Grounding -- it should be okay to just use the PoE

The B5-Lite/C5 has a separate ground lug. Grounding via the PoE alone is not recommended. We’ve had a B5-Lite (same h/w as C5) crash in the field with static buildup as the most likely cause, attributed to lack of a separate ground. While most B5-Lites will go on towers or high spots where it might be possible to find a real ground (easy on towers), C5s are a different story.

There’s no easy way to put a ground on these at most sites. I looked at PoE connectors whose shells had ground lugs, but the ground on the C5 is outside the gland, so running the wire through the gland opening might compromise the seal. Competing WISP client radios do not use separate grounds. An installer is not expected to show up with a ground rod, sledgehammer, and outdoor wire to the radio up on the roof! (Especially here where the ground is largely ledge rock.) It would not go over well with most customers, and would hugely add to the cost of installation. Saving a few bucks on the C5 while requiring a ground wire is false economy. CPEs need to be robust enough, grounded only to the indoor PoE.

We hope to try a group of C5s and C5c’s in the field this summer. I don’t know if the C5c will need a separate ground, but many houses will have them with an external dish, to get the higher gain. But again it won’t be on a metal tower.

How do others feel? Mimosa?


I agree that we should not have to ground with a lug for Customer SM’s, CPE. We have virtually no failures now with our Ubiquiti CPE at customer homes using just the included POE and shielded cable and terminations. Mimosa should follow the same path and allow ground for ESD to happen via the POE and shielded cable/ends.

There was some pretty great discussion about this at WISPAmerica.
I’ll add my two cents to the list to include that the CPE should be able to be grounded by the PoE.

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What about using the Ubiquiti Tough Cable connector with ground wire (TC-GND) ? You would need to enlarge the hole on the wire lug or change for a bigger one.

The ground wire on the connector would be inside the gland, and the grounding screw is outside the gland. That would hurt the weather isolation of the gland, if a second wire (besides the Ethernet) ran out of it. Mimosa however apparently doesn’t think that PoE ground is adequate. Their radio must be too tender.

Agreed re outside the gland - but the rubber + grease would provide an effective seal.

Thanks for the feedback guys. We’re trying to carefully weave between giving flexibility to support the practices we know WISPs prefer to do, and our obligations as well to observe NEC and local codes.

Mimosa’s position is that we require outdoor installations to be bonded to ground prior to entry of a premise, and we further want to prevent ESD from entering the premises using an ESD/NID device, like the Gigabit NID device we introduced at very low $9.99 cost to stimulate the use of it.

As you all mentioned, yes we did provide a standalone grounding post to support best technical practice of grounding the radio. Inside the device, the grounding system also is tied into the metalized internal dish, the PCB ground, the plastics (to bleed of ESD), and to the shielded metal jack on the Ethernet port (which supports 802.3af/at wiring and powering, and consumes 7W max).

Also, much like the satellite dish industry always grounds their dishes, they typically don’t create their own ground with a new rod. Instead they have nifty solutions for clipping to existing power systems and existing house ground.

All of that said, read between the lines, you have all the tools necessary from Mimosa directly to meet “best industry practice” and local/national codes, and also a comprehensive grounding system that gives you flexibility to use alternative like accessories to support your preferred practices for grounding.

In any case, ESD events that damage the radio are not covered under warranty, and we’re simply recommending safety practices.

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I think you’ve overthought the problem, especially the code issue. Maybe the sat-dish industry has a way to clip on to things. But we don’t always have them in the field – not every site is a single-family house with a garden hose outlet!

I would just “read between the lines” and ignore the screw, since the screw is tied to the dish, PCB ground, and Ethernet jack, so the Ethernet jack should also have conductivity to the post and other grounds too. But I’ve got a B5-Lite (C5 hardware, of course) up on a high-rise elevator penthouse that crashed in fair weather. And the only explanation Chris et al can come up with is that it wasn’t grounded well enough. But the Ubiquiti radio is happy. So either there’s a different problem that caused the crash, or the radio is just too sensitive. I’m not sure which way to look.

