Storms have the potential to inflict massive damage on electrical wiring systems. Superstorm Sandy illustrated the devastating impact that wind, snow, ice, and flooding can have and the pervasive damage extreme weather can inflict on to infrastructure. The technologies, materials, and practices chosen to rebuild with should benefit from the lessons learned. Wire and cable can play an important role in hardening the electrical system for future storms.
The reliable delivery of electricity requires that every foot of wire and cable along the path—from the transmission line to the wire behind the outlet—be valued at initial purchase cost, as well as for its ability to withstand damage from storms. Homeowners, commercial and industrial business owners, and utilities will incur significant costs as they rebuild their wire and cable networks. The design of replacement circuits should ensure they are located out of harm’s way when possible and buried underground when appropriate. Furthermore, the materials selected should be the most rugged available and suitable for wet locations.
Install Wire and Cable Solutions that Are More Resistant to Storm Damage
In the rebuilding effort following Sandy, the question of how to rebuild existing circuits and what cables to install are key considerations, arguably the most important considerations from a cost perspective.
Many cable constructions can withstand storm damage, such as submersion, as well as mechanical loads and impact. Installing wire and cable that have specific performance characteristics (e.g., water-resistant or ruggedized) as well as utilizing installation methods that reduce exposure to the elements (e.g., relocation, undergrounding, redundancy) can improve an electrical system’s protection from storm damage.
Impact of Flooding
Much of Sandy’s damage to cables occurred because the flooded wiring was not designed to withstand submersion in water. In the low-lying neighborhoods of New York City, for example, many residential basements were flooded, thus damaging the residence’s electrical system and leaving occupants stuck in the cold and dark.
The problem worsened when electrical equipment had to be inspected before the power could be turned back on. The reason: NM-B conductors, commonly used in residential wiring, are rated for dry applications only. After being exposed to water, they are subject to corrosion and may become a shock hazard.
The answer is to use robust wet-rated cables indoors in any area that can be exposed to flood waters. The National Electrical Code ®( NEC ®) defines “wet” locations in Article 100: “...installations underground or in concrete slabs or masonry in direct contact with the earth, and locations subject to saturation with water or other liquids, such as vehicle washing areas, and locations exposed to weather and unprotected.” Wet locations require moisture-resistant, wet-rated cables.
The Impact of Wind
When replacing pole-mounted transmission and distribution circuits in the wake of Sandy, serious consideration should be given to underground installation, especially for critical distribution lines and those lines that have histories of weather-related disruptions.
Underground installation can reduce outages related to external factors such as wind, downed trees, and flying debris. Reducing exposure to these threats has the potential to significantly reduce customer interruptions and outages. The relative costs of underground and overhead options can vary substantially for individual projects, making generic value-to-cost ratios of very limited use.
Key Technologies, Applications, and Products
The key technologies discussed below can be implemented in many application areas: high-voltage transmission, and medium- and low-voltage distribution in industrial, commercial, and residential installations.
Transmission and Distribution
High-Voltage Underground Transmission
When upgrading line capacity, storm-hardening existing lines, or installing new lines, installers can benefit from the use of underground high voltage cable systems. Available from sub-transmission voltages at 69kV all the way to extra-high voltage levels of 345kV and beyond, cables using extruded dielectric insulation have been used in North America for decades. These highly engineered systems have a history of very high reliability, minimal maintenance, and they are largely immune to high winds and flooding.
Underground power distribution cable systems at voltages up to 46kV can use a variety of cable constructions that are suitable for direct burial and submersible installations. State-of-the-art cables include moisture-resistant conductors, water and tree retardant insulation, and weather-proof shielding and jacketing options. Combined with the right accessories, transformers, and switchgear, main feeders converted to underground cable systems will provide a major benefit to your infrastructure.
There are also better alternatives to standard overhead lines. Covered aerial medium-voltage (CAMV) systems can greatly improve the reliability and reduce the vulnerability of overhead distribution during major weather events. Tree area, narrow right of way, coastal, and multiple circuit installations all benefit from CAMV’s compact, long-span designs, and ability to operate through intermittent tree contact.
Cable-in-conduit products provide installers with a conductor of choice already installed in robust plastic conduit on reels ready for direct burial in a trench, allowing for rapid replacement of cable. Additional cable protection and reduced outage times increase reliability for low-voltage and medium-voltage applications from street lights to feeder cables.
Self-Healing 600V UD Cables
Self-healing cables ensure that minor insulation damage to underground 600V cables is limited. Channels between insulation layers hold a sealant that flows into insulation breaks and seals them permanently, preventing the corrosion failures otherwise unavoidable when exposed to moisture. Applications range from service to the home to street light and agricultural applications.
Industrial and Commercial Applications
Using wet-rated products in industrial and commercial applications, especially in critical circuits, can reduce the time and cost of restoring operations after flooding.
Type MC Cables
Use wet-rated products such as jacketed Type MC multi-conductor armored cable indoors where the conductors could be exposed to flood waters. The cable armor also provides crush-resistance in case of building damage. Although the individual conductors within Type MC cables are moisture resistant, an additional level of protection can be added by sealing the open ends of the armor on the cable. This prevents water that may be carrying contaminants from entering the cable assembly. Type MC cable is available in 600V ratings and also in medium-voltage ratings, with conductor sizes from 18 AWG to 2,000 kcmil.
Type TC Cables
Type TC cables are used for power and control applications in industrial installations. These cables are heat-, moisture-, and sunlight-resistant. They provide a moisture-resistant jacket over the conductors to protect them from water damage. Type TC cables are rated for use in wet locations. They can be installed indoors or outdoors, direct buried, in conduit, or in metal cable trays.
Heavy-Wall Insulation for Single Conductors
In single-conductor applications, rugged heavy-wall conductors, such as RHH/RHW-2/USE-2 multi-rated, provide an insulation thickness of 0.045 inches of cross-linked polyethylene (XLPE). These conductors have better resistance to moisture and physical damage, and can withstand severe conditions better than thin-wall insulated conductors such as THHN/THWN (0.015 inches of PVC and a 0.004 inch nylon jacket) and XHHW (0.030 inches of XLPE).
Residential wiring in basements and other vulnerable areas can be made more flood-resistant by substituting a wet-rated product such as UF-B for the commonly used dry-rated NM-B. This may allow power to be restored to residences more quickly without extensive wiring replacement.
Contractors and Building Owners Should Be Prepared for Storm Recovery
Proactively plan for emergency help and product delivery:
- In rebuilding, specify standard manufacturer’s catalog products so warehouse stock is available quickly from sources across the country.
- Be prepared to access help from other parts of the country, and know contractors and manufacturers who are familiar with the type of construction and wire and cable products typically used in your area.
- Proactively make a connection with a reputable wire and cable manufacturer who is knowledgeable about moisture-resistant cables and can provide emergency support for engineering, installation, and repairs related to flood damage.
- Have a recovery plan with distributors and manufactures. Know:
- who to call
- what to order
- how to expedite orders
- Know ahead of time manufacturers and trade associations that can be contacted for the latest recommendations in managing storm damage. For example, NEMA and UL have industry positions on managing flood-damaged electrical products. Familiarize yourself with this information.
Know processes for replacing water-damaged cable:
- Know what equipment and effort will be needed to replace damaged wire and cable.
- If an electrical system has become wet, have it inspected by a qualified electrician before re-energizing it.
- It may be possible to pull new conductors into metallic conduit, but the conduit must be inspected by a qualified person to confirm the conduit’s integrity and that it is free of any foreign objects.