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CBEMA Guideline
Maximum Allowable Suppression Voltage

What should my surge protector do?

The primary function of a surge protector is to limit let-through voltages to acceptable levels. What is acceptable?

The CBEMA guideline, created by the Computer Business Equipment Manufacturers Association is a realistic, at-the-equipment, maximum allowable voltage that equipment can withstand, without damage or upset.

The Federal Information Processing Standards (FIPS) publication, "Guidelines on Electrical Power for Automatic Data Processing Installations" (FIPS Pub. DU294) includes a susceptibility profile (CBEMA Chart) that’s considered to be a typical design objective for computer hardware designers. The profile shows the relationship between clamp voltage, system voltage and surge duration.

The CBEMA standard essentially defines the threshold computer-based equipment is designed to be able to withstand for short duration, < 200 microseconds , transient voltages if these voltages do not exceed a level that is five times the sine wave peak voltage.

The goal is to protect electrical and electronic equipment connected to the AC power line, limit transient voltage amplitudes to less than the CBEMA guidelines of 5 x E rms x 1.414 volts, for <200us duration impulses. For commercial power lines this works out to be:

Voltage (rms)

Suppression Voltage
120VAC 850V
208VAC 1470V
220VAC 1594V
240VAC 1700V
277VAC 1956V
480VAC 3394V
600VAC 4250V

Conclusion: The CBEMA Standards assert that complex computing equipment will function properly if the transient voltages are limited to less than shown in the above chart.


CBEMA Chart (9575 bytes)

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Last Updated 09/27/10