How to Size Grounding and Bonding Conductors under the NEC
“Grounding cable” is a common commercial term, but it is not specific enough for NEC design work.
Before selecting a conductor size, you must first identify what the conductor is required to do.
It may be:
- An equipment grounding conductor, or EGC
- A grounding electrode conductor, or GEC
- A main bonding jumper
- A system bonding jumper
- A supply-side bonding jumper
- An equipment bonding jumper
- A temporary protective grounding cable used during maintenance
These conductors do not all use the same sizing method.
An EGC is normally selected from the upstream overcurrent protective device. A GEC is selected from the ungrounded supply conductors and grounding electrode rules. Main, system and supply-side bonding jumpers follow their own bonding provisions.
Temporary protective grounding cables used for substation or line maintenance require a different selection process.
This guide explains the differences in simple terms and shows how engineers and buyers can prepare a clearer grounding conductor specification.
Important Code Note
This article uses NEC terminology for general education and procurement planning.
The final conductor size must be confirmed according to:
- The NEC edition adopted by the authority having jurisdiction
- Local amendments
- Project drawings and specifications
- The electrical system design
- The conductor installation method
- Equipment listings and manufacturer instructions
- Approval by the project designer and authority having jurisdiction
Do not use this article as a replacement for final electrical design or code approval.
Quick Answer: Which Grounding Table or Rule Applies?
| Conductor Type | Main Sizing Basis | Main Purpose |
|---|---|---|
| Equipment Grounding Conductor | Upstream breaker or fuse rating and applicable NEC rules | Provides a ground-fault current path with the circuit |
| Grounding Electrode Conductor | Largest ungrounded supply conductor or equivalent parallel area, plus electrode rules | Connects the system to the grounding electrode system |
| Main Bonding Jumper | Largest ungrounded service conductor and applicable bonding rules | Connects the grounded conductor to the equipment grounding path at the service |
| System Bonding Jumper | Ungrounded conductors of the separately derived system | Establishes the required bonding connection at a separately derived system |
| Supply-Side Bonding Jumper | Ungrounded supply conductors associated with the jumper | Bonds metal enclosures and raceways on the supply side |
| Equipment Bonding Jumper | Installation location, OCPD and specific bonding rule | Maintains continuity between equipment grounding components |
| Temporary Protective Grounding Cable | Fault current, clearing time, cable length, clamp rating and work procedure | Protects workers during maintenance on de-energized equipment |
The first question should never be:
“What grounding cable size do I need?”
The first question should be:
“Which type of grounding or bonding conductor am I sizing?”
EGC vs GEC vs Bonding Jumper
These terms are often confused.
Equipment Grounding Conductor
An equipment grounding conductor runs with the circuit conductors or forms part of the wiring method.
Its purpose is to provide an effective ground-fault current path so that the protective device can operate when a fault occurs.
The EGC is not normally selected from the grounding electrode or soil resistance.
Grounding Electrode Conductor
A grounding electrode conductor connects the grounded conductor or equipment to the grounding electrode system.
The grounding electrode system may include:
- Ground rods
- Underground metal water pipe
- Concrete-encased electrodes
- Ground rings
- Building structural metal
- Other recognized electrodes
The GEC is not normally sized from a downstream branch-circuit breaker.
Bonding Jumper
A bonding jumper connects conductive parts to establish electrical continuity.
Depending on its location, it may be a:
- Main bonding jumper
- System bonding jumper
- Supply-side bonding jumper
- Equipment bonding jumper
Bonding helps maintain electrical continuity, reduce potential differences and support an effective ground-fault current path.
It does not guarantee that all touch-voltage risk is eliminated.
Information You Need Before Sizing
Collect the following information before looking at a conductor table.
| Required Input | Why It Matters |
|---|---|
| NEC edition | Article numbers and requirements may change between editions |
| Authority having jurisdiction | Local adoption and amendments control final approval |
| Conductor function | Determines whether EGC, GEC or bonding rules apply |
| OCPD rating | Common starting point for EGC sizing |
| Ungrounded conductor size | Common starting point for GEC and certain bonding jumpers |
| Conductor material | Copper and aluminum use different table columns |
| Parallel conductor arrangement | Equivalent conductor area or individual raceway rules may apply |
| Wiring method | Metal raceway, cable, wire-type EGC or cable tray may affect the design |
| Grounding electrode type | Special GEC rules may apply |
| Environment | Corrosion, moisture, soil contact and physical damage affect materials |
| Terminal rating | Connectors must match conductor material and temperature rating |
| Project documentation | Drawings, grounding schedule and acceptance records may be required |
Without these inputs, a conductor size alone has little engineering value.
