After wire is tight the clamp is held closed, making screw
insertion easy.
Aircraft Spruce offers many options for
sealing holes through the firewall, but the
bottom line is that the firewall must be just
that: a seal to smoke, fumes, and fire. At the
same time the wiring and all controls penetrating the firewall must be suitably
protected from chafing and binding.
In all other areas the wiring must be
protected from chafing and must be
supported. The most elegant solution,
again, is to use clamps, but they are often
difficult to use and impractical. Tie-wraps
are acceptable, but the wire must be
protected from chafing. Any edge that the
wire may come in contact with should be
covered with grommet material of some
sort. You can buy the good stuff or make
your own by splitting something like
automotive rubber vacuum hose and gluing
it in place with RTV or contact cement.
Also, the wire itself can be sleeved with a
protective shield, such as used in auto
applications. Remember that much of the
auto stuff is PVC, which, if there’s an
electrical fire, will produce toxic smoke,
particularly dangerous at 9,000 feet.
The wiring should be laid down as
single strands or in bundles that have no
strain on them. The bundles should not be
pulled tight, nor should there be large
droops or swales in the wire runs. They
should not be in an area where they will
regularly flex, and it is good practice to
keep them bound and at least 3 inches from
flight controls so there is absolutely no
chance of contact. Lastly, wires should
never be run under fluid lines. For instance,
resist the temptation to tie the fuel
quantity sensor wire to the fuel line
coming from that tank. Think for a minute:
Wiring can get hot. Do you want it
saturated with 100LL if it happens to
smoke prior to blowing the fuse? Even
worse, just imagine a wire shorting out on
an aluminum fuel tube.
Richard Koehler, EAA 161427, has been an EAA member
since 1980. He is an active airframe and powerplant
mechanic with inspection authorization, a commercial
pilot with instrument and multiengine ratings, and a
technical counselor and flight advisor. For more informa-
tion about aircraft wiring, review Advisory Circular
43.13-1B/-2B. Aircraft Spruce sells the AC for about $20, or it
can be found online at
www.FAA.gov.
