Changes between Version 30 and Version 31 of poe

08/25/2020 12:16:28 AM (3 years ago)
Ron Eisworth

Added isolation and grounding section


  • poe

    v30 v31  
     98== Isolation and Grounding Considerations
     99All of Gateworks PoE implementations are non-isolated which means the PoE ground will be tied to the boards digital ground. Full isolation requires a significant amount of space for the isolation transformer and adds in extra cost and complexity to the design.
     101Non-isolated designs are acceptable for deployments where the boards ground isn't exposed externally which effectively creates the isolation. In cases where the units ground will be tied into another instrument or supply, this can cause issues if there is a large differential between the switches ground and the unit. In these type of installations, an isolated PoE inserter/injector can be used to isolate the switch from the unit.
     103PoE PSE switches typically use high side switching which means the 48V DC output is always present and ground is switched on when the unit (PD - Powered Device) responds with a correct signature. Issues with this configuration can occur when powering multiple boards from the same switch if the boards share a common ground (for example they are mounted in metal cases and then mounted on a DIN rail or shielded Ethernet cables are used which then can create ground paths between the units).
     105In these cases, with a common ground between the boards, if one board is turned on by the switch, the other board will then try to power on (or create a fault on the switch) since it will utilize the other units ground path. This type of condition can be eliminated if the boards can be isolated to not share grounds. Note this condition can even occur with fully isolated implementations if the units have a common ground.
    98110= PoE Testing