Panel Earthing

Electrical panel earthing is a fault-current problem, not a current-density problem. The protective earth (PE) busbar is sized from the prospective earth-fault current and the protective device's clearing time — not from the phase busbar rating, and not from a company-standard 25 × 6 mm copper flat.

That one rule settles most of the arguments that happen in a design review. The rest of this guide shows how to apply it: PE sizing by the adiabatic method, neutral-earth separation, door and gland-plate bonding, shipping-split continuity, and the earthing checks that belong in FAT.

In our own design reviews at Wisdom Techno Solutions, the earth busbar is the single most frequently under-engineered item in an otherwise well-specified LT panel. Customers write three pages of clauses on the ACB and one line on earthing.

The Question That Starts Every Design Review

A PCC panel has:

3200 A phase busbar

and:

1600 A neutral busbar

What should the earth busbar be?

Should it also be:

3200 A?

Should it be:

50% of phase busbar?

Or should the designer simply use:

25 × 6 mm copper earth bar because that is standard practice?

None of these approaches is universally correct.

The protective earth busbar has a fundamentally different duty from the phase and neutral busbars.

The phase conductor carries:

continuous operating current.

The neutral may carry:

normal return current and harmonic/unbalanced current.

The protective earth conductor should normally carry little or no current during healthy operation, but during an earth fault it may need to carry a very large current for the time required for the protective device to disconnect the fault.

IEC 60364-5-54 addresses earthing arrangements and protective conductors, while IEC 61439-1 provides construction and verification requirements for protective circuits inside LV assemblies.

Busbar	Normal duty	Fault duty	Sized primarily from
Phase (L1/L2/L3)	Continuous full-load current	Short-circuit withstand for the assembly Icw	Current density and temperature rise, then verified against fault withstand
Neutral (N)	Unbalance, single-phase and triplen harmonic current	Depends on system earthing and fault type	Percentage of phase busbar set by load type — commonly 50%, and 100% where harmonic-rich electronic load dominates
Protective earth (PE)	Little or no current in a healthy system	Full prospective earth-fault current for the disconnection time	Adiabatic thermal withstand: fault current and clearing time

Therefore:

Earth busbar sizing is primarily a protective-fault-current problem, not a normal current-density problem.

Earth Busbar vs Neutral Busbar

This distinction is essential.

Neutral Busbar — N

The neutral is a normal current-carrying circuit conductor.

It may carry:

• Unbalanced phase current
• Single-phase load current
• Triplen harmonic current
• Electronic-load current

Protective Earth Busbar — PE

The PE busbar forms part of the protective circuit.

Its purpose includes:

• Connecting exposed conductive parts
• Providing a low-impedance fault-current path
• Supporting automatic disconnection of supply
• Equipotential bonding

Therefore:

Neutral ≠ Earth

and:

Neutral sizing ≠ Earth sizing

Should Neutral and Earth Be Connected Inside the Panel?

That depends on the system earthing arrangement and location of the neutral-earth bond.

IEC 60364 distinguishes earthing arrangements such as:

• TN-S
• TN-C
• TN-C-S
• TT
• IT

Once neutral and protective functions have been separated in an installation, they should not simply be reconnected downstream wherever convenient. This is a general principle of TN-S and TN-C-S design: once PE and N are split at the defined bonding point, the neutral must not be re-bonded to earthed parts further downstream, because doing so creates parallel neutral return paths through the protective conductor and the building steel.

Therefore:

Do not install an N–E link inside an LT panel merely because neutral and earth bars are physically close to each other.

The neutral-earth bonding point must follow the approved earthing philosophy.

How Is an Earth Busbar Sized?

IEC 60364-5-54 permits protective-conductor sizing using defined tabulated relationships or by calculating thermal withstand under earth-fault conditions.

For applicable disconnection times, the commonly used adiabatic relationship is:

S = I × √t / k

where:

• S = protective-conductor cross-sectional area
• I = prospective RMS earth-fault current
• t = fault-clearing time
• k = factor based on conductor material, insulation and permissible temperatures

The k factor is taken from IEC 60364-5-54 Table 54.2 and similar tables. As an indication, k ≈ 143 is commonly used for a PVC-insulated copper protective conductor and k ≈ 159 for bare copper where the conductor is not in contact with combustible material. Confirm the correct k for your conductor material, insulation and installation method before using any calculated figure.

