Monday, April 4, 2011

ITIC Curve is a modified version of the CBEMA power acceptability curve, but the concept remains the same. It was developed by a working group of the CBEMA, which later changed its name to the Information Technology Industry Council (ITI) in 1994. In addition, the ITIC curve was created in collaboration with EPRI's Power Electronics Application Center (PEAC). The intent was to derive a curve that can better reflect the performance of typical single-phase, 120 V, 60 Hz computers and their peripherals, and other information technology items like fax machines, copiers and point-of-sales terminals.

The ITIC curve has been applied to general power quality evaluation, even though it was primarily developed for 120 V computer equipment just like the CBEMA curve. Also, it is used as a reference to define the withstand capability of various loads and devices for protection from power quality problems. This is because the curve is generally applicable to other equipment containing solid-state devices aside from being specifically applicable to computer-type equipment. However, one should be careful and should keep in mind that the ITIC curve is not intended to reflect the performance of ALL electronic-based equipment. There are too many variables - power loading, nominal operating voltage level, and process complexity, to try to apply a one-size-fits-all ITIC curve.
ITIC Curve
ITIC Curve
Compared to the old CBEMA curve, the ITIC curve has an expanded acceptable power area or operating region for the portions of ΔV t plane. Moreover, the instrumentation to check compliance with the curve appears to be easier to design because of the simplified way the acceptable region is represented.
ITIC and CBEMA Curves
ITIC and "Old" CBEMA Curves

A summary of the ITI (CBEMA) Curve in an Application Note from ITI follows:


The ITI (CBEMA) Curve and the Application Note illustrate an AC input voltage envelope, which typically can be tolerated by most Information Technology Equipment (ITE). It is not intended to serve as a design specification for products or AC distribution systems. The ITIC Curve describes both steady-state and transitory conditions.


The ITIC Curve and the Application Note are applicable to 120 V nominal voltages obtained from 120 V, 208Y/120 V and 120/240 V 60 Hz systems. Other nominal voltages and frequencies are not specifically considered and it is the responsibility of the user to determine the applicability of these documents for such conditions.


A brief description of the individual conditions that are considered in the ITIC curve is provided in this section. The term nominal voltage shall mean an ideal condition of 120 V (RMS), 60 Hz. All conditions are assumed to be mutually exclusive at any point in time, and with the exception of steady-state tolerances, are presumed to commence from the nominal voltage. The timing between transients is assumed to be such that the ITE returns to equilibrium (electrical, mechanical, and thermal) before the next transient begin.

A. Steady-State Tolerances

The steady-state range is ±10% from the nominal voltage. Any voltages in this range may be present for an indefinite period and are a function of the normal loadings and losses in the distribution system.

B. Voltage Swell

This region describes a voltage swell having an RMS amplitude of up to 120% of the RMS nominal voltage, with a duration of up to 0.5 seconds. This transient may occur when large loads are removed from the system or when voltage is supplied from sources other than the electric utility.

C. Low-Frequency Decaying Ringwave

This region describes a decaying ringwave transient which typically results from the connection of power factor correction capacitors to an AC distribution system. The frequency of this transient may range from 200 Hz to 5 kHz, depending upon the resonant frequency of the AC distribution system. The magnitude of the transient is expressed as a percentage of the peak 60 Hz nominal voltage (not the RMS value). The amplitude of the transient varies from 140% for 200 Hz ringwaves to 200% for 5 KHz ringwaves, with a linear increase in amplitude and increasing frequency.

D. High-Frequency Impulse and Ringwave

This region describes the transients that typically occur as a result of lightning strikes. Wave shapes applicable to this transient and general test conditions are described in ANSI/IEEE C62.41-1991. This region of the curve deals with both amplitude and duration (energy), rather than RMS amplitude. The intent is to provide an 80 Joule minimum transient immunity.

E. Voltage Sags

Two different RMS voltage sags are described. Generally, these transients result from application of heavy loads, as well as fault conditions, at various points in the AC distribution system. Sags to 80% of nominal are assumed to have a typical duration of up to 10 seconds, and sags to 70% of nominal are assumed to have a duration of up to 0.5 seconds.

F. Dropout

A voltage dropout includes both severe RMS voltage sags and complete interruptions of the applied voltage, followed by immediate re-application of the nominal voltage. The interruption may last up to 20 milliseconds. This transient typically results from the occurrence and subsequent clearing of faults in the AC distribution system.

G. No Damage Region

Events in this region include sags and dropouts which are more severe than those specified in the preceding paragraphs, and continuously applied voltages which are less than the lower limit of the steady-state tolerance range. The normal functional state of the ITE is not typically expected during these conditions, but no damage to the ITE should result.

H. Prohibited Region

This region includes any surge or swells, which exceeds the upper limit of the envelope. If ITE is subjected to such conditions, damage may result.

For a complete copy of the Application Note (Click here)

Dedad, J. (2003). A Curve By Any Other Name Is Still A Curve
Information Technology Industry Council (ITI). (2000). ITI (CBEMA) Application Note 
Kusko, A. and Thompson, M. (2007). Power Quality in Electrical Systems. New York: McGraw-Hill
Kyei, J. (2001). Analysis and Design of Power Acceptability Curves for Industrial Loads. New York: Power Systems Engineering Research Center


Trapp said...

Does anyone know what happened on the ITI Technical page went? Does one need to be an ITIC member to access it? The link in the article to the complete copy of the Application Note does not work.

yepyep said...

Hi Trapp,

Article updated... Thanks for mentioning the problem...

Barracuda Backup Service said...

Thanks for your good website and for sharing your experiences.

Ognjen Gagrica said...


Thanks for sharing this info. I was wondering if ITIC makes sense to be used against events of a grid tied 3-phase PV inverter at 50Hz and utility scale PV plant(1MW)?
Measurements are at 15kV PCC point.

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I am an Electrical Engineer with a Masters Degree in Business Administration. My interest is in Power Quality, Diagnostic Testing and Protective Relaying. I have been working in an electric distribution utility for more than a decade. I handle PQ studies, power system analysis, diagnostic testing, protective relaying and capital budgeting for company projects.