Aircraft Hangar

[thais]

In, NFPA 409 Aircraft Hangars, Section 5.15.1 requires hangars to be provided with grounding facilities for removal and control of static electrical accumulations on aircraft while they are being stored. In the next sections 5.15.2 and 15.15.3, the code requires an adequate number of floor-grounding receptacles with the receptacles to be grounded through driven electrodes or electrically bonded together in a grid system and the grid system grounded to underground metal piping. The grounding wires shall be bare. Of course, all of this must be installed per NEC 513. Is this section requiring Class 1, Div 1 rated grounded floor receptacles? If so, what is an adequate number? Instead of using the normal green conductor as the ground conductor, does the ground have to be bare? Is the "grid system" just the normal grounding system provided on a grounded system? When an aircraft is stored in a hangar, is there a system on-board that is plugged into the grounded receptacle?

Yes, this is my first electrical design for an aircraft hangar. The hangar is to be used for storage only, but the aircraft will have fuel in them.

Thanks for any help.

[wirenut1980]

IMO,the floor receptacles must be wired for Class 1 Division 1 location per the 2002 edition of NFPA 70, Section 500.5(B)(1).

In a design I have seen for an aircraft hangar, the floor recepts have been 400 Hz for maintenance and testing of the aircrafts' onboard equipment. If this facility is for storage only, why the need for recepts, regardless if they are 400 Hz or 60 Hz? I'll try to get back on the other grounding questions when I have time to look up the codes you mentioned.

[wirenut1980]

I just read NEC 513.3 and it looks like below floor level up to the floor is class 1 division 1, and other areas in the vicinity of the aircraft is class 1 division 2 up to 18 inches above floor, and any locations within 5 feet horizontally from aircraft power plants or aircraft fuel tanks extending from floor up 5 feet above upper surface of wings is class 1 division 2. Other rooms that are isolated enough from where the gas is, don't have to be classified. A bit different than the overall description of the locations in Article 501.

I also read the code sections you stated from NFPA 409 and you nailed it on the head about the number of receptacles. An adequate number of recepts is your call. I would talk to the users of the facility and also look at the number of aircraft. I bet the maintenance guys can give you a good number. According to your code reference, the grounding conductor must be bare. I'm not sure if the grid system the code mentions is an equipotential grid system or the Grounding Electrode System. Maybe someone else can help? I pasted the code section below from NFPA 409.

5.15 Grounding Facilities for Static Electricity.

5.15.1* Aircraft storage and servicing areas of hangars housing other than unfueled aircraft shall be provided with grounding facilities for removal and control of static electrical accumulations on aircraft while aircraft are stored or undergoing servicing in a hangar in accordance with 5.15.2 and 5.15.3.

5.15.2 An adequate number of floor-grounding receptacles shall be provided. The receptacles shall be either grounded through individual driven electrodes or electrically bonded together in a grid system and the entire system grounded to underground metal piping, such as cold water or sprinkler piping, or driven electrodes. Where driven electrodes are used, they shall consist of 15.9 mm ( in.) diameter or larger metal rods driven at least 1.5 m (5 ft) into the ground. Floor-grounding receptacles shall be designed to minimize the tripping hazard.

5.15.3* Grounding wires shall be bare and of a gauge that is satisfactorily durable to withstand mechanical strains and usage.

[LarryFine]

These grounding receptacles seem to not be power receptacles, but special, one-conductor receptacles designed for this purpose. I suggest taking a trip to a nearby compliant hangar and looking at the floor there.

[rbalex]

Larry has pointed out he essential element - these are not "typical" power receptacles; rather they are bonding points for dissipating static electricity.

Typically one is installed at every maintenance station. More may be necessary if multiple types of airframes are maintained or serviced.

[wirenut1980]

D'oh! :o