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Why on occasion will QO Circuit Breakers trip when turning on HPS (High Pressure Sodium) lights?

Each HPS fixture has a transformer to generate the high voltage needed to keep an arc going inside the bulb. This transformer draws a huge amount of inrush current when energized. The current can be 10 to 20 times the operating current. This inrush can cause the ``Quick Open`` feature of the QO 15 and 20 amp breakers to trip instantaneously. When all conditions are right, the breaker is seeing the inrush as a short circuit and tripping immediately.
The solutions is to replace the QO115 or the QO120 breakers with QO115HM or QO120HM high magnetic breakers. These are designed just for this application - high inrush lighting circuits.

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