitted "230V" supply voltage (220V - 6%) it will only deliver 75% of its rated power. This has caused me serious problems trying to cool an MRI machine on the hottest summer days. Patients were turned away and invited to vote for Brexit.

If the MRI has been sold to a customer who doesn't have the correct supply voltage, or a designed with a motor which doesn't run off the same supply as the MRI, that's not the fault of the European specification. If I design radio using 24V power parts, and specify it to run off a 12V supply, I can't blame the supply when the transmitter power output falls short.
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4726
  • Thanked: 155 times
  • life is too short to drink instant coffee
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #11 on: 25/09/2016 16:04:22 »
The MRI chiller motor was manufactured in Germany to the EU specification. As for manufacturing MRI in the UK, we haven't done so since 1985.

The UK was, of course, and still is, a member of the union that limited the consumption of domestic vacuum cleaners to 1600W, allegedly "to save energy". Fact is that the newest members of the Union have domestic mains limited to 7 amp sockets, so in order to give their manufacturers access to a genuine single market, the market had to be restricted to 7 A x 230V = 1610W. Politics, not physics, rules the EU.

The giveaway is the proposed limit on hairdryers, kettles and lawnmowers to - you guessed it, 1600W. The official reason is half honest: reduced power (not energy!) consumption and fewer imports into the EU. It's bloody obvious that when it comes to heating or evaporating water, the energy requirement has little or nothing to do with power consumption: indeed a low power kettle will require slightly more energy to heat through a given temperature range because the surface loss rate at any given temperature is the same.     
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3823
  • Thanked: 19 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #12 on: 25/09/2016 17:04:18 »
I apologise for bringing politics into a technological discussion and have removed my strongly held views on brexit.
I worked for Perske Price Services that provided large picture processing Systems from Hell GMBH in Kiel, these were always supplied with multi tap 6 KVA transformers to allow for power supply variations.
« Last Edit: 25/09/2016 18:55:08 by syhprum »
 

Offline William McC

  • Sr. Member
  • ****
  • Posts: 158
  • Thanked: 4 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #13 on: 25/09/2016 17:11:41 »
Quote
I am surprized to learn they use this in the UK.

Alas, no longer! You can still get 240V rms single-phase in Australia,  but the UK standard was dropped some years ago to conform to the EU requirement. The rest of Europe uses 220V but cheats:

from Schneider - Electric UK Ltd

Quote
For many years, mainland Western Europe has used a mains electricity supply rated at nominally 220VAC 50Hz. The UK used 240VAC 50Hz.
 
Currently, ALL Western European supplies are classified 230VAC. In reality there is no 230VAC supply unless you create one locally. 230VAC was a “standard” created during European "harmonisation" to give a single voltage standard across Western Europe, including UK and Irish Republic.
 
Although the ideal would have been to have a single voltage there were too many political, financial and technical obstacles to reduce UK voltage to European levels or to increase European voltage to UK levels, so a new standard was created to cover both. This was achieved by changing the tolerances of previously existing supply standards. UK voltage  to 240VAC + 6% and - 10% and European to 220VAC +10% and -6%  (thereby creating a manageable overlap) and we would call these two combined 230VAC, despite the fact that nobody was intentionally generating at 230VAC!
 
Depending on the voltage sensitivity of the product and the variance from nominal of the actual supplied voltage, it may not be advisable to use a 220VAC specific device in the UK or a 240VAC specific device in Mainland Europe etc. For instance a 240VAC supply can rise to as high as 254.4VAC and still be within tolerance, but the maximum rated voltage for a 220VAC product is only 242VAC. A 220VAC supply can drop as low as 206.8 within tolerance but the minimum rated voltage for correct operation of a 240VAC product is 216VAC It may work perfectly well either way but it could be, technically, outside the specification of the equipment with obvious implications. A 230VAC product must be compatible with all voltages across this range
 
If a product is to be used in the UK a 240VAC rated device is ideal but either 240VAC or 230VAC products can be used with confidence.
 
If a product is to be used in mainland Europe or Irish Republic a 220VAC rated device is ideal but either 220VAC or 230VAC products can be used with confidence.

Problem is  that if you use a 240V motor at the minimum  permitted "230V" supply voltage (220V - 6%) it will only deliver 75% of its rated power. This has caused me serious problems trying to cool an MRI machine on the hottest summer days. Patients were turned away and invited to vote for Brexit.

