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Thread: 3phase domestic SPD protection

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    Smile 3phase domestic SPD protection

    Hello all,

    I'm fairly new to domestic installations and was wondering if someone could shed a bit of light around 3phase surge protection installed in a home at the main DB. What would the more common configuration here in SA be..

    L1-N, L2-N, L3-N and N-E or all the SPD's L1, L2, L3 and N all bridged.

    I realize these two configurations offer different surge protection but was wondering which one is mostly used. The home needing the installation is only looking for protection from all the loadshedding.

    Many thanks in advance

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    Correction, L1, L2, L3 and N all bridged to earth

    Depending on the earthing arrangements and the type of protection it could also be L1-N, L2-N, L3-N, N-E.
    Last edited by AndyD; 19-Apr-15 at 03:15 PM.

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    Diamond Member AndyD's Avatar
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    There's 2 classes of surge protection you might be concerned about with a domestic installation. Class I will protect against direct lightning strikes, they take the brunt of the strike surge but their clamping voltage isn't low enough to ensure protection on their own. They're used in conjunction with Class II SPD's which can't take the same energy that Class I can but they have a lower clamping voltage which protects the equipment.

    You can use just class II SPD's but usually this would be after conducting a risk assessment to determine the likelyhood of a direct strike. If the building has a lightning rod already on it then you'll need class I and class II SPD's regardless.

    Surge protectors aren't cheap, for a combined Class I and Class II SPD setup including fusing protection be prepared to pay at least R10K for the SPD's alone if not considerably more for a 3 phase supply depending on the requirements.

    Here's a beginners guide on the Schneider website. Here's a slightly more involved one from the IEEE. Once you've got the basics take a stroll over to the dehn for the surge protection Bible.
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    Thanks Andy, I'll check those links out. although as mentioned I only need to install surge arresters in the DB to protect the installation against any possible surges when eskom comes back on after an outage

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    Diamond Member AndyD's Avatar
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    If it's just to protect from surges when power is restored after load shedding then Class II protection should be adequate.

    You might also be interested in this related problem as well if you're worried about your electrical appliances and devices.
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    Thanks Andy, very interesting read. Something I'll definitely be monitoring when power is restored. Possibly look at installing even just installing a volt meter to make it easy for clients to check.

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