Conduit Duct Bank Spacing: Intervals, Separation, and Cover

Spacing a conduit duct bank comes down to three numbers: how often you set a spacer along the run, how much separation you hold between conduits, and how much cover protects the finished bank. Get those right and the bank stays on grid through the pour or backfill, concrete flows cleanly around every duct, and future cable pulls go smoothly. This article explains each one and how the duct spacers family holds the geometry your design depends on.

Why duct-bank spacing matters

Even, consistent spacing is what keeps a duct bank performing the way it was engineered. When conduits are held on a fixed grid, concrete or backfill flows around every duct instead of bridging across crowded conduits and leaving voids. Consistent gaps also let heat from loaded conductors dissipate into the surrounding material rather than accumulating between bundled ducts. Just as importantly, a registered grid keeps the bank from drifting or floating during the pour, so the as-built cross-section still matches the drawings the inspector checks against.

Spacing applies to both finishing methods. Whether the bank is encased in concrete or direct-buried in compacted backfill, the spacers are what hold alignment through the most disruptive part of construction.

How far apart to place spacers

There are two intervals to think about. The first is separation between conduits within each cross-section — the side-to-side and vertical gaps that the spacer geometry sets. The second is the spacing interval along the length of the run — how often a spacer set repeats down the trench.

For the interval along the run, a common field practice is a spacer set every 5 to 10 feet and at every coupling. Placing one at each coupling supports the joint and keeps the duct from sagging where it is most flexible. That said, the interval that actually governs your job is the one called out on the project engineering drawings — always defer to the specification rather than a rule of thumb.

Conduit separation and cover

Innovative Plastics base and intermediate spacers are two-piece, interlocking units molded from high-impact polymer. They handle duct trade sizes from 2 through 8 inches and hold 1.5 to 3 inches of separation between conduits, with no banding or tie wire required — the bank locks together mechanically. The base lifts the bottom row off the trench floor so material flows underneath, and intermediate spacers stack each additional row on the same registered grid.

Cover is the protective material around the finished bank. On an encased duct bank, that means concrete between the outermost conduit and the edge of the envelope, plus the earth above it; on a direct-burial bank, it is the depth of compacted backfill over the conduit grid. Required separation and cover are set by the project specification and the applicable code — confirm both before you build rather than estimating in the field.

Choosing the right spacer

Match the spacer to the run:

• Base and intermediate spacers are for stacked, multi-row duct banks in the 2”–8” range, encased or direct-buried, where you need precise horizontal and vertical alignment held through the pour.
• Clip spacers are lighter snap-on spacers for single-tier exposed or underground runs in the 1”–2” range, snapping directly onto the conduit instead of building up from a base.

Once you have the spacing and cover from your drawings, our guide to installing conduit duct spacers walks through assembling the bank row by row.

Pre-assembly is available — just ask. And as always, confirm spacer intervals, conduit separation, and cover against your project specification and the applicable code before you build.