Conduit jamming ratio

Jamming is the wedging of three unbound cables when pulled into a conduit. This usually occurs because of crossovers when the cables twist or are pulled around bends. The conduit jamming ratio is the ratio of the conduit inner diameter $Di_d$ and the cable outside diameter $D_e$. When calculating jamming probabilities, a 5% factor is used to account for the oval cross-section of conduit bends.

The cable diameters should be measured, since actual diameters may vary from the published nominal values.

Cableizer does only indicate the jamming ratio for Three cables unbound. While jamming can occur when pulling four or more cables into a conduit, the probability is very low.

Cableizer indicates the risk for jamming according to the following table. As shown, different references use different ranges for quantifying the jamming risk. Cableizer cannot be held responsible should your cables jam!

Jamming ratio2.
Cableizer / Southwire 1)very smallsmallmoderatesignificantmoderatesmallvery small
General Cable 2)impossiblepossibleprobableimpossible
IEEE Std 1185-2010 3) / Okonite 4)okprobableok
Polywater 5)okprobableok
1) Southwire, 'Power Cable Installation Guide', 2005
2) General Cable, 'Cable Installation Manual for Power and Control Cables', Ninth Edition, September 2011
3) IEEE Std 1185-2010, 'IEEE Recommended Practice for Cable Installation in Generating Stations and Industrial Facilities', 2011
4) Okonite, 'Installation Practices for Cable Raceway Systems', 2011
5) Polywater, 'Pull Planner Documentation', 2019