Re: Balancing the Breaker Box

[Bill]

"RogerN" wrote in message

A person at work was telling about someone that cut their electric bill
approximately in half by balancing their breaker box.

Hogwash!

When I hear people say nonsense like this, I like to challenge them. "Where
did you get that information? Who told you that? Where does it say this?
Etc."

Furthermore it is pretty impossible to "balance" an electrical load in a
home anymore than it already is. Larger loads are 240 volts and already
balanced. This leaves 120 volt lights and 120 volt outlets to balance. Those
mostly used would be kitchen and living room. That's about it!

And just think about this for a moment. With all the technology in our
world, wouldn't electric companies easily be able to design electric meters
which record electric use of any type - balanced or unbalanced? Well they do
and have done so for as long as I can remember. This is the way electric
meters work!

On electric meters...
http://en.wikipedia.org/wiki/Electricity_meter

 

[James Sweet]

Of course the technology is their for the power company to bill for actual
usage, but if they can get away with charging for the high leg amps X volts,
they may choose to do so.

An electrician at work said he knows some people that balanced their breaker
box and their electric bill went down. The power company sent their workers
out to inspect 3 different times. The third time, they asked why the guys
are inspecting their service for the third time. They said it was because
the usage went down so much. The homeowner said that he had the breaker box
load balanced. The power company worker said "Oh, you know about that.".
The homeowner said Yeah. The power company was satisfied and didn't order
any more inspections.

This was supposed to be a true story with actual people known by the person
telling it. This didn't involve anyone selling any kind of product or
service for "free electricity" or anything like that. The person I heard
this from has a brother and cousin that I used to work with and now works at
an Ameren power plant, along with many of the other techs that I used to
work with.

So, I don't know, but it wouldn't cost me much time to ampprobe the lines
and move a couple of breakers if needed to better balance the load, but
maybe (hopefully) it's just BS anyway.

RogerN

If I had a dollar for every time someone started spouting a story like
that in order to look like some sort of "expert"...

It's complete BS, the power company does not charge based on Amps *
Volts (apparent power), they charge by kilowatt-hours (true power), it's
what it says on the bill, and if they were pulling some stunt to defraud
customers there would be a massive lawsuit in no time flat. A kilowatt
is a kilowatt whether it's drawn from one phase, the other, or both, period.

As someone else pointed out, the big loads are 240V anyway so they
already use both legs of the panel and are inherently balanced. The
smaller loads vary so much based on what's being used at the time that
you won't be able to optimize it much beyond what was done when the
house was wired.

 

[Bill]

BTW - If you want to lower your electric bill, there is no "magic bullet".

You need to learn the value of a penny and learn to add. (Pennies saved add
up to dollars, and dollars saved all up to hundreds of dollars!)

Do many things which are small savings on electricity and these combined
will add up. Like replace regular light bulbs with compact fluorescent
bulbs. Many electronic things always use electricity because they are always
"on". Plug these into a power strip and turn the power strip off when not in
use.

An electric water heater can be 30% of an electric bill. Take fewer and
shorter showers. Turn off the water when soaping up, then back on to rinse.
Wash clothes in cold water. Basically use less hot water.

Get new energy saving appliances which use less electricity or less hot
water.

More energy saving tips here...
http://www.energystar.gov

 

[krw]

They could take volts X amps X power factor,

How are you going to measure power factor directly (remember to
include harmonics)?

and the amps could be taken
from the higher leg or they could average the current for each leg. From
the power meter description link from another poster, they read volts from
one leg and amps on the other, if that's the case then they would have to
measure at both legs and average.

"Ather poster" is wrong, too. Power meters measure power directly.
Why mess around with computation?

In my own situation, I have a 240V stove that is off the majority of the
time, an electric dryer that is off the majority of the time, my constant
240V draw would be the water heater. My heat comes from propane and is
supplemented by electric heaters (120V), my AC is 120V, fridge is 120V. So
the big loads are 240V but they are not drawing most of the time. The 120V
loads are present constantly. I know many have 240V heat and air, probably
their major draw. I've never had a problem with any mains kicking out and
if it doesn't save any money their would be no reason to balance unless I
wanted to check when adding a circuit.

Exactly. Somone is blowing smoke up your butt.

 

[daestrom]

They could take volts X amps X power factor, and the amps could be taken
from the higher leg or they could average the current for each leg. From
the power meter description link from another poster, they read volts from
one leg and amps on the other, if that's the case then they would have to
measure at both legs and average.