This illustrates an important principle:

The required PE section depends on both fault current and clearing time.

Indicative PE Cross-Section — Adiabatic Method

The table below applies S = I × √t / k with k = 143 (PVC-insulated copper). It is illustrative arithmetic to show the shape of the problem, not a design output — the actual earth-fault current, clearing time and k value for your project must come from the system study.

Earth-fault current	t = 0.05 s	t = 0.1 s	t = 0.2 s	t = 0.5 s	t = 1.0 s
25 kA	39 mm²	55 mm²	78 mm²	124 mm²	175 mm²
35 kA	55 mm²	77 mm²	109 mm²	173 mm²	245 mm²
50 kA	78 mm²	111 mm²	156 mm²	247 mm²	350 mm²

Now read that table against the habit it replaces. A 25 × 6 mm copper flat is 150 mm². It is comfortable at 25 kA even with a 0.5 s clearing time. At 50 kA with 0.2 s it is already marginal, and at 50 kA with 0.5 s it is not adequate at all.

Our recommendation: treat the earth busbar as a calculated item on the same GA revision as the phase busbar, and record the earth-fault current and clearing time used, on the drawing. When a panel is later retrofitted or the upstream protection is re-set, the next engineer needs to know what assumption the earth bar was built on.

Why Fault-Clearing Time Matters

Consider two identical earth faults:

Fault Current = 30 kA

System A

Breaker clears in:

0.05 s

System B

Breaker clears in:

1.0 s

The thermal energy imposed on the protective conductor is dramatically different.

Therefore an earth busbar suitable for one system may not automatically be suitable for another even if:

Fault current is identical.

Protection settings and PE sizing are connected.

Do Not Size Earth Busbar Using 1.6 A/mm²

WTS uses approximately:

1.6 A/mm²

as an internal preliminary current-density basis for copper phase busbar sizing.

That approach should not simply be transferred to the PE busbar.

Why?

Because the earth busbar is not intended to continuously carry full-load phase current.

Its critical electrical duty is:

fault current for a specified duration.

Therefore earth-bar sizing should be based on the protective-conductor rules and fault duty, together with mechanical and project requirements.

Earth Busbar Must Be Continuous

A protective circuit is only useful if it remains electrically continuous.

The earth path may include:

Incoming PE conductor

↓

Main earth busbar

↓

Panel frame

↓

Doors

↓

Gland plates

↓

Withdrawable/fixed functional units

↓

Outgoing PE terminals

Each connection should provide reliable protective continuity according to the assembly design.

IEC 61439 includes protective circuits within its construction and verification framework.

Panel Body Earthing

The metal enclosure should be integrated into the protective circuit according to the approved construction.

This can involve:

• Main structure
• Side covers
• Doors
• Mounting plates
• Gland plates
• Removable metal covers

Do not assume:

Bolts + paint + hinges = guaranteed earth continuity.

Painted surfaces, removable parts and hinges may not provide the intended low-impedance protective path unless the design specifically relies on and verifies that arrangement.

Should Panel Doors Have Earthing Braid?

Where a door carries electrical equipment or where reliable bonding cannot be assured through the mechanical arrangement, a dedicated flexible protective bonding conductor is often used.

Typical examples include doors containing:

• Meters
• Pushbuttons
• HMI
• Selector switches
• Electrical devices

The exact bonding arrangement should follow the verified assembly design and project specification.

The important requirement is:

protective continuity, not simply the visual presence of a green-yellow braid.

Gland Plate Earthing

Metallic gland plates can become part of the fault-current path.

The design should therefore consider:

• Bonding to main enclosure
• Cable armour termination
• Metallic glands
• PE continuity

A removable gland plate should not unintentionally break the protective path.

Cable Armour Is Not Automatically the Panel PE Busbar

Armoured cables may contribute to protective earthing where properly designed.

But the panel still needs a defined:

main protective conductor / earth terminal architecture.

Do not assume that because every cable has armour:

no main PE busbar is required.

