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Calculating Iimp for DC SPD in PV

Ian Cheek

Hi

BS7671 712.534.102.6 states if I select my Iimp according to PD CLC/TS 51643-32 (which I cant as I dont have a copy, personally cant afford to buy it. I also cant get my company to buy it). I'm left with the selection based on 12.5KA.

The products on the market while some do offer a SPD with a Iimp of 12.5KA, most seem to be rated at 6.25KA tho

I've contacted one such manufacturer who offer the 6.25KA, and they are looking into it to see why they on paper seem to offer a product that does not comply with BS7671.

While I'm quite happy to be a stickler to BS7671 and design and cost for a 12.5KA DC SPD. But I just wanted to ask if I was missing something.

Thank you

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    Well you may find a quick look at the pictures in this brochure helpful to decide which situation you are in , in terms of do you have a lightning protection system, is it spread out so you need multiple arrestors etc. Note that the impulse rating of a surge arrester very much depends on which surge waveform is under consideration (peak current is not the only variable, unsurprisingly impulse duration has a big effect as does rate of rise..)
    So the same device may be both 20kA, 12kA and perhaps something else as well when characterized with different standard tests.

    regards mike.
    PS Example snippet from a datasheet showing what I mean

    Total discharge current (10/350 µs) ITotal(10/350) 12.50 kA
    Lightning impulse current (10/350 µs) Iimp 6.25 kA
    Total discharge current (8/20 µs) ITotal(8/20) 80.00 kA
    Nominal discharge current (8/20 µs) In 20.00 kA
    Maximum discharge current (8/20 µs) Imax 40.00 kA
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  • 0

    Well you may find a quick look at the pictures in this brochure helpful to decide which situation you are in , in terms of do you have a lightning protection system, is it spread out so you need multiple arrestors etc. Note that the impulse rating of a surge arrester very much depends on which surge waveform is under consideration (peak current is not the only variable, unsurprisingly impulse duration has a big effect as does rate of rise..)
    So the same device may be both 20kA, 12kA and perhaps something else as well when characterized with different standard tests.

    regards mike.
    PS Example snippet from a datasheet showing what I mean

    Total discharge current (10/350 µs) ITotal(10/350) 12.50 kA
    Lightning impulse current (10/350 µs) Iimp 6.25 kA
    Total discharge current (8/20 µs) ITotal(8/20) 80.00 kA
    Nominal discharge current (8/20 µs) In 20.00 kA
    Maximum discharge current (8/20 µs) Imax 40.00 kA
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