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BigBoy1
09-05-2012, 06:01 PM
I just returned from a trip to Europe and the power there started be thinking. Why does North America use the 110 volt, 60 cycle as standard household power while in Europe, they have 220 volt, 50 cycle? Is there some scientific or technical reason why the two are different or is is something like, "I'll make mine different because I want to"? Inquiring minds would like to know.

ogre
09-05-2012, 06:26 PM
Im not a certified electrician but i know 220 uses less amps. Someone told me since 220 pulls less amps that it saved money compared to 110. Then i read somewhere(popular mechanics) that that is false. So i dunno whos right anymore but if it does pull less amps and save money then thats my guess..

MaxHeadRoom
09-05-2012, 06:26 PM
The 1ph domestic supply is also derived slightly differently, in N.A. the domestic supply is derived from a 120-0-120v centre tap 1ph transformer, where the 0 tap is the grounded neutral, in Europe where it is 220/240v 1ph, it is derived from a 3 phase transformer, 1 phase and the star (grounded) neutral.
Another difference is that in N.A. the neutral is re-referenced to ground at the service panel, in much of Europe, the neutral is grounded at the source only.
The reason for 240v in Europe cannot really be the load demand issue, as early domestic installations did not have large appliances as is the norm today, much of first installations were for electric lighting to replace piped gas lamp systems.
The same load on 240 and 120 is the same wattage, just lower current on 240. No money saving, just wire diameter is smaller on 240 for the same load requirements.
Max.

SteveF
09-05-2012, 06:47 PM
You got me curious so I did a little searching on the Internet and the answers as to why are all over the place.

When I get the flux capacitor fixed in my DeLorean I'll go have dinner with Tesla, Edison and Westinghouse and get the real story. ;)

Steve

armedandsafe
09-05-2012, 06:47 PM
...wire diameter is smaller on 240 for the same load requirements.

That is the primary advantage of 220 single phase over 110. Cuts the cost of delivery systems by as much as 1/3.

Pops

The Artful Bodger
09-05-2012, 08:11 PM
110 volts or 220 volts, 50 or 60 Hertz? Probably for the same reason that some countries drive on the wrong side of the road.

One advantage of 60Hz may be that there is less iron required in transformers and motors etc?

The Artful Bodger
09-05-2012, 08:13 PM
The 1ph domestic supply is also derived slightly differently, in N.A. the domestic supply is derived from a 120-0-120v centre tap 1ph transformer, where the 0 tap is the grounded neutral, in Europe where it is 220/240v 1ph, it is derived from a 3 phase transformer, 1 phase and the star (grounded) neutral.
Another difference is that in N.A. the neutral is re-referenced to ground at the service panel, in much of Europe, the neutral is grounded at the source only..

Max, I have only vague knowledge of North American practices (except I note the cord on the motel toaster gets really hot if not fully unrolled). This 120-0-120 transformer, is that across one phase of the distributed 3 phases? What happens to neutral of the distribution transformer is that grounded (or maybe they are delta transformers?)?

customcutter
09-05-2012, 08:18 PM
I always heard the electricians at work say that 220 volts would knock you off of it if you happened to get on it. 110 volts would cause the muscle to contract and you would be locked onto it. I've been on 110 US and 220 UK, both hurt.

I also used to tell the electricians at work that I don't like messing with electricity cause you can't see it, and when you do it's too late. Especially when a lot of our work was 4160 volts.

Ken

J Tiers
09-05-2012, 08:37 PM
Max, I have only vague knowledge of North American practices (except I note the cord on the motel toaster gets really hot if not fully unrolled). This 120-0-120 transformer, is that across one phase of the distributed 3 phases? What happens to neutral of the distribution transformer is that grounded (or maybe they are delta transformers?)?


there are a number of systems of local power, depending on usage.

Houses, usually 120V, which is 120-0-120. It is usually obtained thru a transformer from a local 4160V 3 phase line (or one phase of such a line run up a street), most often from line to neutral on the primary. Secondary is the 120-0-120, which is grounded on the "0" line (neutral).

Large apartments.... usually supplied with 120Y/208 3 phase, two lines of which go to each apartment with neutral. That gives 208V between lines, and 120V each line to neutral.

Industrial.... Often 277Y/480V 3 phase, giving 277V to neutral, which can be used for lighting. Office 120V comes through a transformer, most often 208V 3 phase.

Some light industrial can have the same 120Y/208 service as an apartment. We have that at work.

Other industrial include 240V "wild leg" 3 phase, which has the 120-0-120 from one pair of wires, and the 3rd wire is the "high, or "wild" leg, since it is a higher voltage to the 120V neutral. Often found on farms, it supplies lights and office loads as well as 240 3 phase.

240V and 480V "corner grounded" systems are no longer put in, but still exist... these are delta systems with one of the phase wires grounded.

regardless of system, the common voltages are 120/240, 120/208, and 277/480.

lakeside53
09-05-2012, 08:41 PM
That is the primary advantage of 220 single phase over 110. Cuts the cost of delivery systems by as much as 1/3.

Pops



But... it's not delivered any distance at 120 or 240. For residential, your local pole of ground transformer is fed with high voltage distribution. There are more distribuation losses with 60hz than 50 (think of long transmission lines as capacitors to ground).

