Should I have a storm lightning conductor fitted?

[readiescards]

My house is a house in the middle of a field, the nearest tall building is >500m away, the nearest tall tree is >100m away

 

Should I fit a lightning conductor and if so where/how

 

Thanks

[Triassic]

I know nothing about lightning protection, but I did find these two document which might help you answer the question. The first document makes reference to a European Standard lightning risk assessment (the second link below).

 

https://www.dehn.co.uk/en-gb/lightning-protection-guide

 

http://electrical-engineering-portal.com/download-center/electrical-software/lightning-protection-risk-assessment-calculator

[Onoff]

This is a whole different fork of "electrics" and outside the scope of 7671 tbh. Makes interesting reading here:

 

http://www.bbc.co.uk/news/blogs-magazine-monitor-28403025

 

&

 

https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://www-public.tnb.com/eel/docs/furse/BS_EN_IEC_62305_standard_series.pdf&ved=0ahUKEwjPv5zQzpbSAhXLA8AKHUT4DfYQFghhMAg&usg=AFQjCNHH7jKD1pk1Dj__JJGUwd3QiZHSKA

 

My thoughts are I'd seriously consider it  (and surge protection) if I'd just built an isolated, bespoke house. That's a lot of hard work and money to replace. Off the top of my head where is "the path to earth" on some of these fancy roof flashings? Take a leaf out the churches or listed  building's book maybe. 

[Onoff]

A bit of an aside but related: The closest I feel I've ever come to "buying the farm"  is a few years back working on my own in a terraced house with a TN-S earth system. I was tidying up a ring circuit, replacing faceplates, changing to 2G ones etc. I'd pulled the fuse carrier, switched off the DP switch at the cu and checked for dead. Kneeling in front of an upstairs socket I had the two legs of the ring sticking out and the faceplate off. There was the biggest electrical storm ever going on overhead. The property btw was on a hill. All of a sudden there was an enormous clap of thunder that shook the house and windows and I mean really moved things. Openly admit I was very, very on edge.

 

Now for this I've come in for some ridicule in the past but I know what I saw. A bright blue spark came out of the socket I was working on and extended into the room by about a foot. I'd just stopped touching the legs and was rummaging in my tool bag.

 

I can only assume whatever came in on the earth?

 

(Let the pisstaking begin!)

[ProDave]

I spent about half an hour on my boat in a thunder storm. I was never sure what I should do, but in a plastic boat, floating on the sea, with a big metal pole sticking up in the middle I decided it would be a good idea not to touch that or the stainless steel stays that support it.
 

[Jeremy Harris]

1 hour ago, Onoff said:

A bit of an aside but related: The closest I feel I've ever come to "buying the farm"  is a few years back working on my own in a terraced house with a TN-S earth system. I was tidying up a ring circuit, replacing faceplates, changing to 2G ones etc. I'd pulled the fuse carrier, switched off the DP switch at the cu and checked for dead. Kneeling in front of an upstairs socket I had the two legs of the ring sticking out and the faceplate off. There was the biggest electrical storm ever going on overhead. The property btw was on a hill. All of a sudden there was an enormous clap of thunder that shook the house and windows and I mean really moved things. Openly admit I was very, very on edge.

 

Now for this I've come in for some ridicule in the past but I know what I saw. A bright blue spark came out of the socket I was working on and extended into the room by about a foot. I'd just stopped touching the legs and was rummaging in my tool bag.

 

I can only assume whatever came in on the earth?

 

(Let the pisstaking begin!)

 

Lets have fun with some numbers and see what might come in on the earth:

 

Assume:

- Ze at the house was 0.35 ohms

- The incoming cables were overhead for some of the route between the house and the nearest earth point

- The lightning strike was midway along the run between the nearest earth and the house

- The effective impedance to earth at the lightning strike point was half Ze, so 0.175 ohms

- The lightning instantaneous discharge current peak was around 30 kA (seems to be the average figure used)

- There are no surge arrestors on the cable

 

Ignoring local induction effects (which may well be pretty significant) and ignoring reactive effects too, the peak voltage on the incoming earth to the house could be over 5 kV.

