After a bit of digging in the wiring manual; looks like pressing the HYD button unlocks one solenoid and pops the RAT out giving Blue HYDS.
Pressing the ELEC button operates the second solenoid also popping the RAT out, but this switch also sends an input into the Constant Speed Gen.
So either switch will pop the RAT out, but only the ELEC will force the RAT Gen to power its respective systems. It looks like this is the reason for two switches; the RAT Gen takes priority over the systems it feeds.
So, having a HYD failure, pressing the HYD button will get the RAT out without force powering the RAT AC Gen. If you had a HYD failure and still had serviceable engine generators, but pressed the ELEC switch, you'd pop the RAT, still get hydraulics but you'd also force off the good engine generators (only on those bus bars the CSM/G supplies of course).
With HYDS taking priority over ELECS, the system logic would auto shut down the CSM/G if Blue HYDS reached a low pressure.
Clear as mud?!
Last edited by itsresidualmate; 4th Sep 2014 at 08:53.