Mobile ground power unit

for aircraftrunwayhangar

It seems that 400Hz Ground Power Units (GPUs) used for hangar and ramp maintenance have always been in compliance with the US National Electrical Code (NEC) and the European Standard, IEC 60079-10-1. And yet their counterpart, the 28VDC start/maintenance cart appears to remain defiantly non-compliant to certain aspects of these regulations when used in a hangar environment. This is most likely due to ignorance on the part of the user regarding the NEC in cases where the 28VDC mobile unit is unsuspectingly moved into the hangar from the ramp, where it becomes a potential safety hazard. Specifically, there is the wellknown “18in rule” that requires there be no electrical connection allowed within the 18in area above the hangar floor known as a Class 1, Division 2 area. This area is considered hazardous because fumes from spilled jet fuel may not have yet dispersed sufficiently to avoid ignition were an arch to occur; in this context, from a loose electrical connection within a mobile power unit (GPU or cart). For a more thorough explanation of this ruling, one can reference Article 513 of the NEC and IEC 60079-10-1 of the European Standard. I have never seen a 400Hz GPU used in a hangar that doesn’t adhere to this particular safety rule; however, in stark contrast, almost every 28VDC start/maintenance cart used in a hangar isn’t compliant. A simple, clearly visible, warning sign placed on these units would help the using community a great deal. To date, 28VDC start/maintenance carts have been designed for non-hazard areas such as the ramp just outside the hangar or outside of the airport terminal area. Both of these areas are outdoors (no rising fumes concerns),