In Japan the outlet voltage is 100 or 200, 50hz in part of the county, 60hz in the other.

Why 60 verse 50, 120 verses 240? Historical, and first to market.

kf2qd
09-05-2012, 10:48 PM
And 60 Hz is considered to be more dangerous than is 50Hz. The human body seems to lock on 60Hz more than it does on 50Hz. Some military system use 400Hz. Smaller transformers and considered less likely for a human to lock onto 400Hz.

J Tiers
09-05-2012, 11:05 PM
And 60 Hz is considered to be more dangerous than is 50Hz. The human body seems to lock on 60Hz more than it does on 50Hz.

Maybe, maybe not..... A low enough frequency will cause you to jerk in time to it..... and more of it goes deep into you*. The higher frequencies get past the speed at which you can react...causing a general muscle tightening.... so likely 50 OR 60 will cause "lock-on" if the situation is favorable to it....

Bottom line is that ANY of the common power voltages and frequencies can kill you. The relative ease with which they do kill you is not particularly interesting compared with the far more profitable concept of staying totally out of contact with ANY of them...........

One of the problems with the much touted 42V auto electrics was the fact that 42V (really 52V or more under charge) was above the UL and CE limits for "nominally non-hazardous" voltage.... meaning that it would have to be treated essentially just like household 120V or 230V. Naturally with 300V electric vehicles, that's a given, but with ordinary automotive stuff that "Bubba" will try to fix, it isn't so good.

* people are so resistive that the "skin effect" is not nearly as obvious as it would be with copper or aluminum.... but there is still some effect. So high frequencies will tend to go on your skin, low frequencies and DC will go deep. The limits of "low" and "high" may vary a bit depending on your particular case.

basically, just stay out of the wall outlet....... don't be thinking that 50 Hz may not kill you as dead as 60 or any other frequency. If you get zapped and don't die, you know (or ought to know) who to thank.....

Paul Alciatore
09-05-2012, 11:26 PM
To answer the original question, I think you have to go back to the beginnings. Please correct me if I am wrong, but in the USA Edison and Westinghouse were fighting to have their power systems become the standard. Westinghouse wanted AC power and I believe he started with 110 or 115 Volts and 60 Hz. Edison was trying to standardize DC power which had considerable distribution problems. One of Edison's reasons for DC was that it was safer: he even argued that AC power was used for executions by electrocution. He argued that AC was more effective for killing people and his DC system was safer. I am sure that these arguments were not completely dismissed by Westinghouse. That may be part of the reason for keeping the distribution Voltage somewhat lower. It would allow Westinghouse to argue that his system was at least somewhat safer.

I am sure that power distribution in Europe and other areas of the world proceeded along different lines in those areas. Without the presence of Edison arguing against the deadly AC system, they were probably freer to develop the systems for greater the efficiency allowed by higher distribution Voltage.

I am not sure about the timing of the construction of electric distribution networks in every nation, however, I suspect that many of them lagged that development in the US and therefore had better advantage of hindsight. Also less democratic conditions may have made it easier to use higher and potentially more dangerous distribution Voltages.

As for the 50/60 Hertz thing, I doubt that it makes any great differences in the costs of transformers. In fact, a 50 Hz, 220 Volt transformer may be lighter than a 60 Hz, 110 Volt one. The mass of steel needed in the core is inversely proportional to the frequency so 60 Hz has a small advantage there, BUT it is also directly proportional to the current and for the same delivered power, 110 Volt circuits need twice as much current and ashamedly twice as much metal in the core.

OK, some of the above is not completely true in the present forms of power distribution in the US vs Europe. In reality, homes and small businesses in both areas have 220 Volt service to the building. If you are in the US, look at the power feed from the pole to your house. You will see three black wires coming in - ignore the uninsulated steel cable they are wrapped around as it is just for mechanical support. One of these three wires is a ground and the other two are hots. Each hot is 110 Volts above ground and they are 180 degrees opposite in phase from each other so the Voltage between them is 220 Volts. It is only at the power panel where individual 110 V circuits are broken out.

The fact that both of these hots are only 110 V above ground does make this system a bit safer than one where a hot wire is 220 V above ground. I don't know if this is the way European circuits are constructed, so please inform me and the others here.

However, I doubt that this fact negates my original arguments about safety as things are evolved a lot from the time when these things were first created and it was conditions then, not now that determined what we are still using today. It is the history, not present day best engineering practice that was the determining factor here.

darryl
09-05-2012, 11:34 PM
An interesting read on the subject-

History (http://www.ieee.org/organizations/pes/public/2011/jul/peshistory.html)

MaxHeadRoom
09-05-2012, 11:57 PM
If you are in the US, look at the power feed from the pole to your house. You will see three black wires coming in - ignore the uninsulated steel cable they are wrapped around as it is just for mechanical support. One of these three wires is a ground and the other two are hots. Each hot is 110 Volts above ground and they are 180 degrees opposite in phase from each other so the Voltage between them is 220 Volts. It is only at the power panel where individual 110 V circuits are broken out.
.

Technically it is not a termed a ground as it cannot be used as a ground conductor, it has to be re-referenced to ground at the service panel and then the ground and neutral are considered separate conductors.
In Europe and also I believe Australia the neutral is not re-referenced to ground at the panel, only at the source.
This means that a required ground resistance from building ground conductor or ground rods back to the transformer grounded star point conforms to a sufficiently low resistance level.
Otherwise a main GFI or similar unit is used at the main panel for the whole service.
Most of the rest of the world uses one phase of a 3 phase transformer with the star point grounded as a neutral.