 

The above is very simplistic, and I strongly suspect that the chances are that induction from a nearby strike is more probable, but if there were a few thousand amps being conducted through the ground, or another conductor, close to an incoming cable then I reckon you could still get pretty big induced spikes on the imported earth.   Not something I've ever looked at, or thought about, before, so all the usual health warnings that I could be completely wrong apply. 

 

Edited February 17, 2017 by JSHarris

[Onoff]

Try 0.8 for TN-S?

[Jeremy Harris]

12 minutes ago, Onoff said:

Try 0.8 for TN-S?

 

 

Good point, should have used max Ze for TN-S rather than max for TN-C-S.  With the same assumption, that the strike was mid-way along the cable, so Ze at the strike point was 0.4 ohms shoves the peak V on the earth in the house up to around 12 kV.

 

TBH, I'm just a bit surprised at how high these voltages could be.  Maybe explains why you saw big sparks coming out of disconnected cables, though.

Edited February 17, 2017 by JSHarris

[joe90]

So, we now know lightning is lots of volts, what can we do to protect ourselves properly ( I have had two houses I own hit by lightning in the past).

[vivienz]

Joking aside, our new place will have a flat roof and I plan to have all the solar arrays on top of the roof, so they will be the highest points around for some distance, I think.  Somewhere else for the lightning to go makes a great deal of sense to me.

[Ferdinand]

Apropos of a previous thread I cannot locate, Curry's replaced my suspected killed-by-a-power-cut 6 month old microwave without turning a hair.

 

All I did was turn up at the shop with a copy of the receipt and the corpse of the microwave, and they gave me a new one on the spot.

 

Technical explanation was limited to "it died".

 

Impressed.

Ferdinand

 

Edited February 17, 2017 by Ferdinand

[Jeremy Harris]

I think the problem is, how far do you go?  When we lived in Scotland a big, Victorian, Gothic revival, three storey house got hit on one of the two front turrets.  That had what looked like decent lightning conductors, with big copper straps running down the walls either side.  The side that was hit still had a gash down the wall, where the stone had literally exploded, right behind where the copper strap had been (that got vaporised) .  Admittedly that house was fairly high up, and someone must have realised there was a risk of getting a strike to have fitted the lightning conductors, but the structural damage was still so bad that they had to demolish around a quarter of the house and rebuild it.  I wondered at the time if they'd have been better off not having the lightning conductors at all.

 

As our new house is right at the bottom of a steep valley, it's not something I'm going to worry about, but I think that if your house is at risk then you either need to get fully onboard with a protection system that will work without causing extensive damage, or just not bother.  A half-way house scheme might well increase, rather than decrease, the overall risk, I think.

Edited February 17, 2017 by JSHarris
typo, "out" when I meant "our"

[Ferdinand]

Naive question.

 

Is it functionally useful to provide a diversion by either trees close by or a mast of some sort (we used to have our satellite dish on a 6m metal mast near the house)?

 

I expect the answer to be ...  it might help, but only randomly and sometimes.

 

F

[Jeremy Harris]

Just now, Ferdinand said:

Naive question.

 

Is it functionally useful to provide a diversion by either trees close by or a mast of some sort (we used to have our satellite dish on a 6m metal mast near the house)?

 

I expect the answer to be ...  it might help, but only randomly and sometimes.

 

F

 

Could make things worse, as it seems a fair bit of lightning-related damage is from induced current effects rather than a direct strike. 

 

Indirect effects of lightning are one reason cows die when a tree in a field gets struck - the lightning current flows down the tree and out along the ground (as the ground is far from being a perfect conductor).  Cows may well be better conductors than the ground they are standing on, so the current runs up one set of legs, down the other, stopping their heart in the process (doesn't take much, 0.1 to 0.2 A will kill a human, not sure about cows, and a lightning discharge is typically around 30,000 A)

[SteamyTea]

Horses have less tolerence to electric shock than people I believe. Was why those racehorses died when there was a faulty buried cable in a paddock. Think it was at Newbury.

