We know it as a zap to the fingers, especially in winter.
Static electricity occurs when two materials are rubbed together and electrons are transferred from one material to the other.
If it's your keyboard and not your finger, it can be quite damaging to your equipment if you're unlucky.
When your keyboard or other gear is unpacked from its flight case, a considerable static charge may have built up.
If the instrument is connected to a strongly grounded PA system, a large current can briefly flow INTO the instrument's OUTPUT jack, and it's not designed for that.
I often see OUTPUTs on equipment damaged this way.
This can be avoided by ensuring the instrument is grounded.
Or, if that's not possible, it's usually safer to connect the jack cable to the PA system first and then to the instrument.
That way, any static electricity will discharge into the PA's ground connection and not into the OUTPUT on the instrument via the jack cable.
Remember, when the jack is plugged into the instrument, the tip of the jack plug at the other end of the cable is also directly connected to the OUTPUT on the instrument.
When it's then plugged into a jack input on the PA, there's a good chance that, along the way, it touches the ground connection in the PA, and that's when trouble can occur.

Static electricity - bad for your equipment
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