Utilities invest heavily in underground systems in urban areas to keep the streets safer and free of the clutter of overhead wires. While underground systems have many benefits, they are also more expensive and take longer to install and repair than overhead systems and they tend to fail more often. The most common failures are due to transformers, faulty joints, splices and insulation breakdown that can occur due to moisture. An early indicator of an impending failure is the heat signature given off as resistance builds up in joints and splices. Failing insulation as the result of partial discharge also produces heat as current flows through the insulation to ground or phase to phase.
Failures in underground systems can be difficult and expensive to repair. Continuous thermal monitoring in vaults can detect the hot spots along the underground system and provide the utility with an early warning of impending failure. Utilities can take measures such as rerouting power to relieve the strain and avoid an outage until preventive maintenance can be performed.