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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
    Better - the optimum path for the lightning strike is now your neighbour's aerial......

    A long time since I did this at university (or possibly earlier) but dredging my memory banks, the reason lightning conductors are sharp spikes is that the radius of the tip (i.e. how sharp it is) affects the ionisation potential and so makes it a more attractive conductor for lightning. If there is a roof in the way it should make a big difference, particularly if it is raining and the roof is wet, a high probability in a thunderstorm. Of course if your house is on a hill and you have no neighbours it may still make your house the most likely point to be struck.
  • 0

    Alasdair Anderson:

    Better - the optimum path for the lightning strike is now your neighbour's aerial......

    A long time since I did this at university (or possibly earlier) but dredging my memory banks, the reason lightning conductors are sharp spikes is that the radius of the tip (i.e. how sharp it is) affects the ionisation potential and so makes it a more attractive conductor for lightning. If there is a roof in the way it should make a big difference, particularly if it is raining and the roof is wet, a high probability in a thunderstorm. Of course if your house is on a hill and you have no neighbours it may still make your house the most likely point to be struck.




    This is true, but perhaps a little irrelevant to BS 7671.


    BS 7671 doesn't cover direct strokes [not a spelling mistake], so I guess we are really looking at induced or capacitively-coupled voltages. From this perspective, there's probably a slight advantage over external roof-mounted, but perhaps not much dependent on what the roof materials are?

  • 0
    Forgive me to come back to this again, but...


    Take a *row* of small shops in a town centre all joined together, just for instance.  e.g. Urban, commercial and no LPS on the row.


    Reading the Regs, it is mentioned that SPDs are for transients from atmospheric and from switching - but it details that concern is for switching from *within* the installation only, as I read it.


    Therefore if the example shop is not concerned with internal switching i.e. it only has a till and some lights, then the concern is only with atmospheric.


    Given a shop is a commercial activity, a risk assessment approach cannot be taken and Regs state fit a SPD; as an aside, this applies it seems, even if it is a shop selling junk and a shop floor the size of a six-pence and a domestic probably has more 'value' in it. Given there is no LPS on the shop (or the row of), then its a TYPE 2 SPD near the origin (well, in the shop DB).   Correct please ?

    oh and  only when an LPS is fitted is a TYPE 1  required too (or a 1+2).  ?


    Regards

    Habs
  • 0

    psychicwarrior:

    Forgive me to come back to this again, but...


    Take a *row* of small shops in a town centre all joined together, just for instance.  e.g. Urban, commercial and no LPS on the row.


    Reading the Regs, it is mentioned that SPDs are for transients from atmospheric and from switching - but it details that concern is for switching from *within* the installation only, as I read it.


    Therefore if the example shop is not concerned with internal switching i.e. it only has a till and some lights, then the concern is only with atmospheric.


    Given a shop is a commercial activity, a risk assessment approach cannot be taken and Regs state fit a SPD; as an aside, this applies it seems, even if it is a shop selling junk and a shop floor the size of a six-pence and a domestic probably has more 'value' in it. Given there is no LPS on the shop (or the row of), then its a TYPE 2 SPD near the origin (well, in the shop DB).   Correct please ?

    oh and  only when an LPS is fitted is a TYPE 1  required too (or a 1+2).  ?


    Regards

    Habs




    All of these questions are answered in sections 3.7.2 and 3.7.3 of the OSG (pp39-41 of the current edition).

  • 0

    gkenyon:




    psychicwarrior:

    Forgive me to come back to this again, but...


    Take a *row* of small shops in a town centre all joined together, just for instance.  e.g. Urban, commercial and no LPS on the row.


    Reading the Regs, it is mentioned that SPDs are for transients from atmospheric and from switching - but it details that concern is for switching from *within* the installation only, as I read it.


    Therefore if the example shop is not concerned with internal switching i.e. it only has a till and some lights, then the concern is only with atmospheric.


    Given a shop is a commercial activity, a risk assessment approach cannot be taken and Regs state fit a SPD; as an aside, this applies it seems, even if it is a shop selling junk and a shop floor the size of a six-pence and a domestic probably has more 'value' in it. Given there is no LPS on the shop (or the row of), then its a TYPE 2 SPD near the origin (well, in the shop DB).   Correct please ?

    oh and  only when an LPS is fitted is a TYPE 1  required too (or a 1+2).  ?


    Regards

    Habs




    All of these questions are answered in sections 3.7.2 and 3.7.3 of the OSG (pp39-41 of the current edition).


     




    My good man, with respect I say, as are a lot of questions raised on here covered/answered in the usual and other publications !


    I am sorry my question caused that big sigh from you :-)    I do read before I ask anything...perhaps that just makes it worse  haha


    A simple brief yes, no discussion perhaps just to see if I understood what I read.

  • 0
    Whether required: that depends on whether damage to electrical items (e.g. LED lamps, POS terminals etc) would interrupt commercial activity.

    Switching: well, in principle an adjacent  building could be generating switching surges, but that doesn't seem to figure into any of the actual rules (compulsory, or risk assessment etc).

    Type 1's are part of the LPS - they equipotentially bond the wiring system to the rest of the LPS so that there's less chance of flashover between say a water pipe and nearby cabling, starting a fire. Thus they are not intended to provide protection for electrical equipment. For that you need a type 2 in addition, or possibly a combined type 1+2.
  • 0

    psychicwarrior:




    gkenyon:




    psychicwarrior:

    Forgive me to come back to this again, but...


    Take a *row* of small shops in a town centre all joined together, just for instance.  e.g. Urban, commercial and no LPS on the row.


