Where best to fit an SPD all depends on where the surge is generated, and where the victim is, and the type of damage mechanism the victim is likely to experience.
The simplest  is when the impulse is external to the building, and is common mode relative to ground - that is the voltages on  L and N fly up together- rather than voltages moving   in differnent directions - that antiphase  case  is differential mode..

In such a case an SPD near where power enters the building is enough. But, surges may come from other places - wiring to outbuildings ,workshops with welding and machines, and may be a mixture of common and differential modes.

In a perfect world each needs strangling as near the origin as possible - but this is not always practical. Situations where the victim equipment straddles two zones - perhaps mains wiring and a phone line or cable tv, then it may only be possible to tie things together  the victim to avoid the electrical equivalent of the splits...

there is no one size fits all solution that always works.

Mike

Chris Pearson said:

This ought to be a simple question!

Yes!

I make an intelligent guess that only 1% of all houses in Britain have a SPD in the incoming supply.

There are still plenty of houses with prehistoric consumer units fitted with rewirable fuses. Even more with plastic / bakelite consumer units where the original fuses have been replaced by MCBs.

mapj1 said:

Where best to fit an SPD all depends on where the surge is generated, and where the victim is, and the type of damage mechanism the victim is likely to experience.

Would many homeowners possess the knowledge of this in order to determine the optimum location of the SPD?

If they had a workshop with several machine tools, then an SPD for the workshop supply physically located in the workshop could be a good idea in addition to one in the main consumer unit.

For a conventional house an assumption might be made that the surge is external rather than internal.

ebee said:

the cost versus risk needs be analysed too

If your final DBs are (over)due for replacement, the extra cost of ready-installed SPDs is hardly going to break the bank. Given that we have not had a damaging surge here over the past 27 years, the risk must be pretty small.

wise words Chris. just employing murphy`s law

But is the risk increasing?

I would say yes the risk is increasing because we are using more and more appliances that are susceptible.

Not many years ago most stuff was just simple current drawing items, telephone lines were the only things we had much local surge protection for. 

I am highly dubious about the merits of SPDs rated for 'domestic use'. Indeed, I haven't bothered with one for my own installation. Can't say I have ever experienced anything untoward as a consequence.

That is pretty much my attitude, but it could be different if I lived on the top of a hill with an aerial supply.

However, if you are going to install a new CU (either for yourself or in trade) is there any good reason for not including an SPD?

I live at the top of a hill but my supply is underground.

To answer your question - Yes I would, and have fitted them as a swap-out of an existing 3036 job, but I would never recommend a separate retro-fit to an existing installation.

In-CU or Out-CU I don't believe they are effective in either case, but Fusebox do em cheap enough to be a no brainer, and the best of all is that if they 'turn red' nobody will bother replacing them, nor will the customer notice any change in the characteristics of their supply!

whjohnson said:

best of all is that if they 'turn red' nobody will bother replacing them, nor will the customer notice any change in the characteristics of their supply!

That's very uncharitable! People will check them when they press their test buttons twice a year.

whjohnson said:

best of all is that if they 'turn red' nobody will bother replacing them, nor will the customer notice any change in the characteristics of their supply!

That's very uncharitable! People will check them when they press their test buttons twice a year.

Oh of course they will - silly me!

I think that unless you have mission-critical kit, such as a server farm for a merchant bank, and can afford 'proper' SPD protection, then you are tiddling into the wind when it comes to domestic, especially when the things are constructed with dime store jelly bean priced components marked up 100s of percent. Still, it ticks another regs form box, and that seems to be all they are interested in these days.

I ask you - how many instances have there been whereby a house fire has been blamed on the electrics and the insurance company has refused to pay out on account of the cu being an old BS3036 rewirable with no RCD, no SPD and no AFDD present?

Personally, I've never heard of such an instance, and I don't believe there will ever be one. If the insurers went down that route, then no one other than mortgage holders would ever bother with house insurance again.

whjohnson said:

no one other than mortgage holders would ever bother with house insurance

Quite a few folk do not bother with insurance  as it is article in actuarial post suggests ~ 1/4 UK homes no content insurance and more like half for tenants though it is not clear from the articles I suspect the un-insured are those at the poorer end of the market, so les likely to have the all new fuseboard anyway.
Mike

Mike, I think that you have taken whj slightly out of context. I assume that he means that mortgage holders have no option but to have insurance.

In any event, quite a lot of people own nothing of any real value save perhaps for a phone and a telly.

whjohnson said:

If the insurers went down that route, then no one other than mortgage holders would ever bother with house insurance again.

Not sure that I agree. Insurance companies can and do impose conditions such as the installation of fire alarms and burglar alarms. They can get quite picky with high net worth properties and I suspect that some may insist on periodic inspections or failing that, load up the premium.

whjohnson said:

I ask you - how many instances have there been whereby a house fire has been blamed on the electrics and the insurance company has refused to pay out on account of the cu being an old BS3036 rewirable with no RCD, no SPD and no AFDD present?

Personally, I've never heard of such an instance, and I don't believe there will ever be one.

RCD and SPD do not protect against electrical fires. AFDD are very recent technology so insurance companies still assume they are not fitted as standard.

I have some semi-reliable information that insurance companies can refuse to pay out if the fire started in the consumer unit and it had a wood / bakelite / plastic case. If the fire started in the wiring then insurance companies will not differentiate between protection by a rewirable fuse / MCB / RCBO providing it had the correct rating for the wiring.

Insurance companies can refuse to pay out for a fire caused by a faulty plugged in electrical appliance if the latest greatest consumer unit was installed by an unqualified person, or there was no Part P notification, even if it was technically compliant with wiring regulations, and the consumer unit was in no way responsible for the fire and could not have prevented it. They probably will pay out if a consumer unit with rewirable fuses was installed back in the 1960s by some unknown and long deceased person with unknown credentials.

Are homeowners legally allowed to install their own SPD in a consumer unit without Part P notification?

I would be most interested to see your sources for the claims you make. I cannot believe that an insurance company would refuse to pay out under such circumstances. As for Part P, only lip service is paid to it these days. Fitting a SPD inside a cu would be the same as replacing a faulty mcb in my view, so no notification required.