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What's the best form of surge protection

Discussion in 'Electrics UK' started by wonderwire, 29 Oct 2016.

  1. wonderwire

    wonderwire

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    I am going to purchase some high end AV equipment and would like to protect it against unexpected surges (e.g. lightning).

    What's the best way to do this? I know I could buy something like a belkin surge protector to plug into the wall, which covers 650 joules (http://www.belkin.com/uk/BSV603-2M -Belkin/p/P-BSV603-2M ) but was wondering if there's a better way to protect the whole property at, say the consumer unit? This would be helpful as I could continue to use my existing extension leads, adapters, etc.

    I've seen there are some "surge protection kits" from Hager (http://www.hager.co.uk/news-exhibit...ive/2012/surge-protection-kit-guide/13389.htm) but it's not clear if these protect all circuits from the unit or just one.

    If I want maximum protection at the consumer unit, what do I need to ask an electrician to install?
     
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  3. JohnW2

    JohnW2

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    I think the general consensus is that equipment damage due to 'surges' is essentially a myth, and that the consumer devices to protect against it are just a waste of money, consumers being exploited by the manufacturers of such devices.

    In the very unlikely event of your house's electrical wiring, or the wiring feeding your house, was actually 'struck by lightning' you would probably have a lot more than your AV equipment to worry about!

    Kind Regards, John
     
  4. flameport

    flameport

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  5. JohnW2

    JohnW2

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  6. Adam_151

    Adam_151

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    Its got some outputs to drive indicator lamps / relays etc.

    TVSS devices arn't wired 'in line' in the way a surge protetced extension lead is. They are just wired across the supply to clamp down any over-voltages
     
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  7. JohnW2

    JohnW2

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    Ah, I see. Given the pretty low impedance of the 'source loop', I imagine that it must sometimes have to carry some very high currents (from L to N) in order to do that 'clamping down'??

    Kind Regards, John
     
  8. Adam_151

    Adam_151

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    Yes, but these are transiants, so we are only talking for very short durations. If overvolatage is sustained (perhaps some network fault) then the units internal protection will operate.

    Quite often you'll see them fed from a distribution board by the use of a 63A breaker, the manufacturers will tell you thats wrong as the breaker could trip due to the currents involved. I cant remember all the details, but for one particular model intended for use on type B final DB. The manufacturer recommended that as long as the upstream protection was not greater than 160A. then the correct installation was to simply connect the TVSS in with the feed into the main switch
     
  9. SimonH2

    SimonH2

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    Don't forget that you need to also route your phone line to the same place, and use a surge protector on it connected (with a short, thick wire) to the same earth.
    I've seen quite a bit of kit killed by surges through the phone lines in rural areas with overhead lines.
     
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  11. JohnW2

    JohnW2

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    Fair enough. It doesn't take much arithmetic to work out that the currents could be very high - but, as you say, usually only for a small number of ms.

    I don't understand the terminology enough to make much sense of the 'transient specification' of the one flameport linked to. It gives the "Nominal discharge current 8/20 μs" as 20kA, the " Impulse discharge current 10/350 μs Iimp (to earth)" as 6.25kA and "Total discharge current 10/350 µs Itotal (total to earth)" as 12.5kA, but none of that makes me much the wiser! On the face of it, I would have thought that 20kA's worth of current with a fairly modest overvoltage for 20 µs would represent a very substantial amount of energy.

    That makes sense. For what it's worth, the one to which flameport linked specifies a "Max backup fuse rating" of 125A.

    Kind Regards, John
     
    Last edited: 29 Oct 2016
  12. JohnW2

    JohnW2

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    How often can you be sure that that is the cause?

    For what it's worth .... I live in a very rural area, with both telephone and power supplies overhead for miles around. They certainly get affected by nearby lightning - the telephones often 'ping' and RCDs sometimes operate when there is a flash of lightening but, in ~30 years here, I've never had any reason to believe that any equipment, of any sort, has ever been damaged by such events.

    Kind Regards, John
     
  13. ericmark

    ericmark

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    Clearly you can get lighting taking out equipment, one could turn the supply to DC and charge batteries and then turn it back to AC which would likely remove all but a direct strike, using a capacitor instead of a battery that is what a switch mode power supply is. So since the invention of the switched mode power supply the amount of damage due to spikes is less than the damage due to capacitors failing so in real terms it is not worth protecting against.

