You can use a "Voltage Independent" earth leakage protection device (3P or 4P) on balanced two phases network in opposition (phases are offset by 180 degree) of single-wire earth return (SWER) system.
As the earth leakage current detection is based on a magnetic toroid surrounded by all the active conductors the magnetic flux generated in the magnetic toroid depends at all times on the vector sum of the currents in the active conductors (including the Neutral).
So, it means that the earth leakage protection will work correctly whatever the angles between the phases on balanced system as on two phases network in opposition.
As the voltage between phases is 480Vac, for earth leakage protection, we can only recommend to use an RCCB Multi9 GFP 4P (A-SI type) which is certified to be used at UeL/L=480Vac according to UL1053 Std (60Hz) but also according to IEC 61008-1 Std 50Hz in double certification.
The A-SI type is recommended as it's the best proposed immunity to nuisance tripping in all cases of interference.
For instance we can propose to use GFP 4P 40A 30mA A-SI type reference part # M9R81440 according to the connection diagram below with earthed wire (0V) connected on the Neutral pole and the two Phases connected on the two first left phases poles to have correct working of the test button.