How to Size an Equipment Grounding Conductor
An equipment grounding conductor is generally selected using the rating or setting of the overcurrent protective device ahead of the circuit.
Basic EGC Workflow
- Identify the breaker or fuse rating.
- Confirm the adopted NEC edition.
- Find the applicable EGC table and conductor material column.
- Select copper or aluminum.
- Review the installation method.
- Check parallel raceway or cable requirements.
- Review whether any conductor upsizing affects the EGC requirement.
- Confirm terminal compatibility and physical protection.
Illustrative EGC Example
Assume a feeder is protected by a 400A circuit breaker.
Using the commonly referenced NEC EGC table:
| Input | Example |
|---|---|
| Upstream OCPD | 400A circuit breaker |
| EGC material | Copper |
| Table basis | OCPD rating |
| Illustrative minimum EGC | 3 AWG copper |
For aluminum or copper-clad aluminum, the corresponding illustrative table value is 1 AWG.
This is a simple example only.
The engineer must still confirm:
- The adopted NEC edition
- Whether the circuit is installed in one or several raceways
- Whether a metal raceway is used as the EGC
- Whether the phase conductors were increased
- Whether fault-path impedance requires a larger conductor
- Whether special equipment rules apply
What If the Breaker Rating Is Not Listed?
Where the exact OCPD rating does not appear in the applicable table, the next higher listed rating may need to be used.
Do not interpolate between table values unless the applicable rule permits it.
What If the Phase Conductors Are Increased?
Do not automatically apply a universal percentage rule.
If ungrounded conductors are increased beyond their normal required size, check the specific NEC edition adopted for the project to determine whether and how the EGC must also be increased.
The applicable rule may depend on:
- Why the conductors were increased
- The conductor ampacity
- The installed conductor area
- The required ground-fault path performance
- The wording of the adopted NEC edition
Record the design basis in the grounding schedule.
EGCs in Parallel Raceways and Cables
Parallel installations require careful review.
Do not assume one EGC arrangement applies to every parallel circuit.
| Installation Arrangement | What Must Be Checked |
|---|---|
| Parallel conductors in separate raceways | EGC requirement in each raceway |
| Parallel multiconductor cables | EGC arrangement within each cable |
| Conductors in one raceway | Whether one common EGC is permitted |
| Conductors in cable tray | Applicable tray and EGC provisions |
| Metal raceway used as EGC | Listing, continuity, fittings and installation |
| Underground parallel runs | Raceway arrangement and bonding at both ends |
A simplified statement such as “each conduit always gets the same full-size EGC” may not describe every installation correctly.
Use the specific NEC rule for the actual layout.
Can Metal Raceway Be Used as the EGC?
Some listed metal raceways and fittings can serve as an equipment grounding conductor when installed correctly.
The complete path must maintain electrical continuity.
Check:
- Raceway type
- Listed fittings
- Expansion joints
- Flexible sections
- Corrosion
- Painted surfaces
- Mechanical damage
- Bonding bushings or jumpers where required
- Continuity across equipment sections
Where the raceway path is uncertain, a wire-type EGC may be specified by the project designer.
How to Size a Grounding Electrode Conductor
A grounding electrode conductor is generally selected from the largest ungrounded supply conductor or the equivalent area of parallel conductors.
However, the final requirement also depends on the type of grounding electrode.
Basic GEC Workflow
- Confirm whether the conductor is for a service, building supply or separately derived system.
- Identify the largest ungrounded conductor.
- For parallel conductors, calculate the equivalent area where required.
- Select the correct copper or aluminum column.
- Determine the grounding electrode type.
- Apply any electrode-specific sizing provisions.
- Check conductor routing and physical protection.
- Confirm connector and corrosion requirements.
Illustrative GEC Example with Parallel Conductors
Assume a service uses two parallel 500 kcmil copper conductors per phase.
Step 1: Calculate the Equivalent Area
2 × 500 kcmil = 1000 kcmil copper
Step 2: Use the Applicable GEC Table
An equivalent area of 1000 kcmil copper falls within the commonly referenced range of over 600 through 1100 kcmil.
Illustrative Result
The corresponding illustrative GEC size is:
2/0 AWG copper
| Input | Example |
|---|---|
| Conductors per phase | Two |
| Size of each conductor | 500 kcmil copper |
| Equivalent area | 1000 kcmil copper |
| Illustrative GEC | 2/0 AWG copper |
This result may change when electrode-specific provisions apply.
Why the Grounding Electrode Type Matters
The GEC is not always required to be as large as the basic table result.
