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A metal cable tray can form part of a facility's grounding path, but only if every joint along the run is electrically continuous and the tray itself is rated for that use. A tray that looks solidly assembled can still have broken continuity at its joints, especially where coatings, paint, or loose hardware sit between metal surfaces. This guide explains how grounding and bonding work on cable tray systems, where continuity is most often lost, and what to check during installation and testing.
Bonding means joining metal parts so they are electrically connected and sit at the same potential. Grounding means connecting that bonded system to the earth, through the building's grounding system. On a cable tray run, bonding makes the sections work as one continuous conductor, and grounding ties that conductor to the facility's earth connection so fault current has a safe path back to its source.
In many installations, a metal cable tray can serve as an equipment grounding conductor, but only when the tray system is rated or listed for that use and the project's standard allows it. Otherwise, a separate grounding conductor must be run along the tray and bonded to it. International practice differs, so the project specification and local electrical code decide, not the tray alone (see our Cable Tray Standards Explained guide for how different standards treat cable tray).
EN 61537 classifies cable tray systems as either with or without electrical continuity, so a tray supplied for use in a grounding path should be declared as having electrical continuity, and that claim should be supported by its test documentation.
That the tray system is classified as having electrical continuity under the standard the project specifies
That the local code or project specification allows tray to serve as a grounding conductor, rather than requiring a separate conductor
That the joint hardware and splice plates supplied are part of the same tested system
Continuity problems almost always occur at the joints rather than in the tray sections themselves.
Coatings and paint at contact surfaces: powder coating and paint are electrical insulators, so a bolted joint between two coated surfaces can leave the metal underneath isolated unless the hardware cuts through the coating
Loose or under-tightened joint hardware: a joint that is mechanically loose can lose contact over time, particularly under vibration or temperature change
Expansion joints and gaps: where the tray is designed to move with temperature, the sliding joint may not maintain a reliable electrical connection on its own
Dissimilar metals: mixing metals such as aluminum tray with steel hardware can cause corrosion at the contact point over time, which raises resistance
Unprotected cut edges: field-cut ends without suitable finishing or bonding can break the continuity of a run
Use the splice plates and hardware supplied for the tray system, and tighten them to the manufacturer's specified torque
Where surfaces are painted or powder coated, use bonding-type fasteners that cut through the coating, or remove the coating at the contact area following the manufacturer's instructions
Install bonding jumpers across expansion joints, field-cut gaps, and any joint where the manufacturer states the splice alone is not enough
Match jumper and fastener materials to the tray material to avoid corrosion at the connection
Protect bonding connections from moisture and corrosion, especially outdoors, where hot-dip galvanized or stainless steel hardware is a better match (see our SS304 vs SS316 vs HDG Cable Tray comparison for finish selection)
The tray run must also be connected to the facility's earth through a grounding conductor, typically at the ends of the run and at intervals set by the project specification. Where the tray meets other metal parts, each transition needs its own bonding connection.
Tray to building grounding: a grounding conductor and lug at the points the specification requires
Tray to conduit: a bonding connection where conduit leaves the tray, since continuity through the tray does not automatically carry into the conduit (see our How to Install Electrical Conduit guide for conduit bonding)
Tray to equipment enclosures: a bonding connection at each cabinet or panel where the tray terminates
Tray to mounting structure: on solar and outdoor projects, coordinate tray bonding with the racking system's own grounding method (see our Cable Management for Solar Farms guide)
Do not assume continuity from a visual or mechanical check. A joint can look tight and still carry a poor electrical connection. After installation, test continuity along the run using a low-resistance ohmmeter or the method specified in the project documentation, and record the results. Acceptable values and test method come from the project specification and the applicable code, so follow those rather than a generic figure.
Continuity measured across each joint and along the full run
Bonding jumpers present at every location the drawings require
Connections to the facility earth made and tightened
Re-check of connections after any later modification to the tray run
Assuming a bolted joint is a bonded joint without testing it, especially across painted or powder-coated surfaces.
Leaving out bonding jumpers at expansion joints where the tray is designed to move.
Relying on the tray as the only ground conductor when it is not rated or permitted for that use.
Mixing dissimilar metals at a connection, which corrodes the joint and raises resistance over time.
Skipping the bond at transitions to conduit and equipment enclosures.
Cable tray can play a useful role in a facility's grounding system, but only when the tray system is rated for it and every joint is electrically continuous. Using the supplied splice hardware, dealing correctly with coatings at contact surfaces, adding jumpers where needed, connecting the run to the facility earth, and testing continuity after installation are the steps that turn a mechanically sound tray into an electrically reliable one.
No. A joint can be mechanically tight and still have poor electrical continuity, particularly where powder coating, paint, or corrosion sits between the metal surfaces. Using bonding-type hardware, treating contact areas as the manufacturer instructs, and testing continuity after installation are the ways to confirm it.
It depends on the tray's rating and the local code. If the tray system is rated and permitted to serve as the equipment grounding conductor, a separate conductor may not be required for the tray itself, but many projects still specify one. Check the project specification and the applicable electrical code rather than assuming either way.
The coating itself does not, so the connection depends on the metal underneath. Joints between powder-coated sections need hardware that cuts through the coating or a prepared bonding area to make reliable metal-to-metal contact. Hot-dip galvanized and pre-galvanized trays have a conductive zinc surface, which generally makes continuity easier to achieve at the joints.
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