Electrical Risk And Safety.

[electau]

An electrical installation should be free of electrical risk as far as in practicable and must be suitable for the use for which it was designed. First one must identify the hazards, and we will identify the main one.

That hazard is electricity. The risks are shock and fire. The risks in a non compliant electrical installation are high. The risks are minimised by the use of 1. A compliant earthing system 2. Correct circuit protection and coordination. 3. Protection from direct contact with live terminals.4. Use of double insulation. These are examples.

Protection against indirect contact is essential. Fatalities from indirect contact with exposed conductive parts are one of the most common causes of death and serious injury. Protective earthing with RCDs will minimise this risk.

With the exception of testing for supply using approved test equipment electrical work should never be carried out live.

The whole installation ( or the circuit to be worked on) should be switched OFF and then tested. Test before you touch.

Note: Metering and the incoming supply mains are energised at all times unless proved otherwise.

[prestburypark]

Hi Electau,

I have a new house build, finished and moved in, up in Phetchabun. I was not here for the build and there are quite a few things I am concerned about.(electrical).

Do you know of a service/company/person who could come and inspect the house and make any necessary adjustments to the system, or at least oversee the work?

I would really like the peace of mind of a western standard clean bill of health for the house and would be happy to compensate well for such an inspection,

regards,

P Park

[electau]

The electrician or the electrical contractor who wires your house should carry out all tests before connecting to supply, the PEA should carry polarity tests when the meter is connected and check the main earth and electrode.

However saying this in practice it probably will never happen in Thailand.

However one can give you the basic tests to enable your installation to be safe.

If an electrician is qualified and competent he should have no problem testing an installation if he knows the basic test requirements.

[Artisi]

Qualified and competent - now that is asking a lot from some Thai "electricians".

[nakhonandy]

I have a couple of questions here which may seem obvious to you. I am an electronic engineer and have a reasonable understanding of the electrical side but by no means am I a qualified electrical engineer!

As is normal in rural Thailand (65km from Nakhon Sawan) I have a two wire supply to my house. Is the incoming Neutral earthed at the supply transformer?

I am planning to rewire our house as I consider it completely unsafe. I am looking at either the TN-C-S or the TT system for safety, any recommendations?

lastly are there any good websites or reference documents I can use to guarentee the safety of the installation?

Thanks for any help.

[Crossy]

If you are unsure assume TT.

To check for TN-C-S have a look at your supply poles, if the neutral is earthed every 3rd or 4th pole it's TN-C-S and you can link N-E in your distribution board.

Don't forget, if you are TT ALL circuits need RCD protection.

[electau]

All that is required is that the distribution neutral is earthed which it will be but not always at the neutral terminal of the transformer. It will be at one or more points on the distribution system.

To use the TT system. The electrical installation neutral is NOT bonded to the distribution neutral. The earthing systems are isolated. Any earth fault current returns to the neutral of the transformer by way of the main earth and electrode. This is a low fault current high impedance system and RCDs must be used to comply with the disconection requirements.

To use the TN-C-S system. The electrical installation neutral is bonded to the distribution neutral at the main switchboard. The earthing systems are bonded together. Any earth fault current returns to the neutral of the transformer through the consumers main neutral conductor and the distribution neutral. Any current in the main earth may be disregarded.

It is a high fault current low impedance system. On this system RCDs are used as additional protection.

The main earth and electrode with the neutral earthing on the distribution system maintain the neutral to earth voltage as close to 0 volts as practicable.

To give an example, a small transformer is required to supply a single installation. The transformer has the neutral terminal earthed, the neutral at the main switch board is bonded to the main earth. The Installation is TN-C-S or MEN. Multiple means more than one.

If the installation was not bonded ( in this case at the main switchboard) it would be TT.

When using the MEN system polarity testing is essential as there can be several points where errors can be made, 1. at the connection point of the service conductors and the distribution system. 2. at the meter(s) and 3,at the main switch board. The neutral should be clearly identified at each connection point, irrespective of whether it is TT or TN-C-S.

It would be advisable to contact the PEA first if you intend to use the TN-C-S system.

　

Edited November 6, 2012 by electau