Where to install a surge protection device - single phase domestic / light commercial supply

I have just returned from Screwfix/Electrafix to collect an order. I notice in the Electrafix side of the store that there was a poster for electrical stuff showing a BG single module SPD for £24.99. Clearly not a King's ransom.

It would seem to me to be cheap insurance? Certainly much cheaper than most of your electronic filled appliances, the PCB in your boiler and your smoke alarms.

A few years back I lost a modem along with 2 other neighbors after a thunderstorm , We have overhead phone lines. BT master socket with internal surge protection but now have SPD protection on the phone line.

A couple of months back after a storm my TV signal was poor with a lot of pixilation on some weaker stations. Looking outside up at my aerial I installed my self it was pointing uphill rather than previously level as installed. I thought that was the cause of the signal loss also it was an old analogue aerial, 50 ohm comms co-ax not 75 ohm TV stuff and the co-ax no doubt full of water. Not being as brave as I was 25 years ago I thought it was time for a new digital aerial, 75 ohm co-ax installed by a professional. Job done and the aerial fitter measured the signal at the end of the new co-ax before plugging it in to my distribution amplifier saying good signal any more and I would have to install an attenuater. After he left I could see I had an improved signal on the TVs but still some pixilation. I jumped out the amplifier connecting the aerial directly to one TV and no pixilation with more channels than I previously had. Trip to Screwfix to buy and install  a new amplifier thinking the amplifier was spiked. New box fitted TVs now operating better than ever. Opened up the old box to look inside and could see a track between on the PCB between in input socket conection and an adjacent PCB track. I have the photo and have now fitted an SPD to the aerial amplifier.

I already have a Wylex REC 4 isolator with SPD protection inserted in the meter tails. Just need to do something for the recently installed amateur radio 1/2 wave end fed outside antenna.

Happy New Year.

JP

How common is insulation breakdown in PVC?

Melted & charred PVC is common enough - just check the shower switch threads. As I recall the standard for testing AFDDs requires insulation to be charred before the the test - as clean copper to copper doesn't produce nice arcs at all - so I if it's unlikely an RCD will spot the problem it's probably similarly unlikely an AFDD will.

   - Andy.

I suspect insulation break down in well installed PVC or polyethene is almost non-existent, unless there is some other factor.

I'm thinking of things like cables exposed to bright sunshine lose their flexibility, and will perhaps crack if flexed - a problem for T and E on catenery perhaps,  but given the UK weather, only in on a timescale of the odd decade, and maybe never if on the shady side of the building.

Damage by heating for wires stuffed in beside the pipes to the radiators is something I have certainly seen more than once, but neither of these are examples of 'well installed'.  The insulation test may or may not find either of these examples - a crack in a cable or a bit of browned off plastic, may be in a pre-cursor to trouble, but does not reliably result in a low resistance between L and E.

Mike.

????????

How common is insulation breakdown in PVC? It happens with old rubber insulated cables but it's rare to find any still in use nowadays.

There is the possibility of PVC insulation burning as a result of arcing, leading to a low L-E insulation resistance, where a sufficient current flows to trip a RCD before the MCB.

RCD and SPD do not protect against electrical fires.

RCDs are pretty good at spotting insulation breakdown that can lead to fires (both with and without arcing) especially where there's an earthed part in close proximity to the basic insulation - and that's reasonably common - not just in steel conduit and metal clad accessories, but even the humble T&E cable with an uninsulated c.p.c. is pretty likely to produce a detectable earth fault if damaged to the point where fire is likely. For a long time now the regs have recognised that ≤300mA RCDs provide some useful protection (e.g. 422.3.9, 705.422.7).

.I suppose that SPDs may also provide some protection against the initial insulation breakdown that could lead to the parallel arc situation that AFDDs might be able to detect. So also providing some protection, if in a avoidance rather than detection form.

   - Andy.

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.

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?

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.

There were plenty of appliances with semiconductors in them back in the 1980s. What I would say has considerably increased are permanently or semi-permanently connected electrical products with semiconductors in them like USB power sockets, LED lighting, home automation systems, alarms and CCTV etc.

Has there been cost cutting in recent years so that modern appliances are less resistant to voltages surges than their older counterparts?

What appliances that create voltage surges have increased in number?

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.