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You have 240Volt electric water heater.
Lower thermostat is set as low as it can go at 77.
But you want water temperature set to 66?
First thing to remember is that water heater thermostat settings are approximate since they read temperatures through the steel tank wall.
Second thing is that thermostats for electric water heater are generic, and are not made for lower temperature range settings. This is probably since most people complain that water is not hot enough.
I'm looking at a generic lower thermostat from Lowes right now. The low temperature setting is 90 degrees F.
Looking at some older thermostats from a drawer right now: one does not have a lower temperature mark, the other is a Reliance with low temp of 95, the old craftmaster goes down to 80.
So I don't even have a thermostat that goes as low as the one you have, except for gas water heater thermostats that traditionally can be set to 50 degrees for vacation mode to prevent freezing.
More thermostats can be seen on following link:
http://waterheatertimer.org/How-to-adjust-temperature-on-water-heater.html