DC Power Technologies FS3 Version 3 - Technical Hardware Manual - Manual (Page 27)

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Surge Protection of MP130 & MP133 modules
Models fitted with 2 or more MP130 or MP133 charger modules
must be fitted with MOVs across phases as follows:
 3 modules: 625VAC MOV fitted across S&T and T&R.
 2 modules: 625VAC MOV fitted across S&T.
 1 module: No MOV required.
MOVs may be fitted to the terminal blocks in conjunction with the
backplane loom wiring. MOV legs must be sufficient to
Earthed S-Phase Configuration
Some RST models required Earthed S phase, where an addition
earth link is made from the E terminal to the input S terminal.