What causes poor power quality?

There are a number of causes for poor power quality, including, high-voltage, low-voltage, no voltage, electrical noise, impulses, or a combination of these. In addition, research shows that many power quality problems are due to improper ground connections.

Commonly used terms:

High-voltage  |  Low-voltage  |  No voltage  |  Electrical noise  |  Impulses

High-voltage is any voltage exceeding 110% of what is known as nominal voltage: 120, 208, 240, 277, 480 - depending on the application.

Momentary occurrences of high voltage are known as voltage swells and could occur as a result of a sudden decrease in electrical load. A loose neutral connection, or faulty wiring on a 120-volt circuit can allow a voltage swell to damage electronic equipment. Equipment operating at 240-volts such as air conditioners, water heaters, ranges, ovens, etc., are not typically affected by voltage swells.

Low-voltage is any voltage less than 90% of normal.

Momentary occurrences of low voltage are known as voltage sags and can occur as a result of an overloaded electrical system, either on the utility side, or on the internal wiring of the customer's home or business. Electrical faults can cause sags on adjacent circuits or feeders.

The start-up of large motorized devices such as A/C systems or pumps can pull voltage down to where electronic device operation is affected. Many energy efficient heat pumps require large amounts of electrical current to start unless a "soft-start" kit has been installed.

No voltage is a complete loss of power that can last from milliseconds to several hours. Momentary interruptions usually last less than one minute.

Electrical noise or Electro-magnetic disturbances on a wiring system can be caused by improper wiring and grounding, poor internal or external connections, improper shielding, large motors, or the use of arc-type equipment such as welders. Symptoms of these problems for sensitive electronic equipment include audible or visual distortion, erratic data problems or system error messages.

Impulses, known as transient surges, or voltage spikes, are the most common cause of damage to electronic devices and other sensitive equipment. These impulses can be hundreds of volts above normal, but last only millionths of a second. Transient surges are what surge protection devices are designed to arrest or minimize.

If you believe that you're having a power quality problem, the first step is to diagnose your problem.

For example, if your power goes off for 1-2 seconds at random intervals, or during a thunderstorm, that would be classified as a momentary outage, i.e. blinking clock syndrome. This is usually caused by utility circuit breakers opening to clear a temporary fault or short circuit in the power lines. The fault could have occurred due to lightning, high winds, animal or automobile contact with power equipment. If the fault is temporary, the automatic line circuit breakers will re-energize the power line to restore normal service. These line circuit breakers help prevent damage to power lines and equipment which could cause long term outages.

A safeguard against momentary outages, especially if computers might be affected, is the installation of an uninterruptible power supply (UPS), or a stand-by power supply (SPS) unit.

SPS units are the least expensive and feature an electronic switch that transfers the load to a battery upon the loss of regular power. The switch occurs faster than a computer can react and provides power from 8 to 15 minutes, allowing ample time to close down critical programs. These units cost as little as $80, and would be a good investment towards the protection of your computer data.

However, there may be more to the problem than just a power loss. Whatever caused the momentary outage (such as lightning) could also end up causing damage to the customer's equipment. "The power went off, and when it came back on, my computer was damaged!" The real problem was the incident that caused the line circuit breaker to momentarily trip and not the power going off and on.

Protection Against Surges

Warning – a nearby lightning strike could induce a high-voltage surge on your building's interior wiring, bypassing the primary unit at the main service. In this case, the individual plug-in units serve as the primary protector, so a high quality plug-in unit is needed. These units also come with multi-port protection, so that the phone line or video cables going to the sensitive electronic devices could be protected. Phone lines and video cables transmit a large percentage of the surges that can cause sensitive electronic equipment damage.