Description The FE Petro 5800300100 STP-DHI dispenser hook isolation device prevents electrical feedback between dispenser hook circuits as required by most electrical codes. One STP-DHI required per product grade for up to eight dispensers. Key Features Optically isolates inputs from up to eight dispensers preventing damage to dispenser relay boards caused by cross-phasing. Prevents electrical feedback between dispenser hook circuits during periods of maintenance and service as required by NEC 514-6, 1999 and other international codes. Can be supplied factory-wired in tandem with the FE Petro Smart Controller or the FE Petro standard control box. Eliminates false STP run due to voltage leakage of multiple dispensers connected in parallel. Fuse-protected output to submersible pump controller. The STP-DHI can retrofit to any existing site.