Marine Cable & Wire - FAQ

"Can I use 'regular wire' for my boat?". The answer to this common question is a qualified "yes",if the wire is SAE (Society of Automotive Engineering) J378, J1127 or J1128. These wires are designed for "surfacevehicles", not for the special requirements of the marine industry, but meet the minimum standards for boats inlimited circumstances, even if tinned copper, they should not be run in bilge spaces or other areas subject to moisturefrom spray or dripping. They should not be run in engines spaces, unless marked "oil resistant". They shouldnot be used in applications where subjected to vibration or frequent flexing and must never be used for 110 voltapplications. For safety, use only wire which is marked with size and type.

Most importantly, SAE wire is up to 12% smaller than AWG Boat Cable which means that, in many applications, largergauge wire must be used to stay within the voltage drop limits recommended by experts (see Tables C & D, below).The wire charts found in "Chapman's Piloting" and other publications are all for "AWG" wire likeANCOR, not "SAE" type wire.

Using the wrong type of wire can cost you more in the long run. Insist on Marine Grade™ Boat Cable by ANCOR.It is UL approved for the corrosive marine environment and charter boat service. Marine Grade™ Boat Cable isspecially designed to exceed all test standards for cold bend, moisture and oil resistance, heat shock and flammabilityto ensure the safest, easiest to install, longest lasting and ultimately the least expensive electrical system you canbuy. Only ANCOR offers a complete line of Marine Grade™ Boat Cable for every need.

Table A: Marine Wire Color Code

Table B: Conductor Sizes

Ampacity is the ultimate safe current carrying capacity of the wire before damage occurs to the insulation, withoutregard to voltage drop. Because the insulation of most SAE wire types is not the same as ANCOR, this chart should not beused for other conductor types. Use Table C & D to find proper wire size to insure adequate performance.

Table C: Conductor Sizes (AWG) for 3% Voltage Drop at 12 Volts

Use 3% voltage drop for any "critical application" affecting the safety of the vessel or its passengers:bilge pumps, navigation lights, electronics, etc...

Table D: Conductor Sizes (AWG) for 10% Voltage Drop at 12 Volts

Use 10% voltage drop for any "non-critical applications: windlasses, cabin lights, etc...

Important!

Length (feet): Determined by measuring the length of the conductor from the positive (+) power sourceconnection to the electrical device and back to the negative (-) power source connection. Note that the powersource connection may be either the battery, panelboard or switchboard.

Current (amps): Determined by adding the total amps on a circuit.

Conductor sizes not covered in Table C or Table D may be calculated by using the following formula:

After calculating the Circular Mil Area (CM), use Table B to determine the proper conductor size (National FireProtection Agency and Coast Guard require that the next larger conductor be used when the calculated CM area fallsbetween two conductor sizes).

CM=K x l x L / E

CM = Circular Mil area of Conductors
K = 10.75 (Constant representing the mil-foot resistance of copper)
I = Current - amps
L = Length - feet
E = Voltage drop at load (in volts)

For Example...

Q: For example: A bilge pump draws 10 amps. The positive run is l l feet from the power panel, includingthe float switch. The negative run is only 10 feet. What size wire?

A: Use the formula to reach the correct answer:

CM = 10.75 x 10 (amps) x 21 (total length of run) / 0.36 (3% of 12v) = 6,271

Table "B" shows that 12 AWG wire has a CM area of 6,500 and is the correct choice. However, SAE wire hasa CM area of only 5,833. Under NFPA and USCG regulations, 10 SAE wire must be used.