Amprobe A-5000 Sheath Fault Locator - Manual (Page 11)

9
Impedance (Ω) Linear Active/Reference Bars
450 828 12
1K 694 11-12
5K 413 11
10K 302 10-11
20K 222 10
30K 182 10
50K 139 9-10
100K 90 8-9
327K 45 7-8
1M 21 6-7
Additional A-Frame Receiver Features
Battery Access Plate
Located on the underside of Receiver control panel. Remove the two thumbscrews to release the plate. See Figure 9-1.
Conductive Pads
The A-Frame Receiver is shipped with two protective foam pads with large washers attached to the Receiver probes. These
pads are used for tracing on dry, hard surfaces. Protect and save these conductive pads and washers.
PRINCIPLES oF oPERAtIoN
Functional theory
Reviewing the basics of sheath fault locating is a valuable exercise before proceeding even for experienced users. This will
improve the chances of finding the fault and saving time.
Comparing electrical current to water flowing through a pipe applies extremely well to fault locating. Just like trying to find a
leak in a water pipe, you might seal off one end, pump water into the other, and look for water to appear near the leak. The
principles of sheath fault locating are identical. The cable equivalent of sealing off the pipe is to lift all connections at both
ends of the cable, creating a high resistance open condition. The “water” in this case is the current flowing through the cable
towards the fault. We look for the current “leak” with an A-Frame.
Both ends of the cable must be disconnected from ground.
The T-5000 transmitter applies a low frequency signal between an isolated conductor with an earth fault and another ground
point. This 4.8 Hz signal is induced into the ground from the fault location. The A-5000 Receiver contact probes detect this
signal pattern.
A typical hookup for locating a sheath fault, also called a shield-to-earth fault, is illustrated in Figure 5-1.