Which Earthing System Do I Have?

[david96]

If an IT system is used installing a MEN link changes the characteristics of the LV supply.

Instead of their being a high impedance to earth (no connection) there is now a low impedance to the supply neutral on the installation that has the MEN link and other consumers who may have direct earthing or no earthing at all may have a reduced impedance to earth, which, if RCDs are not installed could be hazardous in the event of an earth fault in other installations supplied by the transformer.

If an adjacent consumer has an earth fault it will travel though the general mass of ground to the main earth up the main earth, though the MEN link though the neutral to the transformer.

And that impedance ( to the adjacent consumer) could be in ohms what a TT system would be. The consumer with the MEN would not be affected.

I am not sure if I fully understand what you are saying David, are you suggesting that I should install a MEN-link despite having an IT system? Crossy suggested not!

No, do not install a MEN link at your main switchboard. What one meant was that if you did install a MEN link the characteristics of the distribution network would change, as the transformer neutral will be now be earthed.

It will be TT instead of IT, and your installation only will be MEN.

[stgrhe]

 

I am not sure if I fully understand what you are saying David, are you suggesting that I should install a MEN-link despite having an IT system? Crossy suggested not!

No, do not install a MEN link at your main switchboard. What one meant was that if you did install a MEN link the characteristics of the distribution network would change, as the transformer neutral will be now be earthed.

It will be TT instead of IT, and your installation only will be MEN.

Thank you for clarifying this issue David. One more question, I suppose you also mean to say that all users in the development must not install MEN-links, right?

[david96]

 

I am not sure if I fully understand what you are saying David, are you suggesting that I should install a MEN-link despite having an IT system? Crossy suggested not!

No, do not install a MEN link at your main switchboard. What one meant was that if you did install a MEN link the characteristics of the distribution network would change, as the transformer neutral will be now be earthed.

It will be TT instead of IT, and your installation only will be MEN.

Thank you for clarifying this issue David. One more question, I suppose you also mean to say that all users in the development must not install MEN-links, right?

Yes that would be quite correct.

[david96]

It would be very helpful if one could find out what the actual earthing requirements for the LV distribution system in Thailand is.

Is it IT, TT or TN.

If the PEA/MEA can not advise who can? They should be able to advise on the Act or the Regulations that covers LV Electrical distribution networks.

And there is a 3 wire 220V/50Hz system that is used in some rural areas. It would have a delta

connected LV and would be IT. Consumers take 220V 2 wire A and N through a double pole

switch fuse or circuit breaker.

That system was mentioned in a Thai Electrical Training manual, dated it must be admitted, that I saw in 1998, mentioned VDE standards, some technical parts were in English.

It is a wonder that there is not more deaths and serious injuries from electricity, most deaths seem to be from direct contact with a bare conductor or terminal and severe shocks from exposed metal work are not so frequent. Look at the market areas! The 2 pin socket outlet and the 2 pole National brand MCB with a rating of 1.5kA. 10 to 30A.

And they seem to regard that Saf-T-cut device as protection against direct contact, I saw them promoted on Thai Television in 2005. No mention regarding earthing.

[InterestedObserver]

And there is a 3 wire 220V/50Hz system that is used in some rural areas. It would have a delta

connected LV and would be IT. Consumers take 220V 2 wire A and N through a double pole

switch fuse or circuit breaker.

Where does the "N" (neutral) come from on the LV delta? If you're talking about center tapping one of the phases, that is not a very efficient use of a 3-phase transformer connection and certainly not a true neutral. The only other explanation is that one of the phase conductors (A,B,C) is called "N". Or am I missing something here.

Edited March 3, 2010 by InterestedObserver

[Crossy]

And there is a 3 wire 220V/50Hz system that is used in some rural areas. It would have a delta

connected LV and would be IT. Consumers take 220V 2 wire A and N through a double pole

switch fuse or circuit breaker.

Where does the "N" (neutral) come from on the LV delta? If you're talking about center tapping one of the phases, that is not a very efficient use of a 3-phase transformer connection and certainly not a true neutral. The only other explanation is that one of the phase conductors (A,B,C) is called "N". Or am I missing something here.

Nah, there is no real neutral, it's 220V phase-phase, just one of the phases is called 'N' at the outlet, it's not even the same phase at each dwelling, a recipe for problems if some bright spark grounds 'his' neutral.

The Philippines uses the same system with double pole breakers, has the advantage that your un-grounded PC case floats at about 0V

[InterestedObserver]

Why not just say 3-phase, 3-wire, 220V/50Hz ungrounded delta. There is no "N" (neutral) named wire until after the service entrance at each dwelling and then only because outlets etc. have an "N" terminal.

Edited March 3, 2010 by InterestedObserver

[elkangorito]

After some serious thought & also realising that we've been "barking up the wrong tree" with regard to Thailand's distribution system, I've decided that things are even worse than before.