Max.

The Artful Bodger
09-06-2012, 12:17 AM
The Multiple Earthed Neutral system as used in Australia and New Zealand has the neutral earthed at the transformer and at multiple points along the line and at the consumers' premises. All exposed metal parts of appliances etc are connected by an earth conductor back to a bus bar at the switchboard which is bonded to the supply earth and to local ground. The maximum resistance between the neutral and earth at any point must not be more than 10 ohms.

boslab
09-06-2012, 01:15 AM
Im not sure but the generating sets rpm dictates frequency so 60 Hz equates to a specific alternator rpm as does 50 Hz , the alternator generates a sine wave output, the number of coils is equal to the number of phases at the generator, from memory many more than three, but multiples thereof
in UK the grid has live or phase and neutral but no earth wire, there are 3 lives [used to be red yellow and blue but we changed to blue brown and grey to confuse us as blue is also neutral but the Brussels department of banana length got involved] and one one neutral aka 0 volts
the Earth reference is supplied locally by sticking a 1000 mm copper covered steel rod into the ground as near to the meter as possible and running a 6mm copper green and yellow striped cable to the distribution panel.
the grid has no earth on any transformer only a floating 0 volts which may not be at zero BTW, ive clocked 50v on the neutral against earth.
Im thinking that patents on generators like the Westinghouse sets were the original motivation for differing supply rather than any advantage by either voltage, whilst the UK mains is 230 Volts as a reduction from 240 was made [+10%-6%], strangely enough its still 240 on the isle of man as the transformers on the end of the undersea cable are still the old ones.
All industrial tools in UK SHOULD be 110 volt, and an isolation transformer supplies the outlets so if you go to buy a drill they ask if you want a 110 or a 230,
which could be confusing save for the fact a 230 domestic has a square pin plug and a 110 is a yellow round pin plug [yes they do get wired with the wrong plug regularly which kills them]
int this fun
regards
mark

J Tiers
09-06-2012, 08:34 AM
Technically it is not a termed a ground as it cannot be used as a ground conductor, it has to be re-referenced to ground at the service panel and then the ground and neutral are considered separate conductors.
In Europe and also I believe Australia the neutral is not re-referenced to ground at the panel, only at the source.
This means that a required ground resistance from building ground conductor or ground rods back to the transformer grounded star point conforms to a sufficiently low resistance level.
Otherwise a main GFI or similar unit is used at the main panel for the whole service.
Most of the rest of the world uses one phase of a 3 phase transformer with the star point grounded as a neutral.

Max.

The US system involves lots of "grounds" or "earthing points", but you are not allowed to consider most of them, for a particularly good reason. Essentially it is like the Australian system.

The "zero" point of the 120-0-120 service (which you will note IS 220V service, ONLY the grounding is different... NO need to be "ashamed") is usually connected to earth at every other pole, and at any pole with a transformer supplying a house with 120-0-120 service.

THAT "zero point" wire comes to your house as the uninsulated wire. Most "service drops" here are three wires, with the "support" wire being the neutral, with the "hot" wires insulated and wrapped around it to form a cable.

That ground wire is then connected to earth at your main breaker box. The local "green wire" or "equipment grounding (earthing) conductor is also connected there. So teh original earth connection at the pole is also connected to your local earthing (grounding) system. Local water pipes etc are also connected in most locations.

The REASON for this is that the voltage in ground at various places varies. The conductivity of earth varies also. There is no guarantee that a fault current in the house going to earth will get back to the original source ground effectively. The voltage drop may be too high to keep fault voltages to a safe level.

By connecting everything to the earth AT YOUR HOUSE, it is known that the common possible faults will end up with current back to the source, AND that the local voltage on "earth" will not be raised too much. And it is pretty certain that a local fault will draw enough current to open a breaker.

Relying on a connection to some distant point may not be effective in keeping voltages controlled, or in drawing enough current to open a protective breaker in case of a fault to earth. There is no guarantee on the voltage developed between local earth ground and the wire going to some remote earthed point.
.
.
.
An extreme case of this is in a power substation, where voltages and possible fault currents are often very high. It may be necessary to underlay the entire area with a conductive mesh, or grid. If that is not done, a severe fault may develop enough voltage drop in the earth to electrocute a person who is touching a fence while standing on the ground next to it, even though the fence is not involved in the fault. The voltage across the earth from the feet to the adjacent fence can be that high.

Another example is the requirement to connect the lightning rod ground to the electrical ground. if not done, a very high voltage might be developed between lightning conductors and the grounding system, possibly causing arcs, fires, etc. By connecting all together, the local voltage difference is lower and likely to be non damaging.

