Purpose

Choose PVC or XLPE/thermosetting insulation from the complete system constraints, not temperature rating alone.

Learning objectives

• Compare thermal classes
• Respect terminal limits
• Assess fault and fire behavior
• Use exact product data

A higher conductor temperature rating can increase tabulated capacity, but it can also increase operating conductor resistance, voltage drop and stress on terminals or connected equipment.

Core theory

Common thermoplastic PVC designs use a 70 °C continuous conductor basis, while common XLPE/thermosetting designs use 90 °C within declared standards. Exact limits, overload/fault temperatures and environments come from the product standard and manufacturer.

A 90 °C cable cannot automatically be designed to run at 90 °C when switchgear, accessories or equipment terminals are rated lower. Apply the current standard's coordination rules and manufacturer limits.

Compare voltage drop at the correct conductor temperature, short-circuit k value, flexibility, water/chemical/UV resistance, smoke/acidity and fire performance. 'XLPE' or 'LSOH' alone does not declare every property.

Assumptions: No manufacturer-approved higher-temperature interface is provided.

1. Constraint: The accessory limit is part of the system.
2. Coordinate: Apply the required 70 °C-based selection/limitation or change the engineered interface.
3. Recheck: Recalculate CCC, voltage drop, fault withstand and terminations together.

The cable's 90 °C rating cannot override the accessory's lower declared limit.

Reasonableness check: A series system is constrained by its least tolerant interface.

Knowledge check

Answer: No. Terminal and equipment declarations remain binding.

Practical exercise

Compare two supplied datasheets against a route, terminal, voltage-drop and fire-strategy schedule.

Summary

• Temperature rating is not system permission
• Terminal limits matter
• Compare full product performance