How to Spec Custom Duct Bank Spacers from a Conduit Schedule

Custom duct bank spacers are only as good as the inputs on the print. Electrical and civil teams already know the bank section. This guide turns that section into a clean CNC quote package for HDPE sheet arrays cut in Greenville, SC by Blue Ridge Thermoforming (BRT USA).

Start with rows and columns

The conduit schedule (or duct-bank cross-section) defines the grid. Count how many conduits sit across (columns) and how many sit deep (rows). That layout becomes the hole array on the sheet. BRT does not force a catalog module. Rows × columns follow the schedule you send.

If the bank changes along the run (for example a transition from a 3×4 power section to a mixed power-and-fiber section), treat each unique section as its own board type and note approximate quantities for each.

Hole OD and conduit sizes

Hole diameter is matched to the conduit OD on the drawing. Mixed sizes on one board are normal: a larger power conduit can share a sheet with smaller control or communications conduits when the section calls for it. Call out every distinct OD. Do not assume a single catalog hole size will cover the bank.

Center-to-center spacing

Center-to-center spacing between holes is cut to the bank spacing on the print. That includes spacing between power conduits and any wider gap the engineer wants between power and fiber when both sit on one sheet. BRT cuts the spacing you specify. We do not assign an EMI clearance for you.

Spacing along the run (how often boards appear down the trench) is a civil decision. Typical intervals are every 4-7 ft. Note the interval on the quote so quantity and staging make sense.

Flow, rebar, and ground holes

Concrete-encased banks often need openings beyond the conduit holes:

• Flow holes: allow concrete to move through the sheet during the pour
• Rebar holes: where steel passes through the spacer plane
• Ground-wire hole: when the drawing calls for a dedicated ground path through the board

Mark each as yes or no, and show approximate locations on the section if they are not obvious. BRT cuts them only where the drawing calls for them.

Thickness: 3/8 in vs 1/2 in

Typical boards are 3/8 in and 1/2 in HDPE sheet. Choose the thickness the structural or civil note prefers, or ask BRT which grade and thickness fit the print. Virgin or reprocessed HDPE grades are available; ask which fits the thickness and application. Do not invent a thickness that is not on the drawing or discussed with the plant.

Quote checklist

Send as much of the following as you have. Incomplete packages still get a conversation started, but a complete package speeds CNC programming:

• 1. Drawing or conduit schedule (PDF or CAD section)
• 2. Rows × columns and conduit ODs
• 3. Center-to-center spacing (including any power-to-fiber gap)
• 4. Sheet thickness preference (typically 3/8 in or 1/2 in)
• 5. Flow / rebar / ground-wire hole requirements
• 6. Spacing interval along the run (typically 4-7 ft)
• 7. Quantity estimate and ship-to jobsite vs warehouse staging
• 8. Project location (Southeast corridor deliveries are routine from Greenville)

Prefab and field context while you spec

Specifying the board is only half the job. Note how the crew will use it. Many contractors prefabricate the conduit array outside the trench: assemble on the surface, lower, then pour. CNC sheets support that because the geometry is finished before the dig. Molded chairs can also be stacked in a trench, but they do not invent mixed ODs or non-catalog centers for you.

Along the run, boards typically appear every 4-7 ft. Put that interval next to bank length when you estimate quantity. For data-center campuses with primary service, feeders, generator ties, and fiber sections, list each unique section as its own board type. Hyperscale packages often repeat the same few sections for thousands of feet; repeating CNC boards keep those sections consistent.

BRT cuts in Greenville, SC (184 Commerce Center, Greenville, SC 29615) on in-house 5-axis CNC equipment under an ISO 9001:2015 quality system. Boards ship to the jobsite, including just-in-time and warehouse staging when the schedule needs it. Southeast corridor deliveries (SC, NC, GA, TN, VA) are routine.

FAQ

What if we only have a one-line and not a duct section yet?

Send what you have and note the open items. A preliminary quote can often proceed from a sketched section and conduit list, then lock when the civil section is stamped.

Can one board hold mixed conduit sizes?

Yes. Hole diameter follows each conduit OD on the schedule. Mixed sizes on one CNC-cut sheet are a common request.

Are these molded chairs or CNC sheet?

BRT products for this application are custom CNC-routed HDPE sheets, not interlocking molded catalog chairs. See custom HDPE duct bank spacers for the full spec options table.

Custom HDPE duct bank spacers · Capabilities