Becoming a little specific in this matter, I have asked a question to my training dept. and failed to have an answer, even after an inflight fire training scenario. We applied the new QRH fire/smoke checklist. It says isolate the sourse if possible, (electrical). Switch off the Bus Tfr switch etc. Now, in previous Boeings, after this was done, each Gen was switched off in turn and you waited to see if smoke reduced. In the NG this doesn't happen; you just open the Bus Tfr. How then can you determine which Bus is producing the smoke and isolate it? Help & understanding will be appreciated.