US system is not as inefficient as I once thought

The U.S. Rural Electrification Administration (REA) had as much to do with selecting single phase - 3 wire - 110/220 volts 60 Hz to be the
U.S. Standard as much as anything during the 1930's when farms were being electrified during the Great Depression.
Existing electrical installations were considered (including the European 220 v - 3 phase systems).
The U.S engineers at the time determined that the 3 phase systems could be simplified to single phase 3 wire 110/220 volt which would allow electric motors of up to 10 HP to be used for farm chores, pumping water, etc. (Any AC motor greater than 10 HP is out-of-necessity going to be a 3 phase motor) (Interestingly enough, many AC motors at the 10 hp threshold were of the repulsion start induction run type). Bottom line, the resulting simplification in equipment (one single phase transformer serving perhaps one or two isolated farmhouses with a primary ground return was determined to be the most efficient system. The lower of the two secondary voltages available 110/220 v. was deemed to be important for safety reasons (and compatible with existing US standards). Although 3 phase was desirable, it wasn't considered absolutely necessary for most residential and farm needs that could utilize up to 10 hp motors.
There was much discussion in this newsgroup recently of SWER (Single Wire Earth Return) systems. Presumably, this was not considered in the U.S. due to both safety considerations and the resulting interference that strong ground return currents would have caused to telephone and (in those times) telegraph circuits.
Beachcomber
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Except that earlier systems were almost exclusively delta-connected primaries with two conductors running down roads where 3 phase was not available. The electric poles had a crossmember at the top with insulators supporting a single wire at each end.
Single conductor with ground return didn't seem to become common until the 60s.
--
-Mike

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And depending on what part of the world you're talking about, it isn't 'common' even today. Many rural areas around NY have what I think are wye connected phase running down the country road. One phase on insulators, one grounded neutral that is run above. Grounded neutral high-line seems to serve double duty as a lightning guard wire. Can at pole connected across them on primary, and three-wire output to house/barn.
daestrom
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X-No-Archive: Yes
A 120V incandescent lamp is more efficient than the same wattage 240V lamp within the common residential wattage range(40-100W). For that matter, a 12V lamp is even more efficient. Personally, I think that the higher incandescent lamp efficacy at 120V more than makes up for higher I^2R wiring losses in residential buildings.
We have most of "major" appliances such as dryer, air conditioner, water heater, electric furnance and stove/oven on 240V anyways.
Which voltage do small transformers operate more efficiently? I am talking about 5-15VA mini transformer you'll find in just about all alarm clocks, wallwarts and small electronics.
i.e. 120V to 8V AC 15VA vs 240V to 8V 15VA
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snipped-for-privacy@prontoREMOVETHISmail.com says...

Why? Are you a DimBulb clone?

How do you figure? There *is* IR loss in the wiring.

Sure, to minimize IR loss.

Does it matter? The losses associated with distribution are upstream of the device. The higher the voltage the better. ...until safety becomes an issue. ;-)

--
Keith

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Look at lumen outputs of 120V verses 240V filament lamps which are otherwise identical. The ideal filament lamp voltage for 100W lamp is around 55V, and as you design lamps to run on voltages further away from this figure in either direction, their efficiency drops off.

Sure. Something I really notice about this as a frequent visitor to the US is the voltage drop effects on lighting levels -- it seems rather common that lights noticably change in intensity level when other appliances switch on/off. This is very much rarer in the UK, and even when visible (mostly only rural areas with a long 240V supply line), it happens to a very much less degree here. This would imply to me that the US routinely entertain significantly higher IR losses at least on the supply side to the panel than we normally do in the UK.
--
Andrew Gabriel

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If, as you claim, The ideal filament lamp voltage for 100W lamp is around 55V, then I could put two filaments in series and have a 110V 200W lamp with the same efficiency.
Or I could put two filaments in parallel and have a 55V 200W lamp with the same efficiency.
I could replace the two series filaments with a single one that's twice as long and get the same result.
I could replace the two parallel filaments with a single one that's twice as thick and get the same result.
In fact, I can pick a thickness and length that gives me the same efficiency for any wattage or voltage I choose.
So why, you may ask, are the 12V bubs more efficient than 120W bulbs with the same wattage and physical size?
Because they run hotter filaments.
The low voltge bulb has a shorter, thicker filament which makes it physically stronger.
The shorter, thicker filament can also take more loss from the tungsten boiling off before it burns out.
Light bulb designers know this and raise the filament temperature (which reduces life and boosts efficiency) just enough to balance the longer life from the shorter, thicker filament.
--
Guy Macon, Electronics Engineer & Project Manager. Remember Doc Brown
from the 'Back to the Future' movies? Do you have an "impossible"
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    Guy Macon <http://www.guymacon.com/ writes:

Yes.
Yes.
No.
No.
You are failing to take into account increased need for filament supports (which conduct heat away from the filament), size of bulb and differing convection currents (which effect how much heat is convected away from filament), heat conducted from the filaments by the lead-in wires depending on filament thickness, and that the surface area of the filament (from which light is emitted) doesn't scale linearly with the crossectional area of the filament.
When you do take these into account, that's where the 55V figure comes from. However, it's not a rapid drop when you move away from 55V, but it's getting pretty bad when you get to 240V.

I suggest you patent that, because the lighting industry has been looking for such a method for 100 years. Coiled and coiled-coil filaments is about as good as it's found so far.

