Electrical Wire Calculators

Whenever you are wiring power cables for a DC appliance in a RV, whether it be re-wiring your brakes or adding a new new stereo system, you need to understand that the characteristic of DC wiring is that you will encounter a voltage drop along the wire. This can be significant, especially as the current and wire length increases... even as short as a few feet. The longer the cabling, the more voltage drop occurs. This can be a real problem, resulting in poor or loss of operational performance of the device being powered.

This is a significant concern for the RV owner as one must always be mindful of what the ramifications are when adding loads to an existing circuit, or when sizing wiring for a new circuit. See my tutorial High Power DC Wiring for an in-depth discussion of this phenomenon. Typically you will run into difficulty from voltage drop issues long before you will exceed the current-carrying capacity of the wire.

When determining wire size, you must calculate for the total wire distance. For example, if a wire is used for the negative side (commonly called a ground wire), the distance must be the full round-trip from the power source, to the load, and back, as both + and - wires will reduce the voltage. This is also sometimes called a "floating ground".

However, if using a metal Chassis ground, only the one-way trip needs to be calculated because the Chassis is so massive, any voltage drop would be nil.

These calculators can adjust the result for either type of ground. Simply enter the point A to point B (one way) distance between the source and load, then select the proper "GROUND TYPE". The calculator will automatically use the correct wire length depending on the GROUND TYPE setting.

Notes:
• When using Chassis Ground, the voltage drop on the chassis (ground side) is nil, so the round-trip distance is not required.
• Max Current(Amps) is the current limit at an exact 3% or 10% voltage drop (depending on selection).
• Use 3% Voltage Drop for sensitive electronic components or navigation lighting (boats).
• Use 10% Voltage Drop for non-sensitive/non-critical components, such as lighting or motor circuits.
• For a fiberglass boat, you will typically use the Ground Wire (round trip) option for the Ground Type.
• for a Vehicle with a steel chassis, you will often use the Chassis Ground option.
• For a RV, both Chassis Ground and Ground Wire types are typically used - choose whatever is appropriate for your situation.
• Lead Acid batteries vary from 11.9V for fully discharged to 12.6V for fully charged.
• Marine/RV/Automotive chargers vary from 13.2V to 14.4V depending on brand and charge state (i.e. Bulk, Absorption, Trickle).
• Most wiring is sized according to the American Wire Gauge (AWG)
• Automotive and marine wiring may be sized according to the Society of Automotive Engineers (SAE).
• SAE wiring is 10~12% smaller in diameter, so the results will be different.
• Designed to comply with methodology found in 33.CFR183 - Boats and Associated Equipment.
• Stranded wire only. Solid wire has a different Circular Mil specification and is not appropriate for mobile use.

In addition to the DC circuit section above, a similar calculator exists for AC circuits. When calcuating for AC circuits, note that only a 1-way distance can be entered (the calculator actually does a round trip calculation, but only needs to know the 1-way distance). Even with a grounded neutral, the neutral still carries the current, not the ground, so we need to calculate a round-trip distance.