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Posted by on Dec 22, 2010 in Boat Maintenance, Sailboat Racing, UK, US |

Boat vs. Automotive Grade Wire

Is all wire the same for a given size, no matter whether it's intended for marine or land use?

A friend and I have been arguing about whether there is a difference between automotive wire and marine grade wire. I’m planning on doing some major re-wiring on my boat over the winter. I think 10 gauge wire is 10 gauge wire, period. My buddy says he thinks there are distinct differences. Who’s right?

10gauge-difference

The blue wire is 10 gauge automotive grade wire. The red wire is 10 gauge boat cable. Not the same, even by eye.

Well I hope you didn’t bet on this one, because you lose. All 10 gauge (or any gauge for that matter) wire is not created equal.

The photo here illustrates some of the differences. On the left the blue wire is 10 gauge SAE automotive grade primary wire. On the right is a piece of 10 gauge boat cable. Without looking too hard you can see that the boat cable has many more strands of copper. Also, if you look at the insulation jackets on the two cables closely you’ll notice some cryptic lettering on the red cable but nothing on the blue cable. Further, the strands of the red wire are silver in color vs. the copper color of the blue cable. The silver color is “tinning,” which although not a Standards requirement, we often see on marine graded wire. The tinning is to minimize the effects of corrosion to the individual strands.

The letters and numbers found on the red wire are required under ABYC recommendations for wiring. This information tells the user about actual gauge size, insulation temperature rating, chemical resistance properties and minimum voltage rating for the wire. Nice stuff to know about.

So there is a difference between circular mil area minimum requirements for 10 gauge SAE-rated wire vs. 10 gauge AWG (American Wire Gauge) sizing. The actual differential varies a little from one gauge size to another, but the percentage variation is around 10-20%. The AWG sizing always offers more copper for a given gauge size.

The bottom line here? More copper is better. On boat wiring one of the things you should always be concerned with is voltage drop, which is in part controlled by a wire’s ability to carry current with a minimum amount of electrical resistance. Also, since the boat cable will have more strands for a given gauge size, the wire will by its very nature be more flexible. This characteristic is superior for dealing with vibration and the inherent flexing that occurs in boat cable wire runs.
Ed Sherman