Will PoE over Cat6 cable slow down network speed?

Some users will use AP to transmit signals when they set up Gigabit LAN. Then they will ask, does PoE with Cat6 cable slow down the transmission speed? Will this cause significant speed degradation?

In principle, loading the power supply on the network cable does not affect the transmission of Ethernet signals. The fundamental reason is that the Ethernet signal is a differential signal, and the power supply is loaded on a pair of differential signal lines at the same time, without changing the difference in signal line levels, so naturally, the power supply and signal are not affected by both.

In practice, however, the following problems may occur.

If the quality of the network cable is too poor, or the distance is too long, it will cause the resistance of the Ethernet cable to increase, and the receiving end will not get enough power, which may cause the receiving device to work abnormally (e.g. insufficient antenna transmitting power).

If the PoE switch is 100 megabit, then your rate is definitely 100 megabit, regardless of the network cable used.

If you are not using a PoE switch, but a PoE injector and the PoE injector is not implemented according to the PoE standard, but directly cuts two pairs of differential signal lines for power supply, then the network will be degraded to 100 megabits.

According to the standard, PoE power supply is divided into two modes: A and B, the principle is the same, the difference is that mode A uses blue wire pair and brown wire pair to supply power; mode B uses green wire pair and orange wire pair to supply power. According to the standard, the receiving device should support both modes, that is, no matter how the electricity is sent, the receiving device should be able to get the electricity; and the supplying device can choose to support, that is, choose a way to send electricity. Individual PoE-powered devices violate the PoE standard by supporting only one of these modes, which can result in these powered devices not working with some powered devices but working with others.

In addition, the PoE power supply is divided into different power negotiation levels, with the lowest being the 12-watt level. Through further negotiation, if the supply side supports it, then the power limit level can be increased, with 25 watts, 50 watts, etc. If your powered device requires higher power, but the power supply does not support it, then it may result in the powered device working at a degraded level.

With some PoE switches, there may be a limited amount of PoE power output. For example, a 24-port switch may support PoE on all of these ports, but can only carry up to 8 ports of PoE at the same time, and on the ninth device your plugin won’t get power.

So, how can we avoid possible problems?

Improve the quality of the network cable, while limiting the length of the cable. (The specific length of the network cable should refer to the information of the powered equipment)

It is recommended that powered devices (such as APs, cameras, etc.) be purchased in conjunction with powered devices (switches, injectors, etc.). And read the datasheet before purchasing to confirm the power supply, power supply mode, PoE standard, etc. are compatible.