240V transformer on 277V line?

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rshayes
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Post by rshayes » Fri Oct 12, 2007 12:27 pm

Another alternative is to use a transformer rated for both 50 and 60 hertz. Core heating is mainly determined by the the average voltage times the time of one cycle. A transformer rated for 240 volts at 50 Hz should be able to handle 288 volts at 60 Hz. You would have to be careful to refrain from using it on 277 volts, 50 Hz.

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MrAl
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Post by MrAl » Fri Oct 12, 2007 2:58 pm

Hi again,

I thought you were working with one single transformer you were going
to use at home or something. If i knew you were doing some production
run i would have advised the same as hacklesup did. That is, go out
and find the right transformer for the job and limit your liability, dont
play games with it. The zener or resistor might work, but that just
adds extra complexity and less reliability which you really dont want
with a large number of units. You should also realize that a zener
(unlike a resistor) adds undesirable high frequency harmonics to the line
too.
A fuse is still a good idea, as well as a thermal fuse.
LEDs vs Bulbs, LEDs are winning.

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Lenp
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Post by Lenp » Mon Oct 15, 2007 5:26 pm

For what it's worth, 480/277/240 primary transformere ARE readily available. Get out of the electronic catalogs and go to industrial suppliers.
Many exit lights that are battery backed up use them for the operation of the low voltage lights and the battery charger.

FYI 277 volt lighting is primarily used because more lighting watts (fixtures) can be controlled on a given circuit- breaker/wire switch switch than can be controlled at lower voltages. Remember, conductors,switches and breakers are rated in amps. At a given current, if the voltage goes up, so do the watts, and watts are 'watt' we use and buy!

Mr. Ohm says so!

Len

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