Lightning Protection Device

[Crossy]

Indeed, I had to look twice as well, the 3-phase drawings are differently arranged. We can only assume that the manufacturers know what they are talking about

[David006]

It would definitely help as it appears to provide one (or two) mode(s) of surge protection from Line to Neutral (L-N), and apparently also Line to Earth (L-E) based on how the main L & N wires are shown coming-in and hooked to the main circuit box. A hookup I'm not so sure about. Normally you would like to get protection in all three modes which is Line to Neutral (L-N), Neutral to Earth (N-E), and Line to Earth (L-E). But it depends on what type of electrical supply/earthing system you have and the design of the surge protector if that would be possible and recommended/safe to do all three modes versus just two or one mode.

It does have a one time surge rating of 15KA; supposedly the maximum lightning-induced surge (nearby strike) a person can normally expect at the service entrance is 10KA, but normally the nearby lightning surge would be much less...something down around a few KA. Now, a direct lightning strike like to your electric meter pole is probably going to send more than 10KA into the main service box. The 6KA rating means it can handle such a surge up to 6KA repeatedly...but repeatedly may only be a couple times or up to around 15-20 times...it depends on how the manufacturer has tested and what rating standards he's using....for a brand name like Square D I would think (hope) it's up around 15-20 times. Where the guy said it handles "course" surges he probably means surges from nearby lightning strikes and it only protects in one mode....remember, lightning can find its way into your home via L-N, L-E, and N-E although L-N is probably the most common....plus, a person really needs surge protection at his service entrance to stop the majority of the sure....and to stop the remaining portion of the surge voltage that still gets through the whole house surge protector then other surge protectors, like surge-protected power strips, would handle the rest of the surge just before that remaining bit of surge had a chance to enter your plug-in electronic/electrical devices..

Regarding modes of protection, I have a TT earthing system and although there are surge manufacturers out there that sell whole house protectors for TT which provides surge protection in all three modes for a single phase system I also see many manufacturers and regulations/documents recommend only protection in the two modes of L-N and N-E; L-E is not recommended due to technical factors associated with the TT system and if there was a constant short or a leaking varistor between L-E it could create a shocking hazard since voltage/potential may appear on the cases of electrical items.

I would ask/recommend Crossy and/or electau take a look and comment on the item's installation hookup instructions. Both hookup methods show the Neutral service line coming in and hooking to the Earth bar and then onto the Neutral input lug on the main breaker versus coming in directly to the main breaker Neutral lug. If the house is wired for 3 wires (i.e., includes the protective earth(PE) wire) then a person would be hooking PE to the main service Neutral line as shown in the hookup instructions. If the incoming Line/Phase and Neutral lines got switched mistakenly for whatever reason or the Line/Phase wire shorting to the Neutral wire then it could place voltage on your PE devices to include the main circuit box itself? Right? What kind of earthing system would you call this? Or is this just an error in the installation instructions or something I don't understand? Based on this wikipedia link it appears it could possibly be a TN-C earthing system which is supposedly rarely used but the instructions earthing still don't look right for a TN-C system since earthing in the instructions is at the residence versus the transformer. Then again, maybe the installation instructions are assuming the house is just wired throughout with 2 wires (no protective/safety earth).

Additionally, unless the surge protector has some internal fusing, hook up method one relies totally on the main circuit breaker for over current protection. Whole house surge protectors normally recommend 15A or 50A in over current circuit breaker protection...this whole house protector would probably recommend a 15A breaker since it's only a 15KA protector. But if the main breaker used in a person's main circuit box is higher, like maybe in the 50A to 80A ballpark then if the surge protector decides to short out and if it don't have any surge protector internal fusing (it probably does) then there would be a lot of current feeding the smoke until the main breaker tripped...if it trips. But if it's like a lot of Thai main circuit boxes been feed by a 15A service with a 10A main circuit breaker then this 15KA protector would have the right sized circuit breaker protecting it. And then hook up method two shows "no" circuit breaker protection since the protector hook wires are hooked to the incoming side of the main breaker.