Not all meters are the same. In the UK they sense the current in one
leg and that is enough because the current in the other leg must be
equal to the first leg (they don't have a neutral over there, all of it
is 240).

Meters used in some 3-phase service also only have one current sensing
coil. To measure all three phases it takes at least two meters,
sometimes three.

But the household meter used in the US has two current sensing coils,
one in each hot leg. They don't sense neutral current because that is
simply the difference between the two hot legs (not accounting for major
ground faults)

The torque developed on the wheel is the product of average current in
the two legs and the voltage sensing coil that measures the 240V between
the two hot legs and the phase angle between them. (this is the old
induction style meter, but the modern digital ones do effectively the
same thing, only in firmware).

In single-leg meters, the current flows through two coils, one
positioned on each side of the voltage sensing coil (one of the current
coils is wound backwards from the other). These are positioned, one on
each side of the potential coil. The interaction of the magnetic fields
from the three coils is what turns the disk.

In a residential meter for the center-tapped 120/240 service, one leg of
the 240 is fed through one current coil and the other leg of the 240
service is fed through the other current coil. The potential coil is
fed from across the two hot legs. The neutral conductor passes straight
through the meter box. So it 'senses' the average of both hot leg currents.

In my own situation, I have a 240V stove that is off the majority of the
time, an electric dryer that is off the majority of the time, my constant
240V draw would be the water heater. My heat comes from propane and is
supplemented by electric heaters (120V), my AC is 120V, fridge is 120V. So
the big loads are 240V but they are not drawing most of the time. The 120V
loads are present constantly. I know many have 240V heat and air, probably
their major draw. I've never had a problem with any mains kicking out and
if it doesn't save any money their would be no reason to balance unless I
wanted to check when adding a circuit.

Despite all the stories out there about "...a friend of mine did
such-and-such and saved" or "the power company knows this but doesn't
want to tell anyone...", it just isn't true. The metering schemes have
been reviewed by state commissions for every public utility in the
country. No way are they all 'in on it'. The simple fact is that the
inventors of the modern kWh meter are smarter than that and tested just
about every conceivable combination of imbalance/balance.

I suppose there's a one-in-a-million chance that the power company
installed the wrong type of meter and is only reading one current leg,
but that isn't very likely. Or that some small mom-and-pop coop utility
thought they would save money using the wrong type of meter, but that
ain't likely either.

daestrom

 

[Bill]

"RogerN" wrote in message

I figured if it were true the folks on here would have heard about it

Oh we have heard all sorts of nonsense like this!

We just understand electricity and know these things are not true.

 

[James Sweet]

They could take volts X amps X power factor, and the amps could be taken
from the higher leg or they could average the current for each leg. From
the power meter description link from another poster, they read volts from
one leg and amps on the other, if that's the case then they would have to
measure at both legs and average.

Sure, they could, just like they could have a little hamster in there
running on a wheel to turn the dials, but they don't. Power meters have
coils on both legs that act on a metal disk causing it to rotate in
response to true power passing through either or both leg. Some newer
meters are electronic and do measure the voltage as well as the current
and power factor, again in both legs. There are some good application
notes on Austria Microsystem's website that describe how their offerings
work. The electronic meters also contain various tamper detection
circuitry that will alert the electric company if suspicious
circumstances are detected.

Magical money saving methods to fool or otherwise alter the response of
a residential power meter all fall into the same bucket as the mythical
100 mpg carburetors, fuel magnets and other pseudoscience bullshit. The
short answer is they don't work, but that doesn't stop countless people
from trying every one of them, and failing, while others swear to have
witnessed fantastic results.

 

[James Sweet]

Understanding electricity has absolutely nothing to do with it,
understanding how the KWH meter works has everything to do with it. Power
for an AC circuit is Volts X Amps X power factor, in that equation you could
use amps from either leg or average the amps from each leg. Of course the
correct way would be to use the current from each leg X the voltage from
each leg X the power factor from each leg. Like I said, it has nothing to
do with understanding electricity but everything to do with how the KWH
meter measures it.

RogerN

Which many in here also understand. I have a couple of old KWH meters
sitting around, I've played with them, they're simple devices, and they
just plain don't work the way you seem to believe they do. Being
mechanical, they don't calculate anything, they simply respond to true
power, regulated by the laws of physics. Both sides of the meter act on
the same disk so the result is additive. Draw through either leg and the
meter turns. Draw through both legs at once and it turns faster. The
disk is directly coupled through a gear set to the dials on the face
which do nothing more than count the number of rotations the disk makes.
Trust me, you can't fool it by shifting loads around. About the only
thing that happens to the accuracy is dried up lubricant and/or aged
mechanical parts which normally results in slowing the meter in the
customer's favor.

