[oil pan 4]

After the Texas power grid near collapse it tells us precisely what we need. Don't need no fancy networked gold plated junk. Just a simple under frequency relays would work.
When the power grid frequency drops below say 59.8 pr 59.7Hz your electric hot water heater, hvac electric car charging rig is kicked off line. Until the power grid frequency is restored.

Because the Texas power grid dropped below 59.4Hz that started timers on hard wired safety disconnectors. You have 9 minutes to get the frequency back above 59.4Hz, oh and if you drop below 59.3 it's instant or almost instant. Then power plants start kicking off line, like all of them. And you're in a "black start" condition, which has never happened in the US. We have had large swaths of interconnect go down, but that was the idea. Losing 1/3 of your interconnect and turning the power back on is easy, nothing compared to a black start.