Cable support systems — cable trays and cable ladders (NEN-EN-IEC 61537)

In a large processing hall or growing operation, dozens to hundreds of cables often run over a shared support system: a cable tray (closed or perforated bottom, often with a lid) or a cable ladder (open rungs, for larger cable bundles/heavier cables). NEN-EN-IEC 61537 sets the requirements for the support system itself — mechanical strength, material classification and electrical continuity — and is therefore a different standard from the one regulating the cable or the penetration seal itself (see the fire classification guide and the fire-resistant cable penetrations guide).

What the standard regulates

NEN-EN-IEC 61537 specifies requirements and test methods for cable trays and cable ladders, including:

• Mechanical strength — load class (load-bearing capacity at a given support span), deflection under load.
• Electrical continuity / equipotential bonding — whether the support system itself is suitable as part of the earthing/bonding circuit, and with what transition resistance.
• Material classification — corrosion resistance and (where applicable) reaction-to-fire behaviour of the support system itself.

Cable ladders are traditionally built up from rungs fixed at regular intervals to the side rails; cable trays have a closed or perforated bottom and offer more physical protection but less ventilation than an open ladder.

Note: the exact load class, rung spacing and transition-resistance requirement for a specific product follow from the manufacturer's classification in accordance with NEN-EN-IEC 61537 — this article gives the normative framework, not universal product values.

Why this directly affects current-carrying capacity

The type of support system is not merely a mechanical choice — it also partly determines the installation method used when determining the permissible current-carrying capacity Iz of the cable (see the cable cross-section and current-carrying capacity guide). A densely stacked bundle of cables on a closed cable tray has different heat dissipation — and therefore a different derating factor — than the same cables laid loosely on an open, ventilated cable ladder. Choosing a denser support system without revising the derating factor can result in a cable that runs hotter in practice than calculated.

Practical relevance

• Open cable ladders are often used in industrial halls and growing operations because of the good ventilation (lower derating factor when bundled) and easy expandability.
• Closed cable trays offer better mechanical/dust protection, but require a stricter derating calculation at high load density.
• When extending cabling on an existing support system (additional supply cables for new equipment), the derating factor for the new total bundle density must be reassessed — not just for the new cable in isolation.

Common mistakes

1. Laying cables on a cable tray/ladder without revising the corresponding derating factor for bundling/installation method — the type of support system and the bundle density directly affect Iz.
2. Assuming every cable support system is suitable as an equipotential bonding path without verifying electrical continuity in accordance with NEN-EN-IEC 61537.
3. Assessing only the new cable when extending an existing route — the total bundle density on the support system changes for all cables present, not just the one added.

Related

• Cable cross-section & current-carrying capacity
• Fire classification of cables — CPR