Wire Resistance - IBM 5500 Operational, Installation, And Maintenance Manual

Wire Resistance

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Chapter 6: Twinax Client Cabling Requirements and Problem Solving
Another OEM power monitor provides 8-channel digital storage of external
voltage waveforms. The recorded waveforms may be displayed on a screen.
The recording is triggered when a disturbance occurs that exceeds a
predefined limit.
Wire resistance measurements indicate the presence of opens, shorts, faults,
high-resistance connections, or incorrect wire sizes. Opens, shorts, or faults
usually cause an inoperative network. High-resistance connections or
incorrect wire sizes can cause:
• High error rates
• An inoperative network or attached device
Small wire size can limit the drive capability below the allowable distance
specified.
Measured Wire Resistance Length versus Electrical Length
Comparing the wire length determined by a resistance measurement to the
length measured by a time domain reflectometer can determine whether
different sizes of wire exist in the loop (that is, whether the wiring in the
building is consistent). See "Advanced Time Domain Relfectometry (TDR)
Procedure" on page 113. Do not use loops that contain different sizes of wire
for 5250 protocol transmission.
Wire length that exceeds the specified limits can cause:
• Excessive errors or intermittent errors
• An inoperative network or attached device
Characteristic Impedance
Wire whose characteristic impedance exceeds the specified limits might not
be suitable for high-speed data transmission. Increased error rates can result
from the use of such wire.
Impedance Discontinuities
Impedance discontinuities can be caused by any of the following that exist
along the wire path:
Opens
Shorts
Loose connections
Wiring stubs
Bridge taps
Loading circuits
Telephone jacks
Connector blocks
Excessive impedance discontinuities can cause:
Reflections that can increase the error rate
Planning, Installation, and Maintenance Guide