If the contractors are controlled by the Teensy, we will lose control of them if USB comms are lost.

[JimsterCoder]

It will not be possible to open the contactors if USB comms are lost. This is an unacceptable design. Is there a way to mitigate this?
Is there a way to cycle the power on the Teensy from the Pi so that the relays lose power and reset? This may be possible as on power up/down the Pi controls the power to the USB ports.
We could put the power to the Teensy relays though a relay controlled by the Pi GPIO so we could de-power the relays from the Pi as a way to open the contactors. Only if USB comms are lost.

[NiallDarwin]

As discussed having a Pi-controlled relay controlling power to teensy controlled relays enables Pi to shut everything down in a worst-case scenario.