Cable tray grounding and bonding keeps every metal part of a tray system at earth potential so that a fault to the tray clears quickly and no person can touch two parts at different potentials. Two questions decide everything: can the tray itself serve as the equipment grounding conductor, and if so, are its joints electrically adequate along the full route? Get these wrong and the tray becomes a long, thin, high-resistance fault path — the exact opposite of what a protective conductor must be.
Grounding vs Bonding: The Distinction That Matters
The two terms are often used interchangeably and should not be.
- Grounding (earthing) connects the system to earth — to the installation’s main earthing terminal and ultimately to the earth electrode.
- Bonding connects conductive parts together so that they are at the same potential, eliminating dangerous voltage differences between things a person can touch simultaneously.
A cable tray needs both: bonded along its whole length so every section and fitting is at one potential, and grounded at defined points so the system is referenced to earth. Bonding without grounding leaves the tray floating; grounding without bonding leaves distant sections at different potentials during a fault.
Can Cable Tray Serve as the Equipment Grounding Conductor?
In many installations, yes — but it is a design decision that must be verified against the applicable wiring rules, not an assumption.
What the Standards Say
In North America, NEC Article 392 covers cable trays, and the use of the tray as an equipment grounding conductor is addressed there subject to conditions including the tray being identified for the purpose and being adequately sized for the fault current. Article 250 sets out the general bonding and grounding requirements.
In IEC-influenced markets, metallic cable tray used as a protective conductor must satisfy the protective conductor requirements of the applicable wiring rules — which means the cross-sectional area must be adequate for the prospective fault current and the operating time of the protective device, and the continuity of the path must be assured. IEC 61537 addresses cable tray systems and includes requirements relating to electrical continuity.
The Practical Test
Three conditions must all be met:
- Cross-section adequate for fault current — the tray’s metal cross-section must carry the prospective fault current for the disconnection time required, without reaching a temperature that damages the tray or the cables. This is a calculation, not a judgement.
- Continuity along the entire route — every joint must be electrically adequate, permanently and for the life of the installation.
- Continuity maintained through future modification — if a section is removed for maintenance and refitted, the path must be restored.
If any of these cannot be assured, run a separate equipment grounding conductor sized to the applicable rules, and bond the tray to it. This is the conservative choice and often the correct one.
How Joints Are Bonded
Bolted Joints
A standard tray-to-tray bolted joint is a mechanical connection, not automatically an electrical one. Painted or coated surfaces, and the natural oxide layer on aluminium, can leave the joint resistance far too high for a fault path.
Methods, in order of reliability:
- Serrated or toothed bonding washers / star washers fitted between the tray sections bite through coating and oxide as the bolt is tightened. Common and effective where correctly specified and installed.
- Dedicated bonding jumpers — a flexible or stranded conductor with lugs, bolted between sections. The most reliable method and the usual requirement where the tray is relied on as the fault path. Jumper size is selected to the applicable rules for the fault current.
- Manufacturer’s bonded coupling system — many tray systems supply couplers with integrated bonding features that have been type-tested for continuity. Using the manufacturer’s system as tested is far better than improvising.
What does not work: relying on plain bolts through painted or galvanised surfaces, and assuming that because the tray “looks continuous” it is electrically continuous.
Aluminium Tray: Special Attention
Aluminium forms a hard, insulating oxide layer within minutes of exposure. A joint that is not prepared will have unpredictable and often high resistance. Where aluminium tray is bonded:
- Use bonded couplers or jumpers designed for aluminium, with compatible lugs — aluminium-to-copper connections require bimetallic lugs or an approved jointing compound to prevent galvanic corrosion.
- Do not rely on star washers alone unless the method is covered by the manufacturer’s tested data.
Galvanised Tray
The zinc coating is conductive, so galvanised-to-galvanised joints behave better than painted ones, but coating thickness, paint overspray, and corrosion over time still make dedicated bonding the safe approach where the tray carries fault current.
FRP Tray
FRP is non-conductive. It cannot serve as an equipment grounding path under any circumstance. The design must include a separate bonded conductor running the length of the route, and the tray’s metallic fixings and supports must be bonded to it.
Where to Bond and Ground
Along the Route
- Bond every tray section and every fitting — bends, tees, reducers, and drop-outs. Fittings are the most commonly missed items.
- Bond at every expansion joint with a flexible jumper sized for fault current. An expansion joint is, by design, a break in the metal path.
- Bond across any painted, powder-coated, or anodised surface that sits in the path.
Connection to Earth
- Connect the tray system to the main earthing terminal or to the earth bar of the supplying panel, with a conductor sized to the applicable rules.
- Where a run is long, multiple connections to earth may be required or preferred — follow the applicable wiring rules and the design.
- Ground at the supply end and at the far end where the design calls for it; a single connection at one end of a very long run leaves the remote end relying on the tray’s own impedance.
Bonding to Panels and Equipment
Where tray terminates at a distribution board, enclosure, or item of equipment, bond the tray to that equipment’s earth terminal. The tray and the enclosure must be at the same potential. This is a frequent site omission — the tray arrives at the panel, the cables terminate, and nobody makes the bond.
