I have a Reolink network video recorder (NVR) that provides 802.3af Power over Ethernet to downstream cameras. This NVR is plugged into a uninterruptible power supply (UPS).

I have a switch, whose non-PoE uplink port is plugged into one of the PoE-capable ports on the NVR; this switch normally plugs into the wall to supply PoE to other downstream cameras. For this question, however, there are no cameras plugged in, and the PoE switch is only grounded, not powered. [1]

Diagram of setup

With this setup, the NVR periodically resets. Furthermore, I can cause the NVR to reset by unplugging the UPS from the wall, especially if I rapidly jiggle the plug, simulating a power "glitch."

If the switch is not grounded, the problem does not occur. If the switch is instead plugged into a non-PoE port on the NVR, the problem does not occur.

It is my understanding that Ethernet should isolate the various devices from each others' grounding issues. Which of these devices is at fault, or has a defective design, and what could be causing the NVR to reset? How can I mitigate the problem?

[1]: The funny ground-only connection of the switch is my attempt to reduce the problem to an MVCE. Of course, in real life, the switch is powered.

  • 2
    \$\begingroup\$ The cheaper "big-box store" UPS's switch over using relays after it detects a power failure. This causes a momentary (very short) power loss as the relay switches from the wall socket to the inverter. This may be causing the glitch. The only way around that is to get a "100% online" UPS, which are much more expensive. \$\endgroup\$
    – Ron Beyer
    Commented Apr 17, 2020 at 2:38
  • \$\begingroup\$ Initially I thought that might be the issue, but there's no trouble when the switch isn't plugged in to the NVR (NVR handles the switchover just fine). \$\endgroup\$ Commented Apr 17, 2020 at 2:42
  • \$\begingroup\$ Yeah, this is probably just a non-compliance in the EMC area due to low quality gear. \$\endgroup\$
    – Jeroen3
    Commented Apr 17, 2020 at 5:45
  • \$\begingroup\$ @Jeroen3 I agree, but I can't decide if it's the NVR's fault for not handling it, or the switch's for seemingly causing it. Even an explanation of the transients involved here would be helpful because I don't know how the introduction of PoE changes the isolation of all the gear. \$\endgroup\$ Commented Apr 17, 2020 at 5:49
  • \$\begingroup\$ Either brownout or common mode transient. Maybe it's resolved if the NVR is grounded. \$\endgroup\$
    – Jeroen3
    Commented Apr 17, 2020 at 6:17


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