IBM 1PA, Operational, Installation, And Maintenance Manual

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AC or DC Voltage on Twisted-Pair Wires
The following voltages (depending on the magnitude) can be a safety hazard,
introduce errors into the network, or cause the network to be inoperative:
Ÿ
AC voltage induced into the twisted-pair wires from nearby power or signal
cables.
Ÿ
AC or DC voltage caused by shorts or unintentional connection to other circuits.
Wire Resistance
Wire resistance measurements indicate the presence of opens, shorts, faults,
high-resistance connections, or incorrect wire sizes:
Ÿ
Opens, shorts, or faults usually cause an inoperative network.
Ÿ
High-resistance connections or incorrect wire sizes can cause:
– High error rates
– An inoperative network or attached device
Ÿ
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). Do
not use loops that contain different sizes of wire for 5250 protocol transmission.
Wire length that exceeds the specified limits can cause:
Ÿ
Excessive errors or intermittent errors
Ÿ
An inoperative network or attached device
If you need information about the 5250 protocol that is used for 1 Mbps mode, see
the
IBM 6299 Midrange Hub Planning, Installation, and Maintenance Guide.
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:
Ÿ
Opens
Ÿ
Shorts
Ÿ
Loose connections
Ÿ
Wiring stubs
Ÿ
Bridge taps
Ÿ
Loading circuits
Ÿ
Telephone jacks
Ÿ
Connector blocks
Chapter 4. Troubleshooting
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