Medical premises electrical design atlas 08SD706-2 page 12 outlet box how is L1, L2 into the line?

You also said outlet box for IT systems, since the IT system power supply L1, L2 is the secondary coil of the isolation transformer out of the line, here L1, L2 is not a normal TN-S system phase line, so the voltage between L1, L2 depends on the output voltage of the isolation transformer, rather than 380V.