Agreed. (nt)

 

I understand what you are saying. All of the posters here know how to wire a house and how it works. I was splitting hairs over a definition. I don't consider residential wiring to be 2 phase because no 2 phase devices, such as motors, are possible. 120 and 240 motors in residences are single phase.

Consider an actual 2 phase servo. It is fed from two lines with between 10 and 20 kHz which are equal in magnitude and 90 degrees apart in phase. Draw these on a piece of paper and you'll see they are not opposing. Remember 90 degrees is from zero to peak. They thus overlap in leapfrog fashion.

 

Paul

Sorry, I must have miscounted the posts and picked the wrong one. If I remember right you made a point about residential supplies being split phase.

If you are referring to me the posts are numbered in the top right hand corner. You don't need to count to find it.

You were just plain wrong about adding voltages.

Quote:
I was taught that sinusoids of the same frequency add algebraically only when they are in phase,

PRS,

Bill is quite correct. You will need to get a hold of these concepts to progress in electricity.

Yes your teacher was also correct in your quote above.

But

Your teacher was talking about a different situation from Bill or the original poster.

The addition you refer to happens when the voltages are at a single point.

In this case we are talking about the voltage difference between two points.

What Bill is saying is that if two points (not one ) are at the same voltage there is no voltage difference between them.

What your teacher was saying was if two voltage generators are connected to the same point the resultant voltage, at that point, is the algebraic (or vector) sum of the generator voltages.

I am sure your teacher did not say you could add the voltages at opposite terminals of a transformer, algebraically, vectorially or any other way.

 

Studiot, I answered this above, I think. I don't know how to make this any more clear than what I have already said. To emphasize the difference between single phase and two phase I pointed out that all residential motors are single phase be they 120 volt or 240 volt. The latter means you are connecting to the outermost legs of the supply transformer.

The distinction between 2 phase and split phase is important.

By the way, how does the power system in the UK differ from that of the US?

 

By the way, how does the power system in the UK differ from that of the US?

It is a very long time since we had two phase supplies available in the UK. Local supplies are three phases of 240 volts each, 415 interphase voltage, fed from the area grid at several tens of kilovolts, fed in turn from the national grid at 250kilovolts via three pahse transformers.

In the rest of Europe this supply varies between 220v and 240 volts.

UK Domestic users receive a single 240v phase, neutral and normally an earth to their distribution board, normally fused at 100amps.

Industrial / commercial users can receive the three phase.

We rarely use the 415 volts for powerful fixed appliances, although the Europeans use it for fixed water heaters.


Until the 1970s the colours used to be

Line........Red
Neutral....Black
Earth......Green

Three phase was red, blue, yellow for the phases and black for the neutral. These colours were also used for multiway switching of lights. Single way light switching was acheived by using a cable with red and black conductors and designating the black as red when the switch was thrown!

It was then changed, for 'international harmonisation' to

Line........Brown
Neutral....Blue
Earth......Green/yellow
for portable single phase appliances and final wiring of lighting circuits.

Building and fixed wiring became

Line........Red
Neutral....Black
Earth......Green/yellow

The three phase remained unchanged.

Since 2004 we have been 'harmonised' with Europe. This is bureaucratic speak for politicians revising electrical regulations.

Firstly our (all European) supply was 'defined' as 230. Plus a fudge factor to allow national supplies to continue at their old levels.

Secondly the black neutral became a phase of a three phase system and blue became neutral for both.

A real safety minefield.

A black can therefore be phase 2 of three phase, neutral, or phase1 in a lighting circuit.
A blue can be neutral or phase2 of three phase.

Full information can be had here

http://www.ultimatehandyman.co.uk/electrical.htm

http://www.gaselec.co.uk/CableCol.pdf

 

Thanks, Studiot, that's very interesting. Why the change to a system having only 240 volts available for the household? That seems rather high for small appliances. Do you know if the per capita electrocution deaths are any higher there than here in the US? Incidently I just learned that Australia uses 50 Hz. I suppose American stuff would work over there if the voltages are the same. What's your power line's frequency?

 

Most of the world, including the UK, uses 50Hz.

Saudi Arabia has the most confused system I have ever seen. In the 1970s they used to buy cable from one country, sockets from another and generating sets from a third. You could look at a socket on the wall, you recognised from home. Except there could be anything from 12 volts DC to 415 volts AC coming out, in any configuration. I used to always carry a voltmeter.

