4.4 277 volt lines

Lighting circuits that use 277 volt lines are common for Off-roadway and commercial lighting systems. In some cases at night, the supply voltage may exceed 10% (304.5 volts) over nominal. This is a problem for most multivolt controls rated 105-305 volts. Consult DTL if you are experiencing control failure on 277 volt systems. Best solution is to put a peak reading voltmeter at the luminaire and let it run for a few days. If voltage is ever over 305, it is be the line voltage, not the control at fault. Do not depend on daytime voltage measurements!

DTL has made special controls rated 250-350 VAC specifically for 277 volt lines that run high.