Ubiquiti lightning protection. Recommendations for connecting devices without a grounding screw on the case

Ubiquiti equipment is perhaps the most common and affordable radio access solution in Russia. Much has already been written about the design of channels on this equipment, there are even alternative lines of software - but not so widely as we would like, the topic of grounding is covered. But with incorrect grounding, even the most properly designed network will bring only disappointments and losses.
Today our material is just about the mundane, namely about the grounding. Fortunately, the new Ubiquiti products have arrived to us - all-weather lightning protection .


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So, we are pleased to present the ETH-SP all-weather gigabit lightning protection.



The device is compact and can be attached to the mast with the same tie as the active equipment:



The manufacturer recommends grounding contact directly to the mast (it does not prohibit to fasten the cable with a normal terminal, but the screw with a nut for such fastening is not even put into the box):



The internal structure of the system is quite simple: cable shields are connected to the grounding terminal, surge protection is implemented by arresters - and they are installed for each line, which allows using any of the valid 802.3af / at power supply circuits and passive PoE used for Ubiquiti devices.



The arresters installed in the device make it possible to cut off voltage pulses above the response rating, for example, when lightning is discharged close.

Previously, in the absence of all-weather lightning protection, the following connection scheme was recommended:



This scheme provides a single point of grounding and cable protection from induced impulses. However, now we can offer a more reliable scheme using two lightning protection systems:





With such a scheme, the cable descent length to the nearest ground point is reduced tenfold and, accordingly, the overvoltage drainage conditions are improved. In fact, the installation of two lightning protectors in such a configuration emulates a device with a metal case.
Since the equipment is now grounded at two points (mast and grounding bus below), the potential difference between points 1 and 2 is checked for the installation if possible. For testing, a cable of at least 18 AWG (0.82 sq. Mm) is used. A multimeter (it is better to use true RMS) should show a potential difference of less than 10 mV DC and less than 300mV AC voltage, resistance less than 5 Ohm. At higher values, damage is possible due to ESD (ElectroStatic Discharge - not necessarily during a thunderstorm), which is a non-warranty case. If these values ​​are exceeded, it is recommended to check the earthing of buildings / structures. To connect devices, use high-quality copper twisted pair and connectors. To connect shielded cables, “eyelet” connectors are recommended.
Please note that the manufacturer requires using only shielded cables and connecting the screen throughout the entire route from the device.

Thus, the use of lightning protections, carrying out the screen rupture, is unacceptable from the point of view of the manufacturer and the impossibility of carrying out warranty repairs:

The product does not apply if the Product:
(I)
It has been approved, except for Ubiquiti Networks or Ubiquiti Networks, in Ubiquiti Networks;
(Ii)
has been painted, rebranded or physically modified in any way;
(Iii)
has been damaged due to errors or cabling;
(Iv)
has been subjected to abuse, abuse, negligence, abnormal physical, electrical or electrical stress, including lightning strikes, or accident;

(quoted from the Quick Start Guide for Ubiquiti NanoStation M equipment, Warranty Conditions section - available at http://dl.ubnt.com/guides/NanoStation_M/NanoStation_M_Loco_M_QSG.pdf on the manufacturer's website).

A typical lightning protection scheme with a broken screen is a direct violation of the manufacturer’s recommendations:

Findings:

• The compact and inexpensive all-weather lightning protection Ubiquiti can be effectively applied to equipment with both Gigabit Ethernet and Fast Ethernet ports;
• When installing two lightning protection arises a circuit with two protective earthing, requiring the equivalence of their potentials;
• The use of shielded cable and metallized connectors is mandatory for any grounding scheme.

And in conclusion: the cost of the new Ubiquiti lightning protection at CompTek is $ 12 .