In the UK, we have had between 215 and 240 volts AC, since the days of DC.

Yes this has safety implications, but our earthing regulations have generally been the tightest aound.

Portable tools and lighting are required to be 110 volts on construction sites.

 

The 1970s also brought in 'ring mains' wiring in preference to individually fused spurs.
They are not used in Europe as far as I am aware.

I don't believe you use them in the US?

Of course with only one phase the design of breakers is different from yours and we now use ELCBs for many portable appliances.

 

I did recommend John Panhalt's post#7 to you as exemplary.

He has used the + and - symbols to represent not positive and negative, but the start and and end and therefore the direction of the winding on transformer coils and by implication the direction of the magnetic field and the phasing.

This convention is common in transformer manufacturing circles.

Equipment meant to be used in either the States or England will often ha a power trnasformer with dual primaries, connected in parallel for the increased current rating and lower voltage ratio in US mode and in series for increase voltage ratio in UK mode.
If you parallel connect the wrong ends of these transformers primaries together you get nothing out, so they are marked + and -.

This would be an example of the situation you describe.

 

because no 2 phase devices, such as motors, are possible.

Well they had them in the steel plant my dad worked at. But special generators were used to run them. They were on roll mills if I remember rightly. The generators were run with 240 DC motors so the Hz could be controled and all ran in unison.

I have not read everything in this thread but there is a lot of confusing information so let me confuse it more LOL. In Canada industrial sites use 208-230-460-600 volts. We never had the luck of a 3 phase system for household use which would make for a much more balanced system and smaller services on homes. And 3 phase appliances would last forever. Unless single phased by loss of 1 phase of the 3. In my repair shop we have 208v 3 ph in a star connected 3 transformer arrangement so 130 v is available for lighting. The star is neutral and grounded. I rewind electric motors and other stuff and I see 200 208 220 230 240 320 380 440 460 480 575 and 600 volt motors. In 50 and 60 hz. Fishing boats and others that are built in Europe tend to have 220 380 440 volt on 50 hz We have built a 50 hp 178 to 600 volt adjustable transformer for testing. Its made from a wound rotor slip ring motor and very handy for testing.
Now as for 1 ph 2 phase 3 phase. Tesla experimented with multi/poly phase systems but the 3 phase 60 hz proved to be the best even though lots tried to put him down. My shop has 3 transformers, the primary of each on 1 of the 3 phases and the secondaries connected to give 3 hots and one neutral off the star. I don’t repair pole top trans so I am vague on that but somewhere I have text books on it. Now local residential supplies are fed from one trans hooked to 1 of the 3 phases and hence it is 240/120 v BOTH SINGLE PHASE. That’s why single phase motors have capacitors switches etc to help them start and run. And there are at least 6 or 7 types of single phase motors that come to mind with out thinking too hard. But no one could agree on a world system and that’s why there is such a mish mash of supply systems in the world. It was just by luck that 3 ph was needed near my shop or the local supplier would make you pay dearly to get hooked up. It wasn’t cheap and if we were not a repair shop, they discourage 3 phase services for small users, we would never have got hooked up.
Stew

 

The term "two phase" is misleading. The more universally accepted terms are "split phase," or "split single phase."

 

Terminology matters, I learned something off this thread.

 

The term "two phase" is misleading. The more universally accepted terms are "split phase," or "split single phase."

Well not in Canada at least, 2 phase comes from a generator wound with only A Phase and B phase in the stator or a 2 phase motor can be run off a regular generator with A B C phases but only uses 2. Split phase refers to single phase motors like those on your furnace blower, they have a run winding a start winding and a starting mechanism or relay but no capacitor. They are low torque. Some water pump motors are split phase. And where did you find the term "split single phase"? The residential single phase system here in Canada is refered to by the old timers as the Edison 3 Wire System.
In general I dont completely trust Wikipedia but heres what they have on the subject including some mentions of "the Neutral" and how it works.

http://en.wikipedia.org/wiki/Split_phase

One thing to note near the start of the above referanced article "sometimes incorrectly referred to as "two phase"."

Stew

 

OH another little note if you click on the "two phase" link it takes you to information on what I have been talking about.
Stew

 

why we use the word hot for positive

 

The line is electrically hot if it carries voltage and current. It is a misnomer to refer to it as "positive", though, as AV voltages change polarity 50 or 60 times per second.