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

None of the data sheets I can find seem to classify them as T3 or anything else nor mention any need for an upstream T2 (just a mention that they won't protect against lightning - usually a job for T1s)  - given most seem to come with some kind of free insurance (often £1000 - i.e. significantly more than the sale price) the manufacturers must have some confidence in them. If I were designing such a product I think I'd make it T2+T3 type (or loose equivalent) to make sure I wasn't swamped with claims.

   - Andy.

I support AJJewsbury '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).

As pointed out by AJ and Ive found similar,  there is a distinct lack of tech spec  of critical values (e.g. Up)  on sales pages.  Digging around manufacturers pages   for some has revealed limited info too.

The internet (if you can trust it), suggests that powerstrips  are T3-like intended, in so much as they are 'point of use' .  How well they co-ordinate with any fixed wiring SPD provisions, who knows .

One brand stocked by CEF states it conforms to BS 5733, BS EN 61643-11   (I don’t have the BS docs but is 61643  about SPD types conformance etc). 

As an aside, the 'insurance' offered tends to come with all sorts of small print  - so the internet says  ;-)

I was wondering too, if the PSU that a lot of  electronic kit use would survive or sacrifice just as well as most consume grade powerstrips/leads with surge protection built in  (to a standard, or just cheap parts ... who knows).  If the idea of a T3 'must not use without a T2'  recommendation is because it would get destroyed and be a fire risk etc, then what goods a powerstrip  too.    As said though, may be manufacturers have it sorted although given the power of profit, it might not be as effective as the marketing suggests  on some at least ;-)

psychicwarrior said:

 (I don’t have the BS docs but is 61643  about SPD types conformance etc). 

Appendix 1 of BS 7671 refers to BS 5733 on page 412 and BS EN 61643 on page 427.

I'm thinking that T2s need the cables to and from it to be as short as possible. So how effective would a combined T2&T3 power strip actually be? They could be sited anywhere in a property and are at the end of a bit of flex.

OlympusMons said:

I'm thinking that T2s need the cables to and from it to be as short as possible. So how effective would a combined T2&T3 power strip actually be? They could be sited anywhere in a property and are at the end of a bit of flex

They should protect things plugged directly into the strip OK (as those appliances only see the voltage difference across the SPD itself - presuming they don't have an earth reference to anywhere else - like an old fashioned RS-232 interface to other equipment powered from elsewhere) - but the rest of the installation would receive less, if any, benefit.

In some circumstances drawing the surge through the installation to a remote point might actually harm some upstream devices (I had an unfortunate experience with PC modem on a PBX and a sure protector with a phone line facility some years ago). I suspect most 30mA RCDs for instance would prefer a SPD upstream of them rather than just one downstream.

   - Andy.

I've been out a few moments ago and bought one from the local 'shed'  :-)  ... just to see  (well it will get used).

And...  it states on the label on the body that it is a T3 SPD; Uc 255V Uoc 4kV Up 2.5kV.

So it is a T3   -  with no T2 upfront (in this case) ... but, as noted,  it is not covered by BS7671 of course.

It is there to sacrifice   :-)

well it rather depends on how many events of each level of severity you expect to get per year, The prolific but low level stuff from domestic sources like spikes from tumble dryer motors reversing will be trapped very well by something like this, as will some external things from the neighbours but not very big surges, but there probably are not that many of those anyway, after all there are plenty of installations with no surge protection at all, and not a lot seems to happen.
The problem is one of probability, and that is very location dependent.  

Mike

Yes agreed. A few of us here were having that same discussion ... it being  about location, risk assessment etc  and whether to bother with surge powerstrips/leads.     I've had nothing for decades and have and have had computers, routers and so on like most and nothing has  happened ( that I know of). One never knows though . ;-)

Perhaps folk with really expensive and/or sensitive equipment might employ them but also as part of a coordinated approach.

The point in mind  was that although powerstrips etc are not part of fixed wiring (covered by 7671), they (or some) are indeed T3 SPD (point of use).    It seemed that 7671 was suggesting dont fit anything at all unless i is all co-ordinated, or if not that exactly then at least 'must not' fit a T3 unless suitable SPD provisions upfront.  That's why I was delving into the merits of T3  powerstrips.  It must be better than nothing in some cases ... and may be this is the thing.

Sorry for my wording -  it is poor.

psychicwarrior said:

One brand stocked by CEF states it conforms to BS 5733, BS EN 61643-11   (I don’t have the BS docs but is 61643  about SPD types conformance etc). 

BS 5733 has nothing to do with SPDs and overvoltage protection  and, for the purposes of this discussion, is not really a valid.