Whats the term I'm looking for? Copper between buildings

[Chris_Cook]

Not Wrong, just very over cautious.

 

Think about it. If a switch had mains voltages present on a port, then thats dangerous anyway. Even if it where connected directly to neutral or earth, there can still be enough voltage to give an unpleasant shock at the end of a long cable. They are designed to be connected to cables up to 100 meters, so differences in earth potential is going to be a common one.

 

Switches and other similar equipment are designed so this can't happen, even with a significant fault. There will be physical isolation of wiring, as well as transformers or a well designed switch mode psu to separate the high and low voltage circuits. This is assuming you don't buy really cheap no-name stuff from ebay which probably won't have this level of protection.

 

In order for 2 phases to be connected via the switches you would need to very bad faults in two separate bits of equipment. Even then, the fuse should blow at one end breaking the circuit. Failing that, the cat 5/6 cable will overheat and melt, which should be ok, as long as you haven't buried it in kindling, or run it through a petrol station. Proper installed cabling should be low smoke and self-extinguishing.

 

The amount of things that would have to go wrong for this to become dangerous make it an unlikely scenario.

 

You will almost certainly have problems with noise and packet loss though. So you do still want to use fibre for these kind of long runs between buildings. There might also be problems with rcds tripping etc.

 

You should get a qualified installer to do external cabling, as there are other importan issues running copper between buildings. Direct lighting strikes being one, properly sealing the entry point into the building is the other main one. A qualified installer would almost certainly recommend fibre, I'm sure.

Edited May 26, 2011 by Chris_Cook

[garrya100]

Ahh! Petrol stations! I've had to do them too. Sheilded cables in conduit, buried in 1ft of sand, minimum 3ft underground, with vapour pits no more than 30ft apart, voltage suppression arrestors no more than 50VAC...... I hope I never have to do another one!!!

 

BTW the current flow in the neutral conductor can have a large impact on the PD if the buildings have separate earthing systems. One thing you learn in engineering is that earth is not a particularly good earth! Hence the MEN system that has multiple earths tied to the neutral to establish a solid earth. Bear in mind that the earthing system used in power transmission is designed for safety, not low noise.

 

It's to make sure that when there is a fault, the fuse will blow, or the breaker will trip.

 

Reduced sized neutrals in 3 phase systems, and different earthing conductor sizes, while perfectly legal and adequate for a power system can have large impacts on the PD between buildings. A five volt PD between buildings is no issue for a power system, and the induced currents are small, but for a low voltage data system the difference is huge.

Edited May 26, 2011 by garrya100
typo again!