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In a commercial environment emergency lights are required in offices, classrooms, hallways, warehouses, restaurants, etc. They provide light when there is a power failure.
These lights are usually powered by line voltage from a lighting circuit. A power outage will trigger emergency lights to come on. By code, these lights need to stay on for a minimum of 90 minutes.
Emergency light fixtures contain a rechargeable battery and are charged by line voltage. These fixtures have an indicator light showing power is on to the fixture, and a test button that cuts line voltage to the fixture and allows battery power to light the fixture if the battery is working properly. The indicator light and test button are usually the same.
An Emergency Ballast is a rechargeable battery pack that looks like a fluorescent ballast and provides emergency light functions inside of a fluorescent tube fixture. They work the same as emergency lights. When there is a power failure, the emergency ballast will provide power to one or two fluorescent tubes depending on how the ballasts are wired.
A fluorescent tube fixture with an emergency ballast will contain one or more standard ballasts and one emergency ballast. The standard ballast can be rapid start (wired in series) or instant start (wired in parallel).
There are two sources of power to a fluorescent tube fixture with an emergency ballast. These sources of power are usually provided from the same circuit.
Like emergency lights, emergency ballasts have an indicator light and a test button. Sometimes they are the same, sometimes they are separate.
Standard fluorescent ballasts have one wiring diagram. Emergency ballasts have many wiring diagrams depending on the following.
Emergency ballast wiring can be very complex and difficult to troubleshoot. Some electricians really struggle with them and replace the whole fixture rather than try to figure out where the problem is. The standard ballast has a wiring diagram on it, but an emergency ballast has many possible diagrams that are not readily available.
Electrical101 does not recommend troubleshooting these fixtures and replacing ballasts unless you have prior experience with them. If you really want to troubleshoot these fixtures, we recommend replacing both the standard and emergency ballasts and starting from scratch. A diagram will come with the new emergency ballast to help you wire it properly.
Ultimately, it is best to have a qualified electrician troubleshoot and repair these fixtures.