No idea what cattle can put up with, but Eddison electrocuted an elephant and the video is online.

[reddal]

When we were building our house we got a quote for installing structural lightnight protection (conductors etc) from these people :  http://www.etechservices.co.uk/

 

It was going to be expensive (£4k if I remember) - and they made it clear that normally they don't install this kind of system in a domestic property unless there was a high risk because of its location. I didn't have a high risk so I didn't bother with it. Hopefully won't regret that...

 

I did think about doing something DIY instead - ie getting a massive copper wire or strip - attaching it to a rod on the roof - running it down the side of the house and burying it with a really good earth connection. Then I realised I didn't have a clue what I was talking about and might just make it more dangerous so didn't bother with this either :). Would this have helped?

 

I did get a surge protection system installed on the incoming AC - which might help.

 

- reddal

Edited February 17, 2017 by reddal

[Onoff]

I wonder if a traditional build with masses of copper plumbing in the loft and an incoming steel main is a double edged sword in the event of a lightning strike. You could argue it could help earth some of the "strike" but at the same time could it encourage the strike?

[Jeremy Harris]

45 minutes ago, Onoff said:

I wonder if a traditional build with masses of copper plumbing in the loft and an incoming steel main is a double edged sword in the event of a lightning strike. You could argue it could help earth some of the "strike" but at the same time could it encourage the strike?

 

 

This is the sort of thing that bothers me a bit about fitting a lightning protection scheme that can't cope with the very high peak discharge current - would it actually increase the risk when compared to having no big conductors up in the air?

 

 

 

[Nickfromwales]

Plant / grow a bloody big tree a short distance from the house?

[reddal]

1 hour ago, JSHarris said:

 

 

This is the sort of thing that bothers me a bit about fitting a lightning protection scheme that can't cope with the very high peak discharge current - would it actually increase the risk when compared to having no big conductors up in the air?

 

 

Yes - this is what put me off attempting some kind of DIY solution - ie  :

 

1. I've no idea what spec the conductor / cable / strip needs to be - I remember looking at something like this https://www.electriccable.co.uk/earth_cable_150008.html (120mm2 earth cable) and thinking it might work.

 

2. How do you attach the conductor to the rod on the roof - without this being the weak point? I'm sure with the right clamps or whatever it can work - but I wouldn't have been confident of getting it right.

 

3. How do you earth the conductor to the extent that a skyfull of electricity can flow through without getting jumpy. I guess it needs more than a standard earth rod?

 

Just out of curiosity - I'd be interested to hear from more knowledgable people whether you think my DIY lightning protection would have likely actually worked - or made things worse.

 

- reddal

[Onoff]

Ah yes the sacrificial tree.....lightning hits that, tree explodes and destroys house in a deluge of charred timber shrapnel and molten tree sap!

[Steptoe]

Lightning conductors,

There is a reason these guys pay insurance premiums in 5 and 6 figure sums,

Not a diy job, 

I done some subby labouring for some guys doing a hospital once, everything has specific distances from everything else. 

Tapes need to be certain distance apart, and from other stuff, ground mats have to be in certain places according to the services.

I personally wouldn't even consider touching it myself.

 

 

ps, TN-S on an overhead,? Is that a peculiar English thing,? 

[Onoff]

My firm was once asked to fix some protection tape to a parapet wall for a main contractor as we were there anyway fitting safety harness eyebolts and abseiling points hence had the drills etc.

 

We did it then and came in one morning to find the lot had been nicked. All that was left was an inch square where the fixings were.

[puntloos]

Coming to the same question - does anyone know some 'rules of thumb' around what constitutes good cover for your house? My house is arguably sliiightly higher than the closest other houses, but there's a 4 storey flat about 100m away with a big honking tv antenna on top. Am I good? 

[markc]

Lightning protection is a funny area, if you don’t have a conductor then you may get hit and it may do some real damage, But! If you fit lightning conductors you Will get hit often so it needs to be done right. No “protection” conductor is better than a poorly done arrangement.