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is a surge protected extension/powerstrip any use without upfront SPDs

psychicwarrior

hello goodly morrow

If a T3 SPD, 'must not' be used, as per 7671,  without upfront (T1+)T2 SPD  (for want of better words) ,  what real value is a plugged in surge protected extension lead/powerstrip  (which is a T3 in effect one presumes) without a T2 somewhere upfront ?

Or is it really just a sacrificial item and really is better to have.

Perhaps the components are pretty useless and cheap in most of the consumer grade surge leads/strips.  May be connected devices (via power blocks and transformers etc) can cope just as well  ;-)

Engineering references and regs are not going to use the anything is better than nothing finger in the air style and have to present a considered, tested and  co-ordinated approach. The consumer market takes a different view it seems and makes little to no effort (does it) to advise that surge protected powerstrips/leads 'must not be used' without upfront SPD,  but if course such is not part of fixed wiring any way so no need, or is there a need . 

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    I support  's view ... the product might have components of an SPD in them, but have they even been tested to the SPD product standards in the first place is a good question to ask? Without that, as Andy says, not much to go off regarding performance.

    In the grand scheme of things, the question has two answers:

    (a) For installations in which T1 protection is not necessary, T3 SPDs aren't guaranteed to work for equipment it is intended to protect without T2 further towards the point at which overvoltage is received into the installation (although a combined T2-T3 will).

    (b) In installations that require T1 SPD at the point overvoltage is received into the installation, T1 and then T2, or a combined T1-T2, would be needed to make sure T2 SPDs work.

    T1 is necessary in installations with LPS, or supplied by overhead LV cables.

    The reason I used the term 'point at which overvoltage is received into the installation' is that overvoltages might come from a number of sources. Consider the common example of a building with LPS, that has an LV supply, but also supplies power to equipment such as lighting and EV in a car park. The overvoltage impact needs to be assessed for both the incoming supply, and the feeds out to the car park, as they each go outside the 'LPZ' (lightning protection zone).

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    I support  's view ... the product might have components of an SPD in them, but have they even been tested to the SPD product standards in the first place is a good question to ask? Without that, as Andy says, not much to go off regarding performance.

    In the grand scheme of things, the question has two answers:

    (a) For installations in which T1 protection is not necessary, T3 SPDs aren't guaranteed to work for equipment it is intended to protect without T2 further towards the point at which overvoltage is received into the installation (although a combined T2-T3 will).

    (b) In installations that require T1 SPD at the point overvoltage is received into the installation, T1 and then T2, or a combined T1-T2, would be needed to make sure T2 SPDs work.

    T1 is necessary in installations with LPS, or supplied by overhead LV cables.

    The reason I used the term 'point at which overvoltage is received into the installation' is that overvoltages might come from a number of sources. Consider the common example of a building with LPS, that has an LV supply, but also supplies power to equipment such as lighting and EV in a car park. The overvoltage impact needs to be assessed for both the incoming supply, and the feeds out to the car park, as they each go outside the 'LPZ' (lightning protection zone).

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