A builder wiring a panel, or an owner adding a new radio behind an old one, spends most of the time on where the wires go and how they are held there. The FAA's Advisory Circular 43.13-1B covers that in chapter 11, section 9, "Environmental Protection and Inspection," paragraphs 11-115 to 11-126. It puts numbers on the things that are easy to guess at: how tight a bend, how much sag, how far from a fuel line. The circular is not a regulation, and the airframe or equipment maker's instructions come first where they exist.
Where the bundle runs
Paragraph 11-115 says wire bundles go where they are protected from damage by people, cargo and maintenance work, and not where they will be used as handholds or as a place to hang equipment. Paragraph 11-123 repeats it: where the structure does not protect the wiring, conduit or a mechanical guard is used.
Wiring is clamped so it does not touch equipment or structure. Where that cannot be done, it gets extra protection such as grommets or chafe strips. At a penetration where the wire cannot be clamped, grommets are used in a way that keeps at least 3/8 inch of clearance from the structure, and the wire must not be preloaded against the edge of a grommet or chafe strip. Wiring that crosses a hinged panel is routed and clamped so the bundle twists, rather than bends, when the panel moves.
Power feeder wires get their own paragraph, 11-119: they are routed so they can be easily inspected or replaced, and given special protection against chafing on other wiring, structure or components.
Ties and combing
Paragraph 11-116 suggests tying wire groups separately inside a bundle, so they are easy to identify later, and combing the groups so the wires lie parallel and rub less. The circular shows a combing tool that can be made from any suitable insulating material, with every edge rounded to protect the insulation.
Bends
Paragraph 11-117 sets the minimum bend radius for a wire group or bundle at 10 times the outside diameter of its largest wire. At a breakout, or where the bundle must reverse direction, six times is allowed if the bundle is suitably supported. Coaxial (RF) cable should not bend on a radius of less than six times the cable's own outside diameter. Sharp bends are also to be avoided in wire marked by hot stamping.
Slack
Paragraph 11-118 asks for enough slack that no wire or bundle is under tension, and that wiring to movable or shock-mounted equipment can follow its full travel without tension. At terminal lugs and connectors, there should be enough slack for two re-terminations without replacing the wire, on top of the drip loop and the allowance for movement. Between supports, a bundle normally should not deflect more than 1/2 inch with normal hand pressure; more is acceptable only where it cannot touch a surface that could chafe it.
Water
A drip loop (paragraph 11-118A) is wire dressed downward before it turns up into a connector, terminal block, panel or junction box, so that fluid or condensate runs off instead of into the device. Where practicable, wires enter a box or piece of equipment from below. Where they must come in from above, the entry is sealed or a drip loop is formed. When wire runs in tubing, the circular's figure shows a 1/8-inch drain hole at the tubing's lowest point, drilled after installation, once that low point is firmly established.
Paragraph 11-122 adds that wiring should be routed so fluids drain away from connectors, and where that is not practicable, the connectors are potted. Conduit and flexible sleeving need drain holes so they do not trap moisture. Wiring on landing gear and in wheel wells carries extra jacketing and strain relief, must have neither strain nor excessive slack at flex points with the gear extended or retracted, and is to be inspected frequently and replaced at the first sign of wear.
Heat
Paragraph 11-124 says wiring is routed away from high-temperature equipment and lines, and that each wire must be rated so its conductor stays within its specification maximum once ambient temperature and its own heating from current are counted. Wire with soft polyethylene insulation is not to be used where it gets hot.
Coaxial cable
Paragraph 11-120 says coax is particularly vulnerable. It is damaged by clamping too tightly and by sharp bends, usually at or near the connectors, and it can be badly damaged inside with nothing showing outside. Coax with a solid center conductor should not be used; stranded-center cable can replace it directly. Paragraph 11-121 lists the precautions: never kink coax, drop anything on it, step on it, bend it sharply, loop it tighter than its allowable bend radius, or pull on it except in a straight line, and never use it, or any other wire, as a handle, a place to lean, or a hanger.
Flight controls
Paragraph 11-125: clamps for wiring near movable flight controls are attached with steel hardware and spaced so that the failure of any one attachment cannot let the wiring interfere with the controls. The minimum separation between wiring and a movable control is 1/2 inch, measured with the bundle pushed toward the control by light hand pressure.
Fuel, oil and hydraulic lines
Paragraph 11-126 explains the reason for this one: an arcing fault between a wire and a metal line carrying a flammable fluid can puncture the line and start a fire. So wiring is kept physically apart from lines and equipment carrying oxygen, oil, fuel, hydraulic fluid or alcohol. It is routed above them, at least 6 inches away whenever possible. Where that cannot be done, the wiring must not run parallel to the line, and at least 2 inches must be kept between them, unless the wiring is positively clamped to hold at least 1/2 inch of separation, or it connects directly to the fluid-carrying equipment. The clamps that hold that separation are not to be used to support the bundle; other clamps support it, fastened to the same structure that supports the fluid line, so the two do not move relative to each other.
Sources
- FAA, AC 43.13-1B with Change 1, chapter 11, section 9: paragraphs 11-115 to 11-126 and figures 11-7 to 11-10. Read October 21, 2026.
- Picture: RV 12 interior panel Don Ramey Logan, Don Ramey Logan, December 2016. CC BY-SA 4.0.