It is the "bird on the wire" issue. The bird is safe because it is at the same voltage as everything around it. Only if it steps off the wire and at some point touches both the wire and some grounded item will it be zapped

MaxHeadRoom
09-06-2012, 10:06 AM
Although my Electrical Background is from UK, I consulted with my son-in-law who is an Engineer with the provincial Hydro Service and he confirmed that here in Canada, and I have also heard reports of the same in the US, that the local pad mount transformer delivers a 120-0-120 supply and the 0 is grounded at the transformer with two ground rods, No ground is supplied per-se, just the neutral, the neutral is re-referenced to the water supply service where it enters the building.
I confirmed this with my own supply as being the case.
In UK and parts of Europe, the service supply does not (or did not when I was there) deliver a ground and also does not allow re-referencing the neutral to ground at the service entry.
But a qualified ground has to be confirmed with a ground resistance test for any water service and ground rods used.
(I am not sure what the 'ashamed' refers to?
Max.

jep24601
09-06-2012, 04:53 PM
I always heard the electricians at work say that 220 volts would knock you off of it if you happened to get on it. 110 volts would cause the muscle to contract and you would be locked onto it. I've been on 110 US and 220 UK, both hurt.

I can personally testify that both UK 240v and US 110/120v cause muscle contraction and lock-on.

MaxHeadRoom
09-06-2012, 05:29 PM
I have seen both effects on 240, in my younger days I had one episode, thinking the supply was off, I grabbed hold of a 240v live and neutral, one in each hand, a fairly powerful jolt caused an uncontrolled muscle reaction and threw me back off the conductors.
But a buddy I was with once had an episode where he punctured a live conductor with a conduit and was momentarily paralyzed, he managed to make himself fall forward releasing the pipe.
The Moral, anything can happen if you are not vigilant.
Max.

boslab
09-06-2012, 05:42 PM
Just a snippet of interest, the steel for transformers is silicon steel, 1.3% to 3%, after you cast the steel it has to be hot connected to the mill, you cant let it cool or the slab will burst like toughened glass as the giant silicon matrix forms, you have to roll it to prevent this, crystals in a cold slab of steel can be 10", the same thickness as the slab, you can hear the steel groaning as it cools and the cracks form, they call them chink cracks as that is the sound they make.
the higher the silicon the better and carbon is bad so that gets reduced in a vacuum degasser before casting, down to .003 or so, so really laminations are ultra low carbon silicon iron.
you have to have a lower silicon for motors along with carbon as spinning a silicon causes creep to destroy the motor
these electrical steels are called G.O. or grain orientated, just a little bit of info from the steelplant
regards
mark

ammcoman2
09-06-2012, 06:43 PM
A further comment on the 50/60Hz discussion.

Here in Ontario up 'till about 1950, the frequency was 25 cycles. I think it had something to do with the Niagara Falls Hydro-Electric generator system. In the early days of Electricity nearly all the power was supplied by Hydro.

When the conversion to 60 Hz took place, everyone received free replacement motors!

Another snippet: In Greece back in the old days the household supply was 500V DC.

Geoff

MaxHeadRoom
09-06-2012, 07:07 PM
Another snippet: In Greece back in the old days the household supply was 500V DC.

Geoff

Also isolated pockets in the UK were 120VDC. Back then lighting was the main issue, so it did not matter that much.
Max.

J Tiers
09-06-2012, 09:44 PM
Although my Electrical Background is from UK, I consulted with my son-in-law who is an Engineer with the provincial Hydro Service and he confirmed that here in Canada, and I have also heard reports of the same in the US, that the local pad mount transformer delivers a 120-0-120 supply and the 0 is grounded at the transformer with two ground rods, No ground is supplied per-se, just the neutral, the neutral is re-referenced to the water supply service where it enters the building.
I confirmed this with my own supply as being the case.


With regard primarily to the bolded portion of the post......

The "neutral is, in the usual practice, grounded at the pole, at the least at the pole with the transformer, and typically at every other pole. You can see the wires coming down the pole to the typical "butt-coil" ground as in the old days, or whatever clever thing is used now,..... The "butt-coil" ground was a length of bare copper coiled up on the butt end of the pole (where it would be at the bottom of the hole) and stapled in place, taking care to short the coils with the staples. The rest of the wire runs up the pole and is "bonded to" the neutral wire which supplies the neutral to the residence.

OK, the neutral, which is already grounded at the pole, is re-grounded at your (US) service box, and bonded to the "equipment grounding conductor" (the green ground wire).

Remember, the "neutral" is called the "GROUNDED conductor", because it is a conductor, and it is grounded (earthed). The green wire is called the "equipment GROUNDING conductor", because that is what it does... grounds the cases etc of equipment.

So THERE IS A GROUND SUPPLIED..... it is supplied by the neutral, which is grounded, and connected to the green wire. The connection to pipes, etc is made to ensure that everything you can possibly touch is at the same voltage as the green wire. In older practice, teh pipes alone could be used as the local ground. With plastic pipes these days, that is not so true, and a rod is required in addition to, or instead of, the pipe ground alone.

Mike Burch
09-06-2012, 11:33 PM
New Zealand's two main islands are separately by a particularly unpleasant stretch of water, Cook Strait.
And they are connected by three power cables under Cook Strait. Because the sea would act like one plate of a giant capacitor, an alternating current in the cables would have huge losses, so they in fact carry high voltage DC. This is turned back to AC once ashore by simply reversing its polarity at a synchronised 50Hz, and allowing the electrical inertia in the rest of the network to smooth it out until it looks like a sinewave. Crude, but effective.
I was told years ago that Americans were taught that 110v is safer then 230v, and that some of them believe this - albeit for a very short time...

