NCP1095

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13

PoE System Overview

The overall PoE standard distinguishes between four

Types of PSEs and four Types of PDs.

Table 5 gives an overview of the system parameters that

are allowed and required for operation at a certain power

level (assigned Class).

An important parameter is the cable DC resistance

(determined by cable type and length).

In general a Cat 5 cable is required when using a Type 3

or Type 4 PD or PSE in the system or when both PSE and PD

are of Type 2.

Operation over 4-pair is reserved for Type 3 and 4 PSEs.

Table 5. SYSTEM PARAMETERS OVERVIEW

Assigned

Class

PSE Type

Minimum

Cabling

Type

Number of

Powered Pairs

PD Type

Requested

Class

Standard

1

1

Cat 3 (Note 8)

2p

1

1

802.3af/at

2

Cat 3

3, 4

Cat 3

2p/4p

3

802.3bt

2

1, 2

Cat 3

2p

1

2

802.3af/at

3

Cat 5 (Note 9)

2p/4p

3

802.3bt

4

Cat 5

3

1

Cat 3

2p

1

0, 3

802.3af

1

Cat 3 (Note 10)

2p

1

0, 3

802.3at

2

4

2

Cat 3

1

0, 3

802.3af/at

2

4

802.3at

3, 4

Cat 5

2p/4p

3

3, 4/5/6

802.3bt

4

7/8

4

2

Cat 5

2p

2

4

802.3at

3, 4

2p/4p

3

4/5/6

802.3bt

4

7/8

5

3, 4

Cat 5

4p

3

5

802.3bt

6

3, 4

Cat 5

4p

3

6

802.3bt

4

7, 8

7

4

Cat 5

4p

4

7

802.3bt

8

4

Cat 5

4p

4

8

802.3bt

8. Critical for: 44 V/4 W source connected to 3.84 W load over 20 W.

9. Critical for: 50 V/6.7 W source connected to 6.49 W load over 12.5 W.

10.Critical for: 44 V/15.4 W source connected to 13 W load over 20 W.