Something just don't seem right about how the incoming Neutral service wire is hooked up in the main circuit box but I could be wrong--won't be the first or last time...and Thailand is definitely the Land of Electrical Surprises. Cheers.

Interesting stuff......just wonder if domestic MEN systems possibly increase the risk of lightning damage since it potentially routes a strike to the network open( uninsulated neutral ) to the domestic neutral/ground and thereby maybe negating any protection device across the LN? .

.Wifey usually runs around unplugging stuff in a storm.... don't know where she learned it....weren't me?

[Pib]

Indeed, I had to look twice as well, the 3-phase drawings are differently arranged. We can only assume that the manufacturers know what they are talking about

One thing I have noticed in all my googling/research over the last few months on surge protection that there appears to be a wide variety of surge protection designs and hookup methods between surge protector manufacturers. One thing I'm still googling for is some links/quotes from national electric standards for those countries which use a TT earthing system like used in Thailand. Seems North America/UK/Europe/Australia predominately used the TN-type earthing systems. The wikipedia article says the TT earthing system is used throughout Japan...maybe I'll concentrative some googling towards surge protectors used in Japan.

I also think some of the surge protection documents which recommend on protection method over another are not solely considering design/hookup would provide the best lightning protection in multiple/different modes, but also the earth fault current safety considerations if a surge arrestor fails and then possibly affecting RCDs in the home due/placing voltage potential on the PE line. Possibly coming up with designs which are a comprise between the best lightning protection (i.e., whether 1, 2, or 3 modes) and safety.

[Pib]

As FYI, I stumbled across another surge protection document yesterday by the ABB company which answered/clarified a lot of my surge protection connection questions still outstanding in my mind. What was key for me in this document was it included both internal schematics and hookup diagrams. Where a hookup diagram may indicate the device is hooked/connected say between L-E and N-E, in fact, internally it could actually be wired between L-E, N-E, and L-N....all depends on what model of surge protector you buy.

Rather than repeating a lot of words in this thread, here's the link to my post and the document which I put in another surge suppression ThaiVisa thread a few minutes ago. Link.

Edited June 4, 2012 by Pib

[Crossy]

As I noted in the other thread, that stuff from ABB is good info.

I will be adding a third arrester to my TT installation L-N.

[westom]

... on surge protection that there appears to be a wide variety of surge protection designs and hookup methods between surge protector manufacturers.

The only solution, used where damage cannot happen, defines where hundreds of thousands of joules dissipate. For over 100 years, that was always where a surge would enter the building. Every wire in every incoming cable must be earthed to a 'single point earth ground'.

Earthing is defined by codes for human safety. And may be insufficient for surge protection. Earthing must also exceed what is defined by code. For example, surge protection means that wire must be as short as possible (ie 'less than 3 meters'). It must not have sharp bends. Not inside metallic conduit. No splices. Requirements not necessary for human safety.

If a neutral wire is earthed 10 meters away, then it is earthed for human safety. And not earthed for surge protection.

Some protection solutions have no protectors. But every solution must always have a low impedance (ie 'less than 3 meter') connection to single point ground. Ground (not a protector) defines protection. If a wire (ie Line) cannot be connected to earth directly, then a protector makes that low impedance connection. If that neutral wire is hardwire connected to some distant earth ground, then it must have a protector for the connection to single point earth ground. Yes, two earth grounds ten meters apart are electrically different. Earthing at distant locations can even make household appliance damage easier.

Two essential concepts must be addressed in every solution. All wires must connect low impedance (ie 'less than 10 meters') to earth. An earth ground that does protection must be single point. All ground wires and protectors must connect short to one earth ground.

Electrical parameters defined by those hundreds of thousands of joules means the art (and most attention) is about earthing and how it is connected. Protectors are only simple science. The art is earthing.

[Pib]

Feeding the incoming neutral via the earth bar with a local earth stake is the standard Thai implementation of TN-C-S with MEN, it is incidentally also how the NEC requires the same connection in the US.

Personally I don't like it, but since the local regulations require it, so be it.

HOWEVER.

If you currently have a TT system you should not connect like this, adding a MEN link to an area which is not TN-C-S is potentially dangerous.

