AC Efficiency: Fact or Fiction?

[sophiecentaur]

So i will tease Sophie - his 230 volt system is 'unsafe at any speed.'

You have a point there but the statistics of electric shock are pretty good in the UK because the spec for the equipment is very high and, for the past many years, there has been a requirement for RCD protection. You need to have a certificate for any domestic electrical installations if you want a prospective buyer to get a mortgage so there is very little that your average tinkerer can get away with. I couldn't get like for like comparison on relative number of fatal shocks in UK and US but http://rjqelectrical.co.uk/2013/04/electrical-safety-statistics/ suggests 28 fatalities per year (0.05 per 100,000 total) in UK and this link suggests about 0.2 per 100,000 (industrial) in the US. That doesn't lead one to think that the 240V issue is particularlyrelevant.

Ok so is this thread ready to turn into split phase is better than 240 volt single phase used in the UK? If so I am totally on board!

Better? 240V house wiring is cheaper and appliance leads are thinner. Afaik, the only reason for going away from a simple 120V (=100V) standard in the US was that it wasn't suitable for heating appliances (thick wire etc) and they thought quickly and came up with this dual voltage system which is compatible with both requirements. The split phase feature was a reasonable enough strategy which makes best use of the available copper. I would imagine that people in the UK are actually more scared of 240V and tend to treat it more carefully. 120V is just not scary enough; you can usually cope with a 120V contact without ruffling your feathers but 240V does make you jump. UK plugs and sockets are bulky and expensive but, at the same time, comforting. The fuse in every 13A plug is (should be) tailored to the lead / cord to each device to provide good protection against thin leads catching fire when abused.

 

[jim hardy]

The fuse in every 13A plug

your plugs have fuses in them ?

http://www.electricalsafetyfirst.org.uk/guides-and-advice/electrical-items/plugs/

 

[meBigGuy]

I wonder if the reduced current results in fewer fires from bad electrical connections. I hate it when I find hot plugs or sockets.
I've been hooked across 220 though, and that was a bad experience (I was pulled off).

 

[Averagesupernova]

Afaik, the only reason for going away from a simple 120V (=100V) standard in the US was that it wasn't suitable for heating appliances (thick wire etc) and they thought quickly and came up with this dual voltage system which is compatible with both requirements.

Seriously sophie, I am not sure I am going to put much effort into replying to you in the future. For someone who has such strong feelings about the differences between the split phase system and the single phase 240 volt system in the UK I would think you would remember how the split phase system evolved since I once explained it to you. https://www.physicsforums.com/threa...eutral-and-ground-needed.719066/#post-4554015

 

[sophiecentaur]

your plugs have fuses in them ?

http://www.electricalsafetyfirst.org.uk/guides-and-advice/electrical-items/plugs/

Oh yes. The Ring Main system is a very serviceable and cheap system for providing a lot of sockets in a house without a Star system. The ring is better than the Daisy Chain as there is no 'end of the line' voltage drop. Having the protection associated with each appliance by a fused plug is very good. A low powered lamp, supplied from a high current outlet is a fire hazard without something to protect the thin cord - I think you would agree. But those UK plugs are very chunky (good and bad thing) and are pretty expensive if you don't buy poor quality far-Eastern sourced ones.
There is one thing that amazes me about the fused plug system though and it's that all new plugs are supplied with a 13A FUSE IN THEM! Not a fail safe situation. I should have thought they should, by default, have a 3A fuse and then, when the user connected a new plug to a Kettle, the default fuse would blow - unless they had the sense to use the appropriate fuse value. (You can buy plug fuses in pretty much every shop in the high street except a fishmonger's.
I have read several objections (US origin) on PF to the ring main system but it is well tried and tested and those scenarios that the nay-sayers suggest, just don't seem to arise.

 

[sophiecentaur]

I wonder if the reduced current results in fewer fires from bad electrical connections. I hate it when I find hot plugs or sockets.
I've been hooked across 220 though, and that was a bad experience (I was pulled off).

The fire risk due to overcurrent is much reduced by the low level fuse protection and the risk of overheating connections is low because of the inherently high spec of the 13A plugs and sockets. Your comment about the lower current is also relevant.
The effects of a 240V shock are not nice but moderns systems all have RCD protection which limits the exposure to around 10mA for a very short time. That doesn't stop you falling off a ladder when you stick your fingers in a light socket, of course . . . . . Mains shocks can always be avoided when correct practice is followed in the workplace. I have also had mains shocks but it's always been my fault.

 

[Salvador]

sophies right about mains shocks , it's not like the electricity just magically decides to hurt you or your feelings it's almoust always someone who did something wrong.

As for the Uk plugs , well in the end everyone thinks their system is the best so it's more a mater of opinion than a matter of real life physics.For example here in the much laughed at (especially from UK by the way) eastern europe , we use a simple two pin plug, it has no fuse in it , but then again why would it have one if he fuse is in the apparatus and each device has its own current rating so a different type of fuse and also we now have cirucit breakers in like every appartment building , and given the quality of modern cirucit brakers I highly doubt one needs a separate fuse in the plug itself which makes the plug rather big and takes up unnecessary space.
i have had all kinds of deliberate test short cirucits and in all of them the cirucit breaker has done it's job so why would a fire brake out when the current is stopped in a matter of parts of a second.
and yes we use probably the simplest of all the AC distribution cirucits, the so called Y , were each building has a three phase cable coming into it's main utility box and from there each appartment or house or room has one of he phases together with the common neutral going in.so for single phase the phases can be balanced out and if one needs a three phase power he can simply tap into the utility box main cabl and have his three phases.
and even though I haven't done any maths on this, I highly doubt the single split phase has any real advantage over this simple three phase Y arrangement or the UK sysem too for that matter.

