55 Questions
What is the purpose of measuring DC resistance unbalance in a PoE connection?
To identify potential problems that could interfere with data transmission
Why does gigabit Ethernet require all four cable pairs for bidirectional transmission?
To allow for simultaneous transmission and reception of data
What is the purpose of applying a common-mode voltage between two pairs in a four-pair Ethernet cable for PoE?
To prevent interference with data transmission
What percentage of the installed cabling base is estimated to support gigabit Ethernet and PoE?
85%
What is the term used to describe the delivery of PoE over pairs that are simultaneously transmitting data?
Phantom power
Why did 10/100BASE-T applications leave two spare pairs of a four-pair twisted cable available for PoE?
To support the power needs of PoE devices
What is the formula for calculating the DC loop resistance of a pair of conductors?
$R_{loop} = R_1 + R_2$
According to IEEE standards, what is the maximum allowable channel DC loop resistance for a pair?
25 Ω
What is the formula for calculating the parallel resistance of pair 1 & 2?
$R_{parallel} = \frac{R_1 * R_2}{R_1 + R_2}$
What is the reported DC resistance unbalance between pairs 1&2 – 3&6?
0.11 Ω
What does the Cable Analyzer meter measure to calculate the DC resistance unbalance within a pair?
Individual resistances of each wire of the pair
If the DC resistance unbalance between pairs were approximated from just DC loop resistance, what would the result be?
0.23 Ω
What is the maximum allowable permanent link DC loop resistance according to IEEE standards?
21 Ω
What is the maximum power delivery allowed by the IEEE 802.3af standard?
15.4 W over two pairs
What is the primary purpose of the IEEE 802.3bt PoE Plus Plus standard?
To provide 100W of power
What can lead to saturation of the transformer and distortion of Ethernet data signals in a PoE system?
Too much DC resistance unbalance
What is an effect of poor installation practices in PoE systems?
DC resistance unbalance
What does the IEEE 802.3at standard specify for power delivery?
30 W over two pairs
What is a field test requirement specified by IEEE's PoE standards?
Resistance unbalance testing
What is the maximum DC resistance unbalance specified by IEEE Std 802.3-2012 between conductors?
3%
Why do non-standard conductors like copper coated aluminum (CCA) not support PoE applications?
They have 55% greater DC resistance compared to solid copper cables of the same diameter
What is the purpose of including DC resistance unbalance testing as an extended field testing requirement?
To address issues surrounding CCA cables and meet IEEE-mandated PoE requirements
What does the DSX-5000 CableAnalyzer test for related to DC resistance unbalance?
DC loop resistance, DC resistance unbalance within a pair, and DC resistance unbalance between pairs
What is the DC resistance unbalance test limit for TIA Cat 6A?
Specified in the table provided
Why do poor quality cables with variations in diameter, concentricity, and smoothness pose a higher risk for DC resistance unbalance in PoE systems?
Due to increased heating and lower voltage at the powered device
What is the maximum power delivery allowed by the IEEE 802.3af standard?
15.4 W over two pairs
What does the IEEE 802.3bt PoE Plus Plus standard aim to provide?
100W of power
What is the primary purpose of the PoE Plus and PoE Plus Plus standards?
To cater to power-hungry devices
What can lead to saturation of the transformer and distortion of Ethernet data signals in a PoE system?
Poor workmanship
What is the effect of poor installation practices in PoE systems?
DC resistance unbalance
What is the maximum power delivery enabled by the new IEEE 802.3bt standard?
100W
What is the transition in PoE delivery from the two pair to the four pair with the new IEEE 802.3bt standard?
Two pair to four pair
What is the maximum allowable DC resistance unbalance between pairs according to the proposed IEEE 802.3bt standard?
7%
Why do non-standard conductors like copper coated aluminum (CCA) not support PoE applications?
All of the above
What does the DSX-5000 CableAnalyzer test for related to DC resistance unbalance?
All of the above
What is the maximum DC resistance unbalance test limit for TIA Cat 6A?
7%
Why is testing for DC resistance unbalance within a pair and between pairs crucial for PoE systems?
All of the above
What is the maximum allowable DC resistance unbalance between conductors according to IEEE Std 802.3-2012?
3%
What is the primary purpose of the IEEE 802.3bt PoE Plus Plus standard?
To ensure proper power delivery for future PoE systems
What is the primary purpose of measuring DC resistance unbalance in a PoE connection?
To identify potential problems that could arise due to uneven distribution of current in the cable pairs
What is the maximum allowable DC resistance unbalance specified by IEEE standards for PoE connections?
$3%$
Why does gigabit Ethernet require all four cable pairs for bidirectional transmission?
To provide bidirectional transmission for higher data rates
What can lead to saturation of the transformer and distortion of Ethernet data signals in a PoE system?
High DC resistance unbalance
What is the term used to describe the delivery of PoE over pairs that are simultaneously transmitting data?
Phantom power
What is the reported percentage of the installed cabling base estimated to support gigabit Ethernet and PoE?
85%
What is the purpose of applying a common-mode voltage between two pairs in a four-pair Ethernet cable for PoE?
