# [geeks] D'OH!

Jim Carver jcarver at ipns.com
Sat Feb 2 22:46:24 CST 2002

```"Greg A. Woods" wrote:
>
> [ On Saturday, February 2, 2002 at 16:52:12 (+1100), Scott Howard wrote: ]
> > Subject: Re: [geeks] D'OH!
> >
> > Or 230 volts, or 240 Volts.
>
> The differences are usually a matter of resistance.  :-)
>
> The Canadian Electrical Code specifies 120, 208, 240, 227, 347, 416,
> 480, and 600 volts as the divisors to be used when calculating the
> currents that will result from loads expressed in watts (or VA) for
> low-voltage circuits.

In the U.S and I suspect Canada as well, these are ideal values and are
used for all calculations. On the grid these values are allowed a
deviation of, "+" or "-" 5%.

>
> If I'm not mistaken those are the maximum voltages (that certainly makes
> engineering sense -- i.e. to calculate ampacity with maximum voltages!).
>
> The CEC rules also specify a maximum voltage drop of 5% from the
> consumer service entrance to the point of utilisation.  In-premises
> feeder circuts are limited to 3% drop.  Somewhere else there's a rule
> about the allowable drop for the service feeder line.  I think if you
> add it all up it means that appliances and lighting equipment must be
> designed to operate satisfactorily with supply voltages in the range of
> 110-120VAC, or 220-240VAC.

Most modern electronics as well as most small appliances can tolerate a
deviation "+" or "-" 10%. The most critical value is frequency. It's
been a while since I worked in a system control center, but if memory
serves me, a deviation of 2 cycles was a major event, requiring a ton
of paper work to the North American Electric Reliability Council known
as NERC, www.nerc.com, if you didn't get frequency back to normal within
10 minutes.

> As a result people have been referring to the voltage ratings as 220,
> 230, and 240, even though it's all based on the same engineering.
>
> However you'll also find 4-wire three-phase 120/208VAC systems in use in
> various places around the world (though primarily in North America of
> course where 120VAC lighting equipment is used and thus 120VAC will be
> needed in conjunction with three-pase power for larger motors and such),
> and as a result some "240VAC" equipment will work just fine with 208VAC
> too.

A lot of large office building operate on on a 120/208 "Y" system these
days. The flouresent lights operating on 208, as well as water heaters,