How to Size a Temporary Conduit Plug

A temporary conduit plug is a small part with an outsized job: it keeps water, dirt, debris, and animals out of an open duct while a job is between phases. Picking the right one comes down to a single number — the trade size of the conduit or innerduct you are sealing. This guide explains why plug size matters, how to match a plug to the trade size, and how the plugs ship.

Why plug size matters

An open conduit is an invitation for trouble. Left unsealed between trenching and the cable pull, a duct collects water, mud, sand, and debris, and becomes a sheltered nesting spot for insects and small animals. Any of that can foul a future pull or contaminate the run.

Innovative Plastics temporary plugs stop that by snapping into the duct opening and sealing it. They are molded from low-density polyethylene (LDPE) — a semi-pliable, high-impact material that is chemically inert, has very low moisture absorption, and shrugs off UV, ozone, and temperature swings, so the same plug holds up whether the duct end sits exposed for days or for months.

A correctly sized plug seals fully and stays put. One that is too large will not seat; one that is too small slips or leaves a gap. Getting the size right is the whole game.

Match the plug to the trade size

The sizing principle is simple: match the plug to the trade size of the duct you are sealing. Trade size is the standard call-out printed on the conduit and on your drawings — 2”, 4”, 6”, and so on.

The key detail is what the plug seals. These plugs seal the inside of the duct or innerduct opening, not the outside of the conduit. The tapered body starts easily into the bore, and the scalloped, ribbed side walls flex against the inner wall to form a friction snap-in seal. A flanged lip sits proud of the opening so you can pull the plug back out by hand when it is time to pull cable.

So choose by the trade size of the duct or innerduct, not by the outside diameter of the conduit:

• A 2” duct takes a 2” plug.
• A 4” duct takes a 4” plug.

The semi-pliable LDPE walls flex to accommodate the normal tolerance range within a given trade size, so one trade size covers the typical variation of that duct.

Conduit vs. innerduct

Fiber and broadband runs add a wrinkle. A host conduit often carries one or more innerducts (sub-ducts) inside it, and the innerduct is smaller than the conduit around it. Each opening you seal gets its own plug, sized to that opening:

• Sealing the host conduit? Size to the conduit’s trade size.
• Sealing an innerduct? Size to the innerduct’s trade size — which is smaller, so it takes a smaller plug than the conduit that carries it.

When in doubt, ask yourself which opening the plug has to seal, then size to that.

Sizes and how they ship

Innovative Plastics temporary plugs come in 12 trade sizes from 1” (25 mm) to 8” (200 mm) and are sold by the case, with part numbers in the 2250-0xx series. Rather than repeat all twelve rows here, see the full size and part-number table on the temporary plugs product page for the exact part number and case quantity for each trade size.

A note on the built-in rope-tie

Every plug has a built-in rope-tie, so you can attach mule tape or a pull-line before the plug goes in and leave it staged for the future pull — the plug protects the duct now and doubles as a ready anchor later. The temporary plugs are part of our broader sealing devices family.

As always, confirm trade size, fit, and application against the project specification before you order. When you have your sizes, browse the full range and order by the case on the temporary plugs page.