Just feels like history and tradition has a lot of importance even in physics , even though the differences are sometimes small if any.

 

[CWatters]

I've had shocks from 230V and higher. The most memorable ones were from a old CRT monitor and a cattle fence. I think the cattle fence shock was the worse experience. I was out walking and slipped over, I put one hand on the muddy ground and the other on a fence which turned out to be electrified. Every muscle in my body hurt for about 30 mins. I'd already walked about 12 miles and had to do another 12 afterwards to get back to the car which wasn't much fun.

 

[jim hardy]

There is one thing that amazes me about the fused plug system though and it's that all new plugs are supplied with a 13A FUSE IN THEM!

Hmmm fuses protect wire
i'd think the appliance itself would be fused internally, beyond where the power cord connects.

 

[jim hardy]

Aha ! It was those darn Europeans again...

In the United States, the Westinghouse Company chose to standardize the operating frequency to 60 Hz, as suggested by Tesla, eliminating nine other possibilities. In Germany, however, the standardization was much simpler because one company, BEW, had a monopoly on electricity. The outcome of BEW's standardization was 50 Hz, which was most likely chosen because it fit better with the 1, 2, 5 metric standard. This same company chose to supply its consumers with more power by raising their voltage from 110 volts to 220 volts in 1899. This trend, as well as the 50 Hz operating frequency, spread across Europe over the next few decades [10].
It has been suggested that the US switch to the 220-volt system. In the 1950's the US did consider switching but then decided against it since most consumers already had a number of 120-volt products. A compromise was reached when the US employed Edison's three-wire system: one wire supplied +120 volts, another supplied 0 volts, and a third supplied -120 volts, so that stoves, washers and dryers, and other large appliances could access 220 volts, while smaller appliances could still operate on the lower 120 volts [10].

http://illumin.usc.edu/122/a-powerful-history-the-modern-electrical-outlet/fullView/

 

[CWatters]

Hmmm fuses protect wire
i'd think the appliance itself would be fused internally, beyond where the power cord connects.

Yes the fuse in a UK plug is to protect the wire from the plug to the appliance. Normally that wire is smaller gauge than the house wiring and smaller than the circuit breaker at the distribution board, so it's the first to fail if there is a short in the appliance.

 

[sophiecentaur]

Yes the fuse in a UK plug is to protect the wire from the plug to the appliance. Normally that wire is smaller gauge than the house wiring and smaller than the circuit breaker at the distribution board, so it's the first to fail if there is a short in the appliance.

My scenario is the bedside lamp, with a long length of minimal thickness flex. Someone moves the bed and one of the feet is bearing down on the flex. After a period (months) of people getting out of bed and other antics, the conductors (no earth) are squashed into contact. The flex is passing 8 or 10A and getting hot, sizzling through the PVC sleeving and charring the carpet. The mains fuse knows nothing of this; it's quite happy to pass much more current that the fire making machine is taking. In the UK, the plug fuse (it should be 3A, if the owner is being a good boy) will just blow. My example was of a lamp, which has no internal fuse.

Aha ! It was those darn Europeans again...

As ever. We have started most of the major wars, invented medieval torture instruments and are probably responsible for all the sexually transmitted infections. But don't you just love our culture and out use of irony?

BTW, Happy new year to you guys and all the other readers.

 

[jim hardy]

Metric Bolts, Pb-free solder, auto dimmer switch on the steering column not floor, 230 volt table lamps and Christmas lights
are some Euro things i dislike
but we should have stuck with England's right foot motorcycle shifter .

old jim

 

[jim hardy]

But don't you just love our culture and out use of irony?

Indisputably. I always wanted to be witty like Cary Grant.That line from Mary Poppins about the tea in Boston Harbor being rendered 'unfit even for Americans'
made me wonder a few years later --
Was James Bond's portrayal as a promiscuous gunslinger just for Americans ? We sure went for him.

And Terry Thomas's rant in Mad Mad World to effect "If American women stopped wearing brassieres your national economy would collapse overnight " ...

well they did and it did...

 

[sophiecentaur]

Metric Bolts, Pb-free solder, auto dimmer switch on the steering column not floor, 230 volt table lamps and Christmas lights
are some Euro things i dislike
but we should have stuck with England's right foot motorcycle shifter .

old jim

Remember Statler and Waldorf in the Muppets? That's you and me, that is.
I loved the T Thomas clip.

 

[dlgoff]

Indisputably. I always wanted to be witty like Cary Grant.That line from Mary Poppins about the tea in Boston Harbor being rendered 'unfit even for Americans'
made me wonder a few years later --
Was James Bond's portrayal as a promiscuous gunslinger just for Americans ? We sure went for him.

And Terry Thomas's rant in Mad Mad World to effect "If American women stopped wearing brassieres your national economy would collapse overnight " ...

well they did and it did...

You're killin' me.

 

[Averagesupernova]

Well to back step a bit, I happened to run across this:

http://forums.mikeholt.com/showthread.php?t=173330

Gets into a debate about DC power transmission on about page 5 or so. I would have to say some of the posters on each side of the discussion are a bit misinformed on some things.

 

[sophiecentaur]

New Year's Resolution: Avoid getting into discussions involving 'Neutral'.
I wonder how long I will manage that?

 

[dlgoff]

Avoid getting into discussions involving 'Neutral'.

But, but, ...
You are the engineer of the year.

BTW Congratulations.

 

[sophiecentaur]

Cheers digoff.
"But but" You have a point there.
I shall have to remain neutral in such arguments.

 

[jim hardy]

I shall have to remain neutral in such arguments.

I won't let it faze me, either.

 

[meBigGuy]

more power to you all!

 

[NascentOxygen]

Somewhere in this mire the question of an AC network's inherent efficiency has been answered, and then some. Thanks to all contributors.

Thread closed.