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TL;DR

Wire Sizing: Conductor selection based on ampacity, voltage drop, and derating factors per NEC Table 310.16.

By Valenke Exam Prep Team·Last updated 2026-06-02

Wire Sizing

JOURNEYMAN ELECTRICIANMASTER ELECTRICIAN

Definition

Conductor selection based on ampacity, voltage drop, and derating factors per NEC Table 310.16.

Practical Example

Electrical Calculation: Ohms law

Formula: E = I x R

Variables: E (voltage in volts), I (current in amps), R (resistance in ohms)

Example: 120V circuit with 10 ohm load: I = 120/10 = 12A

Related Procedures

Conductor selection based on ampacity, voltage drop, and derating factors per NEC Table 310.16. Core JE exam calculations.

Relevant formula: Ohms law is E = I x R. Variables: E (voltage in volts), I (current in amps), R (resistance in ohms).

Troubleshooting

Troubleshooting issues related to wire sizing:

Overcrowded box
Box fill exceeds allowable volume per 314.16, common in renovation work
Improper grounding
Bootleg ground (jumping neutral to ground at receptacle) or missing EGC
No AFCI protection
Bedrooms and living areas in new construction require AFCI per 210.12

Documentation

Proper documentation of wire sizing follows facility policies and regulatory requirements. All entries must be dated, timed, and signed. Errors are corrected with a single line through the incorrect entry, initialed and dated. Never erase or cover with correction fluid.

Why It Matters

Core JE exam calculations.

Related Terms

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Frequently Asked Questions

What safety requirements apply to wire sizing?
For wire sizing: Working space clearances per 110.26: minimum 3ft depth, 30 inch width, 6.5ft headroom for under 600V equipment. Lockout/tagout (LOTO): de-energize, lock, tag, try, verify zero energy before working on equipment.
What NEC articles cover wire sizing?
For wire sizing: Article 250 (Grounding and Bonding): 250.66: grounding electrode conductor sizing (Table). Article 430 (Motors): 430.6: use FLC from Table 430.248/250 not nameplate for conductor/OCP sizing.
What formulas are needed to calculate wire sizing?
For wire sizing: Voltage drop: VD = (2 x K x I x D) / CM. Variables: K=12.9 (copper), I=amps, D=distance(ft), CM=circular mils. Example: 20A, 150ft, 12AWG (6530CM): VD = (2 x 12.9 x 20 x 150)/6530 = 11.87V (9.9%).