OVERVOLTAGE TO HOMES CAN CAUSE DAMAGE AND FIRE
Home owners should monitor voltage & seek protection
Incoming overvoltage to points-of service by utility companies is defined as: voltage greater than the legal limit. Overvo
ltage can cause electrical equipment and appliances to overheat, fail prematurely, and result in fire. It can occur anywhere, anytime, without warning.The maximum allowable voltage limit mandated by governmental authorities is: five percent greater than the nominal voltage. The Overvoltage (or undervoltage) cannot be prevented at all times by utilities, and most manufacturers do not provide protection in their equipment. Therefore, home owners are advised to seek their own appropriate protection. Low cost, user friendly, voltage monitors (see photo above) are available to help home owners and service personnel detect overvoltage. Guidance on how to proceed with remedial action, including various recommended protection devices, is provided by a web-based service at www.warrenhvac.com/powerwatch nominal voltage for most homes is 240/120 volts. Therefore, the maximum allowable voltage is 253/126 volts, which is the design limit of most residential heating and air conditioning equipment.
Why Utilities Cannot Control Voltage At All Times
Voltage everywhere within a utility electrical distribution system is constantly varying in proportion to the system’s electrical load demands. Loads are impossible to accurately predict; therefore, voltages are also. In an attempt to stay within the legal limit at all points-of-service, voltages are continuously readjusted (regulated) by utility devices which are installed only at representative points in the system.
Due to cost constraints, voltage regulation devices are not provided at the individual points-of-service. Therefore, only approximate control is provided to the end user. This problem and others such as utility equipment breakdown, inadequate design, or grid operator error, make it impossible to maintain legal voltage to all users at all times.
It is most difficult to control the voltage using this approximation method when the collective demand load increases beyond normal. This typically occurs during extreme weather conditions such as heat waves or severe cold snaps which cause distribution systems to be overloaded and stressed. Utility equipment breakdowns and tripping off of utility overload safety devices cause sudden mass decreases in collective loads on parts of the system, which cause voltages to shoot up on other parts of the system that remain on line. Overvoltage is typically not observed at the points-of-use because there are no voltage monitoring or recording devices in homes. In many cases, by the time service personnel arrive at the scene to diagnose the problem, the voltage has returned to normal leaving no direct evidence of prior overvoltage. Damaged equipment or blown fuses are often replaced without knowing the cause; and the problem may occur again unless protected against.
The Air Conditioning Heating and Refrigeration Institute states: “It must be recognized that . . . there will be infrequent and limited periods when sustained voltages outside [legal] limits will occur. Electrical equipment may not operate under these conditions, and protective devices [if installed] may operate to protect the equipment.”
Three Main Types of Overvoltage and Remedies for Each
A. Extreme overvoltage surges of short duration (one second or less). Surge protection devices are available to protect an entire house or individual equipment. Whole-house surge protectors are available from many utility companies for additional charges. For less cost, many smaller individual equipment surge protectors commonly used for computers and other sensitive equipment are available on the market. Consumers must be cautioned that surge protectors do not protect against types B & C overvoltages (below); and, in fact, certain types of surge protectors can overheat and catch fire if type A or B overvoltage is present.
B. Moderate overvoltage with extended duration (minutes, hours, or days) is mostly due to poor utility voltage regulation. Low cost in-home overvoltage sensing and cut-out devices are available on the market that interrupt power to selected equipment when overvoltage (or undervoltage) is present, and restores power when the voltage returns to normal. The cost for whole-house protection of this type is higher. More expensive devices are available to regulate voltage within legal limits without power interruption. These are used in cases where constant power is critical.
C. Chronic overvoltage with permanent duration is due to inadequate utility distribution design. It can be mitigated with properly sized step-down transformers used in addition to cut-out or regulation devices as described in type B overvoltage.
Many Utility companies provide surge protection devices for Type A overvoltage for an installation fee and added monthly fee; or less costly commercial surge protection devices can be used. However surge protectors do not protect against Types B or C overvoltage. Therefore surge protectors should always be used in conjunction with all Type B or C protective devices.
For more information visit www.warrenhvac.com/powerwatch