[SM4] PoE Technology in NP-SM4 Switches

A switch Netping NP-SM4 has four ports: P0, P1, P2, P3. Their location and numeration are shown at the picture 6.

Picture 6.  Ports Location

A port P3 is designed to feed a power supply to a switch NP-SM4 with the help of PoE-injector or any other PSE device. A power supply voltage range at a port P3 is 42 – 60V. A compatibility determination sheme works at a port P3 with PoE devices of af/at standard. Jumper J6 disables a work of PoE determination scheme and decreases a lower limit of a voltage range to 5 V (more detailed information about J6 is given below).

A switch can be fed with the help of external power supply unit. An input voltage range for a supply unit is 11 – 60 V. A priority is given to a power supply unit. When a voltage on input of a power supply unit exceeds10 V, PoE input is disabled.

NP-SM4 switch can transmit power supply received from PoE-injector or a power supply unit on ports P0, P1, P2.

Important! A partner PoE determination scheme doesn't work on ports P0, P1, P2. When jumpers are installed, power supply is always fed without determining if a partner supports PoE. Power supply is always fed on both pairs for transmitting data and on unused pairs. (А and В variants of PoE standard). It's impossible to choose either one of the variants. 

By default, NP-SM4 switch does not feed the ports P0, P1, P2. There is a need to install jumpers on a board of a switch to feed one or several ports. Two jumpers are responsible for each port. A location of jumpers is shown at the picture 7.

Picture 7. Location of Jumpers on a Board of a Switch

J4 jumpers block is responsible for feeding. Two upper jumpers (when installed) enable P1 port feeding, two middle ones enable P2 port feeding,  and two lower ones enable P0 port feeding.

J6 jumper (when installed) decreases a lower limit of a voltage range of P3 port to 5 V (when J6 is not installed, a voltage on P3 should be in a range 42 – 60 V). This helps to feed a device even with a long cable with a big voltage drop. Installing of a jumper J6 disables a function of auto determination, which is used by PSE devices to determine a presence of PoE consumers (PD devices). Thus PSE devices will feed NP-SM4, which has a jumper J6 installed. J6 jumper is not included into a shipping kit.

Jumpers are installed horizontally. Improper installation of jumpers can damage a switch. An example of a proper installation of jumpers for feeding P2 port is shown at the picture 8.

Picture 8. Proper Installation of Jumpers

Important! A board of switch is under 48 V voltage, which is dangerous for a life. To avoid an electric shock, always turn off a power supply of a switch before removing its lid.A switch operation with an opened lid is not allowed.

Important! Do not turn on feeding of ports, where an equipment, which does not support PoE, can be connected.

To feed a certain port of a switch, it is a necessary to fulfill the following:

  • Turn off power supply of NP-SM4 switch;
  • Remove a lid of a switch, using an end screwdriver. To do this, there are grooves near P3 and P2 ports;
  • Install/remove jumpers;
  • Close a lid of a switch;
  • Turn on power supply of a switch.

A maximum capacity of a NP-SM4 switch (and all PoE consumers, connected to it), should not exceed 30 watts according to the 802.3at standard. Consumers can be connected to different ports of  NP-SM4 switch or to one port, there is no limit to a total power. A maximum power consumption of NP-SM4 switch itself is 2.5 watts, which gives an oppurtunity to join up to 10 NP-SM4 switches in a circuit, using short patch cords. However, it is not recommended to join more than four switches in a circuit.

There is a need to take into account a voltage drop on long lines, as for 100 meter cable segment of class 5 a voltage drop can make up to 10 V on a device. Thus it is possible to join only two devices in a circuit.