277v Lighting Question

[Looksgoodfromhere]

Multiple 3-lamp fixtures with emergency/regular ballasts and some without emergency ballasts. All together on one 277v multi-wire branch circuit. These fixtures have two hot conductors (unswitched and switched), neutrals and grounds ran to them.

The question here is why utilize switched and unswitched conductors over just one switched hot? Going over potential retrofitting ideas.

The EM ballast in these fixtures are LP600s.

 

[infinity]

The question here is why utilize switched and unswitched conductors over just one switched hot?

When the local light switch turns the fixtures off the EM part of the fixture requires constant power so when that goes off the fixture will know if there is a power failure. They also may have a battery that needs to be charged.

 

[hillbilly1]

Most manufacturers instructions say do not use a second circuit, or if a different circuit is used, it must be the same phase. Had a distribution center where the engineer screwed up and used remote control breakers for the EMS. It was either abandon the breaker control, and install contactors, or pull a 24/7 circuit to the fixtures.

 

[LarryFine]

The question here is why utilize switched and unswitched conductors over just one switched hot?

So the light knows the difference between the circuit losing power and the light being switched off.

 

[hillbilly1]

Maybe I misunderstood the question, you need the unswitched hot to keep the battery charged, and as @LarryFine said, sense loss of power. Lights will come on regardless of switch position.

 

[LarryFine]

Right. The other reason is, without the dual feed, the light would turn on and drain the battery every night.

 

[Looksgoodfromhere]

When the local light switch turns the fixtures off he EM part of the fixture requires constant power so when that goes off the fixture will know if there is a power failure. They also may have a battery that needs to be charged.

 

[Flicker Index]

Most manufacturers instructions say do not use a second circuit, or if a different circuit is used, it must be the same phase. Had a distribution center where the engineer screwed up and used remote control breakers for the EMS. It was either abandon the breaker control, and install contactors, or pull a 24/7 circuit to the fixtures.

You can't use a different circuit. If a fire shorts out the switched circuit and trips that circuit, but the always-on on a different circuit remains on, the fixture will see it as the power was switched off and emergency lighting wouldn't come on.

 

[infinity]

You can't use a different circuit. If a fire shorts out the switched circuit and trips that circuit, but the always-on on a different circuit remains on, the fixture will see it as the power was switched off and emergency lighting wouldn't come on.

The lights are normally switch controlled so is it a requirement if a normal circuit trips that the EM lights automatically come on?

 

[Flicker Index]

The lights are normally switch controlled so is it a requirement if a normal circuit trips that the EM lights automatically come on?

Tripped breaker/lost power is often incidental to other things and may affect one circuit without affecting another. For example, a fire that heats up a conduit can melt a wire within it and cause the switched circuit to short and trip. If the unswitched power is on a different circuit, the ballast doesn't seen an outage. There would then be no light to illuminate the escape route from that fire.

 

[hillbilly1]

You can't use a different circuit. If a fire shorts out the switched circuit and trips that circuit, but the always-on on a different circuit remains on, the fixture will see it as the power was switched off and emergency lighting wouldn't come on.

Actually you can as long as there is more than one lighting circuit in the room. Done all the time in big box stores. Fire has nothing to do with it.