SPDs !!!

[JohnW2]

In another thread ...

And 443.4 contains an exception for single dwelling units "where the total value of the installation and equipment therein does not justify such protection" .... Which is surely a judgement call to be made by the person occupying or owning the dwelling. It is certainly NOT the place of the electrician carrying out an EICR to make that call. .... As a homeowner, my judgment is that the chance of any damage being caused by a TOV in my locality is so low as to make the fitting of an SPD unjustified.

I totally agree - and I could easily have written all of the above myself (and have very recently written quite similar).

I am, uncharacteristically, almost 'lost for words' (but plan to write many!)

As above, it seems pretty ridiculous to suggest that a third party can decide whether or not the absence of SPD protection (in a 'single dwelling unit') represents a non-conformity with BS7671 when there is provision for exemption from the 'requirement' on the basis of a judgement which can only be made by the owner or occupier of the dwelling.

I find it even more difficult to understand under what circumstances someone undertaking an EICR (in a 'single dwelling unit') could/would ever feel that absence of SPD protection qualified as "C2".

Nor do I really understand why the 'exemption' applies only to 'single dwelling units', since I imagine that there are many small commercial units (small shops etc.) that have even less 'potentially susceptible' equipment than many/most dwellings.

This seems (to me) to be a totally unprecedented moving of the goalposts. Prior to this, BS7671 was essentially all about 'safety' - almost entirely about direct risks to persons (electric shock) or the risk of electrically-initiated fires in buildings. Although the 'must have SPDs' scenarios mentioned in the regs include things like ..

(i) result in serious injury to, or loss of, human life, or ....

... I have to deeply scrape some barrels to think of scenarios in which that would be applicable, least of all in a domestic dwelling.

In relation to the different 'Types' of RCD/RCBO, I have been moaning (here and elsewhere) for the last year or so about my failure to find any 'chapter and verse' about the nature and extent of the perceived issues/problem, but it's even worse in relation to surge protection. I'm not at all sure how it will ever be possible to determine with any degree of certainty that a particular failure of some equipment was due to 'supply surges', but I haven't even managed to find any data on the frequency of events which were even 'vaguely suspected' as having been due to such a cause.

Speaking personally/anecdotally, for what it's worth, I live in an area in which most of the supply network (including the feed to my house) is overhead, and I have a lot of 'electronic' equipment but, in 30+ years, have not experienced any equipment failures which I have any particular reason to believe were due to 'supply surges'. Indeed, the vast majority of such failures have been 'not unexpected', in equipment that has been in service for very many years. ... so I certainly do not perceive any personal 'need' for surge protection.

Until two or three years ago, many of us were (here and elsewhere) talking very disparagingly about the whole concept of 'surge protection' for electronic equipment, with many suggesting that the only people to benefit from consumer 'surge protection' devices were those who manufactured, marketed and sold them. Has everyone changed their minds about that conceptual view (for what it's worth, I, for one, haven't!!)?

Am I fairly alone in such thinking? What am I missing?

Kind Regards, John

 

[bernardgreen]

I agree with JohnW2

 

[ericmark]

Looking at the John Ward utube video it seems the unit has two modules, one line to earth, one neutral to earth, what is the point in the latter with a TN-C-S supply? It only needs a module line to either earth or neutral as earth and neutral are connected together.

It seems it limits spikes to around 500 volt, which is high enough so the loss of the PEN will not result in prolonged current through the device, but the spikes would depend on how many switch mode power supplies or inverters are connected to the supply, with one odd device there is nothing to reduce the spike but the more devices we have, the less the spike is likely to be, so as we have more and more devices which rectify the mains supply the less the problem will be.

But as to have I lost devices, when all the houses I have lived in have an under ground supply, well yes the odd PC power supply has failed, however one would only blame out side spikes if you lost more than one device at the same time, and that has not happened, so it would seem unlikely to be caused by a spike.

I think mine cost around £32 which is really not enough to worry about, it is a two module unit, so really should have been £16 as I have a TN-C-S supply, and at £16 I am sure most people would fit them, but fusebox is a cheap make. But Wylex, and Crabtree looking at £100 and again only ½ the unit can do any good. BG is £25 and half the size one module thick, again part connected between earth and neutral which clearly not required with a TN-C-S supply.

So

443.2.1 Where an installation is Supplied by a low voltage system containing no overhead lines, no additional protection against overvoltage of atmospheric origin is necessary if the impulse withstand voltage of equipment is in accordance with Table 44.3. suspended cable having insulated conductors with earthed metallic covering is deemed to be an underground cable for the purposes of this section.

So what changed in the 10 years between 2008 and 2018, we had switch mode power supplies back in 1992 and 2001 never mind 2008 so it is not the use of switch mode power supplies or inverters, and nothing in BS 7671:2008 causes serious injury, injury yes, but nothing causes serious injury, however neither can I find death, so suppose that does not mean much, but I simply can't think of any way transient over voltage can cause serious injury, it may damage equipment but that does not mean injury except to bank account.

