How to make your Thai Electrical system safe

[Forkinhades]

Please see attachment for relevant drawings, I have used brown as live and blue as neutral, as european standard, and makes the diagrams a lot easier to read. Thailand uses black for live, and grey for neutral. (Actually any colour that they can get their hands on)

The Thai Domestic Electrical System, below is a typical thai DB that has no earth, and no RCD protection, this is quite common in Thailand, and offers no protection for fault current, this system will only provide over current protection, which is not good if one has an electrical appliance which develops a fault to the metal casing. Which can be fatal.

By following these steps you can make your system safe, how far you go with safety is up to you, which is going to be dependent on cost and whether you rent you buy. These steps should be followed in order.

The first step is to install a Front End RCD, you can get a Safe-T-Cut RCBO which goes before the consumer unit, or now you can replace the main switch with an Safe-T-Cut RCD depending on type and make. The Safe T Cut has settings of between 5mA and 30mA. You can get ones that are am 100mA, so I will use this for my illustration for now. Even without earths installed this is a life saving device, if you touch something that becomes live, then your body will make the path to earth, and open the RCD.

We really do not want to touch things that have become live and get a shock, so the next thing is to install some earth cables together with a 2.4 metre earth rod.

Now if any appliance becomes live the Front End RCD will open. However you can still receive tingles of 50V if an appliance has become faulty. So to stop this we need to install an MEN connection. With an MEN connection you can also get your impedance value low enough for your MCB’s to open in fault conditions, but not necessary in the time specified by any regs.

OK so we have a good safe system, but all the electrics go off after a fault, and you are left in darkness. The next thing you can is to add individual RCBO’s, this is the ultimate solution.

So lets say we have a shower unit with an ELCB on the 32A circuit. This in time becomes faulty, the in built ELCB in the shower has become faulty, well ok, but now our 30mA Safe-T-Cut RCBO should open. Lets say this has become faulty over time, ok so now our Safe-T-Cut RCBO 100mA should open. Lets say this has become faulty, you can now rely on your mechanical MEN connection to open your MCB.

You now have 4 levels of protection, a little like a Jumbo jet with 4 engines, which requires only 1 engine to fully function to land safely.

Interesting to note that current regs in the UK are moving away from Earth Equipotential Bonding and Automatic Disconnection of Supply, and now have Automatic Disconnection of Supply as the main protection.

Also in the UK it is the Electricity Suppliers that do the MEN connection, which is done in the service head, and they ARE the only ones that can do this connection.

Thai Domestic.pdf

Reason For Edit : changed safety cut to : Safe T Cut, which is commonplace in Thailand

[thomasteve]

Regarding the pinned thread it can be summarised as follows :

1. Install a Saf-t-cut or similar ELCB.

2. Ensure appliances and socket outlets are correctly earthed and an earthing rod is installed.

3. Never add a Neutral to Earth MEN link unless you are 100% sure it is required by your supplier.



As for an example of a scenario where earthing can present a danger :



House has no Saf-t-cut or ELCB but has correctly earthed fixed large appliances and socket outlets.

User purchases a metal cased small appliance (rice-cooker, toaster, iron etc.) fitted with a 2 pin plug or Schuko type European plug that does not provide correct earth connection.

This small appliance becomes faulty and the metal casing live but user remains unaware as he is insulated from ground (rubber soled sandals, wooden floor etc.) but then touches another correctly earthed appliance (cooker,fridge) with other hand and will receive severe shock. If there had been no earthing then there would be no potential difference to allow current to pass through user and cause a shock.

I am not advising against earthing but it needs to be done properly and in conjunction with an ELCB.

[Forkinhades]

Also just to add.

You can have many different and effective combinations. But you should be at best looking to get to stage 3.

1. Safe-T-cut
2. Earthing
3. M.E.N connection

[Forkinhades]

ok unlocking this for a while, as we might get some useful posts.

Anything deemed not useful will be deleted.

[Kwanting]

I understand that normal Thai electrical is dangerous and I'm very greatful for this oportunity to learn how I shall make a safe installation in my house.

Not being electrical engineer educated in GB i must ask you about meaning of M.E.N.

I guess that ELCB is an safety breaker? Is it enough with such a breaker set on 30mA if you can accept total darkness after a fault?

Another question: Aren't all transformers Y-coupled on LV-side and the neutral point earthed? In that case neutral and earth have the same potential and all you have to do is to connect incoming neutral with earth bar? Thus you can omit the earth rod?

[Crossy]

@Kwanting.

MEN is very similar to UK PME. Look here for more info, http://en.wikipedia.org/wiki/Earthing_system#Comparison_of_Earthing_systems Thailand is TNC-S with MEN.

ELCB (old term, call it an RCD) is what you might call a Safety Breaker, yes, a single unit on the front end will give adequate protection.

Yes, transformers are Y with a grounded neutral, but N and E are not at the same potential unless you're very close to the transformer. Think about volt drop in the neutral (ohms law). N can be quite a large potential above 'real' earth at your location (enough to feel sometimes).

The multiple earth rods (the M in MEN) help to hold the neutral closer to real ground and reduce touch voltages, in the UK this grounding is provided by the DNO (supply authority), in Thailand it is provided by you, you cannot omit the local rod.

