Network Switch Power Isolation

Question

I run a small office network that uses TP-LINK T1600G-28TS (TL-SG2424) JetStream switches. The office is across two buildings, each fed by a different phase of power.

We've recently installed HD video feeds accross both buildings to power info screens - the source of this video is sat nicely in a server cabinet within building A, which is powered by a National Grid power feed (I'll call it feed A). The video is then sent around that building. Happy days.

We also need the video feed in building B, which is powered by a separate National Grid power feed (I'll call it feed B), despite the building being only 80m away. To carry the feed between the two buildings we use HDMI over CAT6 converters and just run it on a spare underground CAT 6 line.

I have an obvious problem of copper between two power sources. The HDMI over CAT6 RX/TX units are not isolated properly and keep blowing each other up.

My plan is to buy HDMI over TCP/IP, and run this through a VLAN on my switch. Am I correct in thinking that the Switch is isolated? I anticipate that the routing will be as follows:

1. HD Video source (power feed A)
2. HDMI over TCP/IP TX (power feed A)
3. VLAN on TP-LINK T1600G-28TS (TL-SG2424) JetStream (power feed A)
4. VLAN on TP-LINK T1600G-28TS (TL-SG2424) JetStream (power feed B)
5. HDMI over TCP/IP RX (power feed B)
6. HD monitors in building B (power feed B)

I hope this avoids an non-isolated copper connection between power sources. Thoughts and comments?

Obviously the easy way to do this is via a fibre video link. I've thought about it, but this is about 1/10th of the price.

Thanks

Answer 1

On the assumption your two switches in buildings A and B are already communicating properly, you have your answer: certainly it will work fine.

Ethernet has input transformers to ensure isolation. Although ground loops can be a tricky subject, if you have ethernet running between buildings -- as you do -- with different power supplies, you have to pay attention to ground loops. In practice this can be as simple as ensuring you don't have shielded cable.

As a thought on your original problem, you could consider any method of IP-based transmission rather than HDMI over TCP. For example software methods, such as any kind of screensharing, perhaps VNC or X11, which might be cheaper if you start having more screens, but these are for our friends at Serverfault and similar.

Answer 2

HDMI over IP is just a network application - if the network works, HDMI over IP works. Check the network reliability and make it as good as possible - this includes the physical links as well as link-layer bottlenecks. Ethernet uses pulse transformers, isolating the ports from each other - at least in theory: shielding with bad grounding can cause a compensating current that may have a very bad impact on signal integrity. Your experience with HDMI-over-Cat6 is most likely caused by this.

Diagnose and troubleshoot using network tools, not the HDMI connection. If there's noise from earth with STP you should use UTP or improve the ground connection. Using UTP patch cables with STP plenum cable might improve the situation - or it might not. Alternatively, consider running fiber. If you've got bandwidth bottlenecks, widen them or deploy QoS.