CNC HDPE Duct Bank Spacers vs Molded Conduit Chairs

Underground concrete-encased duct banks need spacers that hold conduits in a fixed grid through the pour. Two common approaches look similar on a one-line and behave very differently on the jobsite: interlocking molded catalog chairs, and custom CNC-cut HDPE sheet arrays. Blue Ridge Thermoforming (BRT USA) cuts the second kind in Greenville, SC. This article explains how the products differ, when a custom array is the better fit, and what to send for a quote.

Catalog chairs vs CNC sheet

A molded conduit chair is typically a fixed plastic grid. Snap-Loc-style bases and similar catalog chairs come in preset row and column counts, preset hole sizes, and preset center-to-center spacing. Crews stack or interlock them in the trench. That works well when the bank matches a catalog module and the contractor wants a stock product.

A BRT duct bank spacer is a flat HDPE sheet with the hole pattern your bank actually uses. Hole diameter, rows, columns, and center-to-center spacing come from the drawing or conduit schedule. Flow holes, rebar holes, and a ground-wire hole are cut only where the print calls for them. The board is not thermoformed. It is CNC-routed from HDPE sheet on in-house 5-axis equipment.

The practical difference: a molded chair is a catalog grid you adapt the bank to. A CNC sheet is a custom array cut to the bank you already designed.

When custom arrays win

Custom CNC HDPE sheets tend to win when any of the following show up on the civil or electrical package:

• Mixed conduit sizes on one cross-section (for example large power conduits sharing a sheet with smaller control or fiber conduits)
• Non-catalog row × column counts or center-to-center spacing
• Flow, rebar, or ground-wire holes in positions that do not match a stock chair
• Data center primary service, MV/HV feeders, generator ties, or fiber banks that repeat over long runs
• Prefabrication outside the trench, where crews build the array on the surface and lower it before the pour

If the bank is a standard module available as a molded chair and the schedule does not call for special holes, a catalog product may be the simpler buy. When the drawing is unique, or when the same custom section repeats every few feet along a long run, CNC sheet arrays keep the geometry consistent board to board.

What to send on the drawing

BRT cuts from your drawing or conduit schedule. A usable quote package usually includes:

• Conduit schedule or duct-bank section (rows, columns, conduit ODs)
• Center-to-center spacing between holes
• Preferred sheet thickness (typical boards are 3/8 in and 1/2 in HDPE; ask if the drawing calls for another thickness)
• Yes/no for flow holes, rebar holes, and a ground-wire hole
• Approximate quantity and whether boards should ship staged to the jobsite

You do not need to redesign the bank around a catalog module. Send the section you intend to pour.

Greenville CNC and plant context

Hole arrays are routed on in-house 5-axis CNC equipment at 184 Commerce Center, Greenville, SC 29615. The plant operates under an ISO 9001:2015 quality system. Boards leave Greenville for the jobsite, including just-in-time shipping and offsite warehousing when the schedule calls for staged deliveries. BRT ships across the Southeast, including the South Carolina, North Carolina, Georgia, Tennessee, and Virginia data-center corridor.

For data-center vertical banks (primary service, feeders, generator ties, fiber), see the dedicated page on data center duct bank spacers. For general custom HDPE conduit spacers, specs, and the full options table, start at custom HDPE duct bank spacers.

Spec options that only custom sheet can match

BRT’s spacer options table is built for drawing-driven banks:

• Thickness: 3/8 in and 1/2 in HDPE sheet (ask for other thicknesses if the print requires them)
• Layout: rows × columns from the conduit schedule
• Hole OD / conduit sizes: matched to the conduits on the drawing
• Center-to-center spacing: cut to the bank spacing on the print
• Flow holes, rebar holes, and ground-wire hole: yes or no per drawing
• Spacing along the run: typically every 4-7 ft

That list is how a custom CNC board absorbs a non-standard bank without forcing redesign. Molded chairs reverse the workflow: you often adapt the bank to the chair. Custom sheet adapts the board to the bank.

Prefabrication fits the same story. Crews can build the conduit array on the surface and lower it into the excavation. Hole centers are already in the sheet, so the crew is not building the grid piece by piece underground. Boards stay in the bank and are encased in concrete with the conduits.

FAQ

Are BRT duct bank spacers molded catalog chairs?

No. BRT cuts custom HDPE sheet arrays from your drawings and conduit schedules. Interlocking molded catalog chairs, including Snap-Loc-style bases, are a different product with a fixed grid.

Are these spacers thermoformed?

No. Duct bank spacers are CNC-routed HDPE sheet. They are not thermoformed parts. Heavy-gauge thermoforming at BRT is a separate process used for covers, housings, trays, and panels.

What thicknesses do you cut?

Typical boards are 3/8 in and 1/2 in HDPE sheet. Ask if the drawing calls for another thickness. Spacing along the run is typically every 4-7 ft, per the civil package.

Custom HDPE duct bank spacers · Data center duct bank spacers