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Circuit Voltage (VDC)

Circuit Voltage (VDC)The nominal voltage in the circuit for which you are choosing wire and circuit protection. Lower voltage systems tolerate less voltage drop.

Load Current (Amps)

Load Current (Amps)The amount of current used by the load that the circuit is feeding.

Conductor Length (Feet)

Conductor Length (Feet)The sum of supply and return wire required to complete the circuit (round trip).

Modify default assumptions and set additional derating factors

Default Assumptions:

Allowed Voltage Drop (%)

Allowed Voltage Drop (%)Voltage drop is loss that occurs due to current flowing through the resistance of a conductor over its length. ABYC recommends 3% or less drop for critical loads and panel feeders, 10% for other loads. For some loads, you may wish to choose other allowable voltage drops, for example, 5%. Voltage drop is the critical factor in most 12 Volt installations.

Wire Temp Rating (°C)

Wire Temp Rating (°CInsulated wire is classified by the maximum permissible operating temperature in degrees Celsius. Common values are 105°C, 90°C, 80°C, 75°C. If the wire is allowed to operate above this temperature continuously, the insulation may melt, or be otherwise damaged. Wire rated less than 60°C is not recommended.

In Engine Compartment or Room?

In Engine Compartment or Room?Engine room space is assumed to have a higher ambient temperature of up to 50°C while all other spaces are assumed to have ambient temperatures of 30°C. In a higher ambient temperature environment, such as an engine room, there is less temperature range between ambient and wire insulation temperature rating. Therefore, the higher temperature of an engine room limits the capacity of wires and components.

Additional Derating Factors:

Duration (Minutes)

Duration (Minutes)When current flows through wire, heat is generated because of the resistance that the current encounters in the wire. As current flows through a wire, the temperature of the wire increases until heat flows out to the surroundings at the same rate that is generated. Large wires are slower to heat up to their final value. Therefore, it helps to know how long current will flow in a circuit before current stops flowing and heat is no longer generated. When the duration of current flow is long, larger wire may be recommended under certain circumstances.

Terminated on Fuse?

Terminated on Fuse?Fuses can create considerable heat when current passes through them, especially when current is continuous. Wire directly terminated at a fuse is subject to this additional heat and may fail at the termination even if the rest of the wire is within its temperature limits. Larger wire may be recommended when it is terminated on a fuse and the duration of usage is long.

In Conduit or Sheath?

In Conduit or Sheath?Jackets or conduits around wires provide additional physical protection. However, they increase thermal insulation resulting in temperature rise. Wires clad in conduit or sheath will get hotter when current passes through them compared to wires not clad in a conduit or sheath. This condition is exacerbated when current is continuous.

Extra Thermal Insulation?

Extra Thermal Insulation?Wire may be surrounded by extra thermal insulation such as foam surrounding a conduit between hull and liner. When wire is surrounded by insulation, thermal insulation increases and temperature rises.

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