Sparkies - SPD

[Dibs-h]

At some point the electrics will get upgraded in the house - connecting the shed and new garage & possible upgrade to 3 phase will no doubt end up as a rewire. Highly likely given the consumer unit has the fuse wire and no MCB\RCB's.

Is it worth fitting Surge Protection Device - such as the following ones,

http://www.proteusswitchgear.co.uk/prod ... oduct=4239
http://www.hager.co.uk/energy-distribut ... s/8028.htm

Or any other that should be considered. It may be that, as it's very likely to be a 3Ph supply coming into the house, we'll end up having a commercial type metal DIN panel.

Thanks

Dibs

 

[davebray]

Hi Dibs,
There’s no easy answer to this because it depends on many factors.

Do you think that there a heavy current switching transients in your local area? – i.e. nearby industrial plants turning lots of big motors on and off at all times during the day.
Are there nearby lightning ground strikes? The chances of a lightning strike are higher on hills than in valleys for instance.
Will the 3 phase system be a TNC or TNS or a TT type electrical supply? Ask your electricity supplier or a local sparky.
What do you want to protect from the effects of surge currents and over-voltages?
Do you want to protect against lightning surge currents and switching surge currents or just switching surge currents? If the latter then a Type 2 SPD will do otherwise you will need a combined SPD covering Type 1 and Type 2.

Only a Type 1 SPD is designed to handle direct strike lightning impulse surge currents and you’ll need to fit external back-up fuses (125A or greater) with this type as well.
You can get Type 2 SPDs with built in back-up fuses.
You can get a combined Type 1 and Type 2 SPD but you’ll still need to fit external back-up fuses with this device.

For interest-
A ‘standard test’ lightning strike impulse current is in the order of 100,000 amps (peak) - this is also referred to as the 10/350 characteristic (the 10/350 bit refers to the rise and decay times (in microseconds) of the current waveform shape).
A ‘standard test’ surge current is in the order of 5,000 amps (peak) – and this is the 8/20 characteristic.

You’ll need to consider if the benefits you get is greater than the cost of your SPD installation. In essence you are buying some insurance against the destructive effects of surge currents on your kit (they will not protect the structure of your premises but they will significantly reduce, if not eliminate, the fire risk caused by exploding bits of kit and cable.

I work for a big utility company and we specify SPD products made by Dehn. Their UK office is in Meltham, Holmfirth (your neck of the woods) you may want to try them. I don’t know if they will sell one offs but they are a decent bunch and they really know their stuff. I don’t know how much they cost – I only insist our sparkies fit them on our sites.

All in all if you can live with the idea that your cast iron machinery only needs to be protected from switching surge currents then go for a Type 2 SPD installation. This will also provide an excellent amount of protection against surge currents induced by distant (say at least 500 metres away from your table saw) lightning ground strikes.

Hope this helps
Dave

 

[Dibs-h]

Hi Dave

I really appreciate the full reply.

Lightening Strikes - it's an old Edwardian semi. There is a spiked ball on a rod, on the roof and a metal strip running down to earth. So hopefully that should deal with any strikes. But that's not to say the induced current, etc. wouldn't be an issue. Or it could hit the rod and go sideways.

3phase - will ask, as I don't know what type the supply is or will be, to be honest.

My main requirement would be to minimise the fire risk of kit and cable exploding in the house mainly as stuff is plugged in and either running or on standby. Although I might think about it for the shed\garage if the cost isn't eye watering.

For the house - having a lightening rod\conductor outside, should one treat the risk of a strike to the house as negligible and therefore just concern myself with a Type 2 SPD?

Cheers

Dibs

edit: Believe the existing supply is TNS, as the earth is separate and appears to be the outer sheath of the fat cable that comes in. New supply would be a TNCS.

 

[RogerS]

Question is , dibs.

Why?

I don't know of any houses that are fitted with SPDs. I know a few folks have wee ones inside 13A socket strips but on the incomer?

Many many years ago we must have had some sort of surge down the telephone cable as the modem on the motherboard got fried but TBH I never even thought about an SPD for the mains. I did stick one on our incoming phone line but more in hope than expectation.

 

[Dibs-h]

Question is , dibs.

Why?

I don't know of any houses that are fitted with SPDs. I know a few folks have wee ones inside 13A socket strips but on the incomer?

Many many years ago we must have had some sort of surge down the telephone cable as the modem on the motherboard got fried but TBH I never even thought about an SPD for the mains. I did stick one on our incoming phone line but more in hope than expectation.

Hi Rog

The latest edition of the Regs recommends them. As we will be having a complete rewire - no RCD's, MCB's, just plain wire fuses - it would be a marginal cost (I hope) to fit one and have the peace of mind knowing that expensive kit is protected. I've had surges ruin HD and PC's in the past.

When you look at the cost of a 4-6 way extension with a surge protector and multiply that by 4 or 5 - it may well be cheaper to fit one at the supply\CU, knowing that all circuits are protected.

