The ability of equipment to handle steady state voltage variations varies from equipment to equipment. The steady state voltage variation limits for equipment is usually part of the equipment specifications. The Information Technology Industry Council (ITIC) specifies equipment withstand recommendations for IT equipment according to the ITI Curve (formerly the CBEMA curve). The 1996 ITI Curve specifies that equipment should be able to withstand voltage variations within ± 10% (variations that last longer than 10 seconds).

Voltage regulation standards in North America vary from state to state and utility to utility. The national standard in the U.S.A. is ANSI C84.1. Voltage regulation requirements are defined in two categories:

• Range A is for normal conditions and the required regulation is ± 5% on a 120 volt base at the service entrance (for services above 600 volts, the required regulation is -2.5% to +5%).
• Range B is for short durations or unusual conditions. The allowable range for these conditions is -8.3% to +5.8%. A specific definition of these conditions is not provided.

Other countries have different standards. For example, IEC 61000-2-2 mentions that the normal operational tolerances are ± 10% of the declared voltage. This is the basis of requirements for voltage regulation in EN 50160 for the European Community. EN 50160 requires that voltage regulation be within ± 10% for 95% of the 10 minute samples in a one week period, and that all 10 minute samples be within -15% to +10%, excluding voltage dips.

Other countries have established different limits, based on the characteristics of their distribution systems: Australia, Japan, etc.

Contact Alex McEachern for more information.

Alex McEachern, 1/2004, based in part on work done with Mark McGranaghan