Mod note: Posts that were off topic or confusing were moved to this thread from http://www.doityourself.com/forum/el...anch-240v.html

240v is single phase. Both sides goe from +120v to -120v, out of sync, so the difference is 240.



208 is commercial 3 phase, any 2 sides go from +120 to -120 in 2/3 sync, difference is 208.

 

Not sure what that is supposed to mean. You house is supplied with 240 volts. The 120 volts comes from one leg (not phase) of the 240 and the neutral which is a center tap on the secondary of the supply transformer.

 

Quick question about terminology.

I'm in an area with small towns, classic Norman Rockwell main streets,
brick homes, and early to mid 1900s each little town had their own power company.

For many years, up into at least the 1960s or 1970s, the local power company supplied electric to the residents, which included both 240 service and 120 only service.

What is the correct term for a 120v only service?

If modern +/- 120v service is single phase, then what is 120v only service called?

 

Great. Thanks for the info on the wiring. I think I get the phase thing now:

Residential could be called '2 phase' where two 120V legs are exact inverses (180 degrees) of each other.

Commercial 3 phase is three 120V legs that rather than being exactly inverse, are (merely coincidentally) 120 degrees apart, such that the maximum difference between any two legs is 208 volts (since they are less than 180 degrees apart, the two can never both be at their maximum distance from zero crossing at the same time).

This looks suspiciously like a trigonometry problem.

Sound about right?

 

Well, as I've been reminded, the accurate terminology for a modern 120v/240v system is actually
single phase, as the power rises and falls in sync.

You don't see two phase power in most places, it is an archaic system related to the first AC electric
motors- basically, it allows an antique motor to start without a capacitor.
In modern times, it only seems to have survived in the area around Philadelphia Pa.
Two-phase electric power - Wikipedia, the free encyclopedia

History of Undergrounding Electrical Wires in Center City

 

http://www.doityourself.com/forum/el...anch-240v.html Has a discussion about that.

240V is not +/-120V...it's 240V. Theres no real + or - except in relation to each other, which you could see on an o'scope, but not with a meter, so it's not really correct to mention them with regards to A/C.

Single phase is single phase...period. I think a more descriptive term for typical household 240V would be "split single phase". If you look at 240 or 120 with an o'scope, you'll see a single sine wave thus single phase. The 240 is just center tapped at the transformer so that each of the load ends are 120 IN RELATION TO the center tap.

To kind of get an idea...think of 2 car batteries wired in series. Across both batteries you get 24V, but each battery will only measure 12V. Not exactly the same, just an illustration.

If an old house is wired 120V only...then it would be called 120V single phase service only. If it were the more modern wiring it would be 240/120 single phase. I think that is often listed on home listings and appraisal reports?

 

No it is 240 volts single phase. (Sometimes called split phase.)No. 240 or 480 or greater.

 

What about relation to ground?
Big copper wire running into the Atlantic ocean.

Will that show 240v?


That's why I respectfully disagree.
In relation to ground, it's +/-120v.
Eigenvalue.

Better stated- let's take a volt meter,
drive a steel rod into the center of the earth or drop into the oceans as your ground;
Measure A/C voltage,

US 120v is Hot +120v, neutral 0v and ground 0v.
US 240v is Hot +120v anti-hot -120v and ground 0V
EU 240v is Hot +240v, neutral 0v and ground 0v.

So, European 240v is "true" 240v to ground.
And, US 240v is "relative" it's only 120v to ground, but 240v to the opposite leg.

http://www.doityourself.com/forum/el...ml#post2137432

Better stated -
Let's suppose I'm driving down a rural stretch of the Pennsylvania Turnpike.
My speedometer says 65 mph.
Coming the other way is a Pa State trooper.
His speedometer says 65 mph.
Can he really give me a ticket for doing 130 mph because that is what his radar gun registers?

 

Eh, isn't that EU power- hot is 240v, neutral is 0v, ground is 0v, voltage runs at a single phase?


Isn't EU power 240 volts single phase?
One phase of current goes from 0 volts relative to ground to 240 volts relative to ground?

 

Please look at a transformer diagram. The 120 is a center tap between the two legs. This is why having a solidly connected neutral is important to prevent voltage swings.

 

I have



So, looking at plugs, not diagrams.

What is the voltage between a EU plug, hot and ground?
EU is +240 volts to ground.

What is the voltage between a US 240 plug, either hot, and ground?
US is 240 is +/-120 volts to ground. 240 between.

How fast is a car driving 60 mph down the interstate moving relative to the ground?
Yes, it's moving 120 mph relative to a car doing 60 mph the other way.