    Near every bit of electronic equipment is supplied by switch mode power supplies today.

    I went to an interesting lecture about lighting strikes, you need a conductor in excess of 50 mm² to sink to ground the energy from a lighting strike, it seems the strike from top of cloud is 10 times power of that from bottom of cloud and as the wind blows the cloud it distorts so either at front or rear of cloud you can get these massive strikes. Most the damage is due to boiling the water in brick, stone, or wood so fitting a lighting conductor even if the strike takes it out will likely save the building. However the problem is lighting is attracted by the earth potential so lighting conductors actual attract lighting. However it is not unknown for the lighting to miss what attracted it and hit something near to it.

    So the only real way is to disconnect items when there is a storm near. However when there is a storm near you can get a nasty belt from the item your disconnecting. So since we don't get that many electrical storms in the UK the best idea is not to have any items on the outside of the house earthed so it does not attract lighting.

    With TV for example we have a braid breaker between aerial and first item likely the mast head amplifier or TV so aerial is not earthed. Or use indoor aerials. So yes we do take some steps.

    Some times the old wives tales get us to do the reverse to what we should do, I had been told to earth my aerial in a storm, that it seems was the reverse to what I should do, I should disconnect the aerial but not earth it.

    So simple answer is disconnect aerials when not in use, and select equipment with switch mode power supplies, and finally insure the equipment. Today satellite dishes do not need to be on a chimney so putting them as low as possible the chances of a lighting strike are very low. Since freeview is a pain where they move programs around every week or two there is little gain from using it, one or two local stations may be freeview only, but 99% are on satellite, so hardly worth the risk.

    As to telephone lines again with fibre there is no copper to get the strikes into the home, some does have fibre only to local box, but then the strike would need to be very local.

    As to overhead power lines, except for areas of outstanding natural beauty the whole national grid is aerial, but spark gaps and transformers mean again very little gets into the home. So really the only way to protect from loss is to insure, and if you look at the premiums you will realise the risk is very low.
     
  14. JohnW2

    JohnW2

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    We're not really talking about 'lightning strikes' since, as I said, if that happens one will probably have a lot more to worry about than ones AV, TV or telephone equipment!

    Rather, I think we are talking about transients induced into cables (particularly overhead telephone or power ones) due to 'nearby' lightning. I'm sure that's what makes my telephones 'ping' and RCDs sometime to operate when there is lightning 'around'.

    Kind Regards, John
     
  15. SimonH2

    SimonH2

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    In most cases it's really obvious - in some cases just by visual inspection ! Though I suppose you can argue that it makes little difference whether it's the phone line changing voltage relative to the mains, or vice versa.
    In one case, it was clear that the phone line was part of the circuit by the physical damage to the modem in the laptop and where it had arced over to the main board.
    More typically, it's equipment that is connected to both mains and phone (computer modems, fax machines, answering machines, etc) line is blown - but nothing connected to just mains or just phone line isn't. Some senior managers got through quite a few fax machines !
    The "attack" mode is a strike in the vicinity of either phone lines or mains that creates a common mode voltage on the line. The phone lines are more vulnerable - the mains has both a much lower impedance, and also surge protection in various places, not to mention the step down transformers between large parts of the network and the end user, and then the equipment itself is designed to accept at least 340V during normal operations. If something doesn't have a complete circuit then it tends to survive (unless it's bad enough that parasitic/capacitive routes can pass enough current) - eg a basic phone survives because the whole thing rides up with the incoming voltage but there's no path for any current.
    Provide a circuit (eg because it's plugged into the mains for power) and then you are reliant on the strength of isolation - which usually isn't up to handling lightning level events.

