We seem to have got to a very silly conversation here. The problem is the foolish "feature creep" of supposedly power electrical specifications, and the way in which every standard in existence tries to reference every other standard. The result is a total mess, leading to questions like this. What has Ethernet got to do with power electrical installations? Answer: Nothing whatever. POE does not change this one jot, it provides battery level power, which of course is completely isolated from any mains supply. Why the reference above to RCDs? Ethernet (base T) was designed to be intrinsically safe, connecting two points with cable isolation at both ends. You can cut and hold onto the cables until the cows come home with zero risk. POE slightly changes this as multiple cables may have core centre taps that are common, but still they present no shock risk. None of this is thus the slightest bit relevant to BS7671, although it seems to have become included. Very odd.

David Stone said:

What has Ethernet got to do with power electrical installations?

They are installed alongside each other. 

David Stone said:

supposedly power electrical specification

Not according to the scope. Buildings are full of all sorts of electrical installations these days, I don't think we can look at individual systems in isolation especially when it comes to safety which is literally the object of the Wiring Regulations.

David Stone said:

You can cut and hold onto the cables until the cows come home with zero risk.

We are talking about a structured wiring system that could be used for many things including POE e.g. access control, CCTV, and displays. During the building's life, there may also be a use for which we have not envisaged.

David Stone said:

What has Ethernet got to do with power electrical installations?

They are installed alongside each other. 

David Stone said:

supposedly power electrical specification

Not according to the scope. Buildings are full of all sorts of electrical installations these days, I don't think we can look at individual systems in isolation especially when it comes to safety which is literally the object of the Wiring Regulations.

David Stone said:

You can cut and hold onto the cables until the cows come home with zero risk.

We are talking about a structured wiring system that could be used for many things including POE e.g. access control, CCTV, and displays. During the building's life, there may also be a use for which we have not envisaged.