Dibs

 

[davebray]

The provision of lightning and surge protection is becoming more prevalent and arises from the European IEC regulations 61643 and 62305 ergo our Electrical Regs now recommend SPDs etc. but this is not yet mandatory (I think) in the UK, but may well be eventually!

In Germany and Austria they are mandatory for offices, factories and the like but not for domestic premises; however in Austria they are considering passing a law making them mandatory for ‘houses of multiple occupation’ i.e. apartment buildings etc.
The Irish Electrical Standards Committee (Dublin) is also actively looking at implementing SPD devices in both their workplace and domestic premises, whether anything comes of this is anybody’s guess.

Re 3 phase TNC-S system – a SPD installation is slightly more expensive because you need 4 off SPD modules (one for each of the L1, L2, L3 and N conductors) instead of 3 off modules for the TNC system.
Dehn supply a pre-wired modular Type 2 SPD kit that should do the job for you or you can put one together from the individual modules and accessories. Their UK website is dehn.co.uk. I believe they’re keen to break into the UK domestic market and they positively wet themselves with the thought of the Irish Electrical Standards people.
Dibs, it may be that you become the UK domestic leader .

Re the lighting conductor on your roof – if it gets hit most of the lightning current will travel down the side of your Edwardian house (I’ve always liked this style of house - I’m envious) via the metal strap conductor into the ground. This means it will essentially be a nearby lightning strike so you will get larger surge currents external to your house and its cabling. I’ve had a look at the Dehn specs for you and their pre-wired modular Type 2 SPD kit should be able to give you adequate surge current protection.
If you have some trees taller than house growing nearby (but not close enough to undermine your foundations) then these will help to provide a measure of protection against direct lightning to your house.

At this point I have to say that I am not an expert in this field I have to rely on Dehn for their expertise and if you are keen to progress this then I suggest you contact them directly. This is NOT a brush off, my particular engineering discipline lies in the application of programmable electronic systems and digital communication networks for the automatic control of industrial plant and processes. I specify the IT communications range of Dehn products to protect our digital communication networks on site and have no real expertise in 3 phase electrical power systems.

Cheers
Dave

 

[RogerS]

Dibs...you've clearly looked at the Regs but I thought that 17th edition mandated RCD protection in the consumer unit?

 

[Dibs-h]

Dave - many thanks again. Don't worry - I'm not taking it as a brush off. In fact, extremely grateful for the very informative & useful replies. We do have nearby mature trees (within 10ft) of the house that in almost all cases are larger than the house, so hopefully shield it. I have a question - we have two rather large dormers on the back (10ftx10ft roofs each) with lead roofs. Do these need connecting to the lightening conductor? Never thought about it before.

Rog - the existing system is what came with the house & assuming nothing changes, then it can stay as it is. All the cables are black\red and modern. But obviously with the shed and new garage requiring power, it will mean the house has to get redone, i.e. MCB's, RCD's and the rest of the caboodle.

Dibs

 

[RogerS]

Ah I misread your post which seemed to suggest the opposite!

 

[davebray]

Hi Dibs,
Hell and death - you've got two big lead roofed dormers on the back of your house - now I'm really envious.

I assume these dormers project out from the roofline, have inverted V roofs and the faces of the dormers are setback about 1 metre from the gutters.
There is a technique called the 'rolling sphere' method where one can determine where lightning conductors should be placed to best effect. This technique needs a reasonably accurate scaled drawing of a building to be used properly and this I don't have for your house.

I tried a guesstimated sketch but have to say I wouldn't rely on this at all. What I did think was interesting was the lead roofs (a nice big conducting area) themselves and you considering connecting these to your existing lightning conductor.
You may want to consider putting a small lightning conductor on the apex of each dormer and bonding all 3 lightning conductors together using 50mm2 earth straps and then putting 50mm2 earth straps from the 2 new lightning conductors down the side of your house and into the ground similar to your existing down conductor.
But you are now looking at extra cost, effort and judging by the likely size of your Edwardian house and its two big dormers a big chunk of scaffolding costs as well.
In the event of a direct strike on any one of the lightning conductors then the lightning impulse current will be shared between the 3 off down conductors and dissipate the strike energy much better.

The German approach is to turn their roof areas into a forest of small lightning conductors all bonded together and then to install insulated strap conductors down the building sides and into the ground. They aim to turn the building into something like a Faraday Cage i.e. the strike energy is guided away from the roof and building sides down into the ground. The Dehn factory and offices have been built from the foundations up like Faraday cages, their roofs look like beds of 600mm long nails and every cable that enter or leaves their building is protected by lightning and/or surge protection devices as needed but you would expect this from the people who make all this stuff.

As an aside - in the UK we have something like 7 'thunderstorm days' per year and in Germany they have double that because it's in the middle of a contintental mass. I've seen some statistics that imply the number of thunderstorms per year have been increasing over the last 20 years or so but whether that is a result of better reporting or something else I do not know.

What a lightning or surge protection device does is to very briefly (about 2 milliseconds) act as a direct short circuit to ground and provide a path for the lightning impulse or surge current to ground before it damages the kit on the protected circuit.
It is a specialised technology, if you are keen to protect your property then do contact Dehn. There are other manufacturers of this kit but I know the Dehn kit personally.