MaxHeadRoom
09-06-2012, 11:34 PM
This 120-0-120 transformer, is that across one phase of the distributed 3 phases? What happens to neutral of the distribution transformer is that grounded (or maybe they are delta transformers?)?

A.B. The one feeding my panel has a 1ph pad transformer that is fed from one phase and a grounded star neutral 7200v primary.
Max.

mickeyf
09-07-2012, 12:01 AM
Even in this era of digital clocks, there are probably millions of clocks in North America running on very convenient 60 hz synchronous motors. Makes you wonder about European clocks. Hey! perhaps that explains why they are always hours off from us! Their clocks are slow! ...uh, wait a minute...

On a separate note...

In ordinary North American residential wiring, neutral and ground are tied together in the service section of the main panel, but are separate in the branch section and downstream from there. As you get further from the panel, the actual voltage difference between them will increase. Occasionally you find that some one has used ground as if it were neutral, and although they seem to have gotten away with it (the thing appeared to "work"), this is a Bad Idea.

A ground connection exists at an outlet or device strictly for safety reasons, and unlike the "neutral" side of a 120V line, it will never actually carry current (unless there is a fault). In a 120-0-120 circuit, it carries only the current of any unbalance between the two 120v lines. This may be small, or quite significant. Don't confuse Neutral and Ground or consider them to be identical - they are not.

ogre
09-07-2012, 12:43 AM
I always believed that the voltage isnt what kills you,its the amps. Could be wrong but id like to know for sure curiousity.

darryl
09-07-2012, 12:45 AM
Ok, so I have a wall clock running from ac. For 20-odd years now it has kept perfect time. In the last several months it has started running fast- huh?

I've watched the second hand going around, and it doesn't appear to have any 'rough' spots in its rotation. I highly doubt that the gear train has changed its ratio, and there's no unusual noises coming from the clock. Nothing seems to be amiss.

I'm guessing that the line frequency has gone up very slightly, although from what I've read it's supposed to be corrected to give an average over time that is exactly 60 hz. There are supposedly regulations in place to keep a tight rein on this, but I wonder if, like everything else, it has been relaxed somewhat, or if there's another answer.

mickeyf
09-07-2012, 12:52 AM
My understanding is that when power generating stations have excess capacity, they speed things up a tad, which shifts the phase so that they are feeding that power into the grid. Perhaps BC Hydro has simply been selling a lot of extra power over the summer, for all those air conditioners in LA.

Yes, "average over time", but what period of time? I doubt if it's ever off more than a tiny amount, but we'd need a real power engineer to answer that one.

darryl
09-07-2012, 12:56 AM
In response to ogre, it would take both voltage and current to give the shock. If no current could flow, even momentarily, then voltage itself would be of no consequence. If there was no voltage, then there's nothing to create a current flow. At the very least, a contact with voltage would cause a small pulse of current to flow to charge the mass of the object coming into contact with the voltage. In the case of ac, that charge will flow both ways, so there will be a pulse current flow for every cycle of the ac.

If there's something less than infinite resistance involved, then there will be a more or less continuous current flowing, depending on the voltage and on a few other conditions. Depending on the magnitude of the current, you may not even feel it, or you may experience the effects of shock, one of the more notable of these being death by electrocution.

The Artful Bodger
09-07-2012, 01:24 AM
New Zealand's two main islands are separately by a particularly unpleasant stretch of water, Cook Strait.
And they are connected by three power cables under Cook Strait. Because the sea would act like one plate of a giant capacitor, an alternating current in the cables would have huge losses, so they in fact carry high voltage DC. This is turned back to AC once ashore by simply reversing its polarity at a synchronised 50Hz, and allowing the electrical inertia in the rest of the network to smooth it out until it looks like a sinewave. Crude, but effective.
I was told years ago that Americans were taught that 110v is safer then 230v, and that some of them believe this - albeit for a very short time...

Mike, I recall hearing "somewhere" that one of those cables is positive with respect to ground and another, which is some distance away, is negative with respect to ground, the working voltage is the voltage between the two but the voltage to ground (which is the voltage that must be insulated for) is only half the working voltage

camdigger
09-07-2012, 05:03 AM
A.B. The one feeding my panel has a 1ph pad transformer that is fed from one phase and a grounded star neutral 7200v primary.
Max.

Max

While I fully believe that your local line is a single phase (in fact mine in rural Alberta is a 7500 V line ), I would speculate that somewhere it is drawn off one phase of a 3 phase system in a distribution substation some where between you and the generator station. The other legs of the 3 phase system likely serve other neighborhoods. The balancing of the loads between the phases is a matter of statistical analysis. They need the average draw to approximately balanced. Some tolerance exists between phases, but the closer they can estimate the loads to balance between phases, the better.

As I recall, either the provincial or national electrical code in Alberta calls for a ground at each of the following points: at the transformer, at the main panel, and at each sub panel at each building on the service.

Arcane
09-07-2012, 07:08 AM
...........A ground connection exists at an outlet or device strictly for safety reasons, and unlike the "neutral" side of a 120V line, it will never actually carry current (unless there is a fault). In a 120-0-120 circuit, it carries only the current of any unbalance between the two 120v lines. This may be small, or quite significant. Don't confuse Neutral and Ground or consider them to be identical - they are not.In case anyone is not clear on this, mickeyf no doubt was referring to the neutral in the statement I put in bold type, not the "equipment grounding conductor". The "equipment grounding conductor" from the main panel back to the transformer is in parallel with the neutral and will carry a small percentage of the unbalanced load depending on the resistances involved...not too much resistance on the neutral but the other path has a much higher resistance...dirt compared to metal.