Different rules may apply when the conductor connects only to certain electrode types.
| Electrode Type | Important Sizing Consideration |
|---|---|
| Rod, pipe or plate electrode | A permitted maximum required conductor size may apply |
| Concrete-encased electrode | A separate permitted maximum may apply |
| Ground ring | The conductor may be related to the ground-ring conductor size |
| Underground metal water pipe | Full table-based sizing may be required |
| Structural metal electrode | Confirm applicable table and bonding rules |
| Multiple-electrode system | Check how the GEC and bonding jumpers connect through the complete system |
For example, a conductor connected only to a qualifying rod, pipe or plate electrode may not be required to be larger than the permitted code maximum, even when the general GEC table indicates a larger conductor.
However, if the same conductor continues to another electrode that requires a larger size, the smaller limitation may no longer apply to that conductor segment.
This is why the electrode layout must be known before the final GEC is specified.
GECs for Separately Derived Systems
Transformers and generators may create separately derived systems.
In these cases, confirm:
- Secondary ungrounded conductor size
- Grounded conductor arrangement
- System bonding jumper location
- Grounding electrode connection
- Whether the bonding point is at the source or first disconnect
- Whether parallel neutral paths could be created
- Applicable GEC and bonding conductor rules
Do not treat every transformer secondary grounding conductor as an ordinary feeder EGC.
How to Size Bonding Jumpers
“Bonding jumper” is not one single conductor type.
The correct sizing rule depends on the jumper’s function and location.
Main Bonding Jumper
The main bonding jumper connects the grounded service conductor to the equipment grounding system at the service.
It is generally sized from the largest ungrounded service conductor or equivalent parallel conductor area using the applicable bonding provisions.
System Bonding Jumper
The system bonding jumper performs a similar function at a separately derived system.
The permitted bonding location must be confirmed so that unwanted parallel current paths are not created.
Supply-Side Bonding Jumper
A supply-side bonding jumper bonds metal equipment and raceways on the supply side of the service disconnect or separately derived system disconnect.
Its sizing basis is generally related to the associated ungrounded supply conductors.
Equipment Bonding Jumper
An equipment bonding jumper connects two or more portions of the equipment grounding path.
Its size may depend on:
- OCPD rating
- Equipment grounding conductor rules
- Raceway or equipment arrangement
- The specific NEC section that requires the jumper
Do not assume every equipment bonding jumper uses the same table as a main bonding jumper.
Illustrative Supply-Side Bonding Jumper Example
Assume one raceway contains 400 kcmil copper supply conductors.
Using the commonly referenced bonding table:
| Input | Example |
|---|---|
| Ungrounded conductor in the raceway | 400 kcmil copper |
| Jumper type | Supply-side bonding jumper |
| Sizing basis | Ungrounded supply conductor |
| Illustrative jumper | 1/0 AWG copper |
For an installation with several raceways, each individual supply-side bonding jumper may need to be sized from the conductors in its own raceway.
A single common jumper for the full parallel conductor area follows a different calculation method.
Large Parallel Supply Conductors
Where the total equivalent area exceeds the range shown in the applicable bonding table, a percentage calculation may be required.
For example:
Five parallel 400 kcmil copper conductors:
5 × 400 kcmil = 2000 kcmil
Using an illustrative 12.5% rule where applicable:
2000 kcmil × 0.125 = 250 kcmil copper
This type of calculation applies only when the relevant NEC rule and conductor arrangement support it.
Always confirm:
- Jumper type
- Conductor material
- Parallel conductor arrangement
- Table notes
- NEC edition
- Location of the bonding connection
Permanent NEC Grounding Is Not Temporary Protective Earthing
This distinction is especially important for utility, substation and industrial maintenance buyers.
The EGC, GEC and bonding conductors discussed above are part of a permanent electrical installation.
A portable earthing and short-circuit kit is temporary safety equipment used during maintenance on de-energized equipment.
These products do not use the same sizing method.
| Permanent NEC Conductor | Temporary Protective Grounding Cable |
|---|---|
| Part of the installed electrical system | Applied temporarily during maintenance |
| May be sized from OCPD or supply conductors | Sized from fault current and clearing time |
| Uses NEC installation and bonding rules | Uses temporary grounding equipment standards and site procedures |
| Usually remains installed | Installed and removed for each work activity |
| May use building wiring conductors | Usually uses highly flexible cable assemblies |
| Does not require portable clamps | Requires rated clamps, ferrules and connection interfaces |
Temporary protective grounding selection should consider:
- Maximum available fault current
- Protective device clearing time
- Required cable cross-section
- Cable length
- Cable flexibility
- Clamp rating
- Ferrule and lug rating
- Connection-point geometry
- Mechanical strength
- Thermal withstand
- Work method and grounding sequence
Do not size a temporary grounding cable only from an NEC EGC table.