Our house is currently wired TT, we have two 100kA arrestors L-E and N-E, when we have permanent power (i.e. when we move in) I will connect our MEN link and make it TN-C-S as the area has MEN implemented (this from the PEA inspector who visited yesterday).

Where you say "Thai implementation of TN-C-S with MEN" and "...the area has MEN implemented", any idea what technically makes an MEN (Multiple Earthed Neutral)? Does most of the residences/buildings at the main circuit box be hooked up under TNCS method (i.e., earth spike to earth bar with earth bar hooked to neutral bar)....or, the transformers feeding the residences have their neutral output wire feeding the residences hooked to earth...or soil conditions for earthing....or a combination of aforementioned possibilities... or ?????? I expect it's not a simple answer and may involve many things.

In my large western Bangkok moobaan (approx 750 homes) every couple of blocks the transformer feeding that area has its neutral output wire (the neutral wire leading to all the residences whether 3 phase or 1 phase) earthed by a bare ground wire leading down the pole to earth and the transformer's case is also grounded by a separate bare ground wire leading down the other pole (the transformers are fairly large and mounted on a two pole structure). Well, the ground wires are bare/uninsulated but for the last three meters or so before going into the ground they are encased is yellow PVC pipe for touch protection in case they ever would get accidentally go hot.

To the best of my knowledge since the same developer has been building/selling the great, great majority houses in my moobaan for almost the last 20 years and the dozen houses he built on my soi about 5 yeas ago was the second most recent batch he built, to the best of my knowledge they are all wired up the same way using a TT earthing settup...that is, earth bar and neutral bar are "not" linked and the earth bar hooks to the earth spike via a 10sqmm wire running straight down approx two meters to the foundation where I'm assuming the 10sqmm earth wire is hooked to an earth spike in the foundation and/or the rebar in the foundation. When looking at the some of the houses still under construction about 5 years ago all you would see is a tab sticking up through the concrete foundation and this is where the ground wire would be bonded. So, "if" repeat "if" my home is indicative of how other and earlier homes were built in my moobaan, then they are all wired-up under the TT earthing method.

As FYI, when I went to Global last weekend I was able to look at the hookup documentation for 3 or 4 different main circuit boxes made by differenet manufacturers. Each one showed the hookup method you described with the neutral and earth bars connected. I'm just wondering if Thai electric companies, like PEA and MEA, over the last decade or so have slowly upgraded/modified they earthing system hookup in different areas and regulations/directives on how new residence earthing systems should be made and this in turn has slowly turned some "areas" into MEN areas....and maybe even my moobaan is a MEN area "if" the only technical requirement to classify an area as MEN is the transformer servicing the area has its output neutral wire grounded. Then again, maybe also all/most of the residences in transformers servicing area are suppose to have the circuit box neutral and earth bars hooked together along with a earth spike to make the area MEN. And even if an area is a MEN area now, based on whatever the technical requirements are, the electric companies make no effort to notify current customers that they could easily convert the TT earthing setup to a TN-C-S arrangement by probably just connecting the neutral and earth bars which I have no plans to do. Thai's seem to give little safety regard to electrical wiring and 99.9% wouldn't have a clue about earthing systems (and I wish I understood it better) so they would probably just ignore with glazed eyes any notice from the PEA/MEA that their area is now a MEN area.

Any idea what technically makes an area MEN? Cheers.

P.S. if another similar version of this post shows up I hit the Add Reply button about 30 minutes ago on a similarly worded post but it just never appeared on ThaiVisa...went off into never-never land...hopefully this one will post....here goes.

Edited June 5, 2012 by Pib

[Crossy]

This page describes the various earthing systems http://en.wikipedia....Earthing_system

To make an area MEN it is TN-C-S with the addition of neutral grounding at regular intervals (every 3rd pole or so) then adding local ground spikes at each installation.

[Pib]

Thanks. I had looked at referenced wiki article earlier and it only said for the TN-C-S"...combined neutral-and-earth conductor to real earth at many locations.." Was wondering what the definition of "many locations" was. That is, at every transformer, every pole or maybe every third pole like you mention, maybe all the at the residences also,etc. Here in my moobaan the only poles that have grounds from the neutral wire to earth are the transformer poles.