 

[Guest]

They could take volts X amps X power factor, and the amps could be taken
from the higher leg or they could average the current for each leg. From
the power meter description link from another poster, they read volts from
one leg and amps on the other, if that's the case then they would have to
measure at both legs and average.

They could "take.. other" but they don't - There will be two current coils
for 120/240V 3 wire and a voltage coil (240V). so that (I1+I2)V is measured.
The torque produced is proportional to the real power. It doesn't matter if
all the load is on one leg, split between legs or all line to line - the
real power will be read correctly independently of the power factor. The
energy is measured by counting disc rotations. Accuracy requirements are
stringent.

Balancing the legs will not affect the meter except that there may be a
marginal decrease in losses in the wiring and this gain will be lost as load
balances change with activities.

James Sweet has it right.

 

[krw]

First, I don't have any specific belief on how KWH meters work, I heard that
they run based on the high leg but evidently that is not the case. However
if that was the case it wouldn't have anything to do with fooling the meter,
it would have to do only with using all the power you are paying for.
Digital electronics is not the only way to calculate, it's just what we are
used to in these times. You can also calculate with analog electronics,
pneumatics, hydraulics, fluidics, and even mechanical. A KWH meter converts
power to torque (or speed?) and counts the revolutions, the result is volts
X amps X power factor X time, a mechanical calculator.

No, the meter measures *power*. As others have been trying to tell
you, the torque (hence RPM) of the disk is proportional to the current
times the voltage in the respective coils. No "calculating" at all
and *certainly* there is no power factor calculated or measured.

Thanks for explaining the operation of the meter, sounds like balancing the
load would only help with the overall KWH capacity of the circuit.

....and reduces the neutral current, if that's important to anyone.

 

[James Sweet]

Good answer Don Kelly, I remember you from other posts, you seem to have a
great foundation on these electrical things. At least you could give an
informative answer that most others could not. James Sweet has the idea
right but seems to think it is magical to use the power you are being
charged for.

RogerN

There only thing magical is the belief that you are somehow being
charged for power that you are not using. The meters work, they are
accurate, the response is not altered by balance. If it is already
accurately measuring your consumption, then how do you propose to alter
the reading without somehow fooling it into an inaccurate reading?

Now it's starting to look like you're simply trolling here.

 

[krw]

Duh! Nobody was talking about magical money saving methods. Only using the
power you are being charged for OR not being charged for power you are not
using. Does that appear as magical to you?

Does to me. Power companies aren't in the business of giving away
energy.

 

[krw]

Big secret here, in a single phase AC circuit, Power= Volts X Amps X Power
factor, multiply by the square root of 3 for a 3 phase circuit.

You have it backwards. Power factor is P/VA. Power factor is a "fudge
factor" that describes the difference between apparent power and real
power. PF is not a physical entity and is not measured directly.

Yes, to my complete suprise there are many others here more ignorant about
it than me. At least I can understand how the high leg current calculates
to more KWH then the average current of the 2 legs, others have suggested
things like magic bullets and free electricity

Right, as you were repeating here.

Torque without friction or other limitations is infinite RPM so how do you
get (hence RPM)?

Torque * RPM = HP The motor (meter disk) is doing work.

Without power factor you are being charged for apparent power, not true
power. Are you claiming that power meters measure apparent power, not true
power?

Again, you have it backwards. PF is the conversion factor not what's
being measured. POWER is being measured. Directly. No conversion
needed.

I think Jim Sweet and others have it right, but I'm surprised how many
others are willing to show their ignorance when it's is obvious they don't
understand the subject.

Honestly, the only one here (ignoring Proteus) that doesn't understand
this, is you.

Perhaps a better explanation here: If you were
using 10 KWH between L1 and neutral, and 5 KWH between L2 and neutral, you
would be using a total of 15KWH.

Wierd way of looking at it, but sure. That's the way the meter is
designed.

From what I heard another electrician
saying, the power company would charge you based on the high leg, in other
words you would be using 15KWH but the power company would charge you for
10KWH (the high leg) X 2 = 20KWH.

The power company would be stealing from you. That's not allowed any
more than you stealing from them. Laws are funny that way.

If this were true, what balancing the
breaker box would do is draw 7.5 KWH from each leg so that you would be
using 15KWH and paying for 15KWH.