The complete installation protection philosophy decides.

Incoming Earth Connection

The main earth busbar should provide an accessible and clearly identified location for connection to the plant earthing system.

Important considerations include:

• Conductor size
• Number of incoming earth connections
• Lug arrangement
• Accessibility
• Corrosion
• Tightening method

Avoid stacking numerous large earth lugs onto one small bolt without a defined joint design.

Outgoing Feeder Earth Connections

Each outgoing circuit should have a defined protective-earth path.

For large feeders, this may involve:

• Dedicated PE cable
• Earth conductor within multicore cable
• Armour where permitted
• Dedicated earth-bus termination

The protective conductor must be coordinated with the complete installation.

Earth Busbar Material

Common options include:

• Copper
• Tinned copper
• Aluminium in appropriately engineered systems

Copper is widely used because of:

• Conductivity
• Compact size
• Connection convenience

But material selection alone does not define adequate PE performance.

The design still needs suitable:

• Cross section
• Connections
• Fault withstand
• Mechanical strength

Bare Copper vs Tinned Copper Earth Bar

Tin plating can offer connection/corrosion benefits in suitable environments.

But:

tinning does not increase an undersized earth bar's fundamental fault withstand enough to replace correct sizing.

Select plating based on:

• Environment
• Joint material
• Project requirement

not as a substitute for adequate conductor section.

Earth Busbar Along the Full Panel Length

In multi-section PCC/MCC assemblies, a continuous earth busbar is commonly routed through the complete lineup.

This provides each section with access to the same protective network.

Special attention is required at shipping splits.

When two panel sections are reassembled on site:

the PE bus connection across the shipping split must be correctly restored.

Shipping Split Mistake

A switchboard may pass FAT in the factory as one complete lineup.

Then it is separated for transport.

At site:

• Main phase links are restored
• Neutral links are restored

but:

earth-bus link is forgotten.

This can leave downstream sections without the intended protective path.

Therefore PE shipping links should be part of:

• Installation drawings
• Site checklist
• Commissioning verification

Earthing for Withdrawable MCCs

Withdrawable units require careful protective continuity throughout:

• Connected position
• Test position
• Disconnected position

depending on the selected switchgear design.

Do not improvise earthing arrangements on a withdrawable system.

Use the verified original manufacturer's design.

Earth Fault Current May Be Lower Than Three-Phase Fault Current

Do not automatically use:

3-phase short-circuit current = earth-fault current

for every system.

Earth-fault magnitude depends on:

• Earthing arrangement
• Transformer neutral
• Earth impedance
• PE path
• Generator/transformer source
• Fault location

Calculate or obtain the applicable earth-fault current.

Earth Busbar and Multiple Transformers

A panel supplied by multiple transformers can have different earth-fault conditions depending on:

• Bus coupler position
• Transformer neutral arrangement
• Parallel sources

Therefore the worst credible operating state should be evaluated.

This links directly with the:

2 Incomer + Bus Coupler

protection philosophy.

Neutral-Earth Connection and DG/ATS Systems

Generator systems introduce an important question:

Where is the generator neutral bonded to earth?

This affects:

• ATS 3P vs 4P
• Earth-fault return
• Neutral switching
• Protective device operation

The PE busbar must remain part of a coherent system across all source modes.

PE Busbar Is Not a Current-Carrying Neutral Substitute

Never intentionally route normal neutral current through:

• Panel body
• Earth bar
• Cable armour
• Protective conductor

except where the approved system specifically uses a combined PEN conductor in accordance with the applicable rules.

Once N and PE are separated:

keep their functions separate.

Protective Continuity Verification

Routine panel verification should confirm the protective circuit.

