Cost-effectiveness of RCDs,SPDs, AFDDs etc., in perspective

[ericmark]

As I also always say, it rather intrigues me that good few of those who now advocate (or stronger) SPDs are the same people who, not too long ago, ridiculed (and described as 'snake oil' or 'a waste of money') any mention of 'surge suppression'. Have these people perhaps suddenly strated experiencing lots of equipment failures which might possible be related to supply 'spikes' ... or what?

I am one, who some 10 years ago felt that a spike or surge is unlikely to get past the power supply into a computer, I still don't think that can happen, but maybe it can damage the power supply.

I consider one location, my old (now my sons) kitchen lights. As far back as I can remember been fluorescent, and some times they would fail to strike, and the 65 watt tubes would last around 5 years each.

The demise of the 65 watt tube resulted in using 58 watt tubes, likely the ballast designed for 240 volt, but voltage never seemed to have dropped, but life reduced to around 2 years with 58 watt tubes, then a load of houses had solar panels fitted and the voltage dropped, and now tubes down to 6 months, so due to poor access went to a 24 watt LED tube, removing all control gear, this was not very long lived, around 18 months, replaced with 22 watt, then my son replaced with GU10.

He had a lot fail and blamed them being cheap, but does seem odd, it is the kitchen having problems. As it if switch damaged with fluorescent lamps, or spikes or just cheap.

But I also use cheap lamps, and very few have failed, can count on one hand, and I have a SPD fitted. Once I was indecisive now I am not so sure.

 

[JohnW2]

I recall a design for a medical PSU that created the safe power for the sensor and it's microwatt amplifier using a photo-voltaic cell illuminated by a light source.

Maybe, but the amount of power one can get that way is obviously very limited! At least in the past, I've seen battery-powered electronics on the patient side of an opto-isolator.

Kind Regards, John

 

[JohnW2]

I am one, who some 10 years ago felt that a spike or surge is unlikely to get past the power supply into a computer, I still don't think that can happen..

I don't think either of us can say that it "can't" happen, but I share your view that it's probably extremely unlikely.

... but maybe it can damage the power supply.

Again, no-one can say that it do that, but I again think that, if it happens, it must be very rare. Over the years, I've lived with many computer PSUsand nearly all of them have outlived the useful life of the computer.

But I also use cheap lamps, and very few have failed, can count on one hand ...

Same here. I gave up buying anything other than very cheap LEDs after I had bad experiences with exppenssive ones, and 'the cheapest I can find' seem to last as long as I would expect/hope.

... , and I have a SPD fitted. Once I was indecisive now I am not so sure.

I'm going to want to see a lot more 'convincing evidence' before I am even remotely 'sure' that they have anything significantly useful to offer!

Kind Regards, John

 

[Harry Bloomfield]

I'm really surprised at you guys suffering short LED life, because despite my moving to all LED, on all the regular use lights, beginning seven years ago, I have only ever had one LED fail and that one twice so far (due to enclosed and too hot). I have not made any point of buying either cheap or expensive ones, just whatever I could find that matched my need.

I do sometimes check our mains voltage, when my Fluke is to hand and for decades it has always shown 240v +/- 1v. I have even had a min/max logging Fluke on it for 24 hours, with show the same variation. Unusually, I checked it yesterday it read 244v.

 

[bernardgreen]

Spike or Surge

Let us say there is a fault in the electricity supply network and the Phase to Neutral voltage goes high enough to make the Surge Protection Device ( SPD ) operate.

Now I do not know if the average SPD will cut the power off or whether it will just try to absorb the energy of the surge. Absorbing the energy of a transient SPIKE ( not a surge ) is possible without disconnecting the supply although the Spike Protection Device may need to be replaced.

 

[flameport]

An SPD that's conducting appears as a short circuit across the supply, with the energy dissipated as heat.
For a typical transient with a duration of microseconds that's not a problem.

A longer period of excessively high voltage would result in the SPD conducting for a long period, the end result being it overheating, the internal link melting and disconnecting it. That also shows the 'failed' indicator in the window on the front.
If that internal link didn't fail fast enough, upstream overcurrent protection would disconnect the supply. That might be just to the SPD or it could be for the whole installation, depending on where the protection was installed.

SPDs are not protection against long duration overvoltage. Other devices are required for that.

 

[JohnW2]

I'm really surprised at you guys suffering short LED life, because despite my moving to all LED, on all the regular use lights, beginning seven years ago, I have only ever had one LED fail and that one twice so far ...

As I'm always saying, the same here -so I'm not one of the "you guys" to which you refer! I've certainly had more than just one or two fail over the years, but certainly no more than I would have expected.

I've also often pointed out that many people's expectations are probably over-optimistic, based on a misunderstanding of claimed lifespan. As I always point out, having a lot (anything up to 50%) of 'early failures' (even 'very early failure is not incompatible with a claimed "average" (median) life expectancy of, say, 10,000 or 20,000 hours.

I have not made any point of buying either cheap or expensive ones, just whatever I could find that matched my need.

In the fairly early days of LEDs, many people were, as usual, promoting the idea that expensive 'reputable brand' ones were better (and that the cheap ones were 'tat' or 'rubbish'). I therefore went through a phase of trying various 'expensive' ones - but when I had a number of early failures I decided that paying maybe 3 or 4 times more was probably not going to prove cost-effective. Since then, I've always bought the cheapest I can find, and am far from unhappy with how they have performed/lasted.