[Crossy]

The Wiki is slightly inaccurate.

A true TN-C-S system has the neutral grounded only at the transformer. Ground the neutral at regular intervals and it becomes what we call in the UK PME (Protective Multiple Earthing), add to that additional local ground rods and we get what is known in Oz as MEN (Multiple Earthed Neutral), this is the system that is supposed to be implemented in Thailand.

Many, many locations in Thailand are still TT with no N-E link and no multiple earthing.

Now, if you are the first place to link N-E on what is actually a TT system you notice nothing untoward, everything works just fine. Until there is a neutral fault between you and the transformer, then all the neutral current from those properties downstream from you tries to flow in your MEN link, result hot wire and potentially a fire. If there are lots of N-E connections they share the current and don't get hot.

Chances are that if you are in a moo bahn that all properties will actually have rods and N-E links (MEN) or will not have N-E links (TT), if you don't have a N-E link now do not be the first to install one.

PEA / MEA really want everyone to be on a MEN system, but their upgrade / installation system is haphazard to say the least.

[Pib]

Now, if you are the first place to link N-E on what is actually a TT system you notice nothing untoward, everything works just fine. Until there is a neutral fault between you and the transformer, then all the neutral current from those properties downstream from you tries to flow in your MEN link, result hot wire and potentially a fire. If there are lots of N-E connections they share the current and don't get hot.

Yeap, I read that somewhere in my googling...and I can just image that current flow in my head with my main box smoking itself due to current draw from neighbor houses down the soi. Nope, I won't be hooking my neutral and earth bars together...especially with all the trees growing in/around the power lines in my moobaan...I can also just image a tree breaking the neutral wire and then if I was the only one in my area to have linked the neutral and earth bars my main circuit box/neutral and earth wires may begin to glow.

Edited June 5, 2012 by Pib

[westom]

"A true TN-C-S system has the neutral grounded only at the transformer."

That was originally sufficient for human safety. But also made lightning damage easier. The change to all TT and TN systems is to establish multiple earth grounds along the way.

For example, the Wikipedia article shows earthing only the secondary side of the transformer. The diagram is about human safety. If about surge protection, then it must also show the primary. A lightning strike to the higher voltage distribution wires forms a plasma connection from primary to secondary. Then long after lightning is done, the high voltage primary is still connected (by plasma) to every household appliance.

The transformer is earthed for human safety. But both primary and secondary are earth (the primary surge protection layer) so that a 'follow through' current does not exist. So that primary voltages do not blow out appliances.

First, earth ground originally only did human safety. So one ground reduced costs as noted in Wikipedia:

"TN networks save the cost of a low-impedance earth connection at the site of each consumer."

Now that transistors exist in homes, the old way of doing it is defective. A ground must earth both primary and secondary. And another ground must exist at the consumer's building.

Second, wire length is critical. For example, a 15 meter ground wire might be well less than 0.2 ohms resistance. And that same ground wire might be 120 ohms impedance to a surge. For human safety and low resistance, wire thickness is important. For surge protection and low impedance, wire length is important.

Human safety does not need an earthing wire as short as possible (ie 'less than 3 meters'). But transistor safety demands that low impedance (ie 'less than 3 meter') connection. Transistor safety why the old ways of earthing (only for human safety) have long been unacceptable.

Third, every wire that enters the building must have a low impedance connection to single point earth ground. Protection means every wire is earthed either directly or via a protection. And the connection must be as short as possible.

Codes are mostly about human safety. Transistor safety means exceeding code requirements. Most builders only meet code. Homeowners should inspect and may need to upgrade that earthing.

[westom]

I can also just image a tree breaking the neutral wire and then if I was the only one in my area to have linked the neutral and earth bars my main circuit box/neutral and earth wires may begin to glow.

