Running 6 400w metal halide fixtures. When they start drawing over 16.5 amps they flicker. Unplug 2 of the lights and its ok. Using the 30amp 125v recept

The bulb package should have an average life expectancy printed on it. The typical light bulb is good for roughly 900 hours. At 10 hours a day that's three months. At 24 hours a day it's a little more than a month. If you have 25 bulbs in your house burning an average of three hours each day, a bulb will burn out every twelve days, on average. If you compute the average life of your bulbs and discover it's clearly less than the manufacturer's rated life, then you may have: 1-You may have over-voltage in your house. Occasionally this causes more serious problems. You can get a cheap multimeter at Radio Shack. If the voltage is 125V or higher, talk to the power company about it. 7 or 8 extra volts on a 120V line will cut the bulb life expectancy in half. If it's a slight over-voltage, you can buy special 125V or 130V bulbs, though sometimes they're hard to find.
2-Too high a wattage bulb in too small an enclosed fixture (such as a globe), the heat can't get out--the bulb burns too hot, leading to short bulb life.
3-Recessed lighting fixtures often get covered by attic insulation. This blocks the intended ventilation method--heat can build up around the bulb, causing short bulb life.
4-A vibration problem. Such as, bulbs under a heavily used stairway, on or near an out of balance bathroom or ceiling fan, or near a door that gets slammed, or kids upstairs jumping, etc. You can buy special shock resistant, also called "rough service" bulbs, for this situation, or try one of the new compact screw-in fluorescent bulbs.
Flickering. Intermittent electrical contact can cause flickering. It's like turning the light on-and-off constantly, and will reduce bulb life. It can be caused by a bad light socket, or a poor electrical connection somewhere in the wires leading to the light (most likely right at the fixture). Flickering can cause the bad connection to get hot and possibly start a fire. If you don't locate the cause of the flickering and it affects all or many lights, you could have a bad neutral connection -- a dangerous situation. Another indication of a neutral problem; as larger appliances (washing machines/dish washers) cycle, lights will get quite noticeably brighter or dimmer (minor changes in intensity are normal). If you suspect this problem have either the electric company or an electrician check it out.