The frequency variation allowed is quite large actually! From http://tf.nist.gov/timefreq/general/pdf/2125.pdf
The legally allowable tolerance for the 60 Hz frequency is only 0.02 Hz, or 0.033 %, but under normal operating conditions the actual tolerance is much tighter. At the nominal 60 Hz rate, there are 60x60x60x24 = 5,184,000 cycles per day. If the grid runs .033% fast, there will be 60.0198x60x60x24 = 5,185,710.7 cycles per day. The difference is 1710.72 cycles, which is 28.512 seconds.

Frequency has to pretty well match exactly across North America since if it didn't, the sine waves would get out of sync quite quickly and you would be in the situation where you could be closing in on what would be a dead short when paralleling generation stations. If you deviate from a 60 hz frequency by even 0.001 hz on only one part of the grid, all it will take is ten seconds for that variation in frequency to cause it to begin rising and falling opposite to the rest of the grid. From the same site
The entire power system relies on time synchronization, and synchronization problems can lead to catastrophic failures. For example, the massive August 2003 blackout in the eastern regions of the United States and Canada was at least partially caused by synchronization failures.

J Tiers
09-07-2012, 08:06 AM
In case anyone is not clear on this, mickeyf no doubt was referring to the neutral in the statement I put in bold type, not the "equipment grounding conductor". The "equipment grounding conductor" from the main panel back to the transformer is in parallel with the neutral and will carry a small percentage of the unbalanced load depending on the resistances involved...not too much resistance on the neutral but the other path has a much higher resistance...dirt compared to metal.



The "equipment grounding conductor" should carry NO LOAD CURRENT unless there is a fault. In practice, a tiny leakage current may flow in it, simply because insulation is not perfect, or due to EMI filters in the equipment. But NO LOAD CURRENT.

As for neutral currents.......

The neutral can carry any current from nothing up to potentially almost the sum of the two hot wire currents.

Nominally, it carries the difference current. If one 120V appliance is being run, the difference equals the total load. if two identical appliances are being run, one from each "side" of the 120-0-120, theoretically there is NO neutral current, but nothing is ever perfect. This is a fact which has recently come to the fore as a big problem in europe, where neutrals were traditionally seriously under-sized.

The problem with the neutral is twofold....harmonics, and the relative phase of the currents in each line.

With resistive loads, like incandescent bulbs or heaters, current and voltage are nearly, or entirely "in phase". When voltage increases during the sine wave, current "tracks" with it exactly. There is no "lag", and no distortion (in the first approximation, anyway).

However, with "reactive" loads, such as CFLs, regular fluorescent lights, mercury and sodium lights, motors, computers, etc, etc, current is no longer "in phase". Typically it "lags", meaning that the voltage goes up before the current increases. That is typical of an "inductive" load such as a motor. Some loads are "capacitive", and with them, the current flows as soon as the voltage begins to change, i.e. it "leads" the voltage.

Computers, most fluorescent lighting, and to some extent motors, all create "harmonic currents", they tend to "distort" the current flow so that it is not a sine wave. There is created a current flow at a series of higher frequencies, typically 180 Hz, 360Hz, 540Hz, etc.

harmonics and reactive currents cause the neutral current not to balance out neatly. The neutral current can easily be greater than the current in any single one of the "hot" wires, particularly with the harmonics beginning with the 3rd (150 or 180 Hz). Computers and most "switching power supplies" including VFDS, make relatively large amounts of 3rd harmonics.

In europe, this is such a problem that there are regulations on the maximum harmonic currents allowed, which require a whole other expensive added electronic "stage" to most switching power supplies in computers etc.

So current in teh neutral is never quite so simple as it is often made out to be.

Ed P
09-07-2012, 08:33 AM
An interesting read on the subject-

History (http://www.ieee.org/organizations/pes/public/2011/jul/peshistory.html)

This is an interesting read. It mentions that Japan uses both 50 and 60 hertz in different parts of the country. That must be confusing. It also mentions production of 50 hertz power in California for awhile ending in the 1940's. There was a campaign by the power companies during that time to offer free modifications to customer's clocks to convert them from 50 to 60 hertz.

Ed P

kaje
09-07-2012, 10:00 AM
There's a good short history which explains a lot - see it here (http://wiki.answers.com/Q/Why_power_supplied_to_houses_in_America_is_110v_an d_60hz). Here are a few excerpts:

"In the early years of ac there were many frequencies: each engineering team seemed to pick their own. Early frequencies in the US were 133 1/3, 125, 83 1/3, 66 2/3, 60, 50, 40, 30, 25 Hz. When Tesla joined Westinghouse, it was using 133 1/3 Hz. Tesla insisted upon 60 Hz because his ac induction motor was designed for 60 Hz and apparently wouldn't work at 133 1/3 Hz. "

"Back in the early 1890's Westinghouse was involved in bidding electrical equipment for the Niagara Falls power project. However the Cataract Company (in charge of the Niagara Falls project) had already selected hydraulic turbines running at 250 rpm. So if a 16-pole generator were chosen the frequency would be 33 1/3 Hz and if a 12-pole machine were chosen then the frequency would be 25 Hz. The project consultant proposed an 8-pole generator or 16 2/3 Hz. The compromise was 25 Hz. At the time lower frequencies were easier to handle on transmission lines. Another reason is that the Steel industry liked 25 Hz because of huge slow speed induction rollers, which had a low power factor for 60 Hz and worked better at 25 Hz. Niagara Falls generated 25 Hz way into the 20th century."

