Robust Construction. The WFDEXP series consists of a rugged, NEMA 4-rated cast aluminum housing. Designed for both indoor and outdoor use, the WFDEXP series operates across a wide temperature range, from 32°F to 160°F. Inside, two sets of SPDT (Form C) synchronized switches are enclosed in a rugged terminal block to assure reliable performance. Reliable Performance. The WFDEXP series offers unique features that assure greater operational reliability. By housing the spring mechanism separately from the explosion environment, the sensitivity of the adjustment spring and the detector is protected at all times. Adding to WFDEXP’s reliability is its sealed retard mechanism, which prevents contamination by dust and dirt when the cover is removed.