I do sometimes check our mains voltage, when my Fluke is to hand and for decades it has always shown 240v +/- 1v. I have even had a min/max logging Fluke on it for 24 hours, with show the same variation.

Similarly here, just a little higher - mine is rarely far from 244 V. Interesting, one of the phases is usually about 1 volt lower than the other two.

Kind Regards, John

 

[JohnW2]

An SPD that's conducting appears as a short circuit across the supply, with the energy dissipated as heat. ... For a typical transient with a duration of microseconds that's not a problem.

Do we know anything about the extent to with the resultant very rapid disappearance/re-appearance of supply voltage can damage connected electronic equipment?

Around here, we experience many very brief (often <1 second) 'power cuts', presumably due to the actions of DNO equipment. Albeit invariably a lot longer than 'microseconds', and although I've personally experienced it only once, there have been quite a lot of reports from people around here of such events having killed items of electronic equipment.

Kind Regards, John

 

[Harry Bloomfield]

Similarly here, just a little higher - mine is rarely far from 244 V. Interesting, one of the phases is usually about 1 volt lower than the other two.

I really would not expect them to match, that would depend upon the loading of each being perfectly balanced.

 

[ericmark]

mine is rarely far from 244 V.

That was the same with my last house, until a whole load of solar panels were fitted, at which point the volts dropped, likely due to complaints over the solar panels locking out.

Years ago voltage a little high or low did not matter, it did cause fluorescent lights to use over their rating when high, but no one was really worried. However today if not in the 207 to 253 volt range EV charging points and solar panels can lock out. So today correct voltage is far more important.

Since I have neither don't know answer, but

Around here, we experience many very brief (often <1 second) 'power cuts', presumably due to the actions of DNO equipment. Albeit invariably a lot longer than 'microseconds',

would that lock out solar panels and EV charging points?

 

[Harry Bloomfield]

That was the same with my last house, until a whole load of solar panels were fitted, at which point the volts dropped, likely due to complaints over the solar panels locking out.

Years ago voltage a little high or low did not matter, it did cause fluorescent lights to use over their rating when high, but no one was really worried. However today if not in the 207 to 253 volt range EV charging points and solar panels can lock out. So today correct voltage is far more important.

Since I have neither don't know answer, but

I installed the control for some pretty big pumps at the end of a cull-de-sac which drained the M1, fed from it's own substation, connected to a second substation, not so far down the cull-de-sac. The latter fed a tractor/earth moving factory and every time my pumps were called to start many of the tools in the factory would drop out, due to the sudden volts drop. They eventually resolved it by having to run a new 11kv feed in, but as a temporary fix, I revised the controls to stagger the motor startup sequences, to always favour the smaller pump first.

That system was unmanned, so to alert the remote control room that something was amiss, they used a mechanical pulse phone number dialler, attached to the phone line, with an 8 track player. Except still in the commissioning stage, the dialler had not been properly set up and was dialling completely random local numbers, to private numbers. Eventually, the police managed to ring, when I was on site to answer the phone, let me know and to disconnect it from the line.

More usually, such problems would be reported by telemetry, or via a flashing beacon on the end of a long pole..

 

[JohnW2]

I really would not expect them to match, that would depend upon the loading of each being perfectly balanced.

Sure, but it's interesting that the difference is very consistent - two of the phases always extremely close, and the third (always the same one) anything up to a volt lower.

By pure chance, that 'usually lower' (presumably more loaded) phase is the one that I use least - so I am 'accidentally' helping a bit to keep things balanced

Kind Regards, John

 

[JohnW2]

... would that lock out solar panels and EV charging points?

I've no idea!

Kind Regards, John

 

[JohnW2]

I think there may be an issue that BS7671 is over-simplifying and/or translating imperfectly from "appliance designer terminology" to "electrician terminology".

It is very much possible for a protective earth conductor to be part of the protection and leakage management strategy even if it is not exposed directly to touch by the user and AIUI such an appliance is still considered class 1. This is common with laptop power bricks.

Maybe, and that would make total sense. If live parts are surrounded by earthed metal, then that seems to be Class I, even if that earthed metal is surrounded by (electrically redundant) insulating material, and therefore not 'exposed'. However, as I said, if it hasn't got exposed-c-ps to earth, it seems that BS7671 would not regard it as Class I.

@plugwash - having thought a bit about what you and I wrote (as above), I think that you have indeed probably largely answered the question that I have been asking for years, and the answer probably is that I've only had to ponder and ask that question because of BS767's "over-simplified"/incomplete/'naive'/whatever definitions!

When I have asked my question "If it's not Class I and it's not Class II, then what IS it?", the example I've most often cited has been that of laptop power supplies. Of all the ones I've seen, I don't think any have claimed to be (been marked as) Class II (and all have had 3-core supply cables). However, since the BS7671 definition of Class I is the only definition I've been thinking about, nor could they (per BS7671 definition) be Class I - since they have no exposed-c-ps which could be earthed - hence my asking "so what ARE they?".

As you say above, I think the simple answer is that they ARE Class I, since they use earthing as part of their 'protection', and it is only BS7671's definition which thinks (or, at least, implies) that they are not!

Many thanks. As above, I think you may have largely put to bed this question which has been niggling at me (and which no-one else has ever really managed to answer) for years!

What remains is for me to try to complete my education by discovering what the 'proper' definitions of Class I and Class II actually are!

Kind Regards, John

 

[plugwash]

At least wikipedia claims they come from "IEC 61140" which is titled "Protection against electric shock - Common aspects for installation and equipment"

Kind of expensive though.