According to cJ :
I recently had a brownout due to weather related power grid issues. The
voltage on my 120 volt circuits was down to about 100-105 volts.

For the most part you can trust the utilities to kill the power completely
if it goes outside of the safe-for-equipment range. They have a tendancy
to have to pay for equipment damaged by operating decisions such as this.

Their equipment will automatically kill the system if they can't keep the
voltage high enough.

For the most part, I believe that 90V is considered the minimum safe
value for medium term brownouts, and 85V for _very_ short ones.

The equipment at highest risk are the compressors in your fridge or freezer.

In an extreme brownout, I'd be tempted to turn them off so they won't
cycle, and turn them on for an hour every 4-6 hours to do one long cool-down
run.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.