- One cause of blackouts is squirrels entering a substation to forage for food. A short circuit is created when a squirrel's body touches across two terminals. This trips the internal breakers of the substation, causing the station to shut down. The result is a local blackout. Alan Gomez wrote in 2007 in "USA Today" that squirrels cause thousands of blackouts yearly. Gomez further reported that electrical companies are investigating methods of keeping squirrels out of substations, such as installing special fencing.
- Overdrawing causes blackouts for complex reasons, but it can be compared to a well running dry due to overuse. For instance, in a large city everybody wakes up and turns their coffeemakers on. Right after, all hot water heaters and air conditioners are turned on. This draws an excessive amount of power from the grid, causing a drop in available electricity within a region.
- Intentional vandalism and theft causes blackouts. Thieves steal electrical power lines to sell the copper wire as scrap. This is a dangerous practice, since they are cutting into live electrical lines. Electricity stops flowing when a line is cut. Thieves steal towers, transformers and equipment, also to sell as scrap. The problem was severe in Uganda in 2010, according to the Uganda Electricity Transmission Company. Efforts are ongoing to stop vandalism and thievery.
- Lightning and severe weather are outside the scope of human control. Lighting may hit a power transformer, sending a voltage spike down the line. The spike reaches the closest substation and trips breakers, causing a blackout. Another weather related cause of blackouts is ice on the power lines. Ice weighs down a line, causing it to tear away from the transformers. Another cause is high winds caused by tornadoes. Tornadoes can knock down a power pole, causing the wires to touch and short circuit. When this happens, the main breakers at the substation trip.
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