[thomasteve]

Just a thought about earthing rods, prompted by the comment in another thread about using a short screw in the floor as an earth wire connection when nothing better is avaiable :

If a house has steel roof supports which are welded, in the roof space, to the rebar contained in the house concrete supporting posts would an earth wire connected to this steelwork be a possible alternative ? (similar to the old method of using a buried metal water pipe).

Thinking about it though probably won't work as the rebar is shielded from the ground soil by concrete.

[Crossy]

Just a thought about earthing rods, prompted by the comment in another thread about using a short screw in the floor as an earth wire connection when nothing better is avaiable :

If a house has steel roof supports which are welded, in the roof space, to the rebar contained in the house concrete supporting posts would an earth wire connected to this steelwork be a possible alternative ? (similar to the old method of using a buried metal water pipe).

Thinking about it though probably won't work as the rebar is shielded from the ground soil by concrete.

It actually works very well, our roof trusses measure as a better ground than our rod!

Google "Ufer ground".

That said, Ufers are not recognised by PEA, they want to see a copper coloured rod sticking out of the ground.

[thomasteve]

Just a thought about earthing rods, prompted by the comment in another thread about using a short screw in the floor as an earth wire connection when nothing better is avaiable :

If a house has steel roof supports which are welded, in the roof space, to the rebar contained in the house concrete supporting posts would an earth wire connected to this steelwork be a possible alternative ? (similar to the old method of using a buried metal water pipe).

Thinking about it though probably won't work as the rebar is shielded from the ground soil by concrete.

It actually works very well, our roof trusses measure as a better ground than our rod!

Google "Ufer ground".

That said, Ufers are not recognised by PEA, they want to see a copper coloured rod sticking out of the ground.

Very interesting to learn about that and i will use it temporarily until a proper copper ground rod can be installed.

Also, easy and simple to wire up as the roof trusses are readily accessible just above the consumer unit / fusebox.

Is it still good practice/requirement to earth bond any other exposed metal work such as stainless steel sink tops, metal baths, pipes etc. ?

[Crossy]

Is it still good practice/requirement to earth bond any other exposed metal work such as stainless steel sink tops, metal baths, pipes etc. ?

There has been a lot of discussion on the UK electrical forums regarding when to bond and when not to. There are times when bonding the sink can actually be more of a hazard than not bonding it.

Forky is your man for the latest accepted practice, but the need to bond sinks and the like is much lower now than it was in the bonding heyday 10 years ago.

If you have metallic pipework, it should be bonded to the main earth terminal, but apart from that I wouldn't bother.

[Forkinhades]

^ Sinks are not required to be bonded under current UK regs.

[Bignose]

Gents, while I appreciate this is an excellent forum for discussion and the sharing of opinions, I am more than a little concerned at some of the information being passed back and forward. I have read the "advice" posted by Crossy and it is absolutely spot on, but I would like to go a small step further. No matter how good an instruction or a diagram is, there is absolutely no replacement for training and experience. Unless they are suitably qualified NO ONE should attempt any electrical repairs, testing or upgrades. 230V AC is not to be played with and can be instantly fatal, the old saying "Sometimes a little knowledge can be a dangerous thing" is very, very relevant.

Just a few months ago I contributed to a thread where a member was giving advice on how to install an RCD into an existing installation, it was obvious the person receiving the advice had very little knowledge of what was involved, so I advised them both to discontinue with the work and employ an electrical contractor (without being racist I advised sourcing a western trained and qualified contractor) To be using diagram and photo's as a basis for advice on carrying out electrical work is (to me anyway) just plain dangerous.

Please don't be offended by my contribution as I don't mean any disrespect, but this is an open forum with all information posted available to one and all. Some of the installation work I have seen in this beautiful country turns my blood cold, I don't think we help by posting this kind of information.

[Forkinhades]

Agreed electricity is indeed dangerous, and really should be left to the experts. Which is not an easy thing to do here in LOS.

The advise given here is mainly for the 'fralang' to have a good understanding of how things should be done, and to make sure the 'contractor' installs accordingly.

Sent from my GT-I9300 using Thaivisa Connect Thailand mobile app

[Crossy]

+1 I agree 100% with what Bignose says. Unfortunately finding a remotely competent sparks is easier said than done even in the Big City, out in the sticks, forget it.

Domestic wiring is not rocket science and is certainly within the capabilities of a competent DIYer following a few safety rules.

I remember the thread Bignose refers to, it did indeed become apparent that the OP was not in the "competent DIYer" class.

What to do? If we decide not to offer any electrical advice someone could die, if we offer advice to someone and they mess up, someone could die.

[Mrjlh]

My only comment after experiencing this situation in two different houses and for which I posted a couple of years ago about it, make sure the "Hot and Neutral" lines are not reversed at every wall socket and light fixture in the house. One way to check this is using a "non contact electrical tester" plug an simple multi-plug extension cord with an "ON/OFF" switch into each wall socket. Flip the switch on the extension to "OFF". Using the checker, see if any of the plugs on the extension still has a voltage indicated. If so, strong chances are the wires in the wall socket maybe switched. Turn it on and you should see strong voltage indicated. Also make sure your extension is correctly wired too. I really did find one of those backwards too. Check each light fixture also. Fans are a little more difficult and maybe one of the experts here can offer more advice.

I found at the last house all the wires in the electrical box had been reversed. It really needed to be rewired correctly. I posted pictures of it and Crossy may remember. So the electrician went out to the meter and switched the wires at the pole. Only problem is the next guy who tries to do it right will get it wrong!