It also conducts more heat away from the filament. A 24V lamp would waste less energy conducted away from the filament at its ends because the wire is thinner, and also because it's longer a greater proportion will be away from the ends where this particular loss occurs.
--
Andrew Gabriel

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Excellent point, and one that i missed in my analysis.

...Because I would have two ends sucking out the heat, not four...
That extra factor that I missed changes the answers. It's always good to learn something new. Thanks!
--
Guy Macon, Electronics Engineer & Project Manager. Remember Doc Brown
from the 'Back to the Future' movies? Do you have an "impossible"
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Or you could just switch to compact fluorescent lights like I have and increase your efficiency four fold. :-)
I have often wondered why automotive headlights are so bright considering the fact that such headlights actually use less power than the two 100 watt light bulbs I have in my bathroom. Obviously, the fact that headlights are halogens has something to do with this. But even back in the days when regular incandescent headlights were the industry standard, they still seemed much brighter than regular household lights of equal wattage. I guess the best way to test this assumption would be to take a 12 volt RV light bulb and compare it to a 120 volt (or 240 volt if you're a Brit) light bulb of equal wattage.
Robert
says...

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You'll do even better if you replace the whole thing with low-voltage halogens...

watt
guess
bulb
Automotive headlights are *reflective* (like the little halogen downlights people use these days).
The reflector (mirror) at the rear reflects all light produced by the bulb filament forward - unlike your standard house light which radiates in all directions.
This is the main reason modern "high-efficiency" houses use strategically-located halogen downlights instead of conventional bulb-and-socket lights.
Cameron:-)
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considering
are
Interesting point. I guess this explains why a milliwatt laser can burn your eyes out while a milliwatt light bulb can barely be seen at all. This also explains why the voyager spacecraft can get by with a 21 watt radio transmitter despite being billions of miles away from earth.
Robert
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UK building regs require a proportion of commonly used rooms in a house to be lit with high efficiency lighting. We define that to be at least 40 lumens/W (including control gear losses), and no filament lamp can achieve that.
--
Andrew Gabriel

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Yep!
I have a whole bunch of crap in our house that SHOULD have been designed to run on 240 but plugs along at 120.
Examples: Coffee Maker, Toaster, Microwave Oven, Electric Iron, Hair Dryer, Water Bed Heater, Dishwasher, Clotheswasher.
This stuff draws from 3 to 15 (plus) amps.
Maybe the NEC should start to require at least ONE 240 volt outlet in the kitchen and bath. For safety reason, of course, CHEAP 240 volt GFCIs would come on the market.
Even BUILT IN microwave ovens and dishwashers (that typically heat the water) run on 120 volts. Is that crazy or what?

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remove the urine to answer
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to
would
So exactly *why not* wire the whole house for 240V? Does the NEC permit it?? Then the US would be in line with the rest of the Modern World (sort of.. ;-)
The US plug/sockets I've seen would be quite capable of being safely run at 240V and the wiring insulation would be fine. There could be a chance that someone might plug a 120V appliance in - for a few milliseconds at least - but at the end of the day, 240V certainly makes more sense... from a rank outsiders' view.
Cameron:-)
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Cameron Dorrough wrote:

If you wired the whole house for 240, you would cut the total number of permissible circuits your service panel can provide in half. You would need to add a sub panel to end up with the same number of circuits as would be allowed on a single panel feeding 120 volt circuits. None of the 120 volt devices you already own would work.

No, you can't wire a 120 volt receptacle with 240 volts - you have to use plugs and receptacles listed for 240.

No - see above. 120 and 240 volt receptacles have different physical layouts, so a 120 volt plug won't fit in a 240 volt receptacle, and vice-versa.

Perhaps in a theoretical sense there are some arguments for it making sense - but in a practical vein, it would make no sense to convert the system to all 240 here, just as it would make no sense to convert from 240 to 120-0-120 elsewhere. And you haven't even addressed 50 Hz vs 60 Hz ...

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Not really. "They" might bring a 3 wire circuit into a double box. The box could supply one duplex 240 outlets and one duplex 120 outlet. I haven't seen duplex 240 outlets but they could be made as cheaply as the 120 volt outlet.
The 3 wire circuits would not consume any more panel space than separate 2 wire circuits. When you WANT 120 volt outlets the wiring at the outlet is a little more difficult but the wiring in the panel is a LOT easier: there would only be half the number of WHITE wires to connect - for some reason panels often don't have enough screws for all the white wires and ground wires needed.
I understand that Canada is big on 3 wire circuits running to duplex outlets. If you live there you can cheaply replace any duplex 120 volt outlet with a single 240 volt outlet. Were that to "catch on" you might even see special "duplex" outlets with one each 120 and one each 240 volt. With good design, it may be possible to wire such outlets nearly as quickly as a string of 120 volt duplex outlets.
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John Gilmer wrote:

We're talking different things. If the whole house is wired for 240, there are no 120 circuits. Cameron's post, to which I was replying, spoke of 240 at the receptacles, so the one duplex 240 and one duplex 120 at the box scenario you describe is not germane to that.
HOWEVER - I think my answer may be wrong. UK folks will know - but I just realized I was thinking of interrupting 2 hots with the breaker. In a 240 UK system, does the breaker interrupt both conductors, or is a single pole breaker used? Is one leg hot and the other leg grounded?

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