Re: 110, 115, 117, 120 or 125 VAC ???

From: 	Daryl P. Dacko[SMTP:mycrump-at-cris-dot-com]
Sent: 	Saturday, January 03, 1998 5:37 AM
To: 	Tesla List
Subject: 	Re: 110, 115, 117, 120 or 125 VAC ???

At 10:40 PM 1/2/98 -0600, you wrote:
>From: 	Adam[SMTP:absmith-at-tiac-dot-net]
>Sent: 	Friday, January 02, 1998 7:23 PM
>To: 	tesla list
>Subject: 	110, 115, 117, 120 or 125 VAC ???
>I am curious about mains voltage and equipment ratings.  I have 
>transformers, computers, and all kinds of appliances that can't seem to 
>agree on what voltage they would like to be given.   110, 115, 117, 120 
>and 125 seem to be the most popular values, but why so many subtle 
>variations?  Are these different standards for different parts of the 
>country?  My home's service clearly measures 120.0 VAC, but my newest 
>variac is calibrated for 115V input.  That's why I ask.
>Ditto for the 220, 225, 230, 240 VAC appliances.

Lot of factors are involved (we hear this a lot on this list, don't we?).

Old service was rated to 110 VAC, but some of the newer services run over
120 VAC. The idea is to set up the lightly loaded 'new' lines to a pretty
high voltage, and as more and more circuits are added, the IR losses drop
the voltage to the standard 120 VAC. (I'm talking about services that feed
blocks or neighborhoods, not in your house !) 

There are several ways of deriveing 120 VAC too, each of which 
gives you 'standard' 120 VAC, but which differ in the actual voltage 
delivered. This is a lot like the '208 vs 220 vs 240 vs 260' VAC that
you also see on 240 volt appliances.

Just to make it worse, there are a few areas on the country that still
use nonstandard voltages and frequencies.

Standards have now been set, and the official voltages are 120, 240, 480

As the diffrence is only 12% or so between the voltages, most things will
never notice the change. Old equipment might run hotter than you'd like
but the only real worry might be tube filaments and such.   

You can get buck/boost transformers to adjust your voltages if they really
fall out of line, but they tend to be expensive unless you use the old
trick of hooking up an old 2.5, 6 or 12 volt filament transformer to
act as an autotransformer to buck or boost your line voltage.

Most variacs I've looked at have diffrent taps so you can adjust the
line and output voltage ranges, which means they are designed to take
a pretty wide variation in voltage in stride ;'}