When do you need ordination from Sinai to make a halachic decision? Actually not often. But it does need to come from the Gemara. One of the advantages of the real authentic Shulchan Aruch  is it gives a clear picture of the sugia in the gemara and how it develops into the halacha. But if one does actually know the Talmud well enough to be a מומחה לרבים  [a expert that has been tested by other experts and never found to make a mistake, and whose decision has been accepted by other experts] then he is allowed to decide cases involving money as long as they are not cases of wounding or theft. These last two need ordination from Sinai.


The idea of the halachic based on דינא דגמרא the law of the Gemara is well established even in the Rambam. The Maharshal  wrote it is better to decide from the Gemara itself even if one is wrong than to decide based on the Rambam even if one is right.

The basic idea is this. The mishna says one needs three people to judge monetary cases and three [later Rava will explain this to mean  people with the authentic ordination from Sinai] in order to judge robbery and wounds. It is late here but in short according to the Torah we need three people with authentic ordination for everything but the sages made an exception for loans and cases of admissions. What comes out is that the requirement for authentic ordination is not required in  MONETARY CASES. So far the gemara has not said anything about more general halachic rulings.