You can install buck boost transformers, which are actually very small and rather inexpensive, especially for three phase systems. An 18kw boost system is actually very small they almost look like low voltage lighting transformers.

Sincerely,

William McCormick
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4726
  • Thanked: 155 times
  • life is too short to drink instant coffee
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #14 on: 25/09/2016 17:46:25 »
the reason people voted brexit is that they brain washed by the gutter press are so terrified of immigrants that they would rather see our economy ruined.


Neither true in my case. Simply a lot of experience of the idiocy and corruption that goes into EU Directives (I am a registered European Union Expert Consultant in my field), and the fact that the UK has always had a negative balance of trade with continental Europe: more trade =  more loss, as shown by official EU statistics.

A descendant of fairly recent immigrants, my concern over recent expansion of the EU has been with the mobility of cheap labor from areas with a very low cost of living. I can hire a medical consultant from Romania for the same salary that I would have to pay a first-year UK graduate. It's a good deal for the breadwinner whose family stays in the east (the difference between a migrant worker and an immigrant), and  a good deal for me, but the prospect is that British graduates will become unemployable in the medium term, or unable to live in the UK, and that ain't good.  Meanwhile I can't hire Australian nurses at any price because unlike EU citizens, they have no automatic right to work here or have their qualifications recognised. 
 

Offline William McC

  • Sr. Member
  • ****
  • Posts: 158
  • Thanked: 4 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #15 on: 25/09/2016 18:22:19 »
Take it from an American, who's founding fathers were told by English Lords and Parliament that English law was illegal. George Washington said of this statement that England is truly over because all they had were their twisted laws.

Politics is a planed chaos to hide failure and a lack of science. If you can make sense of politics perhaps you are part of the problem.

As an American I can tell you we went down the same twisted path, we are about over as a nation, hypocrisy has almost devoured all that we had, which was the amazing science that Benjamin Franklin unlocked while doing a hundred other good deeds.

Some years ago Germany started producing micro natural gas turbines. Which could be installed in commercial buildings to supply not only all the electric for the building but also heating and cooling using the heat generated by the turbines operation for both heating and coiling.

If you are not aware many cooling systems like the one in the JFK Airport, U.S. post office, fire oil burners to heat and pressurize lithium bromide, the lithium bromide is allowed to pass through a condenser coil where it is cooled, then still under pressure injected into the chiller where it evaporates and absorbs the heat from the building. That was the plan using these German micro turbines. Now is it the best method no, was it better than what we had yes. The U.S. government had promised tax breaks to any company that installed them. Many small businesses that install such equipment geared up and then the government at the very last second pulled the tax breaks and almost all the small high tech companies went out of business or almost out of business overnight.

Germany needs to have the courage to announce the reality and technology that they are currently trying to slip into our day to day lives. Every time they create something and do not accurately describe it or downplay its efficiency, in the long run they are just hurting their credibility. The only way into our markets is with more efficient products, but they do not want that label. Or the responsibility of describing how it works. 



Sincerely,

William McCormick
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3823
  • Thanked: 19 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #16 on: 25/09/2016 19:05:17 »
The reason why auto transformers to boost the supply from say 220v to 240v are small because the need to supply only the additional 20v with the remaining 220v coming directly from the mains.
Hence a 18KVA transformer needs only a core size appropriate for 2KVA
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8669
  • Thanked: 42 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #17 on: 25/09/2016 20:42:38 »
The MRI chiller motor was manufactured in Germany to the EU specification. As for manufacturing MRI in the UK, we haven't done so since 1985.

The UK was, of course, and still is, a member of the union that limited the consumption of domestic vacuum cleaners to 1600W, allegedly "to save energy". Fact is that the newest members of the Union have domestic mains limited to 7 amp sockets, so in order to give their manufacturers access to a genuine single market, the market had to be restricted to 7 A x 230V = 1610W. Politics, not physics, rules the EU.

The giveaway is the proposed limit on hairdryers, kettles and lawnmowers to - you guessed it, 1600W. The official reason is half honest: reduced power (not energy!) consumption and fewer imports into the EU. It's bloody obvious that when it comes to heating or evaporating water, the energy requirement has little or nothing to do with power consumption: indeed a low power kettle will require slightly more energy to heat through a given temperature range because the surface loss rate at any given temperature is the same.   

"The MRI chiller motor was manufactured in Germany to the EU specification."
So, either it was built to run on 230V as in Germany, or it was built to the EU standard in which case it would have run properly on the bottom end of the EU range.

