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my surge protection 'cpd', such as it is...

psychicwarrior
Good morning all


I have obtained the following [I feel as the] 'best we can do for now' information from the DNO. They were helpful in my test case request for info.


"...address 1:

LV underground - 362m

HV underground to primary-  2000m

No Surge protection devices


address 2:

LV underground to substation - 110 m

HV UG from substation to HV pole is 823m then 301m 11kV overhead then 190m HV UG to the primary substation.

Distance to cable termination with surge protection device from secondary substation is 1124m (823m 11kV UG + 301m 11kV Overhead).  The nearest cable

termination does not have surge protection installed. ..."


In relation to the risk assessment equation variables dealing with distribution cable lengths  ie. the Lpal Lpcl Lpah Lpch, how would one fit the given values into the variables ?


For addr1, ignore the HV (e.g. use zero for Lpah Lpch),  then take Lpcl as 362 and Lpal as 638 ?


For addr2, i'm not sure on this one ?


Thanks for your input.

Habs


  • 0

    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.


     

     




    This might be a controversial statement. But I'm prepared for it (I think).


    Telecomms cabling is definitely within the scope of BS 7671, although you can't simply apply BS 7671 alone (see regulation 110.1.3) - so why do you use the term "everything else", if it's all part of the same electrical installation to BS 7671 ?


    The difference with surge protection for telecomms, is BS 7671 specifically tells you to use BS EN 50174-3 rather than 443, see Regulation 443.1.1 para before NOTE 5.


    If you have been contracted to work on the power circuits alone, then of course there's a contractual boundary here, but I think this is something that should be sorted out at contractual level in that case, up-front where possible.


    Certainly, I don't think you could claim to have installed SPDs in accordance with BS 7671, if you didn't address the telecomms in accordance with BS EN 50174-3. However, you could claim that you were installing SPDs for the mains power circuits in accordance with BS 7671, and you've advised that someone should assess the phone/broadband/cable TV (or MATV) etc. services



    There will be some benefit in installing SPDs only on the mains, but full performance can't be guaranteed in all conditions, and perhaps it would be advisable to make such caveats to avoid the complications of claims in a future overvoltage event. (Although insurers might take matters into their own hands and go for settlement rather than argument.)

  • 0

    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 . . . 




    There is used to be some surge suppression between the two wires, but nothing to earth. Originally, telephones became so popular, they quickly out-stripped the number of copper pairs back to the exchange. One relatively quick option was to install a “party line” option to the exchange. This meant the speech path was shared, so the other property could “listen in” to a conversation. However, the bells were connected to earth on one side, giving the option to ring the bells at the two properties separately. When one phone was in use, both numbers were marked as busy. Newer electronic exchanges did not have the ability to have a “party line” option, so the earth connection at a property no longer had a use, and was disconnected. 


    Regards,


    Alan. 

  • 0

    Zoomup:

    The official advice ........




    Possibly, although the link given seems to be an ex BT Openreach engineer advertising his new business. 


    Regards,


    Alan. 

  • 0
    Here's a quote from the "BEAMA GUIDE TO SURGE PROTECTION DEVICES":

    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.



  • 0
    Agreed, as I said you need the right thing for the job for data these days - need to cope not just with the frequency, but the overall bandwidth for the data.
  • 0
    <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


  • 0
    And cloud-cloud strike when clouds are at low level, can also induce voltages on overhead lines, including telephone.
  • 0

    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.
  • Former Community Member
    0 Former Community Member

    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.




    40 odd years ago I made my own SPD for the telephone line after the fax and answer phone blew up for the third time. I suppose living at 1000ft above sea level I should have expected it. We never had any problems with the OH mains supply?

     

  • 0

    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.

     




    My aerial is inside the loft, so is that better or worse?


    Andy B

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