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Epoxy Busduct: Sealed Power Distribution for the Places Cable and Standard Busway Can't Go

By DHYN Engineering Team  ·  September 4, 2026

Quick answer: An epoxy busduct (also called a resin cast busway) is a bus duct where the conductors are cast solid in epoxy resin instead of sitting inside a sheet-metal housing. There is no internal air gap, no gaskets and no enclosure seams, so the duct reaches IP68 as standard and shrugs off water, dust and corrosive fumes. Spec it for outdoor runs, tunnels, flood-prone basements, coastal and chemical sites. DHYN ELEC GROUP builds it from 400 to 6300 amps, type tested to IEC 61439-6.

Most busway is built for comfortable environments: dry electrical rooms, conditioned shafts, indoor risers. Epoxy busduct exists for everywhere else. Instead of wrapping insulated conductors in a metal housing, the conductors are cast directly into a solid block of epoxy resin. There is no enclosure interior, no air gap, nothing for moisture or dust to travel along. Water, dust and corrosive fumes simply have nowhere to go.

We manufacture our resin cast busway in Yangzhong, Jiangsu, rated from 400 to 6300 amps with tin-plated copper conductors, vacuum-cast in Class F/H epoxy resin and type tested to IEC 61439-6. This article is about our own product, so take the appropriate pinch of salt and check the facts against the test reports. We will send those without being asked twice.

How an epoxy busduct is built

The copper bars are positioned in a mold and cast under vacuum with mineral-filled epoxy. Vacuum casting matters: it pulls air out of the resin before it cures, so the finished body has no voids or bubbles where partial discharge could start. What comes out is a monolithic section of duct where the insulation and the enclosure are the same thing. Class F resin handles a 155°C insulation system temperature; Class H pushes that to 180°C for hot or heavily loaded runs.

Because the resin body itself is the barrier, the duct reaches IP68 as standard. That is continuous immersion under declared conditions, not just rain and spray. Tunnels, flood-prone basements, pump stations, direct-buried runs: this is what the product is for. We covered what the IP digits mean in our IP54 vs IP65 vs IP68 guide.

Fire and corrosion behavior

Two failure modes kill ordinary busway in harsh sites. The first is water ingress at joints and housing seams. The second is corrosion eating through plated conductors and steel hardware. Cast resin removes both: no seams, no internal air, no metal housing to rust.

On fire, the resin is halogen-free, flame-retardant and self-extinguishing, and the system maintains circuit integrity per IEC 60331. With no air path inside the duct, a fire has nothing to feed on along the run. In a real fire, a standard sandwich bus duct loses its film insulation once temperatures climb past a few hundred degrees. A cast resin duct buys the circuit far more time, which is exactly what fire pumps, smoke extraction and emergency lighting need.

Where epoxy busduct earns its cost

Epoxy busduct costs more per meter than sandwich busway. It earns the difference in specific places:

• Outdoor links between buildings, where a duct on brackets sees rain, condensation cycling and sun for decades.
• Coastal and chemical sites, where salt air or acid vapor gets into every gap of a ventilated housing.
• Wastewater plants, tunnels and below-grade runs where standing water is a question of when, not if.
• Wash-down or humid process areas where IP54 or IP65 is not honest protection.

A common project layout uses sandwich busway indoors for its compact size and plug-in tap-off points, then switches to cast resin for the outdoor or wet sections. The two systems connect at standard flanged ends. We compared the two types in detail in our cast resin vs sandwich busway guide.

What "maintenance-free" actually means here

A ventilated busway needs periodic checks: joint torque, insulation resistance, signs of moisture tracking inside the housing. A cast resin section has nothing inside to inspect. The resin does not absorb moisture, does not support tracking and does not degrade under UV. Installed correctly, the expected service life runs past 30 years with no scheduled internal maintenance. You still torque-check external joints at commissioning, but that is the beginning and end of the list.

Quick specification

Rated current	400 – 6300 A
Rated voltage	≤ 1000 V AC, 50/60 Hz
Conductor	Tin-plated copper
Insulation	Vacuum-cast epoxy resin, Class F / H
Protection degree	IP68
Fire performance	IEC 60331 circuit integrity, halogen-free
Standard	IEC 61439-6

If your single-line diagram crosses a wall to the outdoors, drops into a tunnel, or runs anywhere a cable tray would be underwater, this is the product to spec. Send us the layout and load list and we will come back with a section schedule and joint count.