 

On a US 240 plug the voltage between a hot and ground or hot to neutral is 120 volts. The 240 is between the two hots.

I do not follow the EU wiring conventions.

 

What? I thought the voltage on a US plug is constantly changing?
It's only 120 volts at the an instant it peaks, right?

Doesn't it change 60 times a second?

So, like, the average voltage is zero?

 

In relation to what? It might, depending on the potential you were measuring against.
Only because the source is also referencing to ground (0 potential). I have no idea what Eigenvalue is? Even after looking at the definition...it just made my brain hurt.
Don't throw in made up terms...what the heck is "anti-hot"? You'd still get shocked since its a difference in potential. Neutral and ground are normally at the same potential unless there is a problem, that's why it's often called safety ground, since its not the normal path for current flow.

I guess that's one way of stating it, but I'm not familiar at all with power generation esp not in the EU.
I do believe that if you have a straight 240V circuit, it will measure 240 from either leg to ground? Not sure about that and I don't have any such circuit to test... Either way, it's because you have a transformer in the circuit. You can buy transformers with multiple taps, 12, 16, 18, 24V....it's all about the reference point.

Which always have a power supply that takes all sorts of voltage from 110-250 and regulate it to the required voltages. Remember the older ones that you had to turn a switch on the back for the voltage range? Most now just auto adjust using electronics.


That's not the way it works, and you know it. Regular radar has to be stationary (AFAIK) though there were/are some systems that can do valid measurements while the LE vehicle is in motion. VASCAR was an early visual system. I believe there are also rolling radars in use today?


Just to add to the confusion....how about an AC voltage riding on a DC level? Yes, that happens. I can't remember the exact equipment, but we had some like that in the Navy. The AC was filtered out for the circuits that only needed the DC and the DC was blocked for those that only used the AC. Didn't mean the AC was at a higher voltage...it was all about the reference point.

Also in the Navy we had an electrical system that was strange, since you couldn't get a true ground (to the ocean I mean, which would fluctuate) without having major corrosion problems. IIRC both sides of a 120V circuit were hot to ground, so that the equipment would continue to function even with battle damage to one leg or the ground wire. Dunno how it was done. I was an electronics tech, not an electricians mate.

Voltage is all about reference point. If you measure a battery on your car to the ground on another car you get zip. Even if you drove a ground rod into the dirt from both cars, it's unlikely you'd read anything unless they were touching (no, I'm not going to test that either..lol).

 

A USA voltage that is opposite in phase to a +120 volt line. T
The measurement use to get 240 volts, when the measurement to ground for either leg is 120v.

 

Back to basics. You asked, "what do you call dada dada ..." and here is the answer.

The correct term for a U.S. service supplying approximately 120 volts AC via two wires to a panel with one live bus bar for its circuit breakers (or fuses) is 120 volt single phase.

The correct term for a U.S. service supplying AC power via three wires to a panel with two live bus bars for its breakers and a bus bar for grounded conductors, where the hot to hot voltage is approximately 240 and the hot to grounded conductor voltage is approximately 120 is 120/240 volt single phase (or 240/120 volt single phase).

The correct term for a service supplying approximately 240 volt AC power via two wires to a panel is 240 volt single phase.

The above services can be and are often taken from 3 phase systems. If all three hot lines from the 3 phase system were supplied to the panel (which has a bus bar for each phase for breakers) then the service would be called a 3 phase service. There are different kinds of 3 phase services, such as 120/208 volt wye, for which I won't go into detail here.

In each service, one of the wires is usually grounded in which case it is officially called the grounded conductor, and informally called the neutral or the return conductor. It, too, is connected to a bus bar in the panel but this bus bar is normally not connected to fuses or breakers.

 

120/240 single phase is common, 120 split-phase/240 single phase is more accurate since it's either/both depending on how the neutral is used.

 

Once you connect your two wire 120 volt branch circuit to the panel (provided 120 volts is available), the 120 volts (single phase) is the same regardless of what kind of service you have or whether the system providing the service to the panel was a 3 phase system.

Same for a two wire 240 volt branch circuit. And same for a 3 wire 120/240 volt circuit (provided 120 and 240 volts using 3 wires is available in the panel and wires that are strictly equipment grounding conductors are not used as circuit wires).

 

Thanks, that is the terminology I was looking for.

Helped to clarify how phase (single-two-three) is about timing, not amplitude.
Basically, 1 beat per minute for single phase, but 3 beats per minute for 3 phase.

Both legs of a 240v service move at the same beat, so they ARE in phase, although they are moving in different directions. Sort of a Fred Astair / Ginger Rodgers thing- in sync, but doing the opposite.


