The Creative Homebuilder

Phenolic-based bulkhead fitting.

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There are masters among our homebuilding community—people who not only build beautiful planes, but also solve problems with creative inventions. We refer to one of the most prolific inventors of clever and useful tools and small building accessories as The Creative Homebuilder, and he willingly shares his ideas. This new series will look at some of the many ingenious ideas that he has shared with us.

The Creative Homebuilder’s bulkhead insulator is comprised of an Allen hex screw epoxied into the central hole of the male phenolic washer, a mated female phenolic washer, and two metal washers and a hex nut on each side.

One problem faced by many home-builders is how to safely route the starter cable through the firewall. The relatively high-current cable must not touch the firewall and short out. Commonly, the cable passes straight through an insulating grommet, with frequent inspections scheduled to ensure that the grommet doesn’t wear through to allow a short. The perpendicular cable routing can often be problematic on both the engine side and, especially, the cockpit side of the firewall. The Creative Homebuilder developed an inspired solution—a phenolic-based bulkhead fitting.

The assembled phenolic-based bulkhead fitting with one electrical connector attached. A second connector on the opposite side of the firewall would also be placed between two washers in actual use. The Allen hex screw and male portion of the phenolic insulator pass through the firewall.

The key to this DIY bulkhead electrical isolator is mated washers carved from phenolic resin sheet, which provide a tight seal through the firewall. The design, using an Allen hex screw and a hex nut on each face, allows terminal clamping without any torque on the shaft—hence no potential for the shaft to turn free in the housing. Cable connectors placed between the two washers on each side allow acute direction changes and the option to downsize to a smaller, more flexible cable for the run to the starter. More flexible cable means easier routing and convenience.

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Electrical bulkhead isolator installed on a firewall along with bulkhead couplings.

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