TOP 5 POWER QUALITY MYTHS

1) OLD GUIDELINES ARE NOT THE BEST GUIDELINES

Guidelines like the Computer Business Equipment Manufacturers Association Curve (CBEMA, now called the ITIC Curve) and the Federal Information Processing Standards Pub94 (FIPS Pub94) are still frequently cited as being modern power quality guidelines.

The ITIC curve is a generic guideline for characterizing how electronic loads typically respond to power disturbances, while FIPS Pub94 was a standard for powering large mainframe computers.

Contrary to popular belief, the ITIC curve is not used by equipment or power supply designers, and was actually never intended for design purposes. As for the FIPS Pub94, it was last released in 1983, was never revised, and ultimately was withdrawn as a U.S. government standards publication in November 1997. While some of the information in FIPS Pub94 is still relevant, most of it is not and should therefore not be referenced without expert assistance.

2) POWER FACTOR CORRECTION DOES NOT SOLVE ALL POWER QUALITY PROBLEMS

Power factor correction reduces utility demand charges for apparent power (measured as kVA, when it is metered) and lowers magnetizing current to the service entrance. It is not directly related to the solution of power quality problems.

There are however many cases where improperly maintained capacitor banks, old PF correction schemes or poorly designed units have caused significant power quality interactions in buildings.

The best advice for power factor correction is the same as the advice for solving power quality issues; properly understand your problem first. A common solution to power factor problems is to install capacitors; however, the optimum solution can only be found when the root causes for the power factor problems are properly diagnosed. Simply installing capacitors can often magnify problems or introduce new power quality problems to a facility.

Power factor correction is an important part of reducing electrical costs and assisting the utility in providing a more efficient electrical system. If power factor correction is not well designed and maintained, other power quality problems may occur. The electrical system of any facility is not static. Proper monitoring and compatible design will lead to peak efficiency and good power quality.

3) SMALL NEUTRAL TO GROUND VOLTAGES DO NOT INDICATE A POWER QUALITY PROBLEM

Some people confuse the term “common mode noise” with the measurement of a voltage between the neutral and ground wires of their power plug. A small voltage between neutral to ground on a working circuit indicates normal impedance in the wire carrying the neutral current back to the source. In most situations, passive “line isolation” devices and “line conditioners” are not necessary to deal with Neutral to Ground voltages.

4) LOW EARTH RESISTANCE IS NOT MANDATORY FOR ELECTRONIC DEVICES

Many control and measurement device manufacturers recommend independent or isolated grounding rods or systems in order to provide a “low reference earth resistance”. Such recommendations are often contrary to Electrical Codes and do not make operational sense. Bear in mind that a solid connection to earth is not needed for advanced avionics or nautical electronics!

5) UN-INTERRUPT-ABLE POWER SUPPLIES (UPS) DO NOT PROVIDE COMPLETE POWER QUALITY PROTECTION

Not all UPS technologies are the same and not all UPS technologies provide the same level of power quality protection.

In fact, many lower priced UPS systems do not provide any power quality improvement or conditioning at all; they are merely back-up power devices. If you require power quality protection like voltage regulation or surge protection from your UPS, then make sure that the technology is built in to the device.