Typical checks can include:

• Main PE bus continuity
• Door bonding
• Gland plate bonding
• Section-to-section bonding
• Functional-unit earthing
• Outgoing PE terminals

This is especially important after:

• Painting
• Mechanical assembly
• Shipping split reassembly

Protective Continuity Checkpoint Table

Checkpoint	What is verified	Most common failure we find
Main PE busbar	Continuity end to end across all sections	Shipping-split link not refitted at site
Panel doors	Bonding of doors carrying meters, HMI or pushbuttons	Reliance on hinges alone; paint at the hinge face
Gland plates	Bonding of removable gland plate to enclosure	Plate refitted after cable pulling without its bonding strap
Mounting plates	Bonding of painted mounting plates carrying devices	Paint not removed at the bonding stud
Withdrawable units	PE continuity in connected, test and isolated positions	Field-modified earthing on an OEM withdrawable chassis
Cable armour termination	Armour bonded per the design, not instead of the PE bus	Armour treated as the only protective conductor
Outgoing PE terminals	One defined earth termination per outgoing circuit	Several feeders sharing one small earth stud

Common Panel Earthing Mistakes

Mistake 1 — Earth bar selected only as 25 × 3 or 25 × 6 because it is company standard

Verify fault duty.

Mistake 2 — Earth bar sized using phase busbar A/mm²

Protective conductor duty is different.

Mistake 3 — Neutral and earth linked inside every panel

N–E bonding must follow the system earthing design.

Mistake 4 — Hinges assumed to provide reliable door earth

Use the approved bonding arrangement.

Mistake 5 — Shipping split PE link forgotten

A major commissioning risk.

Mistake 6 — Earth bar sized only from three-phase fault current

Use applicable earth-fault conditions.

Mistake 7 — Paint not considered at bonding points

Electrical continuity must be intentional.

Relevant Standards

The current consolidated IEC reference for protective conductors is:

IEC 60364-5-54:2011 + AMD1:2021, covering earthing arrangements, protective conductors and protective bonding conductors.

For LV panel assemblies:

IEC 61439-1:2020

and:

IEC 61439-2:2020

provide the general and PSC-assembly requirements.

WTS Approach to Panel Earthing

For Wisdom Techno Solutions, PE busbar selection should be based on:

• Earthing system
• Calculated earth-fault current
• Clearing time
• Panel fault rating
• Material
• Multi-section construction
• Cable termination
• Neutral philosophy
• DG/transformer arrangement

Depending on project requirements, our FAT includes applicable checks for:

• Protective continuity
• Earth bus construction
• Door bonding
• Gland-plate bonding
• Earth termination
• Section bonding

The key objective is:

Every exposed conductive part that must be protective-earthed should have a deliberate, reliable and verifiable path back to the protective earthing system.

How Wisdom Techno Solutions Handles Panel Earthing

Wisdom Techno Solutions manufactures LT switchgear at Vadodara, Gujarat — PCC and PMCC panels, MCC and PMCC assemblies, APFC and detuned APFC panels, VFD and bypass panels, ATS and AMF panels, DG synchronization panels and PLC control panels — for pharma, chemical, water, solar, BESS and general process plants.

Wisdom Techno Solutions is a licensed partner for three design-verified switchgear platforms: Rittal Ri4Power (Rittal Solutions Partner since 2021 — the Ri4Power system carries Intertek ASTA design verification to IEC 61439-1 and -2 Edition 3, with copper and aluminium busbar systems up to 6300 A), C&S CX (Licensed Partner since 2023, up to Form 4B Type II) and Siemens SIEPAN Elite/8PU (IEC 61439 Solutions Partner since 2024). We build to each system's verified configuration and routine-verify every assembly in-house at our Vadodara, Gujarat facility, for industrial, EPC and infrastructure projects across India. That places the protective-circuit continuity and earth-bar rating inside a verified design envelope.

On earthing specifically, our standard practice is:

• The earth-fault current and clearing time used for PE sizing are recorded on the busbar GA, not carried in someone's head
• Every bonding point where paint must be removed is called out on the drawing, so it does not depend on the assembler remembering
• PE shipping links are listed as separate line items in the site installation checklist, with a signature against each one
• Protective continuity is re-checked after painting and again after final assembly, because the first check does not survive the second operation
• For withdrawable MCCs we use the switchgear OEM's earthing arrangement without local modification

Send us your single line diagram, load list, earthing philosophy and fault level, and we will come back with the earth busbar section, the bonding schedule and the protective continuity checks we propose to run at FAT — before manufacturing starts, not after.

Conclusion

Earth busbar sizing is a thermal withstand calculation driven by earth-fault current and clearing time. Neutral is not earth, and where they were separated they stay separated. The protective path is only as good as its weakest joint, which is usually a painted surface or a forgotten shipping link.

