Majority of the industrial and domestic fire accidents occur due to electric short circuits. Hence, it is imperative to monitor the condition of electric power box to facilitate preventive maintenance. The key reasons for power box failure are overheating, tripping, and arcing/sparking at the electric joints. This paper reports on the online condition monitoring of electric power box using the waveguide sensing technology. The critical components of the power box are monitored, namely; Miniature Circuit Breaker (MCB), Solid State Relay (SSR), and Contactor. A pair of wire waveguides is designed to monitor overheating as well as the occurrence of tripping in the MCB. While one waveguide functions as an active ultrasound temperature sensor, the other acts as a passive acoustic emission based arcing sensor. During the overheating experiments, the ultrasound sensor precisely measures the temperature gradient along multiple points on the sub-components, with a minimum gauge length of 10-15mm. The perturbation caused due to MCB tripping is successfully captured by the passive acoustic emission sensor and the location of tripping is determined. Both the overheating temperature and tripping signature are detected by the waveguide transducer system. This work has potential application in industrial and commercial establishments to ensure improved reliability and workplace safety. © 2021 by ASME