What nobody tells you about Power over Ethernet

Most of us are already using our computers to deliver power to do some of the basic stuff, as we charge our mobile devices using USB ports on desktop and laptop. But the move towards using Power over Ethernet to power and control lighting fixtures is something else altogether.

 

Will your computer always talk to your lighting installation

We have to forget the idea of a light fitting at the other end of a light switch. The entire issue of PoE is that the lighting installation is now another part of the computer network. The first issue that needs to be considered is the security of the lighting. Does the computer know that the lighting installation is there? We’ve all experienced the loss of a printer, or the camera that doesn’t register on the file manager. We can see them; they’re in front of us, but the computer has chosen not to recognise them. 

The first thing to ensure is that the computer system is sufficiently robust to guarantee the presence of the lighting installation.

 

Power outages may mean a re-boot for your lighting installation

Loss of power to a computer network may be rare and very brief, but they do happen. Interruptions to computer power and inappropriate shut-downs can result in glitches in the software. If that glitch results in the system not recognizing the lighting installation, then the corrective work will be done in the dark.

Effort needs to be put into ensuring the reliability of the power supply to ensure that system failures don’t happen and, if they do, that the lighting power is recognised and restored.

 

Electronic noise from the lighting installation may affect the rest of the computer network

The LED lighting is now part of the computer system. That means that the lighting circuitry must operate within the requirements of the computer software. It’s not good enough to buy any lighting fixtures; the lighting load must be designed to work with the rest of the network. The risks of having unwanted power issues on the network could be catastrophic.

The lighting technology must match the operating parameters of the broader network.

 

Limits on the current-carrying capacity of the data cabling will restrict the available lighting loads

At the moment, the amount of power that’s being transmitted by PoE is quite small, but we’re seeing LED lighting loads becoming much greater. There is a reason why ‘commercial’ electricity is transmitted at 240v AC; it was considered to be the optimum voltage to overcome voltage drop along lengths of cable. All cables contain some resistance to the flow of electricity and it’s all a factor of electrical load and size of cable. If we reduce the supply voltage to that required by the LED, and increase the load, and increase the length of cabling, then we may end up with no light at the fixture.

This is a critical issue that comes under the heading of ‘that’s the way things are in this world’. Voltage drop cannot be mitigated for, it can only be designed out of the system.

 

There will always a be a need for an electrical contractor

An argument is being made that PoE wiring will do away with the need for qualified electricians. The argument goes that, because the voltage is so low and the system is a ‘plug-and-play’ system, there is no need for a competent person. But this argument forgets that every cable termination needs to be made into an ethernet plug, and that’s more complex than a standard mains connection into a lighting fixture.

Rather than questioning the use of a qualified electrician, the actual question should be about how competent the qualified electrician is in making off cable terminations of this type.

 

Tiny losses at individual wiring connections accumulate to a substatial loss across the system

Finally, we come to the part that we wish would go away, but isn’t likely to anytime soon. There is an issue about the power rating of the ethernet cable and its terminal connections. With LED power increasing, there is a question  over the design of the wiring for an array of light fixtures over a large area of ceiling.

Connections, even well-made ones using good quality equipment, tend to generate heat because there will be some resistance in the connection. Small amounts of heat may be bearable at an individual connection, but taken across the entire installation that may add to unacceptable energy wastage. A bigger problem, of course, is when the heat generated at the connection cannot be borne by the equipment, and that can only lead to failure of the system.

This has to come down to the choice of equipment and only the very best should be used. It also raises the issue as to whether the current plug-and-play ethernet connection is fit for purpose.

 

 

  • Learn more at Property Technology Live - co-located with LuxLive on 14 & 15 November 2018 at ExCel. The event  is free for developers, commercial tenants, consulting engineers, technologists, designers and contractors working in the property sector. To view the full programme and register, click HERE.

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