Even under worst-case, ungrounded conditions, the UTP cable behaves more like an antenna than the F/UTP cable!

so unshlelded UTP is worse than foil shielded because it acts more like an antenna, even when it's ungrounded. Am I reading that correctly ?

In which case shielded is better, but earthing it isn't critical ?

That's my take on it. But given that you only need to ground one end, that shouldn't be difficult either.

There is a lot of talk about ground loops - but in a domestic environment you're likely to have a common route to ground and earth, so even if you were shielded fully that shouldn't be an issue?

Still, I think I've made my mind up - providing when the time comes there is still not much in the difference between F/UTP and UTP then I'll go for the former for my wall wiring - and this time round I'm going to use ducting. My current house has the issue that if I needed to change a dodgy cable I would have to pull the plaster off the walls.

In reply to a post by yarwell:

In which case shielded is better, but earthing it isn't critical ?

It's a Faraday cage:

In reference to en.wikipedia.org/wiki/Faraday_cage:

Examples
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The shield of a screened cable, such as USB cables or the coaxial cable used for cable television, protects the internal conductors from external electrical noise and prevents the RF signals from leaking out.

The difference is coax and usb are grounded through the end-device (PC/TV grounding etc).

Doesn't matter. A Faraday cage doesn't have to be grounded in order to work. All that's required is that it's a good conductor (steel armouring isn't very good for that) and that any holes in it are small compared to the wavelengths you're trying to screen out (or in).

I should perhaps expand a bit on my previous post... in general it is a good idea to connect screens to earth, but this is largely a safety measure. If a fault provides an "unauthorised" connection between the screen and the power supply, a floating screen can be at a high voltage (depending on the voltages used) even if the fault is high resistance, and the capacitance of the cable can provide a dangerous level of shock if touched.

Obviously this isn't usually a problem at typical computer voltages, but it can be if it's used in hazardous environments (eg explosive gases present).

If it's a more serious, low resistance fault it will draw attention to the fact that something needs looking at by tripping out the power supply.