I have attached some docs for those interested but in a nutshell, the IT system in Thailand (& in my opinion):

1] Is not maintained correctly, if at all. This can have deadly results.

2] It's not implemented for it's intended purpose (reliability)...it seems to be implemented to save a few Baht on cable.

3] It will be a lot more expensive for domestic users to safely use than a TN or TT based system.

Clarifying my above comments;

re 1]

Specific monitoring devices are needed to ensure the integrity of the system. Without these devices, you could end up with a lethal system if many earth faults are apparent. Also, the voltage of the cable used in any installation should be at least rated to withstand 0.6kV to 1kV & be double insulated. This means that all of those "single insulated" extension leads & appliance leads should be banned. The cable the PEA/MEA use (their cables) may be rated appropriately but I have never seen double insulated Consumer's Mains since I've been in Thailand.

re 2]

Reliable power in Thailand is a bit of a joke. Also, the added expense to the PEA/MEA to implement a TT system would be the purchase of some cable, the purchase of a 6m long "hot dipped galvenised" 25mm steel rod & some bushings & bolts. This apparatus would be used at every transformer installation to solidly connect the "star point" (neutral) to earth.

re 3]

For domestic users in Thailand to be safely connected to an IT system, the following will be needed:

a] An IMD (Insulation Monitoring Device)...electronic device & not cheap.

b] High quality surge diverters...you don't want that expensive IMD to fail in a hurry. Nor do you want your cable insulation to be stressed by high voltage transients.

c] 30mA RCD's on EVERY circuit.

d] All cable to be double insulated & rated at no less than 600v for single phase installations & no less than 1kV for 3 phase installations.

e] All Thai electricians must be familiar with fault finding earth faults. They must also be fully aware of how the IT system is supposed to work.

f] Insulation resustance testing is critical BEFORE any new installation is energised. I would not accept anying less than 50Meg Ohms.

If I was a new home owner/builder, I would insist upon a minimum TT system for my own installation. If they didn't know how to do it, I would advise them.

Since some people are not in the same situation as myself, I would suggest civil (& criminal?) action against any energy authority in the case of injury or death. One needs to be sure it was the fault of the "system" & not ones own equipment before proceeding with any such action.

Mediocrity & "this is the way we do it in Thailand" are simply not reasons for unnecessarily being at risk of electrical injury or death in your own home...not in the 21st century.

IT_System.pdf

IT_tech_info.pdf

it_system_maintenance.txt

[stgrhe]

Yesterday I didn't visit the house construction site because I had other engagements, but this morning the construction engineer informed that there had been some people from PEA yesterday who seemed to do some work at the transformer. Being both curious and suspicious I borrowed a ladder so I could clime up a bit and take a photo and this is what I saw:  

So apparently PEA yesterday fitted a clamp on the previous loose end of the right hand side earth cable, the one that before appeared to lead nowhere, to the neutral line. Hence it now seems like I have gotten a TT system all of a sudden!

One can only speculate why the clamp wasn't fitted in the first place, was the only clam damaged or had they forgotten it back at their depot or what? They probably taught it wouldn't matter if it was fitted a few weeks after the transformer's commissioning - Thai style "No Pobmen" perhaps.

[Crossy]

OK, so you have 'at least' a TT system. Are there any other neutral-ground links on other poles (making it MEN / PME)?

Either way, I would NOT install a MEN link until:-

You've confirmed that other properties are also installing

and

You've verified the polarity of your installation, preferably after the permanent meter is installed.

Running TT provided you've got RCD protection is perfectly safe, adding MEN/PME later can only make it safer

[elkangorito]

Sorry but I'm not entirely convinced from what I see in the pic.

Stgrhe, if possible can you take the following pics please:

1] Clearly show the neutral of the transformer & to where it runs.

2] If the cables are run vertically, the neutral is usually the top cable. Clearly show that this cable is connected to this "earth".

3] Show where the "earth" cable goes into the ground.

From what I can see from your pic, it looks like a cable is connected to this "earth" cable, above where you indicated. Not only this but the black cable seems to continue down the pole (obviously to the meter).

If you can also see that the neutral cable is earthed at every pole (or every 2nd or 3rd pole), a TN-C-S system is indicated & an MEN link should not be a problem.

[stgrhe]

OK, so you have 'at least' a TT system. Are there any other neutral-ground links on other poles (making it MEN / PME)?

No there are no other neutral-ground connections as the transformer's primary side is a three wire connection. The only additional earthing is to the chassis of the transformer and that is by a separate earth rod.

[stgrhe]

1] Clearly show the neutral of the transformer & to where it runs.

2] If the cables are run vertically, the neutral is usually the top cable. Clearly show that this cable is connected to this "earth".

3] Show where the "earth" cable goes into the ground.

