Electrical Wire Calculators

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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.

Voltage Wire Calculators for 12 VDC Circuits.

Determine acceptable wire size for a target voltage drop.
(In accordance with 33CFR.183)

 

Supply Voltage:
Circuit Length: Required Wire Size:
Ground Type:   Voltage Drop (volts):
Load (in amps): Voltage Drop (Percent):
Maximum Voltage Drop: ← At selected Voltage → Max Current (Amps):
Wire Type:  Wire Circular Mils:
   Load Voltage (volts):
 
Stranded wire only.

Use this calculator to determine the necessary conductor size given the length of the wire, expected load, and desired voltage drop.

This calculator can provide results for both Chassis Ground or Ground Wire types. A Chassis Ground, such as a metal frame calculates the voltage drop using one-way distance. The Wire Ground calculates the voltage drop as a round trip - that is, using a wire for the negative side rather than a chassis ground.

    Notes:
  • Since a metal chassis is so massive, the voltage drop on the ground side is nil.
  • Max Current(Amps) is the current limit at an exact 3% or 10% voltage drop (depending on selection).
  • For a fiberglass boat, use the Ground Wire (round trip) option for the Ground Type
  • for a Vehicle with a steel chassis, use the Chassis Ground option.
  • 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.

 

 

 

Voltage drop for a given wire size.

 

Supply Voltage:
Circuit Length: Voltage Drop (volts):
Ground Type:   Voltage Drop (Percent):
Load (in amps):  Load Voltage (volts):
Desired Wire Size:    
 
Stranded wire only.

Use this calculator to determine the expected voltage drop when using a specific conductor size for a given length of wire, expected load, and desired voltage drop.

This calculator can provide results for both Chassis Ground or Ground Wire types. A Chassis Ground, such as a metal frame calculates the voltage drop using one-way distance. The Wire Ground calculates the voltage drop as a round trip - that is, using a wire for the negative side rather than a chassis ground.

    Notes:
  • Since a metal chassis is so massive, the voltage drop on the ground side is nil.
  • For a fiberglass boat, use the Ground Wire (round trip) option for the Ground Type
  • for a Vehicle with a steel chassis, use the Chassis Ground option.
  • 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.
  • Stranded wire only. Solid wire has a different Circular Mil specification and is not appropriate for mobile use.

 


Calculator usage tutorial

 

     

 

 

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Last reviewed and/or updated May 10, 2017