> The way it was explained to me is that the power company actually sent a signal through the power supply which would trigger our snowmaking system to shut it

> The way it was explained to me is that the power company actually sent a signal through the power supply which would trigger our snowmaking system to shut itself off. https://en.wikipedia.org/wiki/Utility_frequency#Frequency_and_load https://en.wikipedia.org/wiki/Utility_frequency#Frequency_an... > Modern alternating-current grids use precise frequency control as an out-of-band signal to coordinate generators connected the network. The practice arose because the frequency of a mechanical generator varies with the input force and output load experienced. Excess load withdraws rotational energy from the generator shaft, reducing the frequency of the generated current; excess force deposits rotational energy, increasing frequency. Automatic generation control (AGC) maintains scheduled frequency and interchange power flows by adjusting the generator governor to counteract frequency changes, typically within several decaseconds. If there's more demand on the grid, the generators have to work harder (slower) to generate the power and this shows up as a drop in the frequency of the grid. In New Zealand, that is 50 Hz. https://www.emi.ea.govt.nz/Wholesale/Datasets/FrequencyKeeping https://www.emi.ea.govt.nz/Wholesale/Datasets/FrequencyKeepi... If the frequency drops a bit, it is then an indication for generators to kick on or load to be shed. If the frequency goes above the 50 Hz frequency, it becomes a sign that the price that power is being bought at is lower and so more expensive / dirty power generation should be throttled back or shut down (and batteries should recharge rather than discharge and pumped storage reservoirs should pump rather than generate https://www.energy-storage.news/new-zealand-considers-investing-us9-8-billion-in-5twh-of-pumped-hydro-to-bridge-energy-deficit/ https://www.energy-storage.news/new-zealand-considers-invest... ) On the other side of it, you can see the frequency changes back with the Texas blackout - https://www.houstonpublicmedia.org/articles/news/energy-environment/2021/02/24/392290/texas-power-grid-was-4-minutes-and-37-seconds-away-from-collapsing-heres-how-it-happened/ https://www.houstonpublicmedia.org/articles/news/energy-envi... Those changes are less than 1% of the frequency, but that's all that's needed to signal information between the generators and demand.