SIS XLPE WIRE | UL 3173 / UL 3320

SIS XLPE Wire | UL 3173 / UL 3320, standing for Stranded Insulated Switchboard, Cross-Linked Polyethylene is a specialized 600 Volt, 125°C electrical wire primarily designed for control and power circuits within switchboards, panelboards, and industrial control equipment. It features flexible stranded tinned copper conductors and robust Cross-Linked Polyethylene (XLPE) insulation, providing excellent resistance to heat, moisture, chemicals, oil, and abrasion, while also meeting the UL VW-1 flame test.

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SIS / UL 3173 / UL 3320 Switchboard Wire

SIS wire is a premium, high-performance conductor engineered specifically for the internal wiring of switchboards, control panels, and power distribution equipment. Featuring a rugged Cross-Linked Polyethylene (XLPE) insulation, this wire is designed to withstand higher operating temperatures and harsher mechanical environments than standard building wire. SIS is chemically cross-linked to provide superior resistance to heat, moisture, and environmental stress cracking, ensuring long-term electrical integrity in critical infrastructure. Often dual-rated as UL 3173 or UL 3320, this wire provides the flame-retardant properties required for high-density electrical enclosures where safety and reliability are non-negotiable.

SIS vs. MTW - The XLPE Advantage: While MTW (Machine Tool Wire) is common for general panels, SIS is the preferred choice for utility-scale switchgear. Unlike PVC-based MTW, the thermoset insulation in SIS will not melt or "flow" if it contacts a high-heat component. It also offers superior resistance to "cold flow"—the thinning of insulation under the pressure of tight wire ties or sharp bends over time.

Key Features
  • Thermoset XLPE Insulation: Features cross-linked polyethylene that will not melt or drip under extreme heat or short-circuit conditions.
  • 125°C High-Heat Rating: UL 3173 ratings provide a significantly higher thermal threshold (up to 125°C) while UL 3320 carries a standard 90°C rating.
  • Superior Flame Retardancy: Specifically engineered to meet rigorous vertical flame tests, making it safe for dense switchboard clusters.
  • Flexible Stranded Copper: Utilizes high-quality stranded bare or tinned copper for easier routing and termination in cramped control cabinets.
  • Chemical & Oil Resistant: The XLPE jacket is highly resistant to industrial solvents, oils, and corrosive chemicals found in utility environments.
  • No Outer Jacket Required: The rugged nature of the insulation provides its own mechanical protection, allowing for a smaller outer diameter and easier pulling.
  • Standards: UL 3320 carries UL listings of UL 44, UL 758 and a VW-1 rating while UL 3173 carries a CSA CL1251 and a UL Horizontal Flame Test rating. 
Common Applications
  • Utility Switchboards: The primary choice for internal wiring of high-voltage power distribution and switching equipment.
  • Control Panels & Relays: Used for interconnecting protective relays, meters, and control switches in substation environments.
  • Transformer Secondary Leads: Ideal for internal connections within large power transformers where high heat is expected.
  • Motor Control Centers (MCC): Deployed in heavy-duty industrial starters and controllers for reliable motor management.
  • Power Plant Infrastructure: Used extensively in the control rooms and turbine halls of traditional and renewable energy plants.
  • Battery Storage Racks: Suitable for connecting large-scale battery cells to inverters in energy storage systems.
  • Uninterruptible Power Supplies (UPS): Provides high-reliability internal power routing for critical data center backup systems.