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.]
I seem to recall somewhere seeing that 117V is the exact calculated
RMS value from some specific regulatory "peak" _nominal_ voltage.
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, 240V.
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.
Other reasons are simply habit - what grandpop used to call it.
Like, you say ToMAYto, and I say ToMAWto, but they're both
red fruit ;-)
--
Chris Lewis,
Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.