Cheers
Dave

 

[Dibs-h]

Dave

Really appreciate the reply. The 2 dormers are flat roofed and the roof of each is just under the ridge line. The dormer fronts stop about 1m from the gutter line. I'll take some pictures and post them up.

The roofs of these dormers are lower than the top of the lightening conductor that is fixed to the side of the shared chimney between us and next door.

Access isn't too much of an issue as there are Velux windows on the other side of the ridge, i.e. front.

Many Thanks

Dibs

 

[Digit]

If you get a direct strike on your house

nothing

will protect your home from damage.
My neighbour, two plots up had such a few years ago, he lost the roof, chimney stack, TV, Video, washing machine, fridge the lot!
When I lived in Berkshire as a teenager the overhead incomer was struck and the result was just like a firework display with meter, fuse box and the backing board on fire.

Roy.

 

[RogerS]

If you get a direct strike on your house

nothing

will protect your home from damage.
...
Roy.

Faraday cage ?

 

[Dibs-h]

Hi Dave

Here's a picture of the rear dormers,

Each dormer is about 8' wide and about 8' deep, glazed all the way round and with code 5 lead on the roof. The lead is in 3 sections with wooden rolls (handrails) dividing each roof into 3 (front to back) for the overlaps.

You can just see the lightening conductor on the side of the rear chimney stack. Will measure the size of the conductor on the side of the house and let you know. The top of each roof is actually below the bottom of the lightening conductor pole.

Dibs

 

[Digit]

Faraday cage ?

:lol:

Roy.

 

[davebray]

Hi Dibs,
I’ve now had a look at the Dehn Lightning Protection guide (a pdf copy is a free download from their website).

In my view you are looking at a stack of costs to protect your property and because it is semi-detached you will have to persuade your neighbour to protect his half as well to the same standard as yours.
Anyway here goes on what is needed as far as I can tell –
A lightning conductor on each gable end of the ridged roof and additional ones at approx 2m intervals along the ridge line. The bonding straps between these particular lightning conductors must be supported OFF the ridge tiles at 1.0m intervals.
A lightning conductor on your assumed shared chimney stack.
A lightning conductor on each of your dormer roofs.
A lightning conductor on your satellite dish and other antenna.
Every lightning conductor needs to be bonded together with strap conductors.
A down conductor on each corner of the property.
These down conductors to be bonded together below ground level (minimum 0.5m depth) all to a continuous ring conductor around the entire property (again minimum 0.5m depth and approx 1.0m away from the property walls).
The down conductors also have to be a certain separation distance away from doors and windows (to help prevent ‘flashover’ into the property).

The only saving grace is that you can use aluminium conductors (70mm2) or hot dipped galvanised steel (50mm2) which should be cheaper than copper or stainless steel). All down conductors have to be protected from corrosion to a length of about 0.3m above and below ground level)

So Dibs after all this what do we have? –
In the UK the probability of a direct lighting strike on a low rise domestic property is very low.
The cost of providing a substantial external lightning protection system for a domestic property is relatively high.
On balance I wouldn’t bother installing such a system on my house but your needs and drivers are different to mine.

However I think it would be worthwhile to install Type 2 SPDs on your 3 phase TNC-S incomer and on your single phase incomer to your house. I’ve assumed the 3 phase supply would be terminated in your workshop (assumed to be detached) and a single phase supply from this then taken into your house. These will protect against surge currents induced in the 3 phase supply by lightning ground strikes (if the supply cable is buried) and against cloud to cloud lightning (if supply cable is overhead on poles) and also power surges on the electricity network.
Similarly you can also install low cost SPDs on your telephone line and satellite dish coax cable preferably before they enter the house.
All SPDs must be installed strictly as per manufacturers recommendations.

If anybody wants to read up on Faraday Cages then Wikipedia has a reasonable description as does www.Faraday.org.

Cheers
Dave

 

[Dibs-h]

Dave

Many thanks.

As you say it's about balancing probability with cost. I will most likely bond the dormer roofs with the lightening conductor. The rest I might give a miss. Our gable end is overshadowed by lots of large trees that are taller (and in the neighbouring property) - so hopefully they'd get hit rather than us.

Our house was built in 1918 and the roof, when I redid it 5yrs ago - looked to be original. So no direct strikes in 90 odd yrs - or dealt with by the conductor.

The Type 2 SPD - yes, those I'm looking to fit as the cost is minimal amongst a full rewire. My (original) thoughts were to bring the 3ph supply into the house as the cost is far less (i.e. the DNO costs) and then run SWA of the appropriate size\s to the Garage to it's own 3ph panel and distribute it round the garage and attached shed. The meter is on the side of the house. Might have to have a think about that - as there are things such as trying to balance the loads on the phases, etc to think about.

Many thanks for the replies.

Dibs

p.s. definitely going to look into SPD's for the sat dish, but probably give the telephone one a miss as BT are disconnecting soon - we're moving onto VOIP at home.