One homeowner ignored the missing connection from neutral to earth. After all, the lights still worked. He also ignored lights changing intensity as the neutral wire was failing inside the transformer. Eventually AC electric had to obtain a neutral connection via gas pipes and the gas meter. Fortunately nobody was home when a gas meter gasket finally failed. When the house exploded. An explosion that would happen if the neutral and earth ground were properly connected at the service entrance.

Both human safety and transistor safety wants neutral and earth ground connected where all wires enter the building. Unfortunately some local codes might not yet be upgraded.

Edited June 5, 2012 by westom

[Pib]

This is Thailand...the Land of Electrical Surprises. While Safety First signs may be posted at many construction sites,roadway construction, etc., be sure to watch out for those Safety First signs as a good possibility exists they they positioned in such a way to create a safety hazard. And when it comes to electrical safety/awareness in Thailand that just means don't grab any electrical wire that's creating sparks and smoke; otherwise, most any wiring hookup should be fine. TiT.

[Crossy]

It is likely an exercise in futility to discuss the merits and demerits of each of the earthing systems along with their multitude of variants, suffice it to say that most developed countries have a set of standards which have been deemed acceptable in the local environment.

Thailand, like the UK has a mix of earthing systems, the UK has TT, TN-S and TN-C-S (but not MEN), in Australia all domestic installations must be MEN.

In Thailand, all new installations are supposed to be TN-C-S with MEN, this is supported by the instructions for consumer units, Safe-T-cut devices etc. showing only this installation method.

Many villages are TT, and many homes in those villages do not have grounded outlets or ground spikes.

A lot of condo developments are actually TN-S as they have their own transformer and the additional cost over TN-C-S is negligible.

There are reports of local systems that are IT, this is certainly not a preferred arrangement and is likely a poorly installed / maintained TT system.

THE IMPORTANT BIT Whatever your earthing system currently installed do not mess with it (with one important exception), if you are TT do not convert to MEN, if you are MEN do not convert to TT.

The exception? Simple. If you have no earthing system, install a rod and connect it to equipment that requires an earth (mostly water heaters, white goods and PCs), do NOT connect it to your incoming neutral, leave it as TT.

And the final note, if you don't have one, install an RCD, if only to cover your water heater.

[electau]

If your installation is TT, leave it that way. If your installation is MEN leave it that way. If your installation is a new one contact the PEA/MEA first for their requirements.

If your installation is a condo supplied by its own transformer it should be TN-S that is there is a separate protective earth from the transformer to the main switchboard and from the main switchboard to each units distribution board. The PE will terminate on a earthing bar.

Most likely there will be no protective earthing conductor. There may be indirect contact by way of metallic structural metalwork, but this does not comply with a TN-S system.

RCD/RCBOs should be installed for additional protection , compliant earthing will give basic protection against indirect contact.

If you have no protective earthing use the basic direct earthing method as advised by Crossy.

Note. 2 pin socket outlets are the norm, and 3 pin may not have the earth terminal connected to a protective earth. Many existing Thai electrical installations have no earthing or compliant earthing system.

To impliment the MEN system of earthing correctly there has to be cooperation between the Thai Goverment with mandatory legislation, the PEA/MEA, the Electrical industry, and Consumer groups including the Insurance industry. This of course will never happen.

(In Australia the MEN system has been mandatory since the 1920s for the public distribution system, with exceptions in certain areas of the mining industry where the TT and IT systems may be used. The IT system is used on some final subcircuits in proscribed areas of hospitals for example. Additional standards apply in these cases. In all other cases it is the MEN system and AS3000).

Edited June 6, 2012 by electau

[electau]

The first line of protection is at the transformer, Thyrite lightning arresters are connected to the HV terminals and are earthed to the transformer earthing system. Responsibility of the PEA/MEA.

At the consumers electrical installation - at the main switchboard between the main MCB and the line side of the sub circuit MCBs. Protect with an MCB the SPD. the SPD is earthed to the main earth at the switchboard.

At any distribution board the same applies as above. The SPD is earthed to the protective earth at the distribution board.

At the socket outlets with a 3 pin surge protected power board. ( sensitive equipment that requires protection against normal power surges and spikes)

MEN systems are better protected against the effects of lightning and surges than TT systems due to improved earthing with the MEN system on the network.

