No string or hockey sticks in electrical ducting
The electrical piping that runs from the street to the house has no string/rope going through it and the drive is already laid. What’s the best way of getting a string through the pipe so the electrical cable can be pulled through it?
Replies from 4 tradespeople
The easiest method is usually to suck a lightweight draw string through with a vacuum, rather than trying to push a cable or rod through the whole length.
The easiest and most reliable method to get a draw string through an empty underground ducting pipe without digging up the driveway is the vacuum/compressed air trick.
Here are the best approaches to solve this:
1. The Vacuum / Carrier Method (Most Effective)
Tie a lightweight, strong nylon draw string or mason's line securely around a small piece of plastic bag, sponge, or foam plug (shaped to fit comfortably inside the ducting without jamming).
Place the plug in one end of the pipe.
Use a high-powered wet/dry vacuum at the opposite end of the pipe to suck the plastic plug—and string—all the way through. Alternatively, an air compressor can be used to blow it through from the entry end.
2. Heavy-Duty Cobra Rod / Fish Tape
Use a flexible glass-fibre continuous duct rodder (often called a "Cobra rod" or fish tape).
Push the flexible rod completely through the ducting from one side to the other, attach your draw rope to the eyelet end, and pull it back through.
3. Important Note Regarding Mains Cables
Please note that if this ducting is intended for the main incoming electricity supply cable (from the Distribution Network Operator / DNO), the DNO or qualified electrician will typically mandate specific ducting sizes (usually 32mm or 38mm smooth bore/hockey stick entry) and require a rot-proof draw cord rated for heavy cable pulls.
Always attach a strong, rot-proof draw rope (rather than thin string) once you have pulled your initial line through so it is ready for the heavy cable pull.
This is a common issue, and in many cases it can be resolved without digging up the driveway. The usual method is to use a draw tape (cable rod or fish tape) and feed it through the duct. If the duct is clear, this is often all that's needed.
If the duct is long or has several bends, another effective method is to use a lightweight foam plug or small plastic bag attached to a length of string and use a vacuum cleaner at the opposite end to pull the string through. Once the string is in place, it can be used to pull through a stronger draw rope, and then the electrical cable.
If neither method works, the duct may be blocked, crushed or contain debris. In that case, it should be inspected and cleared before attempting to install the cable. Avoid forcing rods or cables through, as this can damage the duct or leave the cable jammed.
Once the cable has been installed, it's good practice to leave a spare draw rope in the duct for any future cable replacements or additions.
The easiest way is to use cable rods or a draw rope to pull a string through the duct. For longer ducts, a vacuum cleaner can sometimes be used to pull a lightweight string through first.
If this doesn't work, the duct may be blocked and will need checking.