If you take one thing from this guide: the panel that passes FAT as one lineup can arrive at site with its protective circuit broken in three places. Design the earthing, then verify it — twice.

Related Guides

• 3-pole vs 4-pole ATS
• Internal arc and IEC TR 61641
• Form 1/2/3/4a/4b internal separation
• Electrical panel FAT and routine test checklist
• Product page: IEC 61439 type-tested panels

Frequently Asked Questions

How is panel earth busbar size calculated?

The earth busbar is sized from thermal withstand under earth-fault conditions, not from normal current. Where the adiabatic method is used, the cross-section follows S = I × √t / k, with I the prospective earth-fault current, t the protective device clearing time and k a factor for conductor material and insulation taken from IEC 60364-5-54. The standard also permits selection from its tabulated relationships to the phase conductor size.

Is earth busbar sized in A/mm² like phase busbar?

No, not as the primary method. Current density in A/mm² is a continuous-current criterion, and the protective conductor does not carry continuous current in a healthy system. Its governing duty is carrying the full earth-fault current for the disconnection time without exceeding its permitted temperature.

Is neutral the same as earth?

No. The neutral is a live circuit conductor that carries unbalance, single-phase and harmonic return current in normal operation. The protective earth conductor is part of the protective circuit and should carry current only during a fault. They have different duties, different sizing rules and, in a TN-S system, different bars.

Can neutral and earth be connected in an LT panel?

Only where the approved system earthing arrangement places the neutral-earth bond at that location. Once N and PE have been separated upstream, they must not be re-bonded downstream simply because the two bars are physically adjacent. Doing so creates parallel return paths through the protective conductor and the building structure, which corrupts earth-fault protection and can put circulating current into the panel body.

Should panel doors be earthed?

Protective continuity of accessible metallic parts must be assured, and the method depends on the verified assembly design. Where a door carries meters, an HMI, pushbuttons or any electrical device, a dedicated flexible bonding conductor is the common approach. Hinges and painted contact faces should not be assumed to provide a reliable low-impedance path.

What size earth busbar do I need for a 50 kA panel?

There is no single answer, because 50 kA alone is not enough information — the clearing time matters as much as the current. Using the adiabatic method with PVC-insulated copper, roughly 156 mm² is indicated at 50 kA with 0.2 s clearing, and roughly 247 mm² at 0.5 s. This is exactly why a standard 25 × 6 mm bar (150 mm²) is safe on some 50 kA panels and inadequate on others.

Is earth-fault current the same as three-phase short-circuit current?

Not generally. Earth-fault magnitude depends on the system earthing arrangement, the transformer or generator neutral treatment, earth-path impedance and the fault location, and it can be substantially lower — or in some arrangements comparable — to the three-phase value. Using the three-phase figure as a default is conservative for sizing but can hide a protection-coordination problem.

Does tinning the earth busbar improve its fault withstand?

Tin plating helps with joint corrosion and connection stability in humid or corrosive environments, and that is a genuine reason to specify it. It does not meaningfully increase the thermal withstand of an undersized bar. Select plating for the environment and joint material, and select cross-section from fault duty.

Why does the earth link get forgotten at shipping splits?

Because phase and neutral links are visually obvious and physically large, while the earth link is small and often at the back of the panel. In practice the phase and neutral connections get restored during commissioning and the PE link across the split does not. Listing PE shipping links as individually signed-off items on the installation checklist is the only reliable fix we have found.

Which IEC standards apply to panel earthing?

IEC 60364-5-54:2011+AMD1:2021 is the current consolidated IEC reference for earthing arrangements, protective conductors and protective bonding conductors. For the assembly itself, IEC 61439-1:2020 and IEC 61439-2:2020 cover the construction and verification requirements for protective circuits inside low-voltage switchgear assemblies.

Should the earth busbar run the full length of a multi-section panel?

In multi-section PCC and MCC lineups a continuous earth busbar through the full lineup is normal practice, so that every section connects to the same protective network. The design point that needs attention is the shipping split, where continuity must be deliberately restored on site and verified before energisation.