After the Flood

While clean water damages electrical system components, floodwater is especially destructive. Don't assume water-damaged electrical equipment can be simply cleaned and reused.

• By Joseph Weigel
• Oct 01, 2010

In May 2010, Nashville, Tenn. and its surrounding counties were impacted by serious flooding caused by unprecedented weather conditions. This weather event has caused more than two dozen recorded fatalities¹ in Tennessee and, according to the Nashville Planning Department, close to $2 billion² in property damage losses, according to recent estimates.

Weather-related flooding is well documented in inland areas of the United States such as central Tennessee, as well as coastal areas where hurricanes present an annual threat. In addition to the Tennessee flood, numerous other U.S. cities have experienced similar flooding scenarios in 2010.

Water and Electrical Equipment Don't Mix
When electrical equipment in residential, non-residential, and commercial properties becomes submerged or otherwise damaged by the incursion of floodwater, personal safety and facility structures are threatened. As damage assessment begins, the condition of the electrical distribution equipment and controls can be deceiving because of the perception that it may appear to be operable from the outside. Most people understand water and electrical power sources do not coexist well together. Because water is a conductor of electricity, it is very likely that electrical equipment submerged in flooding conditions is damaged. If improperly reactivated, it can result in shock or electrocution hazards, leading to structure fires and causing severe damage to the equipment.

Electrical distribution and control systems are engineered with preventative components that provide protective functions to prevent injuries, electrical fires, and damage to the electrical system. These protective elements are designed to disconnect the supply of electricity if a condition within the system is outside its normal operating conditions. When these components become damaged by water, they often become incapable of providing protection and, as a result, personal injury or facility damage can occur.

Personal Safety Hazards Involving Flood-Damaged Equipment
During or immediately following a flooding event, especially in areas with electrical equipment and controls where standing floodwater has collected or wet conditions are present, hazardous conditions may exist. Electricity may be live, and anyone who makes contact with the water or other wet surfaces could suffer a very serious or fatal shock. Even if the electric utility has disconnected electric power to the facility, it could be reconnected without warning, so an electrocution hazard could always be present. In these scenarios, it is vital to contact a qualified electrical service company or a service representative from the local electric utility before entering a flooded building or home. Qualified electrical personnel can determine whether the electric service has been disconnected and will take steps to prevent it from becoming reconnected unexpectedly.

Those who do not understand the design and construction of electrical systems and components believe flooded electrical equipment will be safe to operate if it is dried out and cleaned up. While it is true some types of water-damaged electrical equipment can be reconditioned, retested, and safely returned to service, this determination can be provided only after a thorough inspection by a qualified electrician or electrical service company.

While clean water damages electrical system components, floodwater is especially destructive because of contaminants and dirt in suspension, which cause corrosion, destroy the integrity of the insulation system, and disable protective functions. If water-damaged equipment is reconnected to its electrical source without proper evaluation and reconditioning or replacement, often it will fail immediately and violently. Even if the equipment doesn't fail immediately and may seem to be operating normally, it often fails sometime later and can cause serious property damage and personal safety hazards to anyone in the vicinity.

Repair or Replace?

• Residential electrical equipment: Generally speaking, the electrical equipment found in homes, such as load centers and circuit breakers (including all arc fault and ground fault circuit interrupters) and related wiring and wiring devices, should be replaced if it has been wet or submerged under water. Non-metallic (NM) cable within walls can be safely reused if it has a nylon or PVC outer jacket and the ends of the wiring runs have not been submerged under water. Older types of residential wiring with a braided cloth or impregnated jacket always must be replaced.
• Non-residential power systems: In non-residential buildings, such as commercial, industrial, and institutional facilities, larger electrical power equipment systems can be reconditioned, retested, and reused in some cases if a thorough evaluation is provided by a qualified electric service company. However, in most cases, reconditioning is either not possible or is not economically feasible, and replacement will be the best option.
• Circuit breakers: Molded case circuit breakers and fuses are not designed to be serviceable; these will always require replacement. Larger power circuit breakers can often be reconditioned, but if these devices are fairly old, the choice to recondition or replace usually will be based on cost. Power circuit breakers with electronic trip units usually require replacement of the electronic elements, as these will be thoroughly damaged by water.
• Transformers: General-purpose transformers commonly called "dry type transformers" must be replaced because water inevitably will damage the insulation properties of the core and coil assemblies. Other large transformer types, usually referred to as cast coil transformers, often can be reconditioned because the epoxy material used to cast the core and coil assemblies inhibits water from entering into the windings. Oil-filled transformers can be evaluated and returned to service after thorough evaluation and testing.
• Distribution panels, switchboards, and switchgear (active and passive): Free-standing and wall-mounted power equipment, such as motor control centers, distribution panels, switchboards, and switchgear, contains both active and passive components. Passive components are made up of the structural metal framework and current-carrying bus structures, while active components consist of circuit breakers and fusible devices. The passive parts of the system usually can be cleaned, tested, and reused; active components should be either replaced or evaluated for reconditioning by a qualified service company.
• Motors: Equipment such as motors, variable frequency drives, and other motor controllers will be severely damaged by water in most cases, and replacement is usually inevitable. This equipment should be thoroughly inspected and evaluated by a qualified service shop before any attempt is made to restart or reuse.
• Automation and control products: Automation and control products, such as programmable logic controllers and machine safeguarding components, are electronic devices that nearly always suffer total damage from water. Because these devices often control large machines, it is vital that their operational integrity is not compromised. Injury or death can result from inadvertent operation of a machine controlled by these types of devices if water has compromised their intended functions.

Leave It to the Professionals
While the guide above points to general scenarios with specific electrical components, water-damaged electrical equipment and controls always should be approached with care to ensure personal and structural safety. Any time flooding conditions are present, owners of facilities and homes should consult a professional electrical service company to determine whether the equipment is safe to operate.

References
1. USA Today (http://www.usatoday.com/weather/floods/2010-05-03-south-storms_N.htm)
2. WATE (http://www.wate.com/Global/story.asp?S=12509981)

This article originally appeared in the October 2010 issue of Occupational Health & Safety.