In "no trip" mode my DL9118 does high current L-N and low current L-E on the one test, afterwards you can press the top 'function' key and it toggles between the Zs/PFC and the Zsupply/PSCC results.
In high current mode it only measures the one you select, which is odd.
My suspicion is it makes some use of the PSCC data to help with the no-trip test, but there is nothing said about any of that in the instruction book, etc. For example, with the 3 wire connection while you measure the L-N drop you could also measure the N-E rise to get some idea of R1 and Rn separately (at least as far back as the N-E link point in the distribution system), and it might help when you do the L-E test to get some idea of R2 by knowing R1 from the first test, etc. But that is speculation!
In high current mode it only measures the one you select, which is odd.
My suspicion is it makes some use of the PSCC data to help with the no-trip test, but there is nothing said about any of that in the instruction book, etc. For example, with the 3 wire connection while you measure the L-N drop you could also measure the N-E rise to get some idea of R1 and Rn separately (at least as far back as the N-E link point in the distribution system), and it might help when you do the L-E test to get some idea of R2 by knowing R1 from the first test, etc. But that is speculation!