Ballast Application Notes

Fluorescent Ballast Technical Support

Ballast Application Notes

Functions of a High-Output Fluorescent (HOF) Ballast:

Rapid-start fluorescent ballasts perform several functions. First, they provide the proper voltage and current to the cathodes at each end of the lamps. Fluorescent lamps are “hot cathode” lamps meaning that they must be warmed before starting. Second, they provide sufficient voltage across the lamp to strike the arc across the length of the lamp. Third, they limit the arc current to the limit specified by the lamp manufacturer so that the lamp performs with proper light output over its expected life.

Allanson’s ballasts include a NON-PCB capacitor for High Power Factor performance. The Thermal Protector inside the ballast limits the operating temperature so that the case does not exceed specified limits in the event of an internal fault. If an internal fault occurs, the protector device opens, and interrupts the power supply.

When the ballast cools to a safe operating temperature, the protector automatically resets (closes) and restores operating power to the ballast. The ballast will continue to recycle until the cause of overheating is corrected.

How to Choose the Proper Ballast:

Please refer to the charts provided and select the appropriate ballast for the length and number of the lamps to be powered. Models 396, 496 and 696 should not be used for 108”, 117″ and 120″ lamps, for these applications use the 4120 Model.

Reliability of HOF Ballasts:

All electrical devices are designed for a given range of operating conditions. Use of the device outside of the intended range will shorten its life expectancy. Excessive heat, moisture, insufficient electrical power supply, lack of grounding or improper installation of lamps, wiring, and ballasts may severely affect service life.


Ballasts generate heat during normal operation and it is necessary to allow heat to dissipate. It is recommended that ballasts be mounted with as much of their surfaces as possible in direct contact with other metal surfaces, which should also be in direct contact with surrounding air.

Several factors affect ballast temperatures and must be considered in all applications:

  1. Supply voltage – Case temperature increases about 1oC for every 1% above rated supply voltage.
  2. Ambient temperature – Case temperature increases from 0.7-0.9 oC for each 1-degree oC increase in ambient temperature.
  3. Fixture mounting – Where the fixture is surface-mounted, there can be as much as a 10oC difference in the ballast temperature, depending on the ceiling material and insulation. A surface-mounted fixture may also operate up to 15oC higher than one that is pendant-mounted.
  4. Fixture design – Variations in numbers of lamps, fixture enclosure, size, material, lenses, and ballast location can amount to a 20 oC temperature differential.

Fluorescent lamp ballasts are designed for application in dry environments protected from moisture and weather. If ballasts are to be used in circumstances exposing them to moisture and weather, special fixtures, enclosures, and/or liquid tight conduits must be used.

Electrical supply:

Line voltage supplied to the ballast must be within +/-3% of nominal voltage rating on the label. Low voltage supply can shorten lamp life or lamps may fail to start. High voltage supply will cause excessive heating, shorten ballast life and reduce system efficiency. Primary power supply wire size and length of run shall be in accordance with appropriate table included in this catalogue.

Secondary Wiring:

For applications where ballasts must be mounted remotely from lamp sockets using extended wire leads, the following guidelines should be followed:

  • For distances up to 15 feet, use #14 wire size
  • For distances up to 25 feet, use #12 wire size

800mA-rated HOF Ballasts have between 3.5 and 4.0 volts filament windings to heat cathodes. It is important that this range be maintained. Too small a wire size or too great a distance will cause improper lamp cathode heating that prematurely destroys both lamp and ballast.


CEC and NEC require that all fixtures and lighting equipment including ballast cases, must be grounded. Failure to properly ground the ballast and fixture combination could result in shock hazard and certain lamps may start to fail. Fluorescent ballasts have painted cases. The paint must be penetrated at the point where a ground connection is made to insure a good connection. This connection can be made by using a star washer in combination with one of the mounting bolts that are used to secure the ballast to the fixture or mounting surface.

Installation guidelines:

1. Wiring – The wiring to and from the ballast must be protected to conform with CEC and NEC. Use wire that is the proper size, voltage rating, and temperature rating. The use of 1000V wire is preferred for applications using 496 size ballasts and larger. All connections should be of the approved method and the wiring connections should have proper physical protection such as permanently affixed and grounded conduit or enclosed wire-way channels.

2. Cold Weather start – All rapid-start ballasts require a starting-aid voltage between the full length of the lamp and a grounded metal surface. The metal of a fluorescent fixture, when grounded is considered a proper surface to act as a starting aid. To assure reliable starting, 40watt lamps should be mounted within one inch of the metal starting aid, especially in double faced signs.

3. Lamp Loading – When using the larger multi-lamp ballasts (4120, 648, 672, and 696 models), be sure to balance the lamp loading evenly. For example, when using a 696AT with four lamps, wire sockets are to be used with 2 lamps on each circuit, not three on one side, one on the other. Similarly with use of two lamps on 4120AT, do not wire sockets for both lamps on one side of the ballast. Failure to follow instructions may significantly shorten the life of the ballast. Additionally, when using lamps of 9 feet and larger, 4120 models must be used. Do not attempt to power 9 or 10 foot lamps with 396, 496 or 696 models.

Service and maintenance:

1. Lamps – Ballast life may be adversely affected by lamps running at or near the end of their service life. Replace lamps at appropriate intervals. Lamps, which are darkened at either end, indicate a lack of (or improper) filament voltage. Confirm that lamps are properly seated in the sockets. Dirt on lamps will cause erratic starting under humid conditions. Dirty lamps should be washed in water and air-dried before reinstallation. Remove lamps which have bent or broken contacts.

2. Wiring and Sockets – Visually inspect all wires and ballast for damaged leads, or for water damage. Visually inspect lamp sockets for spacing, misalignment, breakage, or foreign materials. Defective sockets should be replaced. Confirm that the supply voltage is adequate and that the sign is properly bonded to ground. Check for blown fuses or tripped breakers. If problem continues to exist, run the electrical diagnostic tests as outlined in the Trouble Shooting Procedures that follow.

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