If you want to use the +5V rail, put a transorb between the +5V point and ground (Vishay SA5.0A for example). Do it, or in the long term, all your modules are going to be killed, mostly by µZeus. This is a serious problem that cost me above 10k€.
The inconvenient of using the +5V rail (even with the protection):
- Bigger connector
- Reverse polarity protection is trickier (to make it really work you need to leave some GND pins unconnected, otherwise you can’t prevent some supply rails to be shorted to ground when the connector is plugged backwards)
- There are many power boards without +5V.
- There are many power boards with an underpowered +5V that can’t even be replaced or disconnected.
It’s sad, because I love the idea of a dedicated supply for digital modules - it’s just not implemented in a reliable and consistent way in Eurorack.
There are modules (4ms, noise engineering) with a jumper on the back allowing you to select either the external +5V rail, or an internally generated +5V. That’s a nice solution too if you’re willing to assist customers in deciding on which choice is best.