Siemens Low Voltage s Surge Protection Devices Line of TPS306 as part of the Internal (Integral Mounted) Group. Type 2 SPD. Dimensions (L x W x H) 10.7 x 11.5 x 4.5. 3-Phase 3-Wire Rated 480V surge current 400 kA per phase. Special features mounts internal to SB1, SB2, SB3, and RCS switchboards, TIASTAR motor control center with 12 IN bucket, STP busplugs on SX busways