What is most likely the reason for branch circuit breakers to be extremely hot when used with a rig of 208V HMI fixtures?

Branch circuit breakers can become extremely hot when used with a rig of 208V HMI fixtures primarily due to the effects of harmonics. HMI (Hydrargyrum Medium-arc Iodide) fixtures are often used in entertainment lighting and can draw non-linear loads. This means that they can generate harmonics—distortions in the electrical waveform that occur when the load does not draw a current that is proportional to the voltage.

When harmonics are present in the circuit, they can increase the total RMS (Root Mean Square) current, which is what breakers are designed to respond to. This results in higher currents flowing through the circuit, leading to increased heating of the conductors and components, including the branch circuit breaker itself. Overheating can lead to reduced efficiency and potential failure of the circuit breaker.

While overload conditions, loose connections, and incorrect wire gauge can also cause heat in circuit breakers, the specific context of HMI fixtures and their typical operation makes harmonics a more likely culprit in this scenario. Understanding the nature of the loads connected to the circuit is crucial in diagnosing issues such as excessive heat in breakers.