Cable tray terminology
A practical glossary for reading tray dimensions, cable data and calculator results. Each term identifies a different part of the planning problem.
Dimensions, parts and electrical terms
- Inside width
- Clear width available within the tray. Distinguish it from the overall outside width and the width of the supporting bracket.
- Side rail
- Longitudinal member along the side of a tray. Its outside height does not automatically equal the reference height available for cables.
- Rung
- Cross-member between ladder-tray side rails. Rung spacing is measured along the tray; it is not the tray support span.
- Outside diameter (OD)
- Diameter of the complete cable, including its jacket. Use OD for circular cable area, rather than the nominal conductor diameter.
- Conductor size
- Size of the conducting part, often expressed in AWG, kcmil or mm². It does not by itself specify the complete cable outside diameter.
- Support span
- Distance between tray supports. The allowable span depends on the product and loading conditions; cable area alone cannot determine it.
- Load rating
- Capacity stated for specified test or installation conditions. Read it together with span, load distribution and the maker’s requirements.
- Bend radius
- Radius describing a curved route or cable bend. Identify the measurement reference; a tray’s inside radius and a cable’s minimum bend radius answer different questions.
- Offset
- A change in position along a route. Specify the rise or sideways displacement and the entry and exit directions.
- Reducer
- Fitting connecting different tray widths. A centered reducer moves both sides; an aligned-side reducer keeps one side in line.
- Area fill
- Cable cross-sectional area divided by a stated reference area. Always identify that reference and whether the result is geometric or a specific code evaluation.
- Ampacity
- Current-carrying capacity under stated conditions. A cable-space percentage is not an ampacity calculation.
- Derating / adjustment
- Reduction or adjustment of a current rating for applicable conditions. Do not infer a factor from geometric fill alone.
- Bonding
- Electrical connection intended to establish continuity between conductive parts. It is a separate topic from choosing tray dimensions.
- Grounding / earthing
- Connection to earth. Terminology differs by jurisdiction; distinguish it from bonding and follow the applicable installation rules.
Three distinctions that prevent input mistakes
OD vs conductor size: enter the whole cable’s outside diameter in the fill calculator. A conductor area in mm² cannot be entered into a diameter field in mm.
Rung spacing vs support span: both are lengths measured along the route, but they describe different parts. Changing rung spacing does not establish the permitted distance between building supports.
Fill vs ampacity: first ask how much cross-sectional area the cables occupy. Then address physical arrangement and the applicable electrical rules. A low area percentage is not a current rating.
For measured fabrication geometry, see the offset formula guide and 90-degree bend guide.
Further reading: Cable Tray Institute system overview and standards directory. These definitions explain calculator inputs; they do not replace project specifications.