Low voltage is defined in the UK as being below 1,000 volts, and AFAIK the limit in the USA is 600 volts.
What you are probably refering to, is not low voltage as such, but lower than expected voltage.
This may be caused by overloaded or outdated utility equipment supplying lower than expected voltage, the legal limits vary in different countries, but are often plus or minus 5 or 10%.
In addition, voltage is lost in the consumers installation due to the resistance of the wires. In a properly designed installation this should not exceed a few %, in the USA 3% though not a code requirement, is widely accepted as a guide.
In overloaded or poorly designed installations voltage drop may be much greater than 3%.
Voltage drop may be reduced by useing thicker wires, or by useing a higher voltage for a given load in KW.
Most equipment will give proper service down to about 90% of the nominal voltage, though the manufacturer should be consulted in case of doubt.