For temporary grounding products, review the JINPOWER grounding cable and complete portable earthing kit options according to your confirmed system and work procedure.
Copper vs Aluminum Grounding Conductors
Copper and aluminum must be selected from the correct table columns and matched with compatible terminations.
| Factor | Copper | Aluminum |
|---|---|---|
| Conductivity | Higher conductivity for the same cross-section | Usually requires a larger size for an equivalent table position |
| Weight | Heavier | Lighter |
| Flexibility | Depends on strand construction | Depends on alloy and construction |
| Corrosion considerations | Still requires correct material interfaces | Requires careful control of environment and connector compatibility |
| Terminations | Use listed copper-compatible connectors | Use connectors listed for aluminum or dual-rated use |
| Maintenance | Follow connector instructions | Follow preparation, inhibitor and torque instructions exactly |
Do not automatically apply antioxidant compound to every aluminum termination.
Use it only when required by:
- Connector instructions
- Equipment listing
- Project specification
- Approved installation procedure
Do not re-torque a connection unless the listed product instructions or approved maintenance procedure require it.
Grounding Cable Lugs, Clamps and Terminations
The conductor size alone does not make a reliable grounding or bonding connection.
The complete interface must be checked.
Termination Checklist
| Item | What to Verify |
|---|---|
| Conductor material | Copper, aluminum or copper-clad aluminum |
| Conductor size | AWG, kcmil or mm² |
| Lug listing | Listed for the conductor material and size |
| Number of conductors | Lug approved for one or multiple conductors |
| Temperature rating | Compatible with conductor and equipment ratings |
| Crimp tool | Correct tool and die |
| Preparation | Follow manufacturer cleaning and preparation instructions |
| Torque | Use the specified torque value |
| Contact surface | Remove paint only where required by the approved connection method |
| Corrosion control | Match metals and environmental conditions |
| Strain relief | Prevent movement at the termination |
| Identification | Circuit, size, material and connection point clearly marked |
For more detail, read our guide to grounding cable terminations.
Grounding and Bonding RFQ Checklist
When requesting grounding conductor or hardware pricing, provide a confirmed technical specification.
| RFQ Item | Information to Provide |
|---|---|
| Conductor function | EGC, GEC, bonding jumper or temporary grounding cable |
| Code basis | Adopted NEC edition or project standard |
| Conductor material | Copper, aluminum or tinned copper |
| Required size | AWG, kcmil or mm² |
| Length | Per conductor or per assembly |
| Insulation | Bare, insulated or jacketed |
| Color | Green, green/yellow, black or project-specific |
| Termination | Lug, ferrule, clamp or bare end |
| Connector details | Hole size, palm width, barrel size and material |
| Quantity | Total length or number of assemblies |
| Environment | Indoor, outdoor, underground, corrosive or humid |
| Marking | Circuit ID, length mark, serial number or QR code |
| Documents | Specification, drawings, inspection records or test reports |
| Packaging | Coil, reel, carton, pallet or complete kit |
The final electrical size should already be confirmed by the project designer.
A supplier should not guess the final NEC conductor size from incomplete project information.
Goods-In and Commissioning Checklist
When grounding conductors and bonding hardware arrive on site, check more than the packing quantity.
| Inspection Item | What to Check |
|---|---|
| Conductor marking | Size, material, insulation and manufacturer identification |
| Quantity and length | Match purchase order and drawings |
| EGC schedule | Circuit ID, OCPD and conductor size agree |
| GEC basis | Supply conductor and electrode information are recorded |
| Bonding jumper type | Main, system, supply-side or equipment jumper clearly identified |
| Lugs and clamps | Correct material, conductor range and interface |
| Crimp quality | Correct die marks and no visible damage |
| Torque records | Recorded where required |
| Corrosion protection | Suitable for the installation environment |
| Raceway continuity | Verified where raceway is part of the grounding path |
| Bonding across joints | Jumpers installed at required breaks and transitions |
| Identification | Labels and circuit references remain readable |
| Documentation | Drawings, grounding schedule and inspection records filed |
Suggested Grounding Schedule Fields
A useful grounding schedule may include:
- Circuit or equipment ID
- Conductor type
- OCPD rating
- Ungrounded conductor size
- Copper or aluminum
- Number of parallel runs
- EGC size
- GEC size
- Bonding jumper type and size
- Electrode type
- Raceway type
- Lug or clamp model
- Torque value
- Drawing reference
- Inspection status
Common Grounding Conductor Sizing Mistakes
Treating Every Green Cable as an EGC
A green conductor may be an EGC, but conductor color alone does not define its electrical function.
