Siemens Low Voltage s Surge Protection Devices Line of TPS309 as part of the External (Remote Mounted) Group. Type 1 SPD. Dimensions (L x W x H) 8.3 x 3.6 x 3.0. 1-Phase 3-Wire Rated 120/240 V surge current 100 kA per phase. Special features dry contact and auible alarm, mounts internal to P1 panelboards and busway