BFR Digital POE graphic

Are you still losing IoT (Internet of Things) devices to lightning and Eskom?

IoT (Internet of Things) is here, whether it's an Alexa speaker, CCTV camera, biometric reader or a light bulb the world is moving to connect to and control these devices from smartphones and tablets.

Nevertheless, let's state the obvious; all these smart IoT devices need power! There are two ways of giving electricity to intelligent IoT devices.

  1. They come with a power pack in the box that converts the 220v wall socket mains to 12volts or 5volts USB (the same sort of device you use to recharge your cellphone. I have covered this in detail in other blog posts, should you wish to read the most recent post please follow this link: Want to protect your electronic systems from Lightning and Load-shedding?.
  2. The more integrated and permanent devices like security cameras, access control readers or lights are powered from an IT network switch with POE (Power Over Ethernet). POE (Power Over Ethernet) has become increasingly popular as the POE standard has moved from 15watts to a staggering 90watts in the new IEEE 802.3bt standard.

Today we are going to focus on how to successfully protect the low voltage PoE (Power Over Ethernet) cable. Consider that on a PoE cable, the PoE power can be introduced in one of two ways. Firstly, the power can be added to the spare pairs of the cable. This first method is only used in inexpensive 100Mbps PoE injectors and will soon become obsolete as customers demand higher data speeds.

The second method of introducing PoE power on a cable is to overlay the PoE power over the data signal. This method is the only way forward as Gigabit and higher data rates require all 4wire pairs in the cable. Also, all 4wire pairs are necessary to deliver 30watts or more of PoE power.

Let's take a step back! You may be asking why is PoE receiving so much attention?

Well as engineers find ways of transmitting more power over a network data cable the more inexpensive, it becomes to for example wire lights in a house. Why?

  1. CAT5e communications cable is less expensive than electrical wire.
  2. You don't need to be a qualified electrician to install and terminate CAT5e communications cable.
  3. PoE power can accommodate cable lengths up to 100m.
  4. You can connect smart IoT devices, such as intelligent lighting, security systems and home or industrial automation devices.

You wonder, is this too good to be true? What's the catch?

  1. PoE devices are susceptible to damage caused by surges from lightning and load-shedding.
  2. Generally, one or multiple 24port PoE network switches are installed to cater to various devices on the premisses. Should a network switch be damaged by a surge, then all 24 devices connected to the network switch are at risk of surge damage.

So how do you protect your PoE devices?

Well, firstly you need to protect the 220volt mains. Here is the link again on how to accomplish that.

Secondly, you need to protect the ends of the communications cable, that is both ends by fitting a PoE surge arrester at each end of the CAT5e cable. There are a few things you need to know about PoE surge arresters:

  1. Understand the specifications and quality of the product you are purchasing. There are so many PoE surge arresters on the market, and while most of them are "ok?" That is if you live in a low lightning density area or an area with no rotational load-shedding like most of Europe. But the reality is that we live in South Africa where we have been experiencing some form of rotational load-shedding since 2008, and most of the high-veld, low-veld and Kwazulu Natal are high lightning density areas. These two facts render an "ok" surge arrester useless.

    Here is a picture of a common surge arrester without this second circuit that I have described above.

    Surge arrester without low-voltage protection circuit

    Here is a picture of a POE-GSA-01 (Gigabit PoE Surge Arrester) that features both circuits.

    Surge arrester with low-voltage protection circuit

    So, what should the specifications say?

    1. Surge arrester must start working at around 60volts because PoE+ delivers 30watts of power but at 56volts.
    2. On the top-end, the surge arrester must have a rating of 10KA (Kilo-Amps) which means that it can divert 10KA (Kilo-Amps) of electrical energy from the field cable to the electrical earthing circuit.

  2. The technician must know how to install the surge arrester correctly, which is just as critical as purchasing a quality surge arrester. Why is this so critical? If a surge arrester is installed incorrectly, then it will offer ZERO protection, that is None, Zip!

    How do you install a PoE surge arrester correctly?

    1. Fit the surge arrester as close as possible to the device being protected. Keep the patch-lead short!
    2. PoE surge arresters have an earth connection. Connect this to an electrical earth point that is the same electrical earth as your power distribution board.
    3. If you provide a secondary earthing point by employing an earthing-rod local to the PoE device you want to protect, make sure that this secondary earthing point is connected to the electrical earth on your power distribution board. There must be no potential difference (voltage) between the two earthing points; this is known as equipotential bonding. If you want more information about earthing and best practices follow this link: Want to protect your electronic systems from Lightning and Load-shedding?
    4. Make sure you keep the input and output cables separate. Input cables to a surge arrester are regarded as dirty cables which may carry electrical surge energy. The output cables of a surge arrester are clean cables, free of electrical surge energy. Should the two cables be strapped together, then the electrical surge energy from the dirty cable is induced onto the clean cable, and the electrical surge energy effectively bypasses the surge arrester. This process is known as electro-magnetic-induction.

      Here is a diagram showing the different surge protection components as well as the equipotential bonding. A CCTV camera system example is used as some cameras are usually placed outdoors.

      How to install PoE surge arresters

Man, you could say that this is expensive to implement in the field! I don't dispute that, but one always needs to ask what the risks are? If the IoT device is inexpensive and not mission-critical, then I would ask if it's worth protecting. Still, if the equipment is either expensive to replace or mission-critical then hell YES it is worth putting surge protection in.

But wait, after my lengthy explanation about PoE surge protection and the importance of electrical earthing I have a more affordable method of protecting your PoE equipment. You may say WTF, why not just explain this first? Let me introduce our Surge Blockers, and you will comprehend why I went through this lengthy explanation shortly.

What is a Surge Blocker?

A Surge Blocker is a PoE Surge Protection Device that does not require and electrical earth connection. By removing the need for electrical earth, the cost of the installation is significantly reduced, and the installation process is simplified. Those are the benefits! But what's the catch? As with all new technology it does have limitations, and the limitation of our Surge Blocker is a maximum surge voltage of 1000volts. But if it's installed correctly, it will protect your PoE IoT devices from most electrical surges.

How does a Surge Blocker work?

It works like an automatic on-off switch. When the surge current reaches 750mA, the Surge Blocker disconnects the field cable from the IoT device you want to protect in less than 1 microsecond.

How do you install a Surge Blocker correctly?

It's pretty much the same as you would a PoE surge arrester except for two things, but let us go over all the points:

  1. Fit the Surge Blocker as close as possible to the device being protected. Keep the patch-lead short!
  2. Isolate your IoT device from any metal surface. That is making sure that the IoT device does not make contact with any metal. An easy way of doing this is to mount a UV resistant plastic box on to the metal structure and fitting the IoT device onto the plastic box.
  3. Make sure you keep the input and output cables separate. Remember electro-magnetic-induction! We discussed it above.
  4. Don't forget that you still need to protect the 220volt mains coming into your network switch; you could use a BFR-20KA-INLINE for this.

Here is a diagram of how the installation would be done. Again, I've used a CCTV camera system as an example.

How to install PoE Surge Blockers

Here are links to our PoE Surge Blocker specs:

POE-SBU-01P Single Port Gigabit PoE Ethernet Surge Blocker in DIN Rail mount enclosure.
POE-SBU-01E Outdoor Single Port Gigabit PoE Ethernet Surge Blocker in an IP65 enclosure.

How easy and manageable is that?

Cheers for now,

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