Follow up question -

What is the term to differentiate US 240v power from UK 240v?
(Ignoring 50hz versus 60hz).

UK 240v power is one hot, a neutral and a ground.
UK has 240v between hot and neutral.

US 240v power has two hots and a ground.
US has 240v between the hots.

They are BOTH 240v single phase.
What's the correct term to differentiate between the two systems?

 

Nominal voltage is not measured peak to peak. It is measured Root Mean Squared (RMS) Google that and happy reading.

Also voltages to ground will change depending on your system:
120 volts to ground measured hot to ground on a 120/240 volts single phase system, and 120/208 Wye connected three phase system.
208 volts to ground measured between the high leg of a Delta three phase 120/240 volt system.
277 volts to ground of a 277/480 volt three phase Wye system.
347 volts to ground of a 347/600 volt three phase Wye system.

You can really have any voltage to ground you want depending how a transformer is wired.

 

Police radar measures the speed of the patrol car against the ground and subtracts that from the speed measured against your vehicle moving.

 

Yeah, actually kinda familiar with that.

Took a physical chemistry course once, IIRC, had to derive voltage per cell for a lead acid battery,
extra credit required calculating the electron drift velocity when the battery is engaged.

Back on point -

What is the term to differentiate
UK 240v power, which is 240v from hot to ground,
versus
US 240v power, which is 120v from either hot to ground.

It's not phase, since both power systems work in phase
(although one is 60hz, other is 50hz, but the sine remains the same)

 

UK is normally stated to be a nominal voltage of 220.

 

To make it even more interesting from Wiki...Electrical wiring in the United Kingdom - Wikipedia, the free encyclopedia

Anyway...all electrical standards, supplies, sources, etc are based on what they first started out with and who had the money to start and run the companies (and thus the power to determine standards). Hey, if Edison had had his way, we'd be using DC current and there would be a power station every few miles...lol.

Look at some of the areas of that article. Some UK practices were started during WWII to help with the copper shortage and still in limited legal use today.

Back in the Navy...we were going to use an old re-furbished Army barge for berthing while the ship was in overhaul. Problem was (that they didn't find til it had been acquired) almost all the workshops, lights, convenience receptacles and such were wired for DC! I don't remember the voltage (and I wasn't in the Army) so I can't explain it. Maybe it was designed to run on battery banks for a time? Needless to say, the Yard spent several months rewiring and re-configuring the system. Probably a "cost plus" contract back then, so I doubt they lost money.

 

The only difference between U.S. power and (most) European power of the same voltage from the "point of view" of the light or appliance or tool is the AC frequency. Use the terminology 60 Hz for the U.S. power and 50 Hz for the power in those countries that use that frequency.

There exist 3 phase systems in Europe, too.

Because (most of) Europe does not use 120 volts (give or take), the voltage from "hot" conductor to "grounded conductor" or neutral there is (generally) 240.

The root mean square calculation represents the convention or definition that AC power of X volts delivers the same energy for a given number of amperes as DC power of X volts.

 

Eh?
Don't think so.
IIRC the UK is actually 240v. But, as part of EU, they're technically 230v +/- 5%.


Basically, UK actually kept their 240v system, Germany kept their 220v system,
as the "European Uunion" they just agreed to split the difference at 230v standard.
so that both sides are technically in compliance because their actual voltage is within +10%/-6% of their standard.

 

The point of view of the appliance - perhaps.

The point of view of the user who grabs a metal coffee pot plugged into UK 240v outlet where
wire #1 is 240v hot and wire #2 is neutral and ground;
will be different from the user who grabs a metal coffee pot plugged into US 240v outlet where
wire #1 is 120v hot and wire #2 is 120 hot and is now electrifying the coffee pot.

 

I'm not sure whether in some parts of Europe one of the two current carrying conductors doubles as an equipment grounding conductor and if that were true the power plug must have its prongs arranged so that it fits in the receptacle only one way.

In the U.S. even 120 volt equipment may not have the neutral connected to or touching exposed metal parts.

 

Eh, is that UK, EU or German?

Had a situation with a debtor who had imported equipment,
not sure if it was a dumb operator or inherent incompatibility,
but I do recall problems where italian 240v equipment on US 240v power didn't work.

Heck, my vintage Black and Decker HU-1, drill, IIRC has 2 prong plug.

 

If the Italian 240 equipment did not work on U.S. 240 volt power, then that would have nothing to do with neutral wires connected to exposed metal parts for better or worse. It would have to do with AC frequency, or perhaps incompatible wiring of the plug versus the receptacle if they had more than two prongs/slots, or maybe simply something was broken or loose or defective.

For both nominal AC voltages and actual AC voltages, root mean square values are used.