It is difficult to take photos up top but I shall see what I can do. I identified the top cable to be the neutral. This cable runs across the soi to a second pole where the old transformer used to be. The three lower cables, the three phases, first run to the main breaker cabinet, the meters and then across the soi.

The top bracket you are referring to appears to be a junction on the neutral cable. PEA may have made it with a junction because the run across the soi is only temporarily solution as all cables eventually will go under ground.

If you can also see that the neutral cable is earthed at every pole (or every 2nd or 3rd pole), a TN-C-S system is indicated & an MEN link should not be a problem.

No, as I said in the reply to Crossy's post the feed is three wire only and there are no earthings on the 800 meter run from the main road up to the development site. I have checked every pole.

[stgrhe]

Elk, today I was at the construction site and I shot these photos. Perhaps they will enable you or others to determine whether the system now is in fact TT or TN.

This photo shows where the earth wire goes underground. The earth rod is about three metres away in the direction shown by the arrow. The rod is about two metres long, T-shaped but it didn't appear to be made of copper. It looked galvanized to me.

This photo shows how the earth wire, three phase cables are led down the pole to an electrical cabinet (see another picture below), and that the neutral cable is led upwards on the pole.

This picture shows the electrical cabinet. I do not know what's inside as the door is sealed. The outgoing cables are on the other side of the pole.

This picture shows the three phases led downwards to the electrical cabinet but there is also a thinner black cable that is led from the cabinet and connected on top (the top bracket) to the neutral cable. Below this clamp the picture shows where the earth wire is clamped to the neutral cable.

This picture shows the four temporary cables, with the neutral on top, being fed to a pole on the other side of the soi where the previous single phase transformer used to be. This temporary connection is feeding the two finished houses. Before my house is finished the mains will be dug underground.

[david96]

The distribution neutral is earthed. (T) If you do not install a MEN link at your main switchboard your earthing system will be (T). The TT system has been implemented.

If you were to install an MEN link you would have a TN system. Your earthing system has changed from T to N.

[david96]

Implementing the MEN system in Thailand has the following problems.

Here are some of them.

1. Poor or no regulatory environment.

2. Poor training of electrical workers.

3. No mandatory testing of electrical work.

4. No system of auditing electrical work.

5. No concept of legal obligation (duty of care).

Installing an MEN link changes the characteristics of the LV distribution system.

An IT system becomes a TT one and a TT becomes a TN.

It is this connection at the consumers main switchboard between the neutral and the main earth that is refered to as the MEN link.

In view of the above a MEN connection should not be made unless it is:

1. A mandatory requirement eg, an Act or Regulation.

2. It is clearly documented in the PEA/MEA conditions of supply.

The earthing of the distribution neutral does not mean that the policy of the PEA/MEA is to implement the MEN system. It is earthed to minimise the potential difference (voltage) between the neutral and earth to as near zero (0) volts as practicable.

It would appear that it is now the policy of the PEA/MEA to earth the distribution neutral at one or more points on all new extensions to their 220/380V LV network.

[david96]

With reference to post #38 by Elk, one would agree but there may have been political and economical reasons why the Thai electrical system is like what it is.

As far as the Thais are concerned the system works and is safe.

When Thailand expanded its HV and LV distribution in the 1930s and after 1945 it may have been decided then that an IT or at the very minimum a TT system would be used.

With no earthing, two (or three) pole porcelain switch fuses, no neutral links, double pole switches, 2 pole socket outlets would have been normal, and other countries in Asia used this system.

Earthing if used was just a wire run to an electrode in the ground, common in Asia.

When you only have 2 wires black and white or 3 wires black it is very difficult to make mistakes.

Thailand had been influenced by Japanese engineering standards of the era.

I visited a new 6M Baht Thai house in 2005 in Bangkok, no earthing, no main earth. 2 pole circuit breakers, no RCDs wired in single insulated cable in metal conduit, no earthing of conduit, 2 pin and 3 pin socket outlets.

One developer in Bangkok was offering 2 pin sockets in townhouses and 3 pin in stand alone houses. 3 pin socket outlets and RCDs where in effect "optional extras".

An that IT system may explain why their "Safe-T- Cut" RCDs are switched 5/10/15/25ma.

There is sufficient leakage and low resistance for them to operate, settings to suit ones circumstances.

[elkangorito]

I went for a walk around the local area (Baan Ampur) & every single distribution transformer (about 5 of them) was IT connected.

The pic below is of 2 old transformers that supply about 30 houses behind the local college. They are clearly IT connected.

The below pic is of an 800kVA txer that supplies a 7 storey condo block & a 24hr shop, both of which are less than 6 months old (a new installation).

The below pic shows the 2 earth cables. Both of these cables only earth the hardware (txer tank, surge diverters etc).

Clearly, the IT system is still being implemented where it should not be.

