[geeks] D'OH!

[Greg A. Woods]

[ 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.

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.

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.

FYI the single-phase three-wire 120/240VAC system used in North America
is sometimes called the "Edison System".

-- 
								Greg A. Woods

+1 416 218-0098;  <gwoods at acm.org>;  <g.a.woods at ieee.org>;  <woods at robohack.ca>
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