I agree it will draw half the current. Assuming properly sized
conductors such that voltage loss is negligible, why would 6A at 240V
behave any differently than 12A at 120V? In both cases we're drawing 1440W.
Now it's possible that the motor itself could be designed such that it
runs more efficiently at 240V than at 120V. This isn't necessarily the
case here, but if it is it would be due to the motor design, not the
higher voltage as such.
It's true that electricity will follow all possible paths, but the
higher the resistance of a particular path relative to the other paths
the less electricity will flow through it. The safety ground is a
low-resistance path, so most of the electricity will flow through it
rather than through the operator.
Older electric dryers and kitchen ranges using 3-pin plugs generally run
their control circuitry and lights at 120V using the safety ground as a
neutral. Not ideal, but it's not unusual either.
Huh? Voltage is just potential. You need power to do work, and the
amount of power (and thus the amount of work that can be done) is the
same in each case.
Faster startup implies that the mechanical work of spinning up the motor
is done in a shorter amount of time. This means either the motor is
more efficient at 240V or else it's drawing more power. In both cases
this would be due to motor design, not simply higher voltage.
Ok, again, I am no electrical expert but in my coloring book world of
looking at electricity, You have less resistance up to the motor using 240
vs 120. Each of the 2 wires carrying 120 volts is carrying 1/2 the load up
to the motor than the single wire in a 120 volt application.
There is a direction to the flow in AC. It just reverses every 50th or
60th of a second. But at any given instant of time, the current is
flowing in a specific direction. During that instant, one wire in, the
other out. The next 50th/60th of a second, the in wire becomes the out
and the out becomes the in.
Well, Tom... seeing as we're into semantics now (how unusual for this
group) and I quote you:
That is incorrect as a statement. There are those moments when the
direction reverses when nothing flows in any direction at all. (Unless
you want to open that can of worms called power-factors and phase
anomalies where current and voltage are out of step with each other.
But we need a lot of very sharp crayons to explain that to the
OK, I'll give you that one. 8)
It's true that 100 or 120 times per second (50 or 60 cycle) the sine
wave model of current amplitude crosses zero, and with zero current,
there can be no flow direction.
From the Anti-FAQ, for everyone's edification.
5.1 HOW DO I WIRE MY SHOP?
As my friend Doug, the journeyman cabinetmaker, says: there's only
four things you gotta know about being an electrician:
S--- flows downhill, Payday is on Friday, It may be s--- to you but
its bread and butter to them, and Every asshole is a potential
Oops! That was about plumbers. Forget it. Anyway, Doug is just jealous
of plumbers 'cause they make more money than cabinetmakers, just like
Actually, all the regulars and most of the newbies on the wreck are
electrical experts. That's why any thread on wiring and electricity
gets so many responses. Most of us work with electricity all the time.
After all computers and power tools are electrical, and so's the TV we
watch Norm on. If you want to change the plug on your tablesaw, you
still need to know everything about wiring and amps and volts and
watts and volt-amps and wire gauges and phases and power factors and
impedance and resistance and plug configurations and panel sizes and
capacitors and motors and switches and electrical codes.
But that's OK, don't be afraid. You can trust any wiring and
electrical advice from anybody on the wreck, apply it and be
absolutely sure that it will meet code and be perfectly safe. No point
in getting ripped off by electricians or consulting an inspector. Just
ask away on the group and you can be sure of getting a whole lot of
accurate and consistent responses, just like when you ask any math
question of all the rocket scientists on the wreck.
Well, if we also bring relativity and quantum mechanics into this
discussion, it would be fair to say that at any given time the current
might be flowing in any direction you'd care to choose, and what's
more, we have no way of telling so!
The best argument against democracy is a five-minute conversation
with the average voter. (Winston Churchill)
To have zero volts and some current - all it takes is phase shift.
Phase angle between voltage and current is well known.
Eli the Ice Man
Voltage leads current in inductive (E L I ) L is inductive
ICE Current leads voltage in a capacitive circuit.
So if you attach a motor to the AC lines - The voltage will
go to zero before current does......
Larry W wrote:
On 09/01/2009 01:37 PM, email@example.com wrote:
You forgot the whole "divided by resistance" part. and Potential
divided by resistance is current.
P=(V^2)/R = V*I
As Tom Veatch indicated, in the typical case when you rewire the motor
for 240V you are also increasing the resistance so that the final power
ends up the same.
Again...why would this be the case? The available electrical power of a
motor drawing 6A at 240V is exactly the same as one drawing 12A at 120V.
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