To deliver PoE without interfering with data transmission
What is the formula for calculating the parallel resistance of pair 1 & 2?
$\frac{R1 \times R2}{R1 + R2}$
What is the maximum allowable channel DC loop resistance for a pair according to IEEE standards?
25 $\Omega$
What is the maximum allowable permanent link DC loop resistance according to IEEE standards?
21 $\Omega$
What does the Cable Analyzer meter measure to calculate the DC resistance unbalance within a pair?
Individual resistances of each wire of the pair
What is the reported DC resistance unbalance between pairs 1&2 – 3&6?
0.11 $\Omega$
What is the purpose of including DC resistance unbalance testing as an extended field testing requirement?
To ensure power delivery efficiency
What is the maximum DC resistance unbalance specified by IEEE Std 802.3-2012 between conductors?
3%
What can lead to saturation of the transformer and distortion of Ethernet data signals in a PoE system?
Excessive DC resistance unbalance
Why do non-standard conductors like copper coated aluminum (CCA) not support PoE applications?
Higher resistance per unit length
Study Notes
Testing for DC Resistance Unbalance in PoE Systems
- Poor quality cables with variations in diameter, concentricity, and smoothness of copper conductors pose a higher risk for DC resistance unbalance in PoE systems.
- Non-standard conductors like copper coated aluminum (CCA) and copper coated steel do not comply with industry standards and do not support PoE applications due to increased DC resistance.
- CCA cables have 55% greater DC resistance compared to solid copper cables of the same diameter, leading to increased heating and lower voltage at the powered device.
- ANSI/TIA and ISO/IEC standards require twisted pair data cable to be 100% copper, and testing for DC Resistance Unbalance within a Pair and Between Pairs is essential.
- IEEE Std 802.3-2012 specifies a maximum DC resistance unbalance of 3% between conductors, while the proposed IEEE 802.3bt standard requires the DC resistance unbalance between pairs to be no more than 7% or 50m Ω.
- The DSX-5000 CableAnalyzer is capable of testing DC loop resistance, DC resistance unbalance within a pair, and DC resistance unbalance between pairs.
- DC resistance unbalance test limits for TIA Cat 5e, Cat 6, Cat 6A, ISO11801 PL Class D, Class E, and Class Ea are specified in the table provided.
- The DSX-5000 meter applies PASS/FAIL for the test limit selected when making a permanent link or channel measurement, providing confidence in the cabling's ability to support PoE.
- Consideration should be given to including DC resistance unbalance testing as an extended field testing requirement to address issues surrounding CCA cables and meet IEEE-mandated PoE requirements.
- As more enterprise entities deploy multiple gigabit Ethernet technologies and PoE devices, testing for DC resistance unbalance within a pair and between pairs becomes crucial.
- The deployment of PoE Plus and PoE Plus Plus further emphasizes the importance of DC resistance unbalance testing for current and future PoE systems.
- Using the correct termination tool, such as impact or multi-wire punchdown tools, can help increase termination consistency and avoid DC resistance unbalance in PoE systems.
Testing for DC Resistance Unbalance in PoE Systems
- Poor quality cables with variations in diameter, concentricity, and smoothness of copper conductors pose a higher risk for DC resistance unbalance in PoE systems.
- Non-standard conductors like copper coated aluminum (CCA) and copper coated steel do not comply with industry standards and do not support PoE applications due to increased DC resistance.
- CCA cables have 55% greater DC resistance compared to solid copper cables of the same diameter, leading to increased heating and lower voltage at the powered device.
- ANSI/TIA and ISO/IEC standards require twisted pair data cable to be 100% copper, and testing for DC Resistance Unbalance within a Pair and Between Pairs is essential.
- IEEE Std 802.3-2012 specifies a maximum DC resistance unbalance of 3% between conductors, while the proposed IEEE 802.3bt standard requires the DC resistance unbalance between pairs to be no more than 7% or 50m Ω.
- The DSX-5000 CableAnalyzer is capable of testing DC loop resistance, DC resistance unbalance within a pair, and DC resistance unbalance between pairs.
- DC resistance unbalance test limits for TIA Cat 5e, Cat 6, Cat 6A, ISO11801 PL Class D, Class E, and Class Ea are specified in the table provided.
- The DSX-5000 meter applies PASS/FAIL for the test limit selected when making a permanent link or channel measurement, providing confidence in the cabling's ability to support PoE.
- Consideration should be given to including DC resistance unbalance testing as an extended field testing requirement to address issues surrounding CCA cables and meet IEEE-mandated PoE requirements.
- As more enterprise entities deploy multiple gigabit Ethernet technologies and PoE devices, testing for DC resistance unbalance within a pair and between pairs becomes crucial.
- The deployment of PoE Plus and PoE Plus Plus further emphasizes the importance of DC resistance unbalance testing for current and future PoE systems.
- Using the correct termination tool, such as impact or multi-wire punchdown tools, can help increase termination consistency and avoid DC resistance unbalance in PoE systems.
Test your knowledge of DC resistance unbalance in PoE systems with this quiz. Learn about the impact of cable quality, conductor materials, industry standards, and testing equipment on ensuring proper DC resistance balance for reliable PoE applications.
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