The Velocity Of Propagation or VOP is the speed at which an electrical signal passes through a cable. The VOP is usually expressed as a percentage, where the denominator is the speed of light. Thus, in a cable with a VOP of 90, an electrical signal will travel from one end of the cable to the other at 0.9C.

Reasons why the measurement is not precise

Since the VOP is an electrical property of the cable, whether or not the cable is coiled or straight effects the VOP value.  Also, the manufacturer only tightly controls the VOP in cables that are designed for transmitting high speed electrical signals. Thus the VOP for cables like Romex, and bell wire vary greatly, from batch to batch and manufacturer to manufacturer.  While VOP's are technically a number like 67.345, they are almost never expressed with more than single digit precision, e.g. 67.  Even so, using ShortStop to get within the right ballpark is an immense time savings, especially when you remember that most failures are at a junction and wires are almost never run in a straight path to begin with, they always have bends and loops.  The following table lists many cable types and their associated VOP's (both straight and coiled). Additional VOP`s may be found on our VOP - by Manufacturer page.

Wire VOP (range) VOP (nominal) VOP (flat) VOP (coiled) 12/2 w/G Romex, Coiled or on a spool 63 to 75 -66-     12/2 BX, Coiled 63 to 75 -65-     14/3 BX, Coiled 63 to 75 -70-     12/3 Orange Outdoor Extension Cord 55 to 60 -56-     14/3 Orange Outdoor Extension Cord 55 to 60 -59-     16/3 Orange Outdoor Extension Cord 55 to 60 -59-     8 to 16 Guage THHN in Conduit (See Note 1) 74 to 84 -77-     Belden 8737, 2 wire shielded, R/B     -48- -45- Belden 8737, 2 wire shielded, R/Shield     -55- -53- Belden 9114, RG-6/U 75 Ohm Coax     -78- -78- Belden 8216, RG-174/U     -64- -64- RG-58/U 50 Ohm Coax     -63- -63- RG-59/U 75 Ohm Coax     -63- -72- 300 Ohm Black Foam Antenna Wire     -77- -72- 300 Ohm Brown Antenna Wire     -77- -67- 16 to 22 Gauge Speaker Wire     -77- -58- 18 Gauge Twisted Bell Wire     -73- -69- Quad Flat Telephone Wire, Red/Green     -62- -58- CAT-5, Blue/White pair (See Note 2)     -66- -66-

Note 1:  The VOP for THHN wires inside a conduit varies greatly based on the overall contents of the conduit. For 8 to 16 guage wires in 1/2 inch to 1 inch conduit, the VOP is approximately 77, with a range of 70 (crowded) to 84 (sparse) depending on how crowded the conduit. Note 2:  With double twisted cables such as CAT-5, where the individual pairs are twisted around each other, the length of each of the pairs is slightly different. In CAT-5 cables, this difference from the shortest wire to the longest wire is approiximately 3%.