Identify the system connection and design purpose.
Sizing a GEC from the Main Breaker
A GEC is generally not sized from a downstream breaker.
It is commonly based on the ungrounded supply conductor and electrode rules.
Using the GEC Table for a Bonding Jumper
Main, system and supply-side bonding jumpers follow bonding rules, not the GEC table.
Applying One Rule to Every Parallel Installation
Separate raceways, multiconductor cables and cable trays may require different grounding arrangements.
Ignoring the Grounding Electrode Type
Ground rods, concrete-encased electrodes, ground rings and metal water pipes may not have the same conductor requirement.
Using an Automatic Percentage for Every Upsized EGC
The correct treatment depends on the adopted NEC edition and installation conditions.
Do not apply a general rule without checking the applicable section.
Treating Temporary Grounding Cable as a Permanent EGC
Portable protective grounding sets are selected from fault-current duty and work procedures, not only from a breaker-based EGC table.
Selecting the Cable but Ignoring the Lug
A correctly sized conductor can still fail acceptance if the lug, clamp, crimp or torque is wrong.
Using Aluminum Hardware Without Checking the Listing
Connector material, preparation and environmental suitability must be confirmed.
Providing a Size Without a Design Basis
A grounding specification should record:
- Conductor function
- Sizing rule
- Input data
- Table or section reference
- Material
- Installation arrangement
- Connector details
FAQ About NEC Grounding Conductor Sizing
Is an EGC the Same as a GEC?
No.
An EGC provides a ground-fault current path with a circuit. A GEC connects the electrical system to the grounding electrode system.
They have different purposes and sizing methods.
Is Grounding Cable Size Based on Breaker Size?
Only some conductors use the breaker or fuse as the main sizing input.
An EGC is generally based on the upstream OCPD.
A GEC and certain bonding jumpers use different inputs.
Does a Larger Phase Conductor Always Require a Larger EGC?
Not automatically in every situation.
Check the adopted NEC edition, reason for conductor upsizing and applicable EGC rule.
How Is a GEC Sized for Parallel Conductors?
The equivalent area of the corresponding parallel ungrounded conductors may need to be added together.
The result is then compared with the applicable GEC table, subject to grounding electrode rules.
Are All Bonding Jumpers Sized from the EGC Table?
No.
Main, system and supply-side bonding jumpers commonly use bonding provisions based on the ungrounded supply conductors.
Equipment bonding jumpers may use different rules.
Can a Metal Raceway Be Used as the EGC?
Certain listed raceways can be used as an equipment grounding conductor when installed with the correct fittings and continuous bonding path.
The complete installation must satisfy the applicable requirements.
Is a Temporary Substation Grounding Cable Sized from the NEC EGC Table?
No.
Temporary protective grounding cable should be selected from fault current, clearing time, conductor length, clamp rating and the approved work procedure.
Which NEC Edition Should I Use?
Use the edition adopted by the authority having jurisdiction for the project location.
Also check local amendments and project specifications.
Can JINPOWER Provide the Final NEC Grounding Design?
JINPOWER can supply grounding cable, clamps, lugs and temporary earthing products according to a confirmed specification.
Final NEC sizing, system design and installation approval should be completed by the project designer and authority having jurisdiction.
Final Guidance
There is no single formula for every “grounding cable.”
Use this sequence:
- Identify the conductor type.
- Confirm the adopted NEC edition.
- Collect the correct input data.
- Use the rule for EGC, GEC or the specific bonding jumper.
- Check parallel conductors and grounding electrode type.
- Confirm copper or aluminum.
- Match lugs, clamps and terminations.
- Record the sizing basis.
- Complete inspection and continuity checks.
- Obtain final project and AHJ approval.
The most important distinction is simple:
EGC, GEC and bonding jumpers are not interchangeable.
Temporary protective grounding cables used during maintenance are also not sized by the same method as permanent NEC grounding conductors.
Need Grounding Cable or Connection Hardware for Your Project?
Tell us the confirmed conductor type, copper or aluminum material, cross-section, cable length, insulation, terminal type, clamp interface, quantity, packaging and document requirements.
JINPOWER can support:
- Grounding cable
- Lugs and ferrules
- Grounding clamps
- Grounding sticks
- Portable earthing and short-circuit kits
- Temporary protective grounding assemblies
- Product identification and project packaging
Explore our grounding stick, portable earthing and short-circuit kits, power engineering safety solutions and substation safety solutions.
Final NEC sizing and installation approval should be confirmed by the project designer and authority having jurisdiction.
