UNDERSTANDING NVP
The Cable Gauge makes a very precise measurement of the time it takes for
an electrical signal to travel down a cable, hit a short or open and travel back to
the unit. The time is converted into length based on the speed that the electrical
signal travels along the cable being tested. Different cables have different electrical
properties and the speed that the electrical signal travels will vary based on the
NVP of the cable.
NVP (Nominal Velocity of Propagation) is the relative speed that an electrical
signal will travel through a media. A vacuum is a perfect media with an NVP of
100. All cables have an NVP less than 100 and typically in the range of 50 to 80.
Using the most accurate NVP available will provide the most accurate length
measurements.
The NVP for electrical service cables (such as Romex, BX, UF-B) varies
significantly between manufacturers and even between production lots from the
same manufacturer. Data cables have special manufacturing processes that
produce fairly consistent NVP values. The NVP of a cable can also be different if it
is wound on a spool or laying flat (installed). Data cables have the least variation
between wound and flat and some coaxial cables show significant variation. NVP
is specified for many types of cable and may be printed on the cable spool or
box. Contacting the manufacturer or checking their website can also be a good
source of accurate NVP information. Using the Custom Cable Setup to determine
the NVP of a known cable length provides accurate results. The NVP values
prestored in the Cable Gauge provide typical values for cable types from all
manufacturers.
CABLE TYPE LIST ABBREVIATIONS
The prestored Cable Type List uses the following abbreviations:
NM - Non-Metallic (Romex)
BX - Aluminum Armored Cable with Aluminum Ground
MC - Aluminum Armored Cable with Copper Ground
HC - Aluminum Armored Cable for Health Care Applications
UF - Underground Feeder (Direct Burial Cable)
SOOW - 600V Rubber Jacketed Portable Cord
EXTEN - Outdoor Extension Cable (Typically Orange Color)
W/G - With Ground Wire
ZIP - Lamp Cord
THHN xCDT - THHN Wire in Conduit
CAT - Category
PLNM - Plenum Grade
UTP - Unshielded Twisted Pair
STP - Shielded Twisted Pair
COAX - Coaxial Cable
SPKR - Speaker Wire
TEL - Telephone Twisted Pair
PIC - Plastic Insulated Conductor (Aerial TelephoneCable)
THERM - Thermostat Wire
BOX CONTENTS
•
Cable Gauge Multifunction Cable Meter
•
Carrying Case
•
User Guide
•
Four AA Alkaline Batteries
•
Two Banana Jack to Alligator Test Leads
•
One Banana Jack to BNC Adapter
•
One BNC to “F” Adapter
BATTERY
The Cable Guage operates on four AA alkaline
batteries. Remove the battery cover at the back of
the unit and insert the batteries with the orientation as
shown. Battery polarity is marked inside the battery
well for reference.
INTRODUCTION
The Cable Gauge Multifunction Cable Meter electrically measures the length
of a cable using Time Domain Reflectometry technology. The Cable Gauge
measurement begins by transmitting an electrical pulse into the connected cable.
The electrical pulse travels along the cable until it hits a discontinuity (either a
short or an open) and is then reflected back to the unit. The Cable Gauge
precisely measures the time between launching the pulse and receiving the
reflected pulse. The time measurement is converted to distance using the cable
NVP (Nominal Velocity of Propagation).
Additionally, the Cable Gauge provides a continuous reading of any voltages
present on the cable under test and features four different tone frequencies and
patterns for tracing cables with a tone probe.
MECHANICAL FEATURES
