psychicwarrior:

gkenyon:

psychicwarrior:


Interesting re: the phone line concerns - perhaps all one can do, given it belongs to the phone company up to the master socket and is not BS7671, is advise the client that it too needs looking at and to contact the supplier to have it assessed - or can someone fit something themselves without messing with the master socket - will have to have a read. Then there is fibre (dependng on construction materials) to consider...Or is it really immune as one might think.


Thank you all again.

The requirement in BS 50174-3 (referred to from BS 6701 and BS 7671) is to fit SPDs "at all building entrances if the IT cable contains metallic cable elements, and where inadequate protective measures have been provided in the external IT network".


...

 

Is this saying that if considering/provisioning SPD, 'we' have to do so for everything else too ; should we be inspecting Comms, IT/Data installation cabling and SPD equipment, as a result of the indirect link in 7671 in that case, after the point it becomes not-the-suppliers concern of course. If so, where would such findings get recorded. Maybe time for a new section in Special Installations.


 

 

Sparkingchip:

My phone line was installed in the 1960’s . . . 


. . . The earth electrode is still in place, but the BT guy that replaced the line box disconnected the earth conductor . . . 

Zoomup:

The official advice ........

Note: SPDs for data communication signal and telephone lines (‘Lightning Barriers’) are fitted into the line (i.e. in series). This introduces a small impedance into the line and a capacitance across the line. For twisted pair signalling below 1MHz, this generally causes no problems. However, at higher frequencies this impedance and capacitance would cause problems. Protectors for these systems need to be specially designed to have lower line capacitance and impedance. For impedance matched systems (e.g. coaxially wired computer networks such as Ethernet) it is essential that the protector is impedance matched, in order to avoid reflections.

<snip>

 

(a) I'm not sure it's always the case that surge protection is installed in all NTE5 Master Sockets. I understand that when we moved from ADSL to VDSL, SPDs were removed as they were affecting data rate. (Whilst info on this is sketchy, it's verified by vendors of the sockets, e.g. this listing on a popular internet sales web-site clearly says "Latest Design. Does NOT Contain Voltage Surge Protector as this can reduce BroadBand speeds.")


(b) Even if there is, or you have the older style master socket with the SPD in it, there's definitely no surge protection to Earth at your installation (i.e. your MET), only between the two conductors. (And as the web-page says, protection of your stuff after the master socket is your problem).


</snip>

 

Indeed, I have found that modern NTE's (later than say 2005), tend not even to have an Earth terminal present. With the initial design of NTE5, you could add a 3 terminal Gas Discharge Tube and connect a protective earth to the E terminal (also linked through to the extension wiring. This was not there fundamentally for protection, but as a signalling earth, and likely would do nothing whatsoever with a lightning surge.)

I've installed GDT protection on my incoming VDSL only line, just after the master socket, back to an outside earth rod. There was no effect on the sync speed of the VDSL (still 79.9 Mbit/s). But I am probably not a typical case, as the fibre cabinet is less than 100 cable metres away.

I can definitely confirm however that a nearby lightning strike can induce voltages on the lines, even (or maybe especially) with underground distribution, sufficient to execute a PABX. That was with early 90's tech. With modern network gear, the problem might be even worse

My home, like millions of others in the UK, has an underground electricity supply and an overhead telephone line from a pole in the street supplied by underground cables, so do I need a telephone line SPD more than a electric supply SPD?

Sparkingchip:


So how do I risk assess 25 yo 30 metres of overhead telephone cable or do I just use a telephone line SPD regardless?


A bit back when I was watching German SPD installation videos on YouTube they were including telephone line SPDs, but I have not noticed the manufacturers promoting them in the UK.


Andy B.

AJJewsbury:

My home, like millions of others in the UK, has an underground electricity supply and an overhead telephone line from a pole in the street supplied by underground cables, so do I need a telephone line SPD more than a electric supply SPD?

Or the bit of metal stuck up usually just above the highest point of the building, connected directly to some of the most delicate and expensive electronics inside? (the TV aerial)

  - Andy.