Conduit protects low voltage cable, but it also turns every run into a pull against friction, bends and whatever is already inside. Knowing how to pull cable through conduit comes down to four things: a pathway built with enough pull points, a fill you have actually calculated, a clean pulling head, and a pull that never exceeds what the cable is rated to take.
How do you pull cable through conduit?
Check the run has a pull point at least every 100 feet or 180 degrees of bends, and that the cables fit within the fill your spec allows. Push a fish tape or blow a pull string through, tape the cables into a tapered head, lubricate with a product listed for the jacket, and pull steadily within the cable’s rated tension.
Plan the pull before you open the conduit
Most failed pulls are decided before anyone touches the cable, so walk the run and count its length and bends between boxes.
The Montana State University cabling guidelines give a typical rule set. Pull points must not exceed 100 feet or 180 degrees of bends, whichever comes first, and no section between pull points may contain more than two 90 degree bends or the equivalent.
- Pull from box to box, never through a run that breaks those limits in one go.
- Confirm the conduit ends are reamed. The same guideline says conduits shall be reamed to remove burrs and sharp edges, which otherwise skin the jacket.
- Note what is already inside. Existing cables reduce both the area and the room to pull past them.
Conduit fill for low voltage: a worked example
Fill is area based, the approach telecom specs borrow from the electrical code’s Chapter 9 tables: add up the cross-sectional area of every cable, then divide by the internal area of the conduit. The Montana State guideline states that a maximum fill of 40% is preferred, to leave room for future cable. Your project spec may set its own figure.
A worked example, with assumptions stated. Take four cables with an outside diameter of 0.25 inch, and a conduit with an internal diameter of 1.05 inches. Use real figures from the data sheets.
- Area of one cable: 0.7854 x 0.25 x 0.25 = 0.0491 square inch. Four cables: 0.196 square inch.
- Area of the conduit: 0.7854 x 1.05 x 1.05 = 0.866 square inch.
- Fill: 0.196 divided by 0.866 = about 23%, comfortably under 40%.
- Maximum by area at 40%: 0.346 divided by 0.0491 = 7.06, so seven cables.
Area is only the first check. The same guideline says the number of cables a conduit can take is limited by the allowed maximum pulling tension of the cables. A long run with two bends can reach the tension limit well before the conduit looks full.
Keep low voltage out of power conduits
Low voltage and power belong in separate conduits. The electrical code restricts Class 2 and communications cable from sharing a raceway with power conductors except in narrow listed cases, so check the edition your inspector enforces before planning any shared pathway.
Specs often go further. The Montana State guideline says other trades requiring low voltage raceways need to provide their own conduits, and prefers raceway that does not combine electrical and communications wiring. Where the conduit ends and the cable continues on hooks or tray, the clearances in our guide to J hooks vs cable tray take over.
Fish tape and pull string: getting a line through
If the conduit already has a pull string, use it to pull in a new one with the cable, so a line stays behind. If it is empty, you need to get a line through first.
- Fish tape: a flat steel or fiberglass tape on a reel, pushed from one box to the next. It handles short runs and a bend or two. Use non-conductive fiberglass anywhere near energized equipment.
- Vacuum or blower and a line: a foam piston or a plastic bag tied to light string is drawn through by a shop vacuum, or blown through. It suits long or underground runs where a tape binds.
Leave a line in when you finish. The Montana State installation guideline says pull string shall be left in conduits for future cabling, which spares the next technician this whole step.
Make up the pulling head and choose the lubricant
The pulling head is where pulls usually fail. Stagger the cable ends so the bundle tapers to a point, fold the pull string through and around them, and wrap the head tightly with electrical tape so no edge can catch on a coupling.
Pull on all the conductors and the jacket together, never on one exposed pair. Cut off the head and a few feet behind it after the pull, since that section has taken the strain.
Use a pulling lubricant the cable maker lists as compatible with that jacket, applied at the entry point and at each box as the cable feeds. Soap, oil and grease are not substitutes.
Pulling tension and bend radius: follow the data sheet
Every cable has a maximum pulling tension and a minimum bend radius, and both are on its data sheet. For twisted pair, the Montana State installation guidelines for telecommunications cable state that tensile loading shall not exceed 25 pounds on Category 6A cable, and set the minimum bend radius at four times the cable diameter with no load.
- Pull by hand with a steady, even motion. Stopping and restarting takes more force than keeping the cable moving.
- Have a helper feed the cable straight into the conduit from the reel, so it does not kink or drag over the edge.
- Conduit bends also have a limit: the first guideline sets an inside radius of at least 6 times the internal diameter for conduit up to 2 inches.
Coax, fiber and control cable carry their own figures. For which conductor suits a horizontal run, see our guide to stranded vs solid ethernet cable.
Ways to get a line through compared
| Method | Best for | Limits |
|---|---|---|
| Existing pull string | Any conduit left with one | Pull a new string in with the cable |
| Steel fish tape | Short runs with one or two bends | Conductive; binds on long runs |
| Fiberglass fish tape or rods | Short runs near electrical equipment | Stiffer around tight bends |
| Vacuum or blower with a line | Long or underground runs | Needs a sealed run and the right fittings |
Inside walls without conduit, the job is fishing rather than pulling; our guide on how to run coax through walls covers stud bays and fireblocking.
Where to find cable and pulling supplies
The bulk wire and cable category lists data, coax and control cable by the reel, and the wire and cable management category lists the products that organise runs once they leave the conduit. Both sit in the wire, cables and connectors division. Choose the jacket rating for the space with our guide to CMR vs CMP cable.
For pricing and availability on a job, contact your sales representative through the Bursma contact page, or open a Bursma dealer account.
Frequently asked questions
How many Cat6 cables fit in a 1 inch conduit?
Work it out from the cable’s outside diameter on its data sheet and the conduit’s internal area, at the fill your spec allows. In the worked example above, seven 0.25 inch cables fit by area at 40%, but pulling tension and bends can lower that number.
What can I use to pull wire through conduit if I have no fish tape?
A shop vacuum can draw a foam piston or a small plastic bag tied to light string through the conduit. Once that line is through, use it to pull a stronger rope for the cable pull.
Can low voltage and electrical wire share a conduit?
Generally no. The electrical code restricts Class 2 and communications cable from sharing a raceway with power conductors except in narrow listed cases, and many specs require separate conduits outright.