    Reading the Regs, it is mentioned that SPDs are for transients from atmospheric and from switching - but it details that concern is for switching from *within* the installation only, as I read it.


    Therefore if the example shop is not concerned with internal switching i.e. it only has a till and some lights, then the concern is only with atmospheric.


    Given a shop is a commercial activity, a risk assessment approach cannot be taken and Regs state fit a SPD; as an aside, this applies it seems, even if it is a shop selling junk and a shop floor the size of a six-pence and a domestic probably has more 'value' in it. Given there is no LPS on the shop (or the row of), then its a TYPE 2 SPD near the origin (well, in the shop DB).   Correct please ?

    oh and  only when an LPS is fitted is a TYPE 1  required too (or a 1+2).  ?


    Regards

    Habs




    All of these questions are answered in sections 3.7.2 and 3.7.3 of the OSG (pp39-41 of the current edition).


     




    My good man, with respect I say, as are a lot of questions raised on here covered/answered in the usual and other publications !


    I am sorry my question caused that big sigh from you :-)    I do read before I ask anything...perhaps that just makes it worse  haha


    A simple brief yes, no discussion perhaps just to see if I understood what I read.


     




    Apologies if you took that the wrong way.


    The answer then is not fully.



    Take a *row* of small shops in a town centre all joined together, just for instance.  e.g. Urban, commercial and no LPS on the row.


    Reading the Regs, it is mentioned that SPDs are for transients from atmospheric and from switching - but it details that concern is for switching from *within* the installation only, as I read it.


    Therefore if the example shop is not concerned with internal switching i.e. it only has a till and some lights, then the concern is only with atmospheric.





    Yes, I'm with that.



    Given a shop is a commercial activity, a risk assessment approach cannot be taken and Regs state fit a SPD; as an aside, this applies it seems, even if it is a shop selling junk and a shop floor the size of a six-pence and a domestic probably has more 'value' in it.



    No. This depends on what's going on in the shop.


    So, the commercial activity of the junk shop you describe is unlikely to be affected by a surge event, and the business can probably continue using cash and hand-written receipts. However, the following kinds of shop are a different situation:


    • Supermarkets, butchers and similar with high value of products in refrigerators and freezers

    • Jeweller or antique shop with expensive security systems

    • Businesses that rely heavily on electronic transactions


    Given there is no LPS on the shop (or the row of), then its a TYPE 2 SPD near the origin (well, in the shop DB).   Correct please ?

    oh and  only when an LPS is fitted is a TYPE 1  required too (or a 1+2).  ?



    I think the simplest approaches to consider are:

    Small installation (only DBOs at the origin)


    • Overhead supply or LPS fitted: Combined Type 1 & Type 2 at the origin. Type 3 only necessary at very sensitive equipment where manufacturer recommends it.

    • Otherwise, Type 2 at the origin. Type 3 only necessary at very sensitive equipment where manufacturer recommends it.

    Installation with main board and sub-boards


    • Overhead supply or LPS fitted: Type 1 at the origin and Type 2's at sub-boards. Type 3 only necessary at very sensitive equipment where manufacturer recommends it.

    • Type 2 at the origin. Type 3 only necessary at final boards and/or very sensitive equipment where manufacturer recommends it.


    For all installations, if SPDs are required for the mains, they should also be considered for external metallic telecomms services (not fibre), and vice-versa. Regulation 443.1.1 points you to the relevant standards for this.

    If you send cables outside the building ("Zone") then they may also require surge protection.
  • 0
    @gkenyon  -  and my apologies to you too, if you thought that I'd taken 'it' the wrong way :-)   I hadn't btw.


    Thank you for the followup though - its comments like this that add an interpretative aspect on to Regs etc and I appreciate it, as it allows me to think around the subject based on others' opinions etc.


    I had come to the same conclusion as you with respect to your 'simplest approaches' considerations.  It is the following that you mentioned that is interesting too:


    "...
    No. This depends on what's going on in the shop.


    So, the commercial activity of the junk shop you describe is unlikely to be affected by a surge event, and the business can probably continue using cash and hand-written receipts. However, the following kinds of shop are a different situation:


    • Supermarkets, butchers and similar with high value of products in refrigerators and freezers

    • Jeweller or antique shop with expensive security systems

    • Businesses that rely heavily on electronic transactions ..."



    What you say above makes sense. It had occurred to me that a particular commercial activity may conclude that it can continue and would be unaffected but it would be the business' consideration - almost a risk assessment, though that is not demanded anywhere in the Book - but from a compliance with Regs. for work completed (or later periodic inspection!), is it more that one cannot predict the potential affects and therefore the requirement is to fit one and not get into the 'what may or may be affected' assessment etc.  ie. it is as written, if its industrial/commercial..it has to be fitted...no leeway.    ?


  • 0
    I think this is also linked to how standards relate to contracts, specifications and the expectations of clients - and how BS 7671 might be used to get more out of a contractor than they quoted for on occasion?


    So, for example, you could level the same arguments at Section 444 and assume that you've just got to go the whole hog on EMC. However, the industry is very happy working with 444 and assuming that, for the most part, many installations won't require the all-singing, all-dancing approach, including the use of BS EN 50310, and not every installation will comply with every requirement in 444.


    The big difference I guess with 443/534 being that of claims if and when equipment starts "popping".
  • 0

    Overhead supply or LPS fitted



    I can see the sense of that, but I can only see the LPS bit mentioned in BS 7671 (534.4.1.3) - is the overhead line bit mentioned somewhere else in BS 7671 or is that just accepted good practice that has escaped our regs?

      - Andy.

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