Engineering Application of NH-YJV & NH-YJV22 Fire-Resistant Cables in Life-Safety Circuits

To: Project Design Engineers, EPC Contractors, and Electrical Inspectors
Subject: Technical Specification Requirements for Maintaining Circuit Integrity in High-Rise Buildings and Critical Infrastructure

Standard power cables pose safety risks when used in life-safety systems. The primary objective of fire-resistant circuits is not merely to withstand fire, but to maintain system functionality during a fire event. NH-YJV and NH-YJV22 cables are specifically designed for this purpose, ensuring continuous power supply for 90 minutes at temperatures up to 950°C, thereby providing a critical window of time for personnel evacuation and firefighting operations.

Why do standard XLPE cables fail during a fire, whereas NH-YJV cables continue to operate normally? The answer lies in their insulation structure design.

Standard cables rely solely on organic polymers (such as XLPE or PVC) for insulation—materials that melt at temperatures between 105°C and 150°C. In contrast, NH-YJV cables feature a critical layer of synthetic mica tape wrapped directly around the copper conductor.

Engineering Principle: When the ambient temperature exceeds 350°C, the organic binder within the mica tape burns away, causing the inorganic mica flakes to fuse together and form a rigid, ceramic-like insulating shell.

Result: This ceramic thermal barrier effectively prevents short-circuits to ground; even if the outer polymer sheath is completely consumed by flames, the cable maintains the power supply to critical systems such as fire pumps or emergency lighting.

In accordance with international fire safety standards (such as IEC 60331 and BS 6387), these cables must be used in the following three critical scenarios where system failure is absolutely impermissible:

1. Fire Pumps and Automatic Sprinkler Systems
   Fire pumps must operate at full load during building evacuation. This requires cables capable of withstanding high starting inrush currents and voltage drops over long transmission distances, while maintaining stable performance under thermal stress. NH-YJV cables possess the necessary low-resistance characteristics and high dielectric strength to ensure continuous motor operation.
2. Emergency Lighting and Safety Exit Signage Systems
   Smoke inhalation is a primary cause of fire-related casualties; therefore, maintaining illumination along evacuation routes is a critical safety requirement. The use of Low-Smoke Zero-Halogen (LSZH) materials is essential in these applications. While standard PVC cables produce dense, toxic black smoke that obscures visibility for evacuees, NH-YJV cables generate only minimal amounts of non-toxic smoke, thereby ensuring good visibility.
3. Critical Power Circuits in Hospitals and Schools
   Hospital systems—such as life support, operating rooms, and medical record management—rely on electricity to function, while schools must ensure the safe evacuation of hundreds of students during emergencies. These circuits require an "uninterruptible" power supply. The illuminated distribution panel shown in the image symbolizes the need to provide reliable power to these critical loads, even in the event of a main grid failure.

Consulting engineers specify this type of cable—rather than alternatives such as BTLY mineral-insulated cables or standard YJV cables—primarily based on the following three key principles:

• Ease of Installation: Unlike rigid mineral-insulated (MI) cables, NH-YJV cables share the same handling characteristics as standard cross-linked polyethylene (XLPE) cables. They can be installed using conventional cable-laying techniques and do not require expensive, specialized MI cable terminations.
• Mechanical Protection (The "22" Series Advantage): The NH-YJV22 model features galvanized steel tape armoring. This armor provides physical protection against hazards such as rodent damage and crushing from backfill soil; it also acts as a thermal barrier, delaying heat transfer to the internal mica layer and thereby effectively extending the cable's operational integrity during severe fires (meeting the "90-minute fire resistance" requirement).
• Voltage Drop Control: Voltage drop is a critical factor for long-distance vertical cable runs in high-rise buildings. NH-YJV cables utilize pure annealed copper conductors with very low electrical resistance, ensuring that fire-fighting pumps receive the necessary voltage during startup.

To ensure fire-resistant circuits meet certification standards, the installation process must be executed with precision. A single improper termination can cause the entire circuit to fail the 90-minute fire-resistance rating requirement.

• Do Not Damage the Mica Layer: Avoid cutting inward when stripping the outer sheath and XLPE insulation. Any scratch on the copper conductor or mica tape invalidates the fire-resistance certification. Use specialized stripping tools calibrated for the specific insulation thickness.
• Termination Sealing: Exposed mica tape is hygroscopic (it absorbs moisture from the air). Immediately after stripping the insulation, the cable ends must be sealed using a fire-resistant heat-shrink termination kit or approved fire-rated sealing putty.
• Bending Radius Requirements: The minimum bending radius for NH-YJV cable is typically 15 times the cable diameter (20 times for armored YJV22 cable). Forcing a bend with a radius smaller than specified can cause the mica tape to crack, creating a weak point in the fire-resistant layer.
• Separation Requirements: It is strictly prohibited to bundle fire-resistant cables with standard cables in the same conduit or cable tray without a fire-rated barrier. If a standard cable catches fire, it could ignite the outer sheath of the NH-YJV cable, thereby accelerating the loss of circuit integrity.

(Please consult the JINHONG Technical Engineering Department for project-specific ampacity calculations or SGS/IEC test reports.)
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