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Tom,
It does seem like (and is) a never-ending quest to understand these things.
Maybe I can help. When we refer to 'power-corrected' transformers, we are
refering to transformers which contain a capacitor to compensate for the
transformer's natural inductive characteristics, as seen by the power lines.
These are also called "high power factor" transformers.
Note: "strayfield" (European term) is the regular everyday magnetic type of
transformers we normally use, and they come both power factor uncorrected and
corrected.
The deal is this: uncorrected transformers draw more line current than a
corrected type, because the line must supply power for the neon load
("resistive") AND power to the transformer's uncompensated inductance
("reactive"). The reactive power is returned back to the line [which pisses off
the power company people because almost all losses associated with reactive
power occur on their side of the meter). This is why transformers are rated in
'volt-amps' (VA) rather than 'watts' - VA includes the reactive power.
The bottom line is this: the fuse (or circuit breaker) doesn't care a wit about
whether the power is reactive or resistive - all it knows is AMPS. When we size
fuses, therefore, we need to take into account any reacitve power circulating
through our transformer, if it's uncompensated (not high power factor). The
easiest way to do this is to divide the volt-amp rating, from the transformer's
rating plate, by the nominal line voltage (120) to get amps; add whatever
savety factor you normally use, and select fuses accordingly [amps = va /
volts].
They do sell power factor corrected transformers here (for an extra charge, of
course, which is the primary reason they aren't used in all non-dimming cases),
and are probably worthwhile on large installations to minimize line current (and
are probably required by local code or by power company demands - see comments
above).
Hope this helps.
Regards,
Telford Dorr