When troubleshooting a 400 watt metal halide lighting system you read 120 volts AC in the lamp socket that catalog shows300 volts is the nominal open voltage what would your next step be?

Answer 1

Most HID fixtures have multi taps in the primary winding. Check and make sure that you have the correct voltage applied to the right tap. Also check and make sure that the capacitor is in the circuit. I just worked on a job where the custodian had taken the ballast and everything out of the fixture base and just wired it across the line. I also got 120 volts at the lamp socket.


When checking your voltages a digital meter can give you a phantom reading. If a connection is loose or corroded the digital meter may get enough of a reading to indicate the correct voltage and still not have enough current to do the work needed. You may need to use a solenoid ( wiggins ) meter to make sure you are not getting a phantom.

Check to see if your socket wires have been shorted, grounded, or broken. If any of these have happened, the voltages will look good at all points except the socket, but the circuit may not trip because of the ballast and or the capacitor depending on the specific damage to the socket wires.