Thai Electrical System

[paulfr]

It only takes 10 milliamps thru the heart to kill you.

In US industry, 50 volts is considered dangerous high voltage, altho most feel this is a bit over conservative.

IMO, the only reason for a home to have a ground stake in the earth is to attach to a lightning rod on the roof to provide a path for the transferred charge away from the house. Connection of this stake (or your metal pumbing pipes) to your electrical system is unnecessary and very possibly could cause a fire if connected multiple times.

I would love for someone to refute this with a rational explanation. I am always willing to learn.

[lopburi3]

Wife turned the lights out so was not able to send this until now.  See where the US does have what they call a splitphase system which is fed by a single phase of the normal three phase high voltage lines to the primary and the secondary is a center tap of the 240 volt transformer and use this to feed some residential areas so you end up with two 120 volt legs and 240 end to end.  Guess being overseas 40 years erases the memory as I never recall anything but 208 volts for home use.  Sorry for (my) confusion.  Can see why most homes in US are sold with appliances as they have to be wired for either 208 or 240 depending on where used.

At least I learned something.  Thanks.

<{POST_SNAPBACK}>

I don't know what the electricity was 40 years ago but now I think that almost everyone if not everyone has 240 volts at least on the west coast which is the only place where I have experience. When purchasing appliances which use 240 no one even considers if it s 240 or 208 volts. I vaguely remember that many years ago that people in rural places had a different electrical system. Did you live on a farm?

<{POST_SNAPBACK}>

You can not run three phase motors with this system so it is never used in other than residential areas to my understanding and if you check Sears believe you will find all high voltage stoves and such will be rated 240/208 so it is still around. I lived in New England area. And we always considered the West Coast as somewhat of another country. They didn't even speak the same language.

Edited June 18, 2005 by lopburi3

[lopburi3]

It only takes 10 milliamps thru the heart to kill you.

In US industry, 50 volts is considered dangerous high voltage, altho most feel this is a bit over conservative.

IMO, the only reason for a home to have a ground stake in the earth is to attach to a lightning rod on the roof to provide a path for the transferred charge away from the house. Connection of this stake (or your metal pumbing pipes) to your electrical system is unnecessary and very possibly could cause a fire if connected multiple times.

I would love for someone to refute this with a rational explanation. I am always willing to learn.

<{POST_SNAPBACK}>

Believe you are talking about neutral ground rather than the requirement to have a three wire ground system. Obviously you want that refrigerator case to lead directly to ground and that is what the electric ground wire and a ground stake provides.?.

[Greer]

Firstly I must say I stand corrected - yes, MEN stands for Multiple Earthed Neutral - when I was at college we were told the "M" stood for "Main", hence my confusion - but having just purchased the latest AS/NZ 3000 Australian New Zealand Wiring Standards from the Standards Association in Australia - I can confirm that I am wrong in what I said earlier. Thanks for correcting me, and for providing the push I needed to go out and buy the book...well..PDF anyway (AUD77.00)

Now - power is usually generated in the main authority generating stations in 3 phase, at high voltage (to assist in transmission over long distances, to help minimise "copper loss" by reducing the current to transmit a given amount of power (Watts).

If the voltage measured between Active and Neutral is 120 Volts (yes, I agree I believe most modern US supplies are 120V Phase to Neutral), then the voltage between any two of the phases is 120 x (square root of 3) = 207.8V

In Australia it is 240V phase to neutral so the phase to phase voltage is 415.7V

In a country (such as many places in Europe) with a 220V phase to neutral voltage, the phase to phase voltage is 381V.

Usually houses all over the world are connected between one of the phases (called the Active) and the Neutral - thus in the USA you would have a 120V supply.

In some places (Saudi Arabia that I know for certain - and from what has been said here, possibly some parts of the USA) they supply a house with two of the three phases - thus if you measure from either one of these phases to the neutral you will get a 120V reading, but if you measure from one phase to the other, you will get 208V (approx).

This is done to spread the load over more than one phase. It also results in somewhat of an out of balance situation back at the supply transformer (the one out on the pole or at the substation). An out-of-balance load results in a higher current in the neutral and affects things such as copper and magnetic losses in the transformer, it also makes life difficult at the generating station where these imbalances must be corrected if possible.

For this reason, the supply authority then load up different phases across say different houses or businesses that may have one, two or three phase loads so that the overall effect is to make all phases come out with around the same load.