"As for voltages both Europe and the US seemed to have begun with about 100 to 110 Volts DC because of Edison's success with replacing gas lights with electric lamps. Although many inventors worked on electric lights, generators and electrical systems, Edison was one of the first and was successful in putting together whole systems not just the pieces. Edison picked 110 VDC because that was the voltage he needed to get enough light out of his bulbs to compete with common gas lamps of the time and yet not blow the filaments in his bulbs too soon."

The short answer is that 110v/60Hz resulted from practical considerations, historical accidents, and a healthy dose of "not invented here" syndrome.

Now is we can just figure out why there are several dozen designs for wall plugs. (https://en.wikipedia.org/wiki/AC_power_plugs_and_sockets)

Arcane
09-07-2012, 02:06 PM
The "equipment grounding conductor" should carry NO LOAD CURRENT unless there is a fault. In practice, a tiny leakage current may flow in it, simply because insulation is not perfect, or due to EMI filters in the equipment. But NO LOAD CURRENT.........That's true for the equipment grounding conductor on the load side of the main panel but between the main panel and the transformer, it is exactly as I have stated.

danlb
09-07-2012, 04:33 PM
The only advantage I see of using 110v over 240v is that the insulation can be lighter/smaller. The higher the voltage the further it will arc.

110 is marginally safer, since the amount of amperage available to electrocute you is directly proportional to two things; the resistance of your body and the voltage of the supply. The higher the voltage, the higher the amperage that will pass through your body. 220 cause twice the current, so twice as likely to be deadly.


Body resistance is an important variable when considering electrocution. There is a wide variation in body resistance between people therefore the same voltage level may result in different effects. The typical human body has a hand to hand resistance (R) somewhere between 1,000 and 2,000 ohms. Babies, Children and some other people have less resistance....
Ventricular fibrillation can occur at current levels as low as 30 milliamps for a two year old child and 60 milliamps for adults. Most adults will go into ventricular fibrillation at hand to hand currents below 100 milliamps (0.1 Amp).

Assuming a resistance of 1500 ohms, you will get .073 amps with 110 and .147 with 220. That might be the difference between "Oh Crap!" and dead.

I'm always nervous when working with voltage above 48v, so my hands are moist and therefore an even lower resistance.

Dan

The Artful Bodger
09-07-2012, 05:04 PM
Some years ago we installed a system in the DPRK (aka North Korea) which included a 15KVA UPS. The 'intelligent' battery charger for the UPS continually failed reporting "mains failing" although the mains were clearly on. Checks showed the mains, nominally 50Hz, was actually a nice steady 41.6Hz. We knew from other sources that the frequency at the city power station was steady 50Hz so how could this be explained?

Korea was occupied by Japan in the early 20th century and we know Japan has 50 and 60Hz systems, it is also possible that some 60hz equipment remained as a legacy of the Korean War. The only credible explanation we could conceive is that somewhere in the "facility" where we were working there was a motor alternator frequency converter, intended to convert 60Hz to 50Hz, busily whirring away (converting 50 to 41.6Hz) wasting power and slowly cooking every motor and transformer on the site. It was not practical for us to pursue this matter further.

So how did we solve the battery charger issue? A sat phone call to the Swedish makers brought us the advice to select 15Hz mains which they assured us would be quite satisfactory as the same systems were in use on many European railway networks.

The Artful Bodger
09-07-2012, 05:09 PM
Regarding current in neutral lead.

Although current in the neutral lead of a fully balanced multi phase system should be near zero this is not so for installations where a neutral and a phase line form the feed to a single phase load in which case the neutral and phase currents should be the same, if they are not the same that would indicate earth currents are flowing and an almost certain fault condition.

kf1002002
09-07-2012, 05:17 PM
In the early days many schemes were tried i.e. dc, 2 phase 25 hz, 2 phase 50 hz, 2 phase 60 hz, 3 phase 25 hz, 3 phase 50 hz, 3 phase 60 hz plus some weird ones such as 16 2/3 hz, and 66 2/3 hz. Don't laugh, I came across both 16 2/3 and 66 2/3 hz many years ago. But the strange one's dropped out of use simply because there was no advantage to them other than possibly 16 2/3 or 25 hz for electric street cars but even there the advantage was marginal. I don't think wire size enters much into the 110 and 220 volt question as for normal household use the minimum wire size (#14 in N.A.) is set more by physcal strength than current capacity. It's simply a matter of being able to install it without damage. Even in this country (Canada) I came across a 3 ph 4 wire 120v per phase system with the Y point tied to ground and to the 4th wire. This supplied 208v 1 phase but you had to be careful as the neutral was displaced from the centre of the 208 volts.

Wit any luck this will have confuse every one.


ken

Evan
09-07-2012, 05:21 PM
50 hertz makes it a lot easier to build metric clocks.