    I've also first hand experience with serial links and earth potential differences. Where I used to work, I think it's something like 20 years ago now, the report came back along the lines of "it went really dark, there was a h**l of a bang, now there's a burning smell from the computer room". At the time, their main computer system was a small Unix box with 64 (4off 16 port units) serial ports connected to terminals and printers around the building. 3 of the 4 units were "dead" - one with melted case. There was a direct correlation between location and damage incurred for the equipment on the other end of the links.
    Within the office, many devices were blown - but the Wyse60 terminals were mostly repairable by replacing the serial driver chips (I vaguely remember them being 1488 and 1489 devices) which conveniently acted as a sacrificial fuse. By the time we got to the other building, they were toast as enough energy got through the 1488 & 1489 chips to kill other stuff. The "other building" was literally a few feet from the main building, and from the same on-site substation. I concluded that there had been a ground strike near to the building, causing massive voltage gradients in the earth, and with the electrical earth in each building linked to real earth by all the steelwork in the ground and with electrical gear bolted to it.
    Of course, in this case it is possible that induced current in the conductors was a factor ...

    It's a specialised field and I only know enough to know how much there is to know. But general advice is to create a protected zone with nothing conductive going through the boundary without having "proper" protection. That ideally means routing all circuits via a small physical location so you don't have long cables between them. If the phones come in at the back of the house, and the mains at the front, then the temptation is to put a surge protector where the phone line comes in, and run an earth lead to the MET - this is bad practice as even a thick earth wire has considerable impedance when you throw a spike the rise time of a lightning strike at it. Better to run the phone line to near the MET so all the surge protectors are very close together - the earthing of the MET may be "weak", but there aren't large differential voltages between different circuits/components.
    By way of illustration, back when I started as an apprentice, we had a short session on noise and filtering - different but with some common issues/fixes. They'd setup a demo with a small DC motor fed through a very expensive* filter earthed to the alli panel with about a foot of very stout earth braiding. The filter was ineffective as the earth braid was too high an impedance to the noise - as an amplifier attached to the DC supply demonstrated. To show it was this, the instructor just pushed on the filter and flexed the J mounts* till the filter was directly earthed - and the noise stopped.
    * This was an establishment making "bespoke vessels" for her Maj
     
  16. SimonH2

    SimonH2

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    I had to check, your profile saws you're in Flintshire - and so I assume you're stuck with the same systems as the rest of us. Unless you are in one of the areas supplied by some altnet or one of the couple of villages where BT ran an "all fibre" experiment, you'll still have copper wire which even if you are on FTTC has a DC circuit back to the BT exchange.
    It's a complete lie when all these providers sell "fibre broadband" because it's not fibre, it's still copper. All they've done is move the DSLAM from the BT exchange to the a green box nearer to you - which reduces attenuation at higher frequencies and allows the higher bit rates.
     
  17. ericmark

    ericmark

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    Interesting what SimonH2 says, I noted that BT master sockets have spark gaps, and other items to protect from non direct lighting voltages, however in my house there is no earth run to the master socket, so the protection devices will do very little.

    However with my mothers house the GPO have fitted a steel earth rod and a bare copper wire from it to the first telephone box. As to if still used I don't know?

    I know back in the 1950's when the phone was fitted there was a shortage of lines, so my dad was put on a party line, which did not really work as whole idea of phone was he was on emergency stand-by from work, and if the other party was on the phone, then the emergency phone call could not get through. So we were not on a party line for long.

    I am not sure if the earth stake was to do with the party line or to stop damage due to lighting strikes? [​IMG] the SP1 device was the spark gap, R1 and C1 were to make the bell ring, but there seems to be no earth connection.

    The broad band filter [​IMG] seems to isolate the phone, but not the modem, ups sorry should not be called a modem with broadband as it only swaps the voltage from 50 to 5 it does not modulate or demodulate the signal.

    So what we would need is a wiring diagram of the voltage dropper, does the device which will often have other functions like being a switch isolate? Most are fed with 2.5 amp fig of 8 sockets so no earth, so even if they do isolate there is nothing to ground and spikes before it goes any further.

    We were as radio hams shown how to ground using a series of large resistors and fit spark gaps so that after the storm has passed one does not get a nasty belt when one comes to re-connect the aerial. Idea was not to ground the aerial, but provide a leakage path so any voltage differential is not maintained.

    Today I don't transmit from home, and I do not use Freeview so only the telephone can bring in voltage surges. It does seem some master sockets do have an earth [​IMG] but not all, so I suppose it depends on what Open Reach have fitted and what router is used as to what nasties can get into the house. Since we simply don't know, only way is to insure against ones loss should equipment be damaged.
     
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