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Good “reading”. Yes, I’ve never confused thinking, and getting agreement out of lawyers.

I’m carefully watching a couple of specific tower (non home) deployments and their grounding (or lack thereof) that seem to be misbehaving. Been a couple cases that we are investigating but simply haven’t seen a widespread issue amongst the very big installed base now on the B5-Lite. I’ll update you as soon as we know more, we’re not done looking at the issue from a technical perspective, but it’s been a difficult one to capture.

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Thanks -useful “info”

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Ive got a b5 lite that reboots whenever its bad weather. We even tried a different unit and experienced the same problem.

join the club. slightest sniff of rain and this thing bounces like a beach ball

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Just to clarify, i have no rf issues at all, the device power resets!

All, if you’re having a weather reboot or a link drop in weather on the B5-Lite, please contact support, we’ve gotten to the bottom of the issue and they can help you out ASAP. Apologies for the problems, it’s a limited issue that we’ve resolved. @Kent had some experience with it and helped us test the resolution.

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The fix works. The fixed units went thru 6 days of thunderstorms and rain with without a single drop.

Like Jaime said, contact support if your seeing weather related issues. They will take of you.

can we have the solution shared on here?

We are going to be testing our first set of gear soon, and we want to be well studied so we can make the best decisions during the installs.

What is the ‘fix’ for the weather issue?

Hi Sam,

The fix is to replace any unit that reboots in the rain AND is properly grounded at the tower.

Some early B5-Lite radios were more vulnerable to ESD-caused reboots, but the majority of radios do not reboot when grounded well. It greatly depends on the installed conditions. We have since updated the B5-Lite design to include additional ESD protection that has proven effective in these cases.

Of course, there are a fair amount of other weather-related reboot reasons due to input power problems that result in similar symptoms. For us to definitively determine the root cause for any reboot, we need to review the Support Info log (.tar file). This avoids confusing this with other types of more common problems.

We’re these lites not using grounded cables with was drain?

Does this issue apply to c5s?

Lastly, is a grounded Ethernet cable + earth ground efficient? In many cpe installs surrounded by wood, we can tie the ground screw to a ground pigtail on our cable with this head vs the non pigtale model (see attached)

Or we can run a long 12guage ground line back to inside/or a vent pipe prob 50 ft away.

We have never had read issues with our ubnt equipment which these are slated to replace and we need them to work 100% on day one with no learning curve during install.

It sounds like they need more care than ubnt with esd.

The hard part is no disty’ have the accessories and the radios. So it’s a difficult acquisition.

Do the c5s come shipped with current firmware or can we flash them up to date in the field before any traffic goes on them. (minutes before they are in production) I take it the cloud will take a bit to sync and flash it

Hi Sam,

The B5-Lite internal grounding was improved over time to compensate for other external factors. We just started shipping C5’s last quarter, so they have the design change that better protects them. Also, most C5’s will be installed on residences where the electrical environment is less challenging than a tower / lightning rod.

Mimosa recommends following all national and any applicable local electrical codes for grounding. If using a PoE with a ground input, it should be plugged into a grounded outlet. The radio should also be grounded.

The B5-Lite should have a ground wire attached to the tower (the shorter the better - usually 1 meter or less).

Please see this discussion about C5 grounding recommendations: Grounding -- it should be okay to just use the PoE

These are pretty common recommendations meant for equipment safety, but also to prevent circulating ground currents from causing electrical problems with any type of equipment.

Mimosa also recommends high-quality, shielded CAT6 cable with metal end connectors because we’ve found that it provides lower capacitance and better EMI protection that could otherwise affect GigE connections. I should mention that there are plenty of users who have installed with unshielded CAT5e and have no problems, so performance is situation dependent.

The first batch of C5’s require a firmware update before use, but we are working toward removing that requirement because we understand the burden it creates. Yes, you can update them in the field, but I recommend generating an unlock code from the cloud and bringing it with you on the install in case you don’t have an internet connection. That is another area that we are actively working to improve.

How can I determine if I received one of the updated models?