My company is supplying equipment to an aircraft manufacturer, one piece of equipment is giving me fits. The equipment in question is a movable steel platform that is for all intents and purposes isolated/insulated from the building, it moves on air bearings to and from it's intended working position next to an aircraft during assembly and testing.
This platform has one 480/277vac 60hz panel that is fed from a receptacle and portable cordage, this cord has 4 conductors + ground. This panel supplies power for 277vac lighting and powers a 480/115vac transformer for gfci receptacles placed about the platform. The ground conductor is bonded to the panel and the panel is bonded to the platform.
There is also a 200/115vac 400hz distribution panel mounted on this platform that is also fed from a receptacle. The portable cord for the 400Hz supply is aircraft power cable, 6x #4, and 1x #2. This cable has NO grounding conductor. The lack of a grounding conductor is standard for aircraft power cable.
The platform also has ground based test computers and electronics that run tests on the avionics of the aircraft.
My electrician is telling me that the 400Hz cable must contain a grounding conductor per NEC.
The only thing I can find that remotely addresses this is 250.26
And this awesome article. http://ecmweb.com/design/electrical-equipment-issues-parked-aircraft
The avionics engineer is also telling us that he needs a solid ground.
My fear is that if we have 2 separate grounding conductors bonded to the platform we may/will have ground loops. I am also concerned that noise will be radiated to the grounds from the 400Hz inverter.
Any thoughts and recommendations are vastly appreciated.
This platform has one 480/277vac 60hz panel that is fed from a receptacle and portable cordage, this cord has 4 conductors + ground. This panel supplies power for 277vac lighting and powers a 480/115vac transformer for gfci receptacles placed about the platform. The ground conductor is bonded to the panel and the panel is bonded to the platform.
There is also a 200/115vac 400hz distribution panel mounted on this platform that is also fed from a receptacle. The portable cord for the 400Hz supply is aircraft power cable, 6x #4, and 1x #2. This cable has NO grounding conductor. The lack of a grounding conductor is standard for aircraft power cable.
The platform also has ground based test computers and electronics that run tests on the avionics of the aircraft.
My electrician is telling me that the 400Hz cable must contain a grounding conductor per NEC.
The only thing I can find that remotely addresses this is 250.26
And this awesome article. http://ecmweb.com/design/electrical-equipment-issues-parked-aircraft
The avionics engineer is also telling us that he needs a solid ground.
My fear is that if we have 2 separate grounding conductors bonded to the platform we may/will have ground loops. I am also concerned that noise will be radiated to the grounds from the 400Hz inverter.
Any thoughts and recommendations are vastly appreciated.