Comparison of Bonding Methods
| Method | Reliability as fault path | Installation effort | Typical use | Main risk |
|---|---|---|---|---|
| Manufacturer’s tested bonded coupler | High — verified by type test | Low | Whole system from one supplier | Mixing components from different systems breaks the verification |
| Serrated / star washer at joint | Moderate | Low | Supplementary bonding where a separate earth conductor exists | Washer may not penetrate coating or oxide fully; degrades with corrosion |
| Dedicated bonding jumper with lugs | High | Medium | Where tray is the equipment grounding conductor; across expansion joints | Wrong lug for the metal; loose termination; jumper omitted at refit |
| Separate equipment grounding conductor | Highest — independent of tray joints | Medium–high | Conservative design; FRP systems; where continuity cannot be assured | Adds material cost; must still bond the tray to it |
| Reliance on plain bolted joint | Low — not acceptable as a designed method | None | None | Unquantified resistance; fails on coated and oxidised surfaces |
Application Case: Data Centre with Segregated Routes
Scenario Constraints
A data centre has segregated cable routes: power tray in a ceiling void serving distribution units, and a separate data tray below for structured cabling. The two must not share a tray. The power route includes a 40 m straight run crossing a building expansion joint. Power distribution is TN-S. The design intends to use the metallic power tray as the equipment grounding conductor to save a separate conductor.
Approach
Using the tray as the fault path is defensible only if the cross-section is verified against the prospective fault current and disconnection time at the far end of that 40 m run — the remote end is the worst case, because the tray’s impedance adds to the fault loop. The designer must calculate the loop impedance at the furthest point, confirm the protective device disconnects within the required time, and confirm the tray cross-section is adequate for the resulting thermal stress.
At the building expansion joint, the tray’s metal path is broken by design. A flexible bonding jumper sized for the fault current must bridge it, and it must be long enough to accommodate the movement without being strained. This is the single most common omission in this kind of installation.
The data tray below is bonded to earth for equipotential purposes but is not relied on as a fault path — and segregated from the power tray so that a power fault does not couple into the data route.
Common Mistakes
- Designing the tray as the earth path without checking the far-end loop impedance. The path gets longer and more resistive exactly where the fault current is lowest and the disconnection time is longest.
- Omitting the bonding jumper at expansion joints. Very common and completely invisible once ceiling tiles are in place.
- Bonding tray sections but not fittings. Bends, tees, and reducers are the parts that get missed.
- No bond at the panel termination. The tray and enclosure end up at different potentials during a fault.
- Using copper lugs directly on aluminium tray. Galvanic corrosion degrades the joint over time. Use bimetallic lugs or an approved compound.
- Painting over bonding points after installation. A retrofit paint job can insulate the very joints that were bonded.
Acceptance Checks
- Continuity test along the full tray run — measure resistance from the supply-end earth point to the far end and to each fitting; record values, not just a pass.
- Visual inspection of every bonding point — confirm jumper presence, lug type, and tightness.
- Confirm bonding across expansion joints — and that the jumper has slack for movement.
- Verify earth electrode / main earthing terminal connection — conductor size and termination integrity.
- Loop impedance test at the furthest point — confirm disconnection time meets the applicable requirement.
- Record all values in the commissioning documentation — including the method used, so a future extension can be checked against the same baseline.
Frequently Asked Questions
Does every cable tray section need a bonding jumper?
If the tray is the equipment grounding conductor, every joint in the fault path needs a verified electrical connection — either a tested bonded coupler or a jumper. If a separate adequately sized grounding conductor is installed and the tray is bonded to it at intervals for equipotential purposes, the requirement on each joint is different. Follow the applicable wiring rules and the manufacturer’s tested method.
Can I rely on bolts through the tray for the earth path?
Not as a designed method. Coatings, paint, and oxide layers make the resistance unpredictable. Use serrated bonding washers as a supplement, and a dedicated jumper or tested coupler where the tray is the fault path.
What size bonding jumper should I use?
Size it to the applicable wiring rules for the prospective fault current and the disconnection time of the protective device, in the same way as any protective conductor. Do not select by matching the tray thickness — the two are unrelated.
Do I need to bond cable tray to the distribution panel?
Yes. Where tray terminates at a panel or enclosure, bond it to that equipment’s earth terminal so tray and enclosure are at the same potential. This is a commonly missed item at commissioning.
How do I handle bonding across a building expansion joint?
Fit a flexible bonding jumper sized for the fault current, with enough slack to accommodate the designed movement without strain. The mechanical expansion joint is an electrical break; the jumper is what restores continuity.
Does FRP tray need bonding?
FRP is non-conductive and cannot be a fault path, so it does not need electrical bonding itself. But a separate equipment grounding conductor must run the route, and the metallic supports and fixings must be bonded to it.
Should power and data tray be bonded together?
They must both be earthed and at the same potential in the overall equipotential bonding system, but they should not share a tray or a common cable route. Segregation reduces electromagnetic coupling; bonding is about safety. Both requirements apply and are not in conflict.
Specify Bonded Cable Tray Systems with BANGE Electric
BANGE Electric supplies cable tray systems with manufacturer-tested bonding couplers, expansion joint bonding kits, and compatible accessories across galvanised, stainless, and aluminium ranges — so continuity is a verified system property rather than a site improvisation. Share your route length, fault level, disconnection time requirement, and whether you intend to use the tray as the equipment grounding conductor, and we will specify the bonding method and jumper sizes accordingly.
Review tray support and span requirements or contact our technical team.
Requirements may vary by application, market, and applicable standard. Figures given here are illustrative examples; always confirm against manufacturer data and your project specification.