Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 191
Aircraft Equipment Problem Critical
Flight Crew Overcame Equipment Problem; General Declared Emergency
Procedure; Aircraft
On downwind leg vectors for the ILS we experienced a #2 Source Off light. I directed the First Officer to run the QRH. After the read-respond-do process; the #2 Generator switch was bussed back on. Instead of coming back on the attempt actually tripped off the #1 Generator; leaving no generator powering the electrical system (down to battery power). The crew then ran the Dual Generator Failure checklist and started the APU; however; initially it would not bus to the L or R side. After some delay and ATC vectors; the crew was able to get APU to bus to the left side. Upon regaining sufficient systems and instruments. We ceased checklists and troubleshooting and elected to land with the Captain flying the ILS. An emergency was declared with Approach Control and some priority vectors were offered to final. After landing; the flight was uneventful.I suggest that we look at QRH Electrical SOURCE OFF procedures and possibly add a bullet to check volts/amps on the disconnected circuit prior to attempting to re-bus the generator. If out of tolerance readings are found; consideration should be given to 'NOT' attempt to bus the failed system. As in our case; it made a minor problem major in nature. It appeared that the tripped generator actually kicked the good generator off-line as well when we tried to re-bus it.
[No substantive additional information was provided in the secondary narrative.]
A B737-700 flight crew ended up on battery power only when one bus failed and the second tripped off when the crew attempted to return the failed system to the bus.  They ultimately were able to regain one functional bus and made and uneventful landing.