SPDs !!!

[ericmark]

I have lost aerial boosters in the past, it seems likely these protected my video and TV, however not had a fire as a result, but when diodes fail it can result in over heating and fires, so spikes can have a knock on effect.

At around £30 for the fusebox SPD it was not worth taking a chance, if never used or required so what, but at £100 for some makes, then we start to say hang on do we need that?

It is the same with people trying to get away with just two RCD's, we are looking at £70 to £250 for a cheap make of consumer unit like fusebox between just two RCD's and no SPD and all RCBO and SPD, but for a Hager consumer unit likely looking at £500+ with SPD £100 and £35 for each RCBO it soon mounts up.

So screwfix website

two consumer units same price, in fact the most expensive they do, to left two RCD's at only 63A so questionable if it complies unless only a 60 amp DNO fuse, and to right no SPD, so top of range clearly the Crabtree is more expensive really as no MCB's included, a BG SPD is £25 and one module thick so cheap enough to add and Crabtree MCB's £3.50 so add another £35 plus two RCD's well no that does not work, as best Screwfix offer is type AC 80 amp, so it would seem unlikely buying from screwfix the Crabtree could be made to comply. However BG do two RCBO's on screwfix web site both are type AC.

So Screwfix website most expensive consumer units on offer both type AC RCD's so could not be used to supply and electric car charging point, one with under rated RCD's and one without a SPD. Clearly not a trade supplier, but it shows the problems.

 

[davelx]

However BG do two RCBO's on screwfix web site both are type AC.

So Screwfix website most expensive consumer units on offer both type AC RCD's so could not be used to supply and electric car charging point, one with under rated RCD's and one without a SPD. Clearly not a trade supplier, but it shows the problems.

That's SF's choice though - BG type A, B&C curve RCBOs are readily available from other suppliers, including TLC, for about £14.50.

 

[ericmark]

I got caught out, went to local supplies think they are called Link, and picketed up new consumer unit etc, I was not doing the fitting, but casual look saw type B written in large writing on the RCBO's and thought "Oh good only expected type A." however after all done looked at board and realised curve B type AC. If I want an electric car then can get type A, but now fitted I have no intention of renewing them all, most light bulbs use a capacitor to limit current first so they can not allow DC, cooker hard wired so even if the induction hob goes wrong likely not a problem, so one ring that supplies fridge/freezer, freezer and washing machine all with inverter drives is really the only one I would consider changing, did order two type A, but 4 months latter still not arrived so cancelled.

However with a RCBO should DC freeze the RCD part, it is only one circuit, so the risk is very low, but with a RCD + MCB the freezing of the RCD can effect so much. And one assumes if SF sells them, some one must be buying and fitting them. I can understand bargain basement cheapest of the cheap missing out some protection to keep down price, but these two were top of range.

 

[JohnW2]

Interesting reading. Does your house have a lightning protection system. ? That will affect the type of SPD(s) that should be fitted.

If that is directed at me, no, I don't have a "lightning protection system" (or "protection from lightning system") as such. I do, however, have a 120+ feet tall Wellingtonia tree (previously ~150 feet - see **) about 50 feet from the house, which is easily the tallest object for miles around and seems, in some senses, to 'serve the purpose'!
[ ** It was struck by lighting about 15 years ago. As a result, the top 25 feet died and, a couple of years later 'fell off' in a gale ]

It is an odd term "lightning protection system" .... surely it should be "protection from lightning system"

Maybe, and maybe 'odd', but it's a pretty common form of language, the meaning of which is usually totally clear - we talk about such things as "fire protection" and "flood protection" etc. without meaning that it is the fires or floods that are being 'protected'. Closer to home, we talk about "fault protection" and "over-current protection" etc. (and even, in context, "surge protection"!!) - again, without meaning that it is the faults, over-currents or 'surges' that are being 'protected'

Kind Regards, John

 

[bernardgreen]

If that is directed at me,

No not directed at you.

 

[JohnW2]

I have lost aerial boosters in the past, it seems likely these protected my video and TV, however not had a fire as a result, but when diodes fail it can result in over heating and fires, so spikes can have a knock on effect. .... At around £30 for the fusebox SPD it was not worth taking a chance ...

