WorksheetCode-sensitiveLast reviewed April 29, 2026
Electrical reference chart
Ground Fault Loop Chart
Use this worksheet after the calculator result to record loop impedance, prospective fault current, conductor path, equipment grounding path, connection resistance, and protective-device review.
Quick reference table
A ground fault loop chart is a calculator-led protection planning worksheet. It connects loop impedance and prospective fault current with the conductor path and protective-device follow-up before breaker or equipment review.
Ground fault loop worksheet
| Item | Record from calculator | Follow-up |
|---|---|---|
| Voltage and source | System voltage and transformer/source data | Confirm actual supply condition |
| Circuit path | Conductor size, material, and length | Check installed route and temperature basis |
| Grounding path | EGC size and path assumptions | Verify bonding and terminations |
| Loop impedance | Ohms or milliohms result | Compare with measured loop test if available |
| Protection | Prospective fault current | Check protective-device clearing and rating |
Ground-fault path review lanes
| Path item | Record on worksheet | Reason for separate review |
|---|---|---|
| Equipment grounding path | Conduit, EGC, bonding jumper, raceway notes | The fault path may not match the phase conductor path |
| Protective device | Breaker, fuse, GFPE, relay, setting | Clearing depends on device type and actual settings |
| Available fault current | Source and transformer basis | Prospective current changes with upstream source data |
| Field verification | Continuity, impedance, or test method note | A calculation does not prove installed bonding condition |
Formula basis
Prospective fault current = system voltage / ground-fault loop impedance.
- System voltage is the line voltage used by the calculator for the fault path.
- Loop impedance includes source, conductor, equipment grounding path, and connection resistance assumptions.
- Prospective fault current is the calculated current available for the selected loop path.
- Protective-device review compares the result with breaker, fuse, or relay behavior using verified equipment data.
Worked examples
Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.
- The worksheet screens a modeled fault path and does not prove field continuity, breaker operation, or equipment duty by itself.
- Fault current and clearing behavior depend on source data, conductor temperature, connections, protective-device settings, and installed conditions.
Code and standard notes. Planning limits that should be checked before final equipment selection.
- Use this chart as a calculation record; verify adopted NEC grounding and overcurrent requirements, equipment ratings, protective-device data, manufacturer instructions, OSHA safety controls, AHJ expectations, and qualified-person review before relying on a fault-current path.
How to use this chart
Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.
- Capture circuit dataRecord voltage, source impedance, conductor size, material, length, EGC size, and connection resistance.
- Capture result dataWrite loop impedance, prospective fault current, and any modeled disconnect note.
- Capture protection reviewList protective device, settings, equipment rating, field test status, and reviewer.
Common mistakes to avoid. Review these before turning chart current into an equipment decision.
- Comparing prospective fault current with a breaker label without checking settings or time-current data.
- Ignoring field connection condition when using a calculated loop impedance.
- Treating a loop impedance estimate as proof that installed bonding, terminations, and grounding continuity are acceptable.
Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.
Can loop impedance alone verify a circuit?
No. It must be tied to protective-device data, equipment ratings, bonding condition, test method, and the installed path.
Why document connection resistance?
Loose, corroded, or numerous connections can change loop impedance and reduce available fault current at the end of a circuit.
Related calculators
- Ground Fault Loop CalculatorCalculate ground fault loop impedance (Zs) and prospective fault current. Verify protective device coordination against the adopted NEC edition, equipment documentation, and AHJ requirements.
- Short Circuit Current CalculatorEstimate available fault current from transformer impedance, feeder impedance, or known source impedance.
- Circuit Breaker Sizing CalculatorCalculate standard breaker sizes for general loads, continuous loads, and simplified motor branch-circuit reviews
- Grounding CalculatorNEC Article 250 grounding and bonding conductor screen for main bonding jumpers, equipment grounding conductors, and grounding electrode conductors.
Related charts
- Short Circuit Current ChartPlan short-circuit current checks from utility data, transformer kVA and impedance, voltage, conductor path, motor contribution, and equipment SCCR/AIC.
- Breaker Size ChartPlan breaker size from load category, continuous duty, conductor protection, interrupting rating, equipment listing, and calculator result notes.
- Grounding Resistance ChartUse a grounding resistance chart to document soil assumptions, electrode geometry, measured ohms, target basis, spacing notes, and field-test follow-up.