Edited March 8, 2010 by elkangorito

[david96]

With reference to post #48 by Elk.

This is where the theory of the IT system and its implementation in practice as a distribution system differ.

The use of an IT system is generally limited to parts of an existing electrical installation such as areas of hospitals, laboratories some shipboard installations etc. The earthing system is in these cases is direct and any fault will be detected by earth monitoring and an alarm may operate if the fault current exceeds a predetermined value.

However when an IT system is used as a distribution system a fault to earth on one phase and another fault on another phase perhaps in different electrical installations all that will occur is some ground fault current which will be low. The faults could be hundreds of meters apart.

The impedance of the neutral to earth over the whole distribution network will be low, low enough for a small value of current to operate a RCD. Thai RCDs have adjustable settings, 5/10/15/25 and then the direct setting. Earthing is used just to remove the effects of minor leakage current.

But the implementation of the IT system has been proven to be practicable as a distribution system. It would appear that it has minimal problems.

Edited March 9, 2010 by david96

[elkangorito]

The impedance of the neutral to earth over the whole distribution network will be low, low enough for a small value of current to operate a RCD.

But the implementation of the IT system has been proven to be practicable as a distribution system. It would appear that it has minimal problems.

Sorry David but I disagree.

Just look at how many of us report getting zapped from something. Dog knows how many electrical deaths go unreported in this country.

The impedance to earth of either Active or Neutral should be high under normal circumstances. The system is generally earthed by it's "system leakage impedance" and the touch voltage is held down by the high impedance.

Assume a system impedance of 3200 ohms;

Leakage current = 220/3200

= 0.06875 amps.

Touch voltage of appliance if a 10 ohm fault occurs to it's metal chassis (earthed).

E = I x R

= 0.06875 x 10

= 0.6875v

Touch voltage not dangerous (is less than 50v).

The problem arises when the system impedance is reduced (old insulation, insulation failure, equipment failure, aging transformers etc). In this case, the touch voltage is most likely to be dangerous due to the significantly reduced impedance.

If the integrity of the insulation is maintained, it is a very safe system but as you know, as equipment & cable gets old, leakage currents increase. As you said, this system is mainly implemented when a reliable supply is important i.e. medical facilities, ships etc. In these installations, they don't simply rely on RCD's as the sole protection against shock. I don't see many IMD's in Thai homes.

Since RCD's & circuit breakers are the only things available (& known) for domestic use here in Thailand, a TT or TN system is far safer than an unmaintained IT system.

Just to be on the safe side, RCD's are a must for such a system & since such devices are prone to failure (voltage surges, lightning etc), they need to be tested very regularly. Also, in order for any SCPD to operate correctly (0.4s max trip time), loop impedance is critical.

Based on Loop Impedance alone, most installations in Thailand are a "lucky dip" because testing is not carried out. In essense, it doesn't matter what system you use in Thailand...the devices may not work properly due to a lack of testing. Looks like it's a total reliance on RCD's until Loop Impedance testing is implemented.

[david96]

With ref. to post #50 by Elk.

Loop impedance testing was introduced into Australia in 2000 in AS3000 as a result of harmonisation with the IEEE rules in the UK. It is only of value if the MEN system is implemented. If an RCD is installed on socket outlets loop impedance testing is not required as the RCD will trip in less than 0.4secs.

RCDs have been proven to be very reliable protective device. They must be tested when initially installed and at regular intervals thereafter.

The loop impedance of a TT system is going to be high so RCDs must be used.

An there is a problem in implementing a TN system in Thailand and that is a legal one.

[david96]

This post might try to explain the earthing system as implemented in most Thai electrical installations.

Two pin socket outlets are very much the standard. TIS ( Thai Industrial Standards) permit both the 2 pin and 3 pin socket outlets.

Mild shocks are often experienced from electrical appliances are by indirect contact and they are more pronounced in wet areas such as kitchens and bathrooms and from such items as refrigerators, washing machines etc.

These shocks are low in severity and are caused by normal leakage currents as in switch mode power supplies, moisture and in some cases inductive or capacitive effects.

These electrical shocks can be minimised by earthing.

To remove the effects of these mild shocks the Thai system of implementation is to earth the equipment individually to either the ground with an earth electrode or directly to the wall or floor by means of a metallic fastening. Building materials are electrically conductive. Often this conductor is only 1.0 sqmm.

What this does is to equipotentially bond the equipment and the floor/wall so the potential (touch voltage)between the equipment and floor/wall is lowered to near zero volts. To a person in contact with the equipment and the floor/wall the risk has now been minimised.

The use of RCDs will ensure disconnection of supply if the touch voltage exceeds 50VAC or 25VAC in wet areas. But they may not be installed.

(The risk of receiving an electric shock of 10 ma or greater is minimal. But to minimise the risk install RCDs).