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 4-Wire Rated 600/347 V surge current 250 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