Edited June 6, 2012 by electau

[Pib]

Just as FYI for those of us trying to get a better understanding of the different earthing systems, here's a couple documents on earthing systems I googled up. Plenty of such documents out there in internet land but I thought these two were pretty good. One concentrates on how the different earthing system came into being from the Thomas Edison days of electricity. And the other one gives some fairly good layman's talk and pictures on the different earthing systems.

Review of Earthing & History.pdf

Earthing_Your Questions Answered.pdf

[Rimmer]

Most interesting thread!

Last night we had another strike I assume on the overhead internet cable in the road, but following on from the strike last time I had fitted one of the small inexpensive boxes in the copper ADSL line that divert any overcurrent to an earth rod in the ground,

Here is the bizarre part, the grounding device in the ADSL line was fairly well scorched on the two line terminals and the earth terminal so it had definitely done something but a small current had traveled a short distance along the cable into the house and found its way to the UNPLUGGED telephone line which was resting on the modem case.

The case where the telephone plug was resting was scorched, the telephone plug was burnt and the modem was fried.

No other damage as everything was unplugged.

[Pib]

Ain't lightning and the surges they can send our way a wonderful thing--NOT!!!!

[westom]

Here is the bizarre part, the grounding device in the ADSL line was fairly well scorched on the two line terminals and the earth terminal so it had definitely done something but a small current had traveled a short distance along the cable into the house and found its way to the UNPLUGGED telephone line which was resting on the modem case.

If your phone line was properly earthed (via a protector) then scorching is, maybe, an incoming surge on AC electric finding earth via ADSL.

Once that surge is permitted inside a building, then nothing can stop a destructive hunt for earth. Apparently a surge (incoming on AC electric or other wire) found earth ground on the phone wire. Because that was the best connection to earth. Because the surge was not earthed BEFORE entering.

Second, never ground an appliance to protect it. Protection is about earthing a surge BEFORE it enters the building. Protection is not about earthing anything inside the building. Protection means energy is not inside a building.

The next post quotes key points in an AT&T recommendation for DSL protection.

Edited June 6, 2012 by westom

[westom]

From AT&T: "How can I protect my DSL/dialup equipment from surges?":

Surge protection for DSL and dialup service. Surge protection takes on many forms, but always involves the following components: Grounding bonding and surge protectors. ...

Grounding is required to provide the surge protector with a path to dump the excess energy to earth. A proper ground system is a mandatory requirement of surge protection. Without a proper ground, a surge protector has no way to disburse the excess energy and will fail to protect downstream equipment.

Bonding is required to electrically connect together the various grounds of the services entering the premises. Without bonding, a surge may still enter a premise after firing over a surge protector, which will attempt to pass the excess energy to its ground with any additional energy that the services surge protector ground cannot instantly handle, traveling into and through protected equipment, damaging that equipment in the process. ...

Now, if all the various service entrance grounds are bonded together there are no additional paths to ground through the premise. Even if all of the grounds cannot instantly absorb the energy, the lack of additional paths to ground through the premise prevents the excess energy from seeking out any additional grounds through that premise and the electronic equipment within. As such, the excess energy remains in the ground system until dissipated, sparing the protected equipment from damage. ...

By far, the whole house hardwired surge protectors provide the best protection. When a whole house primary surge protector is installed at the service entrance, it will provide a solid first line of defense against surges which enter from the power company's service entrance feed. These types of protectors can absorb/pass considerably more energy than any other type of protector, and if one does catastrophically fail, it will not typically be in a living space. ...

Plug in strip protectors are, at best, a compromise. At worst, they may cause more damage than they prevent. While they may do an acceptable job of handling hot to neutral surges, they do a poor job of handling any surge that must be passed to ground. ...

Then, to add insult to injury, some strip protectors add Telco and/or LAN surge protection within the same device, trying to be an all-in-one sale. Remember bonding? When Telco or LAN protection is added to a strip protector, if the premise ground, which is not designed to handle surges, cannot handle all of the energy, guess where that excess energy seeks out the additional grounds? You got it! The Telco and LAN connections now becomes the path, with disastrous results to those devices. ...