It's NOT true, so saying "if it were" is a meaningless exercise.

Sorry for all you electrical engineer
wannabees,

No wannabees here. Well, perhaps you wannabe.

but that is not a magic bullet, getting power you're not paying
for, or anything like that. It would simply be using the power you're being
charged for, there is nothing wrong with that.

Of course it is. It's a promise that cannot be fulfilled. Hucksters
sell this sort of magic pill all the time.

Sorry, I'm not generally trying to be a smart a$$ but the golden rule is to
treat others how you want to be treated. So for those that gave smart a$$
replies I reply back to you as you have replied to my post.

Sorry you feel that way, but what you're posting (and continue to
post) is crap. That's not the way things work, as you've been told
here by *everyone*. Your electrician friends need to go back to
school (and I am being kind).

 

[Dean Hoffman]

I think Jim Sweet and others have it right, but I'm surprised how many
others are willing to show their ignorance when it's is obvious they don't
understand the subject. Perhaps a better explanation here: If you were
using 10 KWH between L1 and neutral, and 5 KWH between L2 and neutral, you
would be using a total of 15KWH. From what I heard another electrician
saying, the power company would charge you based on the high leg, in other
words you would be using 15KWH but the power company would charge you for
10KWH (the high leg) X 2 = 20KWH. If this were true, what balancing the
breaker box would do is draw 7.5 KWH from each leg so that you would be
using 15KWH and paying for 15KWH. Sorry for all you electrical engineer
wannabees, but that is not a magic bullet, getting power you're not paying
for, or anything like that. It would simply be using the power you're being
charged for, there is nothing wrong with that.

Sorry, I'm not generally trying to be a smart a$$ but the golden rule is to
treat others how you want to be treated. So for those that gave smart a$$
replies I reply back to you as you have replied to my post.

RogerN

Several of the guys who answered you are probably EEs. They
don't generally say much about it. Once in a long while, one might
mention something he did in college or something about their
certification. They don't have to brag about it. They'll generally
know by reading each other's writing. They'll know in an instant I'm
not one if the subject is at all technical.
I didn't see much that looked like wise assed remarks. There
wasn't anything close to the flames I've seen other places. People
are just stating facts.
The public service commissions or possibly the states' attorney
generals should be all over this if it was real.
I know scales at farmer's coops are tested for accuracy by the
state. Gas pumps have stickers on them assuring their accuracy. States
have bureaus of weights and measures to make sure things are according
to hoyle. Why would they ignore the utility companies?
What about all the lawyers running around? Think of the money a
lawyer could make from a class action lawsuit if he won against a major
utility. Here's a list of some of the things lawyers have sued for:
http://overlawyered.com/tag/class-actions/
One example there is a lawsuit against the makers of Froot Loops
because they don't contain fruit.

Dean

Not an EE, and I don't play one on TV.

 

[James Sweet]

Well, it was you that told me my calculation using power factor was wrong
but then gave the same formula solved for power factor instead of power. My
education was in electronics technology and we didn't go into the details of
power meters and such, that is why I bring my question here. I don't have a
problem being told that what I heard is not how a power meter works, I have
a problem with those that try to tell me that a meter could not work that
way or if it did then balancing the load would be like stealing electricity.

RogerN

None of us are telling you that meters *could* not work that way, or
that *if they did* work that way you would not be correct. What we are
telling you is that meters *don't* work that way, so speculating what to
do if they did is like speculating if the moon were made of cheese how
best prepare it to eat. We know that it's not, so why worry about what
to do if it is?

Given the way meters *do* work (they accurately measure power used),
getting them to read less (not accurate, false reading) is stealing
power. If the meters were ever behaving in a manner that caused you to
get billed for power you did not actually use, regardless of the load
balance, that would be fraud on the part of the power company. Again,
this is irrelevant outside of this imaginary situation because this is
not how they actually work.

I'm not sure what is so difficult about this concept. There is nothing
to optimize, the rest of the discussion is a hypothetical (imaginary)
situation.

 

[krw]

If Power factor is P/VA then solved for P, P = Power factor X VA.

No, there is a difference between the physical quantities measured and
the conversion factor between them. You can't measure power factor,
only derive it from power and VA.

If you have a given torque on the meter disk, what limits the RPM? Is it
generating a back EMF?

Nothing limits RPM, other than the power measured. The whole idea is
to measure the revolutions.

Well, I don't understand the stuff that's wrong.

There's lots of things a person can save money on or use more efficiently
and it's not illegal even though it is pretty near stealing. One example is
a 20oz soda often costs more than a 2 liter bottle of the same soda.