Do you have any good reason for believing that mains-borne 'spikes' were responsible for the losses of your aerial boosters? There are clearly some alternative possibilities, which SPD protection of the electrical installation would have done nothing to prevent.

In passing, at least in my experience, when diodes fail, and particularly when they fail because of over-voltage ('spikes' or otherwise), they virtually always fail open-circuit.

Kind Regards, John

 

[JohnW2]

No not directed at you.

At whom, then?

Kind Regards, John

 

[bernardgreen]

Interesting reading. Does your house have a lightning protection system. ?

Interesting reading. Seems to suggest the decision a person has to make about whether to have SPDs fitted depends on whether they have a lightning protection system installed.

 

[ericmark]

I remember the sign on Shap "Beware of the man eating haggis" lovely bit of ambiguity.

As to lighting went to a very interesting lecture, two things stuck in the mind.
1) Often wind and lighting go together, so often it misses the highest point and hits some thing near the highest point. So tree might attract the lighting but it is some thing near the tree which is hit.
2) Earthing an aerial is a bad move and it will attract the lighting, large resistors so voltage can leak away, even a spark gap yes, but earth it no, that's asking for it to be converted into copper balls on the garden.

And yes likely it was voltage on the aerial not mains born that saw off the aerial booster.

But be it SPD or type AC RCD's how would you know if not having a SPD or if had it been a type A if it would have saved the day.

 

[bernardgreen]

This simple method to reduce the risk of damage to equipment when the aerial is hit by a lightning strike can work. The rapidly rising voltage is impeded by the impedance of the loop and instead jumps to the metal plate and to ground. I saw one of these after a strike, the aerial feeder was written off but the TX was still functional.

 

[JohnW2]

And yes likely it was voltage on the aerial not mains born that saw off the aerial booster.

That was obviously my implication - so, despite your having said "...At around £30 for the fusebox SPD it was not worth taking a chance...", an SPD would probably have done nothing to 'save' your aerial boosters.

But be it SPD or type AC RCD's how would you know if not having a SPD or if had it been a type A if it would have saved the day.

One obviously could never be certain, any more than one could ever be certain that, say, operation of an RCD had "saved someone's life".

However, that's the sort of not-evidence-based 'emotive' argument that has been used for many years to sell expensive 'surge protection' devices (and all sorts of flavours of 'snake oil') to gullible consumes.

Where I think you are wrong (just as I now feel about BS76r71) is in talking about Type AC RCDs and SPODs 'in the same breath'. I still haven't managed to learn enough to be able to personally make an informed judgment about the 'RCD Type' issue - but if it is possible that, under certain circumstances, a Type AC RCD may fail to clear a fault and leave people exposed to possible electric shocks, that is a 'safety' issue which has to be taken seriously.

However, when it comes to SPDs, I think one really has to scrape lots of barrels to come up with scenarios in which the absence of SPD production would present any significant risk to life, limb or even buildings. Unless someone can convince me otherwise, I therefore do not regard SPDs (or their absence) as being a significant 'safety' issue.

Kind Regards, John

 

[JohnW2]

This simple method to reduce the risk of damage to equipment when the aerial is hit by a lightning strike can work. The rapidly rising voltage is impeded by the impedance of the loop and instead jumps to the metal plate and to ground. I saw one of these after a strike, the aerial feeder was written off but the TX was still functional.

That makes sense. However, I think this slide into discussions about 'lightning strikes' is illustrative of one of the problems in relation to some of the confused/confusing things which are written, and thought, about "SPDs".

Kind Regards, John

 

[bernardgreen]

slide into discussions about 'lightning strikes'

It would appear that lightning strikes are probably the only events that will cause the MOV in SPD to start to conduct and suppress the "spike " or surge.

 

[JohnW2]

It would appear that lightning strikes are probably the only events that will cause the MOV in SPD to start to conduct and suppress the "spike " or surge.

There's surely a big difference between 'lightning strikes' as normally understood (as in 'balls of molten copper', the top of my tree falling off, house fires etc., such as the scenario you illustrated) and lightning-induced 'spikes' in the electricity distribution network which SPDs may do something to help?

Kind Regards, John

 

[Swwils]

I think SPD were included to get everyone used to the possibility of eventual mandatory AFDD.

Either that or insurance companies are bearing costs of surge related incidents!