Edited June 6, 2012 by westom

[Pib]

Plug in strip protectors are, at best, a compromise. At worst, they may cause more damage than they prevent. While they may do an acceptable job of handling hot to neutral surges, they do a poor job of handling any surge that must be passed to ground. ...

Just as additional info, almost all 3 wire power strip surge protectors I've bought to date (usually in the 300 baht ballpark) have only had one each 10mm (2.5KA surge current capability) varistor across the L to N...one strip had one each 10mm varistor from L to E. Basically one mode of protection versus the desired three modes...L-N, L-E, and N-E for a single phase system. For those surge protected power strips which had the varistor across the L-N if the lightning comes in on the both the L and N lines which can occur from a direct/very close strike to power lines the varistor don't see a voltage differential large enough across L-N to make it turn-on/switch to a low resistance to divert the surge to neutral/ground. Therefore the surge continues on to your electrical devices. Or said another way, the surge protected power strip with one mode of protection for L-N didn't protect anything...didn't even beat down the surge a little bit.

I have modified all of my 3 wire power strips by removing the one each 10mm varistor they came with which was usually installed across the L to N and installed three 20mm (6.5KA to 8KA) varistors (they cost less than 8 baht a piece) to provide three modes of protection. So, if the surge comes in on both the L and N lines, I have a L-E and N-E varistor connections which divert the surge to E (my earth spike on my TT system).

And for those folks which only have two wire surge protected power strips (i.e., only L and N wires, no E wire), well, you just better hope the surge don't come in on both the L and N lines because the varistor will most likely not provide any protection since it didn't (couldn't) activate. So, if the surge has to come, hope it only comes in on one line, hopefully the L line so the surge can be diverted to the N line.

And for those of you who are thinking we'll I'll just buy a 1000 baht surge protector strip...well, I say to that that protector may only be designed to protect in one mode only also...the L-N. So, be sure to read the specs (which will probably be vague) to see if it says it protects in all three modes versus just one or two modes.

[electau]

The earthed neutral system. or MEN

The SPDs are connected one from L to E.

The TT or unearthed neutral system.

The SPD is connected, one from L to E and one from N to E.

All SPDs must be protected by a MCB and be connected between the Main Circuit Breaker and the line side of the circuit MCBs. Normally the MCB is rated at 32A and the earthing is a minimum of 6 sqmm. The MCB protects against short circuit. When the SPD fails the module is replaced.

Make sure that the incoming polarity is correct.

Fine protection is by means of a surge protected power board with 3 pin plugtop and 3core lead. The socket outlet must be earthed.

[Rimmer]

Because we have so many problems with blown computers, modems, CCD cameras and small transformers being blown during a storm My wife contacted the local PEA office for advice. They came down Monday afternoon made some recommendations and turned up the next day Tuesday (yesterday) to implement them.

It seems that because we have our own transformer coming straight off the 22kv HT lines (which for some reason do not have an overhead earth wire above them) we are constantly getting high fault levels back into the house during a storm.

They fitted three small circular surge suppressors on each of the phases after the transformer but before the three small J Type fuses, each suppressor was then connected to a heavy stranded earth wire that they ran down the pole and connected to two five foot earth rods buried deep in the ground right up to the hilt

Hopefully that will do the trick!

Not had a bill yet so don't know how much.

[westom]

They fitted three small circular surge suppressors on each of the phases after the transformer ..., each suppressor was then connected to a heavy stranded earth wire that they ran down the pole and connected to two five foot earth rods buried deep in the ground right up to the hilt

That is the primary surge protection layer. A transformer also must be earthed "so that a 'follow through' current does not exist." As defined in a previous post.

Also stated:

Third, every wire that enters the building must have a low impedance connection to single point earth ground. Protection means every wire is earthed either directly or via a protection. And the connection must be as short as possible.

That 'as short as possible' (low impedance connection) is your secondary protection layer. Better protection is 2.5 or 3 meter ground rods. Each protection layer is defined only by what does protection. Where energy is absorbed. A single point earth ground.