By Nigel Calder
Conductor sizing is critical to the performance and safety of electrical systems. Undersized conductors create excessive resistance, which results in voltage losses from one end of the conductor to the other (voltage drop) and, in extreme cases, temperatures high enough to melt insulation and start fires (most notably if there is a ‘short circuit’ and the circuit does not have adequate overcurrent protection – circuit breakers and fuses).Â
Conductor Sizing Terminology
In the boat world, we have various tables that help us determine an appropriate conductor size for any application. In the USA, the best known are the tables developed by the American Boat and Yacht Council (ABYC). In Europe, we have the tables developed by the International Organization for Standardization (ISO).
A quick perusal of the standards will reveal conductor sizing that is variously referenced in terms of American Wire Gauge (AWG), diameter, Circular Mils (CM), and cross-sectional area (CSA), with additional references to Society of Automotive Engineers (SAE) sizing. Both imperial (inches) and metric (millimeters) units are used. It can be confusing, especially given that some of these sizing methodologies are counterintuitive, notably the AWG and SAE systems in which the smaller a conductor, the larger its ‘gauge’ number.Â
Let’s unpick these various sizing methods, starting with American Wire Gauge.
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