Odd wire gauges for aircraft wiring

Have you ever wondered why only even wire gauges are produced (e.g. 8, 16, 20, etc.) for aircraft wiring? For centuries, wire manufactures have produced even wire gauges because there has been little or no demand for odd wire gauges. Further, there is a slight difference between a 22AWG and 23AWG and a 23AWG and 24AWG. However, with the present drive to reduce weight on aerospace platforms, some manufactures are seeking odd gauge wires. The goal is to use odd wire gauges, particularly on smaller circuits, where the limited current draws would not require a larger conductor. The wire weight saving as a result of smaller wire gauges can significantly reduce fuel consumption over the aircraft’s service life.

According to AS50881, the smallest wire that can be used on an aircraft for chassis wiring is 22AWG, due to maintenance difficulties of smaller wires. Because of this regulation, the use of odd gauge wire will likely be limited to avionics boxes and other LRUs.

The use of odd gauge wires is an interesting idea, but there is more than just a one-for-one replacement of wires. Multiple areas through the supply chain would be affected with this change. From an OEM point of view, this would require different stripper blades for insulation removal. Furthermore, the wire terminations from crimps to contacts would need to be procured and performance verified. From an engineering perspective, there are no industry standards on current ratings for odd wire gauges, but these can be interpolated (contact Lectromec on availability of wire derating tools).

Further down the process, once systems are developed using odd wire gauges, new tools and terminations will need to be procured. With these being non-standard parts, they are likely to have long leadtimes or at least might be difficult to find. How long before long stretches of the odd gauge wires are spliced in with a larger gauge wires and then completely remove weight savings?

It is a good idea to save weight, but there are several factors that need to be analyzed before changing from a 22AWG to a 23AWG wire.

If you are interested in aircraft wiring, you may want to read Lectromec’s Wire Flammability for Aircraft Wiring article.