Or, it just wasn't up to the job- It's not clear how leaving the EU would stop German manufacturers making duff motors.

Could you expand on that for us?

This "As for manufacturing MRI in the UK, we haven't done so since 1985. "
only matters if the only business in the EU is the manufacture of MRI machines.

Whenn everyone has finished grumbling about power limits they don't really understand, we will be using less energy to vacuum our carpets (and saving money in the process)
It's a counterpoint to the daft state of affairs where cleaner manufacturers were playing the same silly "numbers game" that PC makers did with clock rates a decade or so back.

The energy used by a cleaner is the product of the power and the time taken. A 10KW vacuum cleaner doesn't mean you can walk round the room in a 20th of the time it takes to walk round with a 500W one

Meanwhile, on the morning of the Brexit the UK lost a lot of money- something like the value of the Greek economy.
Also, that morning,  their main spokesman Mr Farrage, admitted that he had lied about the biggest factor they were able to put in favour of leaving (The lie about funding the NHS).

However I'm still waiting for an explanation of how us leaving the EU will improve the regulations (It seem that both you and I were involved in the rules- you implement them and I was involved in drafting them)
There's no way round the fact that UK manufacturing industry will still have to stick to the EU regs for much- probably most- of their market.
Now they won't have any representation on the drafting of those rules.

How is that better?
 

Offline William McC

  • Sr. Member
  • ****
  • Posts: 158
  • Thanked: 4 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #18 on: 25/09/2016 21:21:55 »
The MRI chiller motor was manufactured in Germany to the EU specification. As for manufacturing MRI in the UK, we haven't done so since 1985.

The UK was, of course, and still is, a member of the union that limited the consumption of domestic vacuum cleaners to 1600W, allegedly "to save energy". Fact is that the newest members of the Union have domestic mains limited to 7 amp sockets, so in order to give their manufacturers access to a genuine single market, the market had to be restricted to 7 A x 230V = 1610W. Politics, not physics, rules the EU.

The giveaway is the proposed limit on hairdryers, kettles and lawnmowers to - you guessed it, 1600W. The official reason is half honest: reduced power (not energy!) consumption and fewer imports into the EU. It's bloody obvious that when it comes to heating or evaporating water, the energy requirement has little or nothing to do with power consumption: indeed a low power kettle will require slightly more energy to heat through a given temperature range because the surface loss rate at any given temperature is the same.   

"The MRI chiller motor was manufactured in Germany to the EU specification."
So, either it was built to run on 230V as in Germany, or it was built to the EU standard in which case it would have run properly on the bottom end of the EU range.

Or, it just wasn't up to the job- It's not clear how leaving the EU would stop German manufacturers making duff motors.

Could you expand on that for us?

This "As for manufacturing MRI in the UK, we haven't done so since 1985. "
only matters if the only business in the EU is the manufacture of MRI machines.

Whenn everyone has finished grumbling about power limits they don't really understand, we will be using less energy to vacuum our carpets (and saving money in the process)
It's a counterpoint to the daft state of affairs where cleaner manufacturers were playing the same silly "numbers game" that PC makers did with clock rates a decade or so back.

The energy used by a cleaner is the product of the power and the time taken. A 10KW vacuum cleaner doesn't mean you can walk round the room in a 20th of the time it takes to walk round with a 500W one

Meanwhile, on the morning of the Brexit the UK lost a lot of money- something like the value of the Greek economy.
Also, that morning,  their main spokesman Mr Farrage, admitted that he had lied about the biggest factor they were able to put in favour of leaving (The lie about funding the NHS).

However I'm still waiting for an explanation of how us leaving the EU will improve the regulations (It seem that both you and I were involved in the rules- you implement them and I was involved in drafting them)
There's no way round the fact that UK manufacturing industry will still have to stick to the EU regs for much- probably most- of their market.
Now they won't have any representation on the drafting of those rules.

How is that better?

The problem is that 208 voltage motors run nicely up to 220 volts. Which is what you get from 208 volt supplies. 208 volt motors will run on higher voltage but sometimes you start to get that angry hum out of them just above 230. And at night you can get that very angry hum.

The truth is that if you examine the wave forms they are no longer what we paid for. So they raise and lower voltage specific to areas to compensate for large equipment starting up.

At nighttime in industrial parks 540 volts or more from 480 volt systems that used to be 460 volt systems, and before that 440 is not uncommon.

