On Thu, 28 Jun 2007 20:24:57 -0000, (Chris
Lewis) wrote:

According to Mark Lloyd :
On Mon, 18 Jun 2007 18:57:11 -0000, (Chris
Lewis) wrote:

Power specifications take into account permissible voltage drop
under load. The permissible voltage drop includes the +/- 5%
tolerance or so permitted at your service panel's 120/240V
and the 5% or so voltage drop permitted over the house wiring
and supply cords.

OK, about the voltage drop and permissible voltage ranges. However
that doesn't seem to explain how you got that specific number (117).
Are you measuring peak voltage somewhere and calculating from that?

The outlets in my house are normally supplying 120V with no load
(other than the kill-a-watt meter). Where is the 117V in that?

Stick a toaster on the line, and you'll see something _other_
than 120V ;-)

[Our house power, according to my reasonably accurate meter,
is 127V. Which makes sense where we live.]


Voltage drop with load. I've made different tests. Usually with that
meter in an outlet, then plugging in a hair dryer and seeing the
voltage change. The amount of voltage drop would vary greatly (usually
in the 1V-5V range) depending on things like amount of load and
distance from panel.

I was wondering why the SPECIFIC value of 117V was mentioned in an
earlier post.

I seem to recall somewhere seeing that 117V is the exact calculated
RMS value from some specific regulatory "peak" _nominal_ voltage.


In college I was taught that peak voltage = 1.414 * RMS voltage. In
that case, 117V RMS would equal 165V peak. The post I responded
mentioned "110 to 120", supposedly referring to the permitted range of
supply voltages. This differs from 165V.

The point being that because of resistive losses and power station
management, it is _allowed_ (by code and power regulations) to vary
a fair bit. This means in practise there's a considerable variation
in the voltage present on a given outlet, moreso when you figure that
many voltmeters aren't very accurate on AC RMS voltages either.

BTW, The voltage numbers I remember hearing about are 110V, 115V,
117V, 118V, 120V, 120V and 220V, 230V, 235V, 240, 250V.


For some unknown reason, 250V got neglected when I made that list so I
fixed the omission.

Think about them as being dialects of "power speak", all meaning the
same thing in the end.

One of the reasons for that is pragmatic - Eg: motor HP and current draw
are often specified at the lower end of the permitted range, because
that's worst-case for heat generation/ultimate limits on the device.


If the permitted range is still 110V to 130V, the lower end is not
117V.

Other reasons are simply habit - what grandpop used to call it.


Older people do usually refer to "110V" or "220V".

Like, you say ToMAYto, and I say ToMAWto, but they're both
red fruit ;-)

Since the text from , that I responded to got
snipped, here it is below. I was wondering where the specific number
of 117 came from:

IIRC, if you calculate the actual rms voltage, a "110" or "120" volt
line is actually 117v. Of course this is nominal, since it excludes
noise and IR drops.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Never underestimate the power of stupid
people in large groups"