Copper Wiring Troubleshooting Facts

Split Pair

When a single wire in two different pairs is reversed at both ends. For example, if instead of the solid green wire, the solid brown wire is matched with the green/white wire in pins 1 and 2. With a split pair configuration, the cable might still work (especially if it is short), but it could introduce crosstalk. · When the T568A/B standards for making drop cables are followed, one pair is split to meet the standards. In this case, a common split pair error is simply placing all wire pairs in order in the connector instead of splitting the pair according to the standard. · When cables are connected using a punch down block, pairs are not split.

Transceiver Mismatch

Well-manufactured network devices have interfaces that can be tailored to different cable types, protocols, and speeds. This is done by connecting a hot swappable transceiver to the interface. When connecting one network device to another, matching transceivers must be used. For twisted pair cabling, a mismatch in speed is a common issue.

Bad Connector

a damaged connector that is causing connectivity issues. For example, a broken locking tab on an RJ45 connector can cause intermittent connection problems. Another common connector is when there is a bent or damaged pin, especially on female RJ45 connections and the center wire of a coaxial cable.

Wiremapping

matching a wire with a pin on one end with the same pin on the other end. For example, an error in the wiremapping results when the wire at pin 1 connects to pin 4.

Incorrect Termination

occurs when an incompatible or incorrect connector is used. This can result in reduced performance or complete connection loss.

Short

occurs when electrical signals take a path other than the intended path. In the case of twisted pair wiring, it means that a signal sent on one wire arrives on a different wire. they occur when two wires touch; this can be caused by worn wire jackets, crushed wires, or a metal object piercing two or more wires.

Attenuation

the loss of signal strength from one end of a cable to the other. This is also known as dB loss. · The longer the cable, the more attenuation. For this reason, it is important never to exceed the maximum cable length defined by the networking architecture. · Cables at a higher temperature experience more attenuation than cables at a lower temperature. A repeater regenerates the signal and removes the effects of attenuation.

Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI)

Electromagnetic interference and radio frequency interference are external signals that interfere with normal network communications. Common sources of EMI/RFI include nearby generators, motors (such as elevator motors), radio transmitters, welders, transformers, and fluorescent lighting. To protect against EMI/RFI: · Use fiber optic instead of copper cables. Fiber optic cables are immune to EMI/RFI. · Use shielded twisted pair cables. Shielded cables have a metal foil that encloses all of the wires. Some cables might also include a drain wire that is a bare wire outside of the foil, but within the cable jacket. The drain wire can be grounded to help absorb EMI/RFI. Avoid installing cables near EMI/RFI sources.

FEXT

Far-end crosstalk (FEXT) is measured on the end without the transmitter. For example, when a signal is sent on one wire pair, far-end crosstalk measures the interference on an adjacent wire pair at the opposite connector end.

Crosstalk

Interference that is caused by signals within the twisted pairs of wires (for example, current flow on one twisted pair causing a current flow on an adjacent pair). · The twisting of wires into pairs helps reduce crosstalk between pairs. · Each pair of wires is twisted at a different rate to reduce crosstalk between pairs. · is often introduced within connectors, where the twists are removed to add the connector. can also occur where wires are crushed or where the plastic coating is worn.

NEXT

Near-end Crosstalk is measured on the same end as the transmitter. For example, when a signal is sent on one wire pair, near-end crosstalk measures the interference on an adjacent wire pair at the same connector end.

Open Circuit

is when a cut in the wire prevents the original signal from reaching the end of the wire. it is different from a short in that the signal stops (electricity cannot flow because the path is disconnected).

Mis-wired Cable

is caused by incorrect wire positions on both connectors. Several wiring problems might exist: *Reverse Connection *Wiremapping *Split Pair

Alien Crosstalk

is introduced from adjacent, parallel cables. For example, a signal sent on one wire pair causes interference on a wire pair that is within a separate twisted pair cable bundle.

Open Impedance Mismatch (Echo)

the measure of resistance within the transmission medium. · is measured in ohms (Ω). · All cables must have the same -- rating. The rating for the cable must match the rating of the transmitting device. · is mostly a factor in coaxial cables used for networking. Be sure to choose cable with the correct rating (50 or 75 ohm) based on the network type. Never mix cables with different ratings. · When signals move from a cable with one rating to a cable with another rating, some of the signal is reflected back to the transmitter, distorting the signal. With video (cable TV), -- mismatch is manifested as ghosting of the image. Cable distance does not affect the --of the cable.

Reverse Connection

when a cable is wired using one standard on one end and another standard on the other end, creating a crossover cable. While this condition might be intentional, it can cause problems when a crossover cable is used instead of a straight-through cable. This will reverse the transmit and receive match up; the transmit pins on one end maps to the transmit pins on the other end when they should map to the receive pins on the other end.