Businesses are often supplied with three phases to spread the load out, but also because they may make use of three phase load devices such as 3 phase motors - these rely on the 120 degree phase difference between supply "legs" to cause the generation of a rotating magnetic field, and this in turn drags the rotor around with it. This is the basis behind 3 phase AC motors, but of course there is a lot of other theory etc in how they operate, etc - irrelevant in this forum.

Transformers used to step down from the high voltages used for transmission across the "supply grid" are usually wired in Delta/Star formation. The incoming circuits at high voltage connect so that the three primary windings of the transformer are each connected between two of the phases - this makes a triangle with the points of the triangle being where the incoming supply connects - this is called a Delta configuration (as it looks like that Greek letter).

The secondary windings are connected in a "Y" or "Star" configuration such that the arms of the Y are the output connections (the three phases) and the centre of the Y or star point is the Neutral. The voltages referred to above are thus either across one winding (active to neutral) or across 2 windings (phase to phase).

The reason that the voltage is not simply double the single phase voltage is that there is a phase angle of 120 degrees between the waveforms of the supply on one leg and on the other leg. The two supplies are 120 degrees apart, not 180 degrees apart.

The neutral is connected to the earth so that there is a return path for fault current - meaning that if a device (lets say a toaster) accidentally shorts to the outside case of the device, the current will then flow out via the three pin plug using the earth lead which connects to the exposed metal surfaces of the toaster, through the ground connection, and eventually back to the neutral of the supply transformer, thus creating a huge rush of current.

This rush of current has one effect - if you have fuses - they will be destroyed, thus disconnecting the mains, if you have a breaker, it will do the same.

If you have a Core Balance Circuit breaker system, it will detect that there is an imbalance of more than a certain amount between the current going to the device (via the active) and that being returned from the device (via the neutral).

This system is very useful because it does not rely on a huge rush of several thousand amps to destroy the fuse or trip the breaker, but detects that current is leaking out of the normal supply/return path through some object - often a human body - and immediately shuts the power down.

This imbalance is often adjustable on the breaker itself, but is usually in the region of 10 milliamps or so - in some countries the regulations call for a setting closer to 5 milliamps. Earlier research showed that a current of around 21mA will destroy the electrical nodes in the heart, but I see someone has made mention of 10mA - I will check this and see if the figure has in fact been revised - as it could well have been.

Lopburi was right in clarifying that the neutral and earth are usually linked inside the distribution switchboard, and my only addition to this is to say that as some places in Thailand (my rented house being one) do not have an earth bar, the earthing spike is actually connected directly to the various power points and devices that I need earthed. This seems to work just as well, but is certainly not a very elegant solution - and would not pass regulations in the west.

To clarify another point - earth spikes are used to provide an earth connection for the switchboard these days rather than making a connection to the water pipe as in many countries, the water pipes are being replaced with plastic, and even if they are not all plastic, if a break between the water tap outside on the house wall where the earth is connected and the main water pipe is repaired with a plastic pipe (usually underground where it will not be noticed) you will have lost the earthing.

A properly installed earth spike is a much more reliable earth than the water pipe system.

It is also important NOT to use the lightning protection earth rod as the main house protection earth too - they should NOT be the same, although to maintain equipotential earthing, it is often required that the two are joined - my personal preference is to keep them separate.

Hope this info helps...

Edited June 18, 2005 by Greer

[chownah]

..............

Lopburi was right in clarifying that the neutral and earth are usually linked inside the distribution switchboard, and my only addition to this is to say that as some places in Thailand (my rented house being one) do not have an earth bar, the earthing spike is actually connected directly to the various power points and devices that I need earthed. This seems to work just as well, but is certainly not a very elegant solution - and would not pass regulations in the west.

...................

<{POST_SNAPBACK}>

I would like you to clarify something. Does the AS/NZ 3000 Wiring Standard call for the neutral supply line and the spiked earth to be connected in the distribution switchboard (sometimes called the supply panel)? There is some confusion in my mind about this.

[Greer]

According to AS/NZS 3000:2000 Wiring Rules, Section 5 Earthing Arrangements, Sub-Section 5.3 Multiple Earthed Neutral, Figure 5.1 Multiple Earthed Neutral (MEN) System of Earthing - MEN Link at Customers Main Switchboard (on page 136) - the configuration is as follows:

1. At the Main Switchboard the Neutral Bar and the Earth