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SPDs AMD 2

Chris Pearson
Well, I'll kick off the debate on SPDs. Once again, the emphasis seems to be on domestic (we all, or virtually all of us live in a home of one sort or another) so are the proposals an improvement or not?
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    The term "strokes of lightning" has been used in a literary manner, as of brush stroke in the sky

    Might that be part of the point though - to me a lightning stroke is the (arc) flash across the sky, a lightning strike is where it hits something (usually on the ground) - since we're taking about the effects from the arc - i.e. include "cloud-to-cloud" lightning, talking about an actual strike in the locality could be misleading.

       - Andy.
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    Another problem with dwellings has occurred to me. When a new estate of houses is built, or at least designed, speculatively, the future occupiers are unknown, so it is not possible to make the value judgement as to whether to provide SPD or not. (The case would be stronger for 4 or 5 bed houses than 1 bed maisonettes.)


    ETA: in view of the uncertainty, perhaps builders should be obliged to perform the risk assessment and install accordingly?
  • 0
    How about this for simplified SPD criteria:


    An SPD must be installed if any of the following apply:

    (i) risk of injury or to life;

    (ii) risk of financial / data loss;

    (iii) if the owner and designer etc have reached a consensus that damage would be intolerable, unless a risk assessment shows transients unlikely.
  • 0
    An SPD of the sort considered here will not protect against a lighting strike (where the line of ionized gas terminates on the wiring in question)-  The currents and voltages are too high to do anything about, short of immersion under a few metres of sea water.


    SPDs may, in a limited subset of cases, help against voltages induced by  lightning overhead or that terminates some distance away-  though only for a limited range of radii - far away events would have had no effect anyway, and too near and the over-voltage is too extreme.


    So the question reduces to calcualting how big an effective  capture area the local LV network represents.

    That ought to have units of square metres, so that it can be multiplied by a strike density per area per year, to get events per year.

  • 0
    Obviously my dictionary is older than the English language. However, I am not going to argue further, in a PC world it is probably safe to say that my hitting someone is simply a "stroke of the hand" in court or that swimming strokes are GBH. I will however stand up for exact and clear communication, which these examples are not!


    Moving on, it is not clear what the SPDs are supposed to prevent, if it is not large electrical discharges (which is what the test waveform is meant to represent) just what is it? It seems to be being suggested that all mains connected electronic power supply failures are caused by "mains transients" of some description, with the general form of lightning, which is simply not the case. I have always had and operated large quantities of Electronics, and none of it has ever been damaged by any kind of mains transient, whether from a generator or "mains" supplies. Obviously there has been the odd failure, but I could not say that transients had been the problem, usually heat, age, or normal component failure. Much of the equipment has various transient suppression features, VDRs, snubber networks etc. but these are part of robust designs. This seems to me to be a solution looking for a problem again, a problem that I don't and never have had. The only damage I can think of was telephone line related, in that this was a couple of miles long and lightning tended to damage my modem, and in one case the phone too. Also, the line filters were remarkably unreliable, but the components in there were probably rated for 50V when the ringing voltage was greater than this, and the DC was pretty much 50V. Bad design to the fore. Again I see problems elsewhere being cured at the consumers' expense.
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    davezawadi (David Stone):

    Obviously my dictionary is older than the English language. However, I am not going to argue further, in a PC world it is probably safe to say that my hitting someone is simply a "stroke of the hand" in court or that swimming strokes are GBH. I will however stand up for exact and clear communication, which these examples are not!


    Moving on, it is not clear what the SPDs are supposed to prevent, if it is not large electrical discharges (which is what the test waveform is meant to represent) just what is it? It seems to be being suggested that all mains connected electronic power supply failures are caused by "mains transients" of some description, with the general form of lightning, which is simply not the case. I have always had and operated large quantities of Electronics, and none of it has ever been damaged by any kind of mains transient, whether from a generator or "mains" supplies. Obviously there has been the odd failure, but I could not say that transients had been the problem, usually heat, age, or normal component failure. Much of the equipment has various transient suppression features, VDRs, snubber networks etc. but these are part of robust designs. This seems to me to be a solution looking for a problem again, a problem that I don't and never have had. The only damage I can think of was telephone line related, in that this was a couple of miles long and lightning tended to damage my modem, and in one case the phone too. Also, the line filters were remarkably unreliable, but the components in there were probably rated for 50V when the ringing voltage was greater than this, and the DC was pretty much 50V. Bad design to the fore. Again I see problems elsewhere being cured at the consumers' expense.


    443 PROTECTION AGAINST TRANSIENT OVERVOLTAGES OF ATMOSPHERIC ORIGIN OR DUE TO SWITCHING


  • 0
    wallywombat:

    How about this for simplified SPD criteria:


    An SPD must be installed if any of the following apply:

    (i) risk of injury or to life;

    (ii) risk of financial / data loss;

    (iii) if the owner and designer etc have reached a consensus that damage would be intolerable, unless a risk assessment shows transients unlikely.


    Why don't you submit a comment suggesting that ...


  • 0
    gkenyon:

    Why don't you submit a comment suggesting that ...




    I was going to wait for feedback from this forum first!


  • 0
    I recently retired from Scottish Fire and Rescue Service and was responsible for publication of fire statistics amongst other things. I agree with mapj1 that SPDs will not protect the electrical installation against a direct lightning strike. Though thankfully rare, such direct strikes typically cause severe property damage in a resulting fire.


    I mention this as fire is always a risk to life, which renders the suggested wording about SPDs being installed if there is a risk of injury or to life somewhat problematic. There is a clear risk to life as a result of fire if a direct lightning strike on a property occurs, yet SPDs will not prevent the electrical installation and the property itself from being damaged in such circumstances. (Even if no fire-related injuries occur the event can be so frightening that indirect injuries can occur - in one case during a storm the SFRS were called to a property where the householder suffered a cardiac arrest as a result of various sockets exploding and smouldering throughout the property). 


    SPDs may prevent downstream electronic devices from being destroyed by the transients induced as a result of an indirect strike but whether this is sufficient reason to require their installation in the consumer unit is another matter. 


    I live in a rural area, and a lightning strike in a field about 100m away from my house three or four years ago took out my broadband router and the motherboard of the PC to which it was connected, as a result of the induced transient in the phone line (see gkenyon's comment about phone master sockets not being protected). The phone line remains unprotected, but since then all my TV and computer equipment has been connected to the mains via surge-protected adapters at relatively modest cost and without change to the consumer unit.
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    I think the "injury/death" is targeted more along the lines of "if a transient of any form takes out some electrics, does the failure of those electrics risk injury/death? E.g. medical locations.


    Also my understanding was that type 1 SPDs do help to an extent in direct hits - in that rather than protecting downstream equipment, their job is is to temporarily equipotentially bond the live part of the electrical system to the LPS - so there is less chance of a flash-over between, e.g. cabling and structural metalwork, and thus less risk of a fire starting. You'll still expect physical damage.


    Type 2 and 3 SPDs are more about protecting electrical /electronic equipment from relatively low energy transients, e.g. 4kV with a rise time of 8us. These are likely to cause brief arcing in electronic equipment. Repeated over time, this erodes insulation (think of carbon deposits building up between two adjacent PCB tracks) until eventually the normal 230V supply overwhelms the device.

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