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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

    "...address 1:

    LV underground - 362m

    HV underground to primary-  2000m

    No Surge protection devices





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



    To my way of thinking (which may or may not be correct), we only consider the last 1km to the customer so if the LV is 362m we do consider the last 1000-362=638m of HV. The values are in km rather than m, so if both are underground I'd have LPAL=0, LPCL=0.362, LPAH=0 and LPCH=0.638.

     

    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. ..."



    It sounds like the DNO's SPD is more than 1km away from the customer - so we can ignore that and still count the last 1km of cable to the customer (if the SPD had been closer we could have stopped at the SPD rather than the full 1km). So I think we've got 110m of LV underground, supplied by 823m of HV underground - that only comes to 933m so we also need to consider the next 67m of HV as well (overhead).


    So my first stab is:

    LPAL=0, LPCL=0.110, LPAH=0.067 and LPCH=0.823.


       - Andy.
  • 0
    You only take into account the LAST kilometer of distribution cabling (nearest to the premises), or the distribution cabling distance to the first upstream overvoltage protective device in the distribution network (if any), whichever is closer.


    In this case, there is no overvoltage protection in the network (if you can't get information, assume there are none).


    Therefore (hopefully my maths head is working today and I've not made any schoolboy errors - but I'm sure others will be quick to chip in if I have), working back from the premises a cable distance 1 km:

    Address 1
    LV underground, LPCL = 0.362 km

    HV underground, LPCH = 0.638 km (because you're working back from the installation a maximum distance of 1 km)

    Which also means:


    HV overhead, LPAH = 0 km

    LV overhead, LPAL = 0 km

     


    So, LP = 2 × 0 + 0.638 + 0.4 × 0 + 0.2 × 0.362 = 0.7104


    Address 2

    LV underground, LPCL = 0.110 km

    HV underground, LPCH = 0.823 km

    HV overhead, LPAH = 0.067 km (because you're working back from the installation a maximum cable distance of 1 km)

    Which also means:


    LV overhead, LPAL = 0 km

     


    So, LP = 2 × 0 + 0.823 + 0.4 × 0.067 + 0.2 × 0.110 = 0.8718




    Just for the sake of examples:

    High Ng - If we use the worst-case Ng in Figure 44.2, Ng = 1.4


    If Address 1 is rural/suburban, CRL = 85/(0.7104 × 1.4) = 85.5, and as this is less than 1000, protection against transient overvoltages of atmospheric origin is required

    If Address 1 is urban CRL = 850/(0.7104 × 1.4) = 855, and again protection is required


    Since for Address 2, LP is greater, CRL will be smaller (as it's a divisor), and hence protection will be required there in either case also.


    Low Ng- If we use a lower value of Ng = 0.8 (which if you look at the map of the country, probably much of the landmass of the UK has Ng ≤ 0.8)

    If Address 2 is rural/suburban, CRL = 85/(0.8718 × 0.8) = 121.9, and as this is less than 1000, protection against transient overvoltages of atmospheric origin is required

    If Address 2 is urban CRL = 850/(0.8718 × 1.4) = 1219, and this time, protection is NOT required


    Similarly, Address 1 would require protection in rural/suburban (CRL = 149.6) but not urban (CRL = 1496)

  • 0
    or just fit the consumer unit that the electrical wholesaler has on a special offer with SPDs preinstalled by the manufacturer?


    Andy B
  • 0

    Sparkingchip:

    or just fit the consumer unit that the electrical wholesaler has on a special offer with SPDs preinstalled by the manufacturer?


    Andy B




    And don't forget to advise the customer to get any copper cable TV and phone/broadband lines surge protected, because it's little use doing the "mains" without these also being protected - as BS 7671 advises, see BS 6701 and BS EN 50174-3.

  • 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?


    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.
  • 0
    AJJewsbury‍ gkenyon‍ Thank you for plumbing the figures in - especially in addr2 scenario.  In addr1 I made a daft mistake, presuming that the HV should be ignored and that the difference left from taking the underground LV away from 1km, was to be attributed to some assumed overhead LV part...when in fact of course, there is not one declared by the DNO - so as you have done, it had to be attributed to the underground HV they detailed. I've not said that well I dont think, but I have understood your approach.


    There are boards being supplied with SPD as Sparkingchip‍ pointed out and that is useful, but this was more about trying a real world-ish scenario. I'm glad I asked here about it...thanks again.


    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.
  • 0
    My phone line was installed in the 1960’s back in the days when you had a big battery at the house and the phone line was earthed.


    The earth electrode is still in place, but the BT guy that replaced the line box disconnected the earth conductor then the guys who installed my uPVC porch frame took it upon themselves to rip the part of the earth conductor that went through the old softwood porch frame out with it completing the disconnection.


    Andy B.

  • 0
    The official advice ........

    http://phonefault.com/lightning-damage/


    Z.
  • 0

    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".


    There are telecomms-specific devices available to do this.


    These days, it's important to ensure you purchase SPDs that can cope with the VDSL2 bandwidth.



    Zoomup:

    The official advice ........

    http://phonefault.com/lightning-damage/


    Z.




    There's a statement on this linked site, that says " There is lightning protection fitted inside each Master Socket – even if it’s the old style."


    There is almost certainly surge protection at the Exchange and the FTTC cabinet.


    However:


    (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).


    FTTP is a different story of course - fibre doesn't import overvoltages.




    So, the question as to whether SPDs affect broadband speeds when using VDSL?


    Well, I'm not 100 % sure. Quite possibly, the original inexpensive types did affect data rate.

    There are certainly devices that operate OK for CAT5 and CAT6 networks, and there are various options available for broadband lines (but probably outside the cost of the NTE5 master sockets).


     

  • 0

    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.


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