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The ITIC (CBEMA) Curve was published by Technical Committee of the Information Technology Industry Council (ITIC) formerly known as the Computer & Business Equipment Manufacturers Association (CBEMA)
The curve describe an AC input voltage envelope which can be tolerated by most Information Technology Equipment & it is divided into three zones:
1- Prohibited region: Any surges or swell in this region will result in damage to the IT equipment.
2- No damage region: Voltage sags & dropouts in this region are not expected to damage the IT equipment but will affect the operation.
3- No interruption in function region: Voltage sags & dropouts in this region will not damage the IT equipment or affect the operation.
As a result any voltages in this range +/- 10% from the nominal voltage may be present for an indefinite period and are a function of normal loading and losses in the distribution system, that’s why over & under voltages can be adjusted to +/- 10% from the nominal voltage.
Following the zero volts line, it can be seen that the power supply will operate for 20 milliseconds after AC supply voltage drops to zero, meaning that transfer can be done between two different power sources (break-before make) without interrupting the IT equipment operation if that happened in less than 20 ms which can be typically done by static transfer switch (STS).
