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 XLPE Wire is a specialized electrical wire primarily used for control and power circuits within switchboards, panelboards, and industrial control equipment. The acronym SIS stands for Stranded Insulated Switchboard wire. It features flexible stranded tinned copper conductors and robust Cross-Linked Polyethylene (XLPE) insulation.

SIS XLPE Wire is known for its high performance in demanding environments. Key characteristics include:

  • Insulation: Cross-Linked Polyethylene (XLPE) provides excellent resistance to heat, moisture, chemicals, oil, and abrasion.
  • Conductors: Flexible stranded tinned copper offers durability, corrosion resistance, and ease of installation in tight spaces.
  • Safety: It meets the UL VW-1 flame test, indicating good flame retardancy.

This wire is primarily designed for internal wiring within enclosed electrical systems. Common applications include:

  • Switchboards and Panelboards: For control and power distribution.
  • Industrial Control Equipment: Such as motor control centers (MCCs), programmable logic controllers (PLCs), and variable frequency drives (VFDs).
  • Electrical Cabinets and Substations: For internal connections and instrumentation wiring.

These are UL (Underwriters Laboratories) Appliance Wiring Material (AWM) style numbers that define specific construction and performance criteria. UL 3173 specifies a single conductor hook-up wire with stranded tinned copper conductors and XLPE insulation, rated for 600V and 125°C, suitable for internal wiring of appliances and control panels. The category also includes UL 3320, which shares similar characteristics for switchboard and control applications.

SIS XLPE Wire is rated for 600 Volts. The insulation is capable of withstanding continuous operating temperatures up to 125°C (257°F). However, for specific switchboard applications under the National Electrical Code (NEC), the maximum operating temperature is often limited to 90°C.

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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.