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Joined: Mar 2007
Posts: 101
Are you sure it is actually dual fed I did a Barnes & Noble awwile back with the same readings 90 volts on the "red" ballast come to find out it as a voltage drop on the lighting circuit thru the emergency ballast.

Joined: Mar 2011
Posts: 98
Originally Posted by Tesla
Yet the EM ballast world is not oriented towards 277 VAC; namely the battery inverter scheme.

Bummer for the commercial EM ballast world since 80-90% of them ARE 277 VAC.......

Joined: Oct 2002
Posts: 830
Mike, I got my voltage readings directly off the switched wire with ballast disconnected. Steve...

Joined: Dec 2001
Posts: 2,498
That sure is an interesting discussion... I always thought the 80% rule merely applied to good design (as in not overloading a circuit right from the beginning) rather than to actual breaker tripping. Interestingly enough, breakers commonly used in the 230V part of the world (B or C trip curve DIN rail components) are designed to hold 100% inifinitely and overload tripping is specified as within less than 1 hour at 145%. The EU low voltage directive (on which to some extent most European electrical codes are based on) also only specify 100% circuits in the form of Ib<=In<=Iz (the load current must not exceed the CB rating which in turn must not exceed the current carrying capacity of the circuit conductors). As it says <= you can perfectly well load a 20 amp circuit to 20 amps, but not 20.01 amps.

From this point of view, a breaker that trips at 80% seems to be very limiting, if not pointless - after all, it could then be called a (current rating*0.8) amps 100% breaker all the same.

Joined: Jul 2004
Posts: 9,788
Likes: 14
When you read the actual technical literature it never really says the breaker won't hold 100%, in fact the trip curve seems to imply it will hold 100% up to an ambient of 40c. They simply reference the NEC rule. This may be lawyers trumping engineers.

Greg Fretwell
Joined: Oct 2002
Posts: 830
Greg, I think I may have found a solution for one of my problems, the egress lighting we discussed on page 2. I should be able to tie the emergency ballast straight into the hot wire (120 volts)so that the fixture stays on all the time. I would just wirenut off the switch leg to the fixture, and have a hot wire going to the test switch and also straight into the emergency ballast which feeds the regular ballast. That way they can turn the rest of the hall lights off at nights and on the weekends, plus it seems I have the right voltage on the hot wire, so that should take care of those fixtures at least. Got to give my wife a little credit here. We was going over the whole scheme again, and she mentioned something to that effect, and the light bulb went off in my head:) I looked at the ballast diagram again, and it should work. Probably the way it was ment to be to start with:)

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