What does R S T stand for?

Answer 1

There are 52 possible answers given in just one source (see link below). Other sources will provide different options.

AnswerThe letters, R-S-T, have been used in Germany (and other countries) to indicate each line conductor (or terminal) of a three-phase system. The sequence of these letters also indicate the standard phase sequence of the system -i.e. the order in which the potentials of each line reach their maximum values. There is no particular relevance to the choice of letters, R-S-T, other than the fact that they are in sequence.

Other countries use different letters, numbers, combinations of letters and numbers, or colours to indicate three-phase line conductors or terminals. For example, A-B-C, 1-2-3 , L1-L2-L3, red-yellow-blue, brown-black-grey.

The current European Union standard uses the colours brown-black-grey which, no doubt, Germany has now adopted.

It is a misconception that these letters/numbers/colours represent 'phases'. They always represent lines. Phases are connected between lines (delta systems) or between lines and neutral (star/wye systems) and, so, are identified as A-B, A-N, etc.