The Artful Bodger
09-07-2012, 05:35 PM
The practice here (NZ) is/was to wire houses on a street to phases in sequence (first, second, third house on phases 1,2,3 and so on). It was not unheard of for neighbours to run a lead next door to get another phase to run their valve radio transmitters or 3 phase firewood saw benches, or so I have heard!

J Tiers
09-07-2012, 10:20 PM
That's true for the equipment grounding conductor on the load side of the main panel but between the main panel and the transformer, it is exactly as I have stated.

Except that there ISN'T one....... all there is is the "neutral"...... 3 wires only from the pole. No "equipment grounding conductor" at all, just a "neutral" which happens to go to ground at both ends. Naturally the neutral carries whatever unbalance, harmonics, etc may exist.

J Tiers
09-07-2012, 10:23 PM
The practice here (NZ) is/was to wire houses on a street to phases in sequence (first, second, third house on phases 1,2,3 and so on). It was not unheard of for neighbours to run a lead next door to get another phase to run their valve radio transmitters or 3 phase firewood saw benches, or so I have heard!

We get that on the opposite side of the street. There is a main 3 phase feeder line behind the houses, and each group of 3 houses is on a different transformer, connected to a different line. When 1 or 2 phases go out (blown fuses from trees down etc) groups of 3 houses will be dark (or the only ones with power, depending. So you may have 6 houses with power, 3 without, another 6 on, 3 out etc, etc.

Arcane
09-07-2012, 11:01 PM
Except that there ISN'T one....... all there is is the "neutral"...... 3 wires only from the pole. No "equipment grounding conductor" at all, just a "neutral" which happens to go to ground at both ends. Naturally the neutral carries whatever unbalance, harmonics, etc may exist.
Except the earth is conductive Jerry. It joins the ground rod at the transformer to the ground rod at the house and since both the ground wires are bonded at each end to the neutral it is a high resistance parallel path for whatever unbalanced load there is. The lions share of the unbalanced load goes through the neutral and a small but definite portion of that unbalanced load does flow through the ground rods and earth.

J Tiers
09-08-2012, 09:56 AM
Except the earth is conductive Jerry. It joins the ground rod at the transformer to the ground rod at the house and since both the ground wires are bonded at each end to the neutral it is a high resistance parallel path for whatever unbalanced load there is. The lions share of the unbalanced load goes through the neutral and a small but definite portion of that unbalanced load does flow through the ground rods and earth.

That's a given..... but as you say, it is so small in general as to be almost non-existent..... A "technically true " point without much practical application....

I have had a storm cut my neutral drop but it left the hot wires. Neutral current went through the metallic water piping to adjacent houses. While as much as 8A was measured in the pipe before I canceled all large non-essential electrical loads, the current in earth ground connection was un-measureable with my clamp-on meters. In that case the piping was an alternate conductor to earth, of course.

Taking the earth connection as a net of say 12 ohms (25 ohms is permissible in the US), and the neutral as 100ft of #6 aluminum..... the aluminum will have a resistance of around 0.08 ohm. Current divides according to the inverse relative resistances.

The wire will take roughly 150 x the current, or more. That's more than even "the lion's share"....it seems to include the buzzards and rodents share as well.... ;) Out of 8A, about 50 mA would potentially flow through the earth. I have not measured the size of the service drop neutral conductor here, it's biggish, and could be #4 aluminum, with somewhat less resistance, and so may carry a greater proportion..

And there is no "equipment grounding conductor" in that circuit, all the grounded wires are bonded together at the service box. What you have is the neutral, and the conductor to the ground rod/pipes/etc

KyMike
09-08-2012, 12:35 PM
I have heard that the reason 220V. became the standard in Europe was because of the high cost of copper there compared to the U.S. The higher voltage would reduce the amount of copper needed in the distribution network for an equal amount of power.

Mike

Paul Alciatore
09-08-2012, 01:16 PM
50 hertz makes it a lot easier to build metric clocks.

Metric clocks? Hummm!

100 m-seconds to the m-minute. 100 m-minutes to the m-hour. And 10 m-hours to the day. That divides the day into 100,000 m-seconds or 1,000 m-minutes. I like it. The workday becomes 3 m-hours which is shorter then 8 regular hours. I like it more. 3 m-hours is just about what I sleep anyway so no problem there.

The m-second is somewhat shorter then the regular second (1/100,000 day as opposed to 1/86,400 day). I can live with that.

The m-minute is somewhat longer than the regular minute. That could have been a problem in my youth. "Sit in the corner for ten m-minutes, young man." And my wife may not like it. "See you in ten m-minutes."

And it is going to be hard to divide a year into 100 or 1000 m-days. 500 may be easier, but where is the symmetry in that?

Perhaps we need a binary clock. 64 b-seconds to the b-minute. 64 b-minutes to the b-hour. And 16 b-hours to the day. I really like that. But you still have problems with the days/years thing. Gonna take some really big rockets.

I am going to run for King of the World. My platform will include:

A binary clock.
NO cracks in the sidewalks.
And a Three swipe limit at the checkout. After that, it is free.

Bet'cha I win in a landslide.

mickeyf
09-09-2012, 12:01 AM
Ha! My platform also includes saving tax dollars by getting rid all the stop signs. No one seems to pay attention to them anyway...