You're talking nonsense again.

Nobody is selling anything, the guy telling this is not trying to get
business balancing breaker boxes or anything like that. We work at as
electrical techs in a factory repairing automated manufacturing machines,
not wiring or rewiring houses.


Well, it was you that told me my calculation using power factor was wrong
but then gave the same formula solved for power factor instead of power.

I didn't say your calculation was wrong, just that you had the horse
before the cart. You don't measure PF directly. It's the difference
between watts and volt-amps.

My
education was in electronics technology and we didn't go into the details of
power meters and such, that is why I bring my question here. I don't have a
problem being told that what I heard is not how a power meter works, I have
a problem with those that try to tell me that a meter could not work that
way or if it did then balancing the load would be like stealing electricity.

It *would* be stealing. In this case it would be the power company
stealing form the consumer.

 

[Tzortzakakis Dimitrios]

Go back and read over the replies again because nobody (aside from perhaps
one of the trolls) has ever said that is the case. Trying to balance the
breaker box is absolutely not stealing, nor is it magically creating
electricity. The simple fact is that it will have zero measurable effect
on the meter reading.

It was simply stated that since the meter already reads correctly,
anything that did cause it to read slower (which does not include
balancing) would be stealing power because given it already measures
correctly, to get it to run slower without actually using less power would
mean you are using some power that it is not measuring. Again, balancing
your panel will *not* cause this to happen.

The meter, is an electromeechanical integrator. It measures,integration
calculus [from 0 to 2pi]tan (omega * t) dt where omega=2*pi*f (frequency in
HZ=f)
So, it's not to be fooled by trivial methods, like putting all loads to a
high leg, etc. like some poster said, is like the elusive 100mpg carburetor,
or fuel additives that increase mileage, etc.

 

[Guest]

Big secret here, in a single phase AC circuit, Power= Volts X Amps X Power
factor, multiply by the square root of 3 for a 3 phase circuit.


Yes, to my complete suprise there are many others here more ignorant about
it than me. At least I can understand how the high leg current calculates
to more KWH then the average current of the 2 legs, others have suggested
things like magic bullets and free electricity


Torque without friction or other limitations is infinite RPM so how do you
get (hence RPM)?


Without power factor you are being charged for apparent power, not true
power. Are you claiming that power meters measure apparent power, not
true power?


I think Jim Sweet and others have it right, but I'm surprised how many
others are willing to show their ignorance when it's is obvious they don't
understand the subject. Perhaps a better explanation here: If you were
using 10 KWH between L1 and neutral, and 5 KWH between L2 and neutral, you
would be using a total of 15KWH. From what I heard another electrician
saying, the power company would charge you based on the high leg, in other
words you would be using 15KWH but the power company would charge you for
10KWH (the high leg) X 2 = 20KWH. If this were true, what balancing the
breaker box would do is draw 7.5 KWH from each leg so that you would be
using 15KWH and paying for 15KWH. Sorry for all you electrical engineer
wannabees, but that is not a magic bullet, getting power you're not paying
for, or anything like that. It would simply be using the power you're
being charged for, there is nothing wrong with that.

Sorry, I'm not generally trying to be a smart a$$ but the golden rule is
to treat others how you want to be treated. So for those that gave smart
a$$ replies I reply back to you as you have replied to my post.

RogerN

What you heard from the" another electrician" was, purely and simply, BS.
Balancing the load between legs is optimal with respect to losses but
doesn't actually increase the KW capacity (not KWH) of the system. It just
means that you can use the capacity slightly more efficiently.
If you have a load of 15KW on one leg and 0 on the other, you will have more
losses and poorer voltage regulation than if you have 7.5 KW on each leg.
The meter simply measures what you actually use (+ losses on your side of
the meter). Now the high leg metering X2 would be a cute but highly illegal
trick that, along the way, would become apparent and the cost to the
utility in class action suits would be prohibitive. Honesty in metering is
something that is actually practiced.
As to your torque without friction leading to infinite rpm- take a look at
your meter- see those magnets which provide drag proportional to the speed
of the disc? The result is that at any given torque, there will be a speed
at which this torque is balanced by the drag. Adjustments to the meter does
involve the positioning of these magnets.

 

[Guest]

Good answer Don Kelly, I remember you from other posts, you seem to have a
great foundation on these electrical things. At least you could give an
informative answer that most others could not. James Sweet has the idea
right but seems to think it is magical to use the power you are being
charged for.

