304 Percentage Timer

About the 304 Percentage Timer from the Automatic Timing and Controls division of Marsh Bellofram Corporation:

Easily the most rugged and dependable of industrial percentage timers, the ATC 304 incorporates heavy-duty contacts that are capable of switching loads as large as 4.6 KW directly.

LARGE CONTACTS: Self-cleaning silver contacts are 3/8 inch in diameter, larger than in any other make of percentage timer. They easily provide 1,000,000 operations at the full rated load of 25 A (non plug-in models).

RUGGED AND TROUBLE-FREE: Every component of the 304 has been refined and improved over the years to provide dependable operation for at least 3,000,000 cycles. Its classic simplicity of design makes it virtually trouble-free.

CONVENIENT ADJUSTMENT: Graduated in easily read 1% increments, the 304 provides continuous adjustment of on time between 5 and 95%. It also switches the load off continuously when the pointer is set below 3%; and on continuously, when the pointer is set above 98%.

TYPICAL APPLICATIONS: Ideal for controlling wattage input to electrically heated equipment, the 304 non-plug-in models can pulse loads up to 4.6 KW directly through the SPST load switch; the plug-in models can switch up to 2.3 KW loads directly.
The 304 can be used with other types of electrical equipment to control the ratio of on time and off time in a fixed time cycle. In many types of ratio and cascade control systems, the 304 provides rate-of-rise set point drive control; special dial calibrations are available for this application.



  • Classic design
  • Convenient, continuous adjustment.
  • Available in choice of 15, 30, and 60 sec. time cycles. 60 Hz.
  • 3/8″ self cleaning silver contacts.