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Topic Title: Surge protection devices.
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Created On: 19 November 2011 02:14 PM
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 19 November 2011 02:14 PM
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sparkingchip

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I have seen some technical articles on SPD's over the last few months, none has answered the basic question of when they need to be installed.

Will it be required to install SPD's for new domestic installations and will they be required for consumer unit replacements in domestic properties?

Andy
 19 November 2011 02:38 PM
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Legh

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I think there was something mentioned that where there was the possibility of lightning strikes, such as overhead power lines, which would presuppose TT installations. also switching industrial/commercial Inductive loads might cause large voltage surges.

Many DBs are now modular in design which means that they could be installed quite easily into any installation, obviously dependent up the DB.

Legh

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 19 November 2011 04:33 PM
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daveparry1

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which would presuppose TT installations
----------------------
Why's that Legh?

Dave.
 19 November 2011 04:57 PM
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Legh

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Originally posted by: daveparry1

which would presuppose TT installations

----------------------

Why's that Legh?

Dave.


Lightning strikes generally come from the sky, overhead supply cables run on poles above ground, so I've been told.

So Lightning strikes the Tx up the pole and a large voltage surge suddenly appears across the phase and neutral at the domestic DB.

I've never heard of underground lightning strikes, have you?

Legh

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 19 November 2011 05:18 PM
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daveparry1

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True Legh but I live in an area where there are lot's of overhead supplies and the majority of it is now pme so it doesn't necessarily follow that overhead supplies are going to be TT.
Also I don't think the "sarky" reply was called for, quite unlike you, have you had a bad day?

Dave.
 19 November 2011 06:06 PM
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Testit

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My impression is yes it would. Surge protection protects not just from lightening, but transient voltages, surges through cut cables etc. My understanding is that it states something about that surge protection should be installed at the origin of the installation to cover the whole premises. Got the green book but not really looked it up yet, my understanding is from feedback and conferences etc....

Having said that the ones I have seen wont go into a consumer unit, unless something new comes out, they are independant items which need to be self monitoring. Due to additional cost I think I will be stating it as an option that will need to go down as a non compliance if not taken. I will however possibly review that after spitballing through the green book some more....

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 19 November 2011 06:31 PM
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daveparry1

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Last time it was rcd's, this time surge protection devices, I wonder what they will dream up for next time!

Dave.
 19 November 2011 06:44 PM
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sparkingchip

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It is not a difficult question really is it, come next year should I be including SPD's in quotes for new domestic installations?

Why is it I think we are going to struggle to come up with a definitive answer? I am still having trouble convincing people they should include mains/ battery heat and smoke alarms in their rewiring quote, never mind SPD's. If I was planning to rewire my own house I don't think I would consider include SPD's as a matter of course, I would need convincing myself as to any benefits.

So what's it all about?

Andy
 19 November 2011 06:54 PM
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Angram

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It is Telephone lines that need SPDs more than CUs

Things like Routers and Sky Kit are the meat in the sandwich between the well earthed mains supply and the telephone network.

The Telephone network is the main threat with lightning.

SPDs at the incomer should be specified for greater surges than the SPD at an appliance. Also what goes underneath the SPD? What size surge does it need to see before it operates as compared with the withstand voltage of the appliance/asset?

We ought to be doing similar calculations to those for LV protection devices but we don't seem to have the data?
 20 November 2011 09:08 AM
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sparkingchip

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I have actually skimmed through the regs. book and have a very simple answer in mind to this question!!

Andy
 20 November 2011 11:33 AM
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gkenyon

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Originally posted by: Legh

I've never heard of underground lightning strikes, have you?
No, but look up "Rise of Earth Potential", as the grounnd can see potential gradients (and also underground cables subject to capacitive and inductive effects) from both lightning strikes, and HV faults/switching.

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 20 November 2011 04:00 PM
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Legh

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Originally posted by: gkenyon

Originally posted by: Legh

I've never heard of underground lightning strikes, have you?
No, but look up "Rise of Earth Potential", as the grounnd can see potential gradients (and also underground cables subject to capacitive and inductive effects) from both lightning strikes, and HV faults/switching.


Yes, Ok, A rise in potential across underground electrical systems is likely to cause all sorts of reactive implications.

I've actually seen lightning sprouting out of the ground like fluorescent celery when I was in Canada. A most bizarre fraction of a second !

True Legh but I live in an area where there are lot's of overhead supplies and the majority of it is now pme so it doesn't necessarily follow that overhead supplies are going to be TT. Also I don't think the "sarky" reply was called for, quite unlike you, have you had a bad day?

Dave.



Dave,
No offense mean't

Legh

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Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 20 November 2011 05:14 PM
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Jaymack

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A surge due to lightning, is also a common problem with overhead telephone line on poles for house service. I was in the house in South Africa one day, there was a flash outside and crack at the answering machine, resulting in one U/S machine. Luckily I wasn't using the phone; or it would have been a case of handstands in the shower! South Africa has one of the highest rates of lightning incidents (isokeraunic), in the world; every afternoon in the summer time, there was fascinating donner and blitzen with downpours for 2 or 3 hours, it is a good test bed for all things requiring lightning protection!

I bought a telephone surge protection device after this incident, did it work? I'll never know!.

Regards
 20 November 2011 05:54 PM
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Pacific

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Used to love sitting on the veranda watching the storms, G&T in hand, one hailstorm resulted in a total whiteout, well we didn't have a TV
 20 November 2011 09:29 PM
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eclectica

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How long before building control catch on to the fact that if an overhead supplied TT property is protected then it endangers neighbouring properties by possible injection into the earth?! (according to Dehn - at least that is what I understood them to mean ) Insurance companies will catch on too no doubt - any excuse not to pay seems to be the way these days.

Having lightning blow up 3 modems and 2 network cards at home in the last 10 years means I have a lightning protection module on phone line with a nice 10mm2 to a dedicated earth stake array. So far so good .

E.

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 20 November 2011 09:57 PM
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KFH

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From what I have read and been told: in the UK we are in a low risk area for lightning and if you do a risk assessment most premises would not need surge protection BUT if there is a lot of expensive equipment at risk it would be advisable to recomend it and let the customer choose.

I would be interested to hear if my conclusions are wrong.
 20 November 2011 10:15 PM
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sparkingchip

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At last someone thinking like me!
 20 November 2011 10:30 PM
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Legh

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I've also read that lightning strikes appear to be limited to around 25 per year for this country. So there's no need to take precautions.......

Well, I must admit I've only experienced half a dozen in the last 5 years, but then it only takes one well aimed strike and its goodnight to all your electronic kit and other things as well !

My experience of a lightning strike close by caused me to switch off and disconnect as much as I could find but it still got the telephone. The lightning must have reprogrammed the ROM chip because it now tells porkie pies on the answering facility about the time and day that people leave messages

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 20 November 2011 10:35 PM
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sparkingchip

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I had a very close call once, never to be forgotten, lightening striking within six feet of me.

I trust it was a once in a lifetime experience.

Andy

It is too late on a Sunday night to start chewing over what it is in the latest regs book. another night perhaps!
 20 November 2011 10:40 PM
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alancapon

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When deciding whether to incorporate SPD as per section 534 of the green book, you first have to read section 443. This section specifically deals with the risk assessment to determine whether SPDs are applicable to the installation.

Regards,

Alan.
IET » Wiring and the regulations » Surge protection devices.

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