Sounds like they are connected to a supply line that is too small to handle the load.
Wide fluctuations in voltage could be due to another large intermittent load (eg. large motor with high starting current or a furnace of some sort) also connected to this line. When that load comes online the voltage quickly drops & vice versa.
Voltage drop is dependent on the impedence of the circuit. If the lines are too small/long, or the transformer impedence too high, then wide voltage fluctuations will result.
An on-site voltage regulator will not be able to respond fast enough to a large intermittent load, but will work well for slowly increasing/decreasing loads.
Another small possibility is that there are some bad connections in the circuit. They would show themselves up eventually by burning out. A thermal scan of the circuit would also pick those things up.
NMG Price at posting:
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