Why wire size matters
A conductor must be suitable for the current it carries and for the conditions in which it is installed. Undersized conductors can experience excessive heating or voltage drop.
Start with circuit current
The expected load current is one of the first inputs used when selecting a conductor. The required ampacity depends on the applicable rules for the circuit and load type.
Conductor material
Copper and aluminum conductors have different electrical and thermal characteristics. A size suitable for one material should not automatically be assumed suitable for another.
Temperature and installation conditions
Ambient temperature, insulation temperature rating, the number of current-carrying conductors and installation method can affect allowable conductor ampacity.
Account for circuit length
A conductor may satisfy an ampacity requirement but still produce undesirable voltage drop over a long run. Longer circuits may therefore require a larger conductor.
Ampacity and voltage drop are different checks
- Ampacity concerns how much current the conductor can carry under specified conditions.
- Voltage drop concerns how much voltage is lost along the conductor.
- A conductor should be checked for both where applicable.
- Protective-device ratings and terminal limitations also matter.
Why a simple wire-size calculator is only a starting point
Online calculators can provide a preliminary estimate, but a real installation may involve additional correction factors, equipment requirements and jurisdiction-specific rules.
Do not use a simplified online estimate as the sole basis for mains-voltage wiring. Final conductor selection should follow the electrical code and standards applicable to the installation and should be reviewed by a qualified professional where required.