I think it is mostly due to unbalanced three phase loads.

Our electrical voltage test meters started out reading voltage higher and higher from the electric company, so they introduced RMS meters, then the RMS meters started reading voltage higher than what we were supposed to read. So they introduced true RMS meters. I do not know what is coming next because I can often read 253 volts from company supplied 240 volt AC current from a true RMS Fluke meter. The voltage from the duplex outlets in the store were reading 125 volts. The owner made a call and suddenly we had 118 volts at the same time of night.

Sincerely,

William McCormick
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4726
  • Thanked: 155 times
  • life is too short to drink instant coffee
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #19 on: 25/09/2016 23:02:42 »
Quote
There's no way round the fact that UK manufacturing industry will still have to stick to the EU regs for much- probably most- of their market.
What manufacturing industry?

From the Office for National Statistics
Quote
In the 3 months to April 2016, the UK’s trade in goods deficit with the EU widened by £0.6 billion, to a record 3 monthly deficit of £23.8 billion. In the 3 months to April 2016, exports of goods to the EU increased by £2.1 billion and imports of goods from the EU increased by £2.7 billion, to a record 3 monthly level of £58.6 billion.

Quote
Now they won't have any representation on the drafting of those rules.
Puts us on a par with China and India, who export all sorts of stuff to the EU. Fact is that if your product meets the CE specification, it can be placed on the market in any of 28 countries without having to meet individual national specifications. And since the CE specification is generally the same as the ISO specification, you'd have to meet it anyway to sell to the USA. 

Quote
How is that better?
We won't have to pay for the privilege of being outvoted and told what to do.
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3823
  • Thanked: 19 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #20 on: 26/09/2016 14:54:20 »
It would seem to be a simple matter to install an auto transformer on the MRI machine to boost the voltage to the cooling motor or to demand that the manufacturers install a motor appropriate for UK mains supply, I understand that making a modification to the machine would require dispensation from the makers but if they had any sense they would get one of their technicians over double quick if you explained why it was out of action and you were losing money because a unsuitable motor had been fitted.
This would seem to be a much less drastic response than what you had suggested.
it is my experience with the Germans that they consider all non German speaking countries as primitive and third world so if have any telephone discussion of this problem it would be best to find a native German speaker to assist.     
 

Offline William McC

  • Sr. Member
  • ****
  • Posts: 158
  • Thanked: 4 times
    • View Profile
Re: Why is mains electricity 240v AC?
« Reply #21 on: 27/09/2016 01:07:48 »
Also you might want to have a tech check the pressures and sub-cooling differential. A slight over charge, will not be noticed, until you get a very hot day. With R-410A the amount it takes to overcharge the system is almost comical. The system will run with much lower RLA Run Load Amps if you properly charge it. A lot of techs do not know you have to run the unit on second stage cooling, if the unit has a second stage in order to check sub-cooling. Many techs do not know how to do a sub-cooling test. You can just google it, there are a couple of old timers that explain it well. To simulate a hot day we often cover the condenser with cardboard or plywood, to simulate a very hot day.

If it is a package unit with multiple compressors and they share a condenser cooling air discharge both compressors should be running for any testing.

The new Field Piece HVAC gauges are pretty cool and have temperature sensors built it. But you can do a sub-cooling with regular old fashioned gauges and a thermocouple attached to a multi-meter. Sometimes I cheat and use the infrared temperature sensor.

It is remarkable how the amperage goes way up on very hot days. One other trick that is pretty cool is installing a small bypass damper, a barometric damper. This allows your evaporator to run a bit cooler which also lowers your amperage substantially. It will also cause the output air from the evaporator to be a bit cooler. As long as you do not freeze over your evaporator it is a very efficient thing to do. It only cuts down the CFM a little bit. It is less efficient technically, however it is often much more practical and useful.

If you are running a rack system with hermitic or semi hermitic compressors, with a chiller, condenser, and chilled water piped to your air handler, you can check the cooling tower water flow to the condensers, and the water output temperatures, lack of enough cooling tower water flow will cause high head pressure and higher RLA. If you are getting air output that is not cool enough from your air hander, you might try lowering the fan speed in the air handler, that circulates the room air. This can sometimes be accomplished by a pulley change, or by other controls. That will definitely lower your RLA.

Sincerely,

William McCormick
 

The Naked Scientists Forum

Re: Why is mains electricity 240v AC?
« Reply #21 on: 27/09/2016 01:07:48 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length