RogerN

I disagree with you regarding your interpretation of James Sweet's position.
It was quite clear and correct.
Otherwise I would have argued with him.

 

[James Sweet]

So if you have a 100A service I don't understand how having 100A X 120V is
the same power as having 100A drawn from each leg, 100A X 240V. I would
think at any given power factor 100A X 240V is more than 100A X 120V. I
would think balancing the load so that you use 100A from each leg would
increase your KW capacity of the service.

It isn't, that's not what he said. Think in terms of Watts, if you draw
100A at 240V that is twice the wattage as drawing 100A from 120V because
with a 240V 100A load it is drawing 100A from each side. If your loads
are so badly balanced that you are drawing 100A from one side and 20A
from the other and it is a 100A service, you cannot add any more 240V
loads. The capacity is there, but you are already at the max of 100A on
one side. If you can shift some of the load over to the under utilized
side then you will have freed up capacity, but you will not affect the
reading of the meter by doing so. The important part, which is beating a
dead horse at this point is that there is a coil on each leg, and both
coils create torque on the same disk so whether you draw 100A on one
side and 0A on the other, 50A on each side, 10A on one side and 90A on
the other, it doesn't matter, in any of these situations the disk will
see the same torque and turn the same speed, the only thing changing is
which of the two coils supplies more of the total amount of torque. It
doesn't matter if one box of rocks weighs 500 lbs and the other box of
rocks weighs 100 lbs, if both boxes of rocks each weigh 300 lbs, or if
one box weighs 600 lbs and other other is empty, if you put them both on
a scale, it will read 600 lbs either way. Balancing the panel is taking
rocks from one box and placing them in the other, it is not changing the
total number or weight of rocks and will not affect the reading on the
scale.

If meters measure true power then they are measuring VA X Power factor
integrated over time, I was surprised no one took issue with krw stating
that meters just measure true power and not VA X Power factor, since they
are equal, but seems not according to krw. Also as explained with power
producing torque in the disk I didn't understand how it controlled the speed
of the disk unless their was also a drag or friction that controlled the
speed. If you just apply a constant current to a motor the speed varies a
lot according to load, doesn't seem to be useful for a meter unless, as you
explained, there is a controlled drag or friction. If you make a constant
current source and use it to supply a motor, the speed will change to keep
the torque constant. If you have a constant voltage, torque (and current
draw) will change to try to hold the speed constant. I know this varies
according to type of motor, but even induction motors with variable
frequency drives can use volts per hertz. Also stepper motors, though their
speed is controlled by the step rate, they are capable of higher speeds with
higher voltage.

RogerN

Yes they do measure true power, and no, they do not measure VA * PF over
time, they are different. I think what is happening here is the common
failure to differentiate between *equal to* and *equivalent to*. Volts *
Amps * PF is *equivalent* to Watts (true power) but it is not *equal*
to, it is not the same thing. Power can be measured directly, if you
then know any two of the three other variables, Volts, Amps, and PF, you
can calculate the third, but any one can be measured on its own without
knowing any of the others.

Look at it this way, the speedometer in a car indicates vehicle speed in
miles (or kilometers) per hour. This is equivalent to miles traveled
divided by trip time, but it is not the same. Sure you could make a
speedometer that recorded the distance traveled and time the vehicle was
in motion and use that to calculate the speed in MPH and the answer
would be right, but that isn't how real speedometers work. A mechanical
speedometer, not to be confused with the odometer, has no concept of
time or distance, rather it measures speed directly by magnetically
coupled torque acting against a known friction, in this case a spring.
In the same way, a mechanical power meter measures true power by energy
passing through coils, causing a proportional amount of work to induce
torque on the disk which rotates against a known amount of friction. In
either case you have to have a known quantity of friction in order for
the reading to have any meaning. Ignoring real world issues like
insulation breakdown, a mechanical kWH meter doesn't know or care
whether the voltage is 10V or 10,000V, rather it directly measures the
amount of work being done by the power by acting on the disk with a
proportional amount of work.


As for motors, there are many different types of motors, each with their
own characteristics, and the sort of motor in a power meter is unlike
any you're likely to find anywhere else. The reason stepper motors need
higher voltage to achieve higher speeds is that the windings are
inductive and it takes time for the current, and hence the magnetic
field to build up. The faster the motor is turning, the less time you
have per step, so the higher the voltage needs to be in order to create
a magnetic field of a given strength in the time available. Similar
reasons dictate the need to vary the voltage with the frequency of
induction motors.