 

[JohnW2]

Looking at the John Ward utube video it seems the unit has two modules, one line to earth, one neutral to earth, what is the point in the latter with a TN-C-S supply? It only needs a module line to either earth or neutral as earth and neutral are connected together.

Indeed.

It seems it limits spikes to around 500 volt, which is high enough so the loss of the PEN will not result in prolonged current through the device ...

I'm not sure what 'lost PENs' have got to do with this?

But as to have I lost devices, when all the houses I have lived in have an under ground supply, well yes the odd PC power supply has failed, however one would only blame out side spikes if you lost more than one device at the same time, and that has not happened, so it would seem unlikely to be caused by a spike.

Same here. As I said, I can't really see how one would ever to be remotely sure that failure of a single bit of equipment had anything o do with any 'supply surges/spikes'. I suppose that, as you say, simultaneous failure of two or more pieces of equipment might raise a suspicion - but that's something I have never personally experienced in the past 50+ years.

So what changed in the 10 years between 2008 and 2018, we had switch mode power supplies back in 1992 and 2001 never mind 2008 so it is not the use of switch mode power supplies or inverters, and nothing in BS 7671:2008 causes serious injury, injury yes, but nothing causes serious injury, however neither can I find death, so suppose that does not mean much, but I simply can't think of any way transient over voltage can cause serious injury, it may damage equipment but that does not mean injury except to bank account.

As I said, I agree with all that.

I know that some of us have been known to be somewhat critical of various of the evolving regulations, but this one seems to be in a whole new ballpark - and verging on the 'incredulous' for me

Kind Regards, John

 

[ericmark]

I'm not sure what 'lost PENs' have got to do with this?

A lost PEN can cause an over voltage of up to 400 volt, so any device designed to sink to earth a voltage under 400 volt could be asked to handle 100's of amps, and clearly a device of that physical size could not take that amount of current. In fact John ward showed it did start at under 570 volt which would be the peak voltage with a failed PEN, I did not fit my CU so no idea if the SPD is before or after the isolator, not that it matters in my case as an independent isolator that I can use to turn off the CU, but the big question is if with a loss of a PEN the SPD could cause a CU fire?

 

[JohnW2]

A lost PEN can cause an over voltage of up to 400 volt, so any device designed to sink to earth a voltage under 400 volt could be asked to handle 100's of amps ....

For a start, is not 400V stretching things a bit for a standard 'lost PEN'? In reality/practice, it's surely usually going to be no greater than the line/phase potential, at worst?

In any event, when you talk about "sinking to earth", are you talking about "sinking to extraneous-c-ps" since loss of a PEN would obviously mean loss of the normal 'earth' as well as of the N?

However, this is all a bit tangential to my my points. Even if you have identified a situation in which SPDs could could 'present a problem', most of what I've said relates to the need/point (or otherwise) in having them in the first place!

Kind Regards, John

 

[ericmark]

With a lost PEN you have a voltage depending on load from zero to 400 volt AC, in practice unlikely to be either extreme, of course same is true with a lost neutral, I have seen the results, but the SPD is not designed to protect from that. However the point is if it works at under 570 volt it may try, however just gone back to John Ward's video

and he says capped at around 600 volt with a 1 MΩ resistance so unlikely to cause a problem.

 

[JohnW2]

With a lost PEN you have a voltage depending on load from zero to 400 volt AC, in practice unlikely to be either extreme ...

I need to think about that but, on the face of it, I don't see how a voltage as great as that could appear in any (single-phase) installation, since the only pd of ~400V within the LV distribution network will be that between two phases.

... however just gone back to John Ward's video .... and he says capped at around 600 volt with a 1 MΩ resistance so unlikely to cause a problem.

I need to think about that, too!

However, yet again, this is tangential to my my points.

Kind Regards, John

 

[bernardgreen]

Change the name from "Surge Protection Device" to "Transient Absorption Device" and the device may then be more accurately named.

The SPD ( or TAD ) will not operate ( it seems ) until the supply voltage is more than 400 Volt.

Surges of voltage between Live and Neutral seldom exceed 400 Volts unless the local supply transformer goes into meltdown and isolation between 11kV primary and 440 V secondary breaks down. A puny little Metal Oxide Varistor ( MOV ) is not going to last long in that situation.

What an MOV will do is absorb short duration over voltage transient where the energy of the transient is too small to burnt out the MOV

 

[SUNRAY]

I need to think about that but, on the face of it, I don't see how a voltage as great as that could appear in any (single-phase) installation, since the only pd of ~400V within the LV distribution network will be that between two phases.
I need to think about that, too!

However, yet again, this is tangential to my my points.

Kind Regards, John

I need to think about that but, on the face of it, I don't see how a voltage as great as that could appear in any (single-phase) installation, since the only pd of ~400V within the LV distribution network will be that between two phases.
I need to think about that, too!

However, yet again, this is tangential to my my points.

Kind Regards, John

A lost neutral is often due to a castrophic event on the network, in one event I had some involvement in it was caused by a chiller unit incorrectly wired and when a contactor operated two phases were shorted together which blew only one 200A fuse in the dis board feeding the chiller and the 300A fuse in the other phase feeding the board. Additionally it took out the neutral bar connexion link.
The high load on the remaining unaffected phase pulled the failed neutral very close to it leaving the other phase to neutral very close to 400V, actually in those days it was far mor likely to be more like 420V.

 

[JohnW2]

A lost neutral is often due to a castrophic event on the network, in one event I had some involvement in it was caused by a chiller unit incorrectly wired and when a contactor operated two phases were shorted together which blew only one 200A fuse in the dis board feeding the chiller and the 300A fuse in the other phase feeding the board. Additionally it took out the neutral bar connexion link.
The high load on the remaining unaffected phase pulled the failed neutral very close to it leaving the other phase to neutral very close to 400V, actually in those days it was far mor likely to be more like 420V.

I still need to think more, since I have yet to get my head around a 'credible' mechanism that could result in ~400V (between anything and anything else) in an dwelling fed with a single-phase supply (the PEN of which has been 'lost'). Maybe I'll 'get there' with some more thought

However, yet again. this side issue has nothing to do with my comments/thoughts about SPDs.

Kind Regards, John

 

[plugwash]

I'd be more inclined to take SPDs seriously if they had a means of disconnecting the protected installation on failure of the SPD.

 

[JohnW2]

I'd be more inclined to take SPDs seriously if they had a means of disconnecting the protected installation on failure of the SPD.

What do you mean by "failure of the SPD".

If you are talking about failure of SPD functionality, if one did not take 'surge protection' seriously in the first place, one wouldn't really be too concerned about failure of that alleged functionality, would one?

Kind Regards, John

 

[RF Lighting]

I still need to think more, since I have yet to get my head around a 'credible' mechanism that could result in ~400V (between anything and anything else) in an dwelling fed with a single-phase supply (the PEN of which has been 'lost'). Maybe I'll 'get there' with some more thought

However, yet again. this side issue has nothing to do with my comments/thoughts about SPDs.

Kind Regards, John

Apologies for the crude drawing but hopefully it makes sense. House 1 is fed by L1 and N and has a heavy load connected. As the neutral is open circuit it will rise in potential to L1 voltage.

House 2 has low loading and is connected to L2 and the shared neutral which is now at L1 potential which will have a voltage of up to 400V depending on loading

House 3 has zero load as they’re on holiday.

If each of the houses were using exactly the same power then the neutral drops to 0V and the more out of balance the phases become the higher the neutral voltage.

 

[flameport]

I find it even more difficult to understand under what circumstances someone undertaking an EICR (in a 'single dwelling unit') could/would ever feel that absence of SPD protection qualified as "C2".

There are none. It's C3.
The section about loss of life / injury and the rest is for commercial or industrial installations, where C2 could apply if SPDs were not installed or were not functioning.

one neutral to earth, what is the point in the latter with a TN-C-S supply?

Reduces the distance between the conductors and the SPD, relying on the N-E link at the origin would significantly increase the length of one of the conductors if only the N or E was connected to the SPD and reduce it's effectiveness significantly.

however one would only blame out side spikes if you lost more than one device at the same time

Many transients (surges) are not caused by things external to the installation. They are caused by switching within the installation.

Lost PEN situation is unrelated, SPDs will be of no use there or in any other situation where the supply voltage is too high. Overvoltage detection devices already exist and can be installed if required.

, I don't see how a voltage as great as that could appear in any (single-phase) installation, since the only pd of ~400V within the LV distribution network will be that between two phases.

Single phase supplies to dwellings are typically from a 3 phase transformer with a 3 phase cable in the street, one phase and NE tapped off of that cable for each house.
A break in the NE part of that cable before it connects to a selection of dwellings is disconnecting the neutral in a 3 phase system that has unbalanced single phase loads (each house), and the neutral point will shift depending on the loads connected. Some may get a lower voltage, some might get a relatively normal voltage, others could be significantly higher. The various voltages are likely to shift as multiple devices fail and disconnect from the system. Fire and destruction is inevitable.

Change the name from "Surge Protection Device" to "Transient Absorption Device"

Surge is a particularly poor name, a TAD would be far better. Unfortunately it's too late, they are SPDs.
'Surge' is also used to refer to moderate increases in voltage for a period of seconds to minutes, however that's entirely unrelated to SPDs.

What an MOV will do is absorb short duration over voltage transient where the energy of the transient is too small to burnt out the MOV

Yes, and that is exactly what they are intended for, and in the context of SPDs, short is in the realm of microseconds duration but can easily be thousands of volts.

The primary use case for SPDs is to protect equipment within the installation from damage. LED lighting being one of the main items that's relatively easy to destroy with transients, along with other installed devices such as heating and lighting controls.

Most of what's in BS7671 regarding the use of SPDs is next to useless, including the risk assessment for lightning strikes and the nonsense about excluding domestic dwellings that have nothing of value in them.