Grounding NEC 250 Calculator

NEC grounding size calculator for electricians, apprentices, and electrical engineers. Three calculators in one app: Equipment Grounding Conductor (EGC) from Table 250.122, Grounding Electrode Conductor (GEC) from Table 250.66 with sole-connection exceptions, and Bonding Jumper from Table 250.102(C)(1) with the 12.5% rule. This electrical grounding calculator works 100% offline on the job site.

Whether you're sizing an EGC for a 200A circuit, determining the GEC for a 500 kcmil service with a ground rod electrode, or calculating a bonding jumper for parallel service conductors, this grounding calculator gives you accurate NEC-compliant results in seconds - perfect for grounding system design and installation verification.

THREE CALCULATORS IN ONE:

EQUIPMENT GROUNDING CONDUCTOR (EGC):
• Size EGC per NEC Table 250.122 - all 21 table rows from 15A to 6000A
• All 37 standard OCPD ratings per NEC 240.6(A) selectable - including 30A, 40A, 50A, 70A, 125A
• Copper and aluminum conductor support
• Voltage drop adjustment per NEC 250.122(B) - proportionally increase EGC when circuit conductors are upsized
• Original and adjusted wire size selection for accurate proportional calculation
• Automatic rounding up to next standard OCPD rating

GROUNDING ELECTRODE CONDUCTOR (GEC):
• Size GEC per NEC Table 250.66 based on service conductor size
• Support for copper and aluminum service conductors
• Parallel sets calculation (1-6 sets) with automatic equivalent area computation
• Sole-connection exceptions per NEC 250.66(A), (B), and (C):
- 250.66(A): Rod, pipe, or plate electrode - GEC capped at #6 Cu / #4 Al
- 250.66(B): Concrete-encased electrode - GEC capped at #4 Cu / #4 Al
- 250.66(C): Ground ring - GEC capped at #2 Cu / #2 Al
• Five electrode types: Water Pipe, Rod/Pipe/Plate, Concrete-Encased, Ground Ring, Other

BONDING JUMPER:
• Size bonding jumpers per NEC Table 250.102(C)(1)
• Same ranges as Table 250.66 for conductors within table limits
• Automatic 12.5% rule for service conductors exceeding 1100 kcmil Cu or 1750 kcmil Al
• Parallel sets support with combined circular mil area calculation

CALCULATION RESULTS INCLUDE:
• Conductor size in AWG or kcmil with alternative material
• Exception applied with NEC section reference
• NEC article references for every result
• Detailed notes for parallel sets and electrode exceptions

NEC REFERENCES INCLUDED:
• NEC Table 250.122 - Equipment grounding conductor sizing
• NEC 250.122(B) - EGC increase for voltage drop
• NEC Table 250.66 - Grounding electrode conductor sizing
• NEC 250.66(A) - Rod, pipe, or plate electrode exception
• NEC 250.66(B) - Concrete-encased electrode exception
• NEC 250.66(C) - Ground ring exception
• NEC Table 250.102(C)(1) - Bonding jumper sizing
• NEC 250.102(C)(1) - 12.5% rule for large conductors

PRO FEATURES (one-time purchase):
• No ads - clean interface for professionals
• Save grounding calculation history with labels
• Export calculations as PDF reports for permits and records
• Dark theme support

PERFECT FOR:
• Licensed electricians sizing grounding conductors daily
• Electrical apprentices and journeyman exam preparation
• Electrical engineers specifying grounding systems
• Electrical inspectors verifying conductor sizes

OFFLINE & PRIVACY:
• Works 100% offline - no internet needed on the job site
• No account required
• No data collection - your calculations stay on your device

Simplify your grounding and bonding calculations on the job site.

Recent changes:
Added a link to TradeTools — the one-app version of this calculator and 61 more, for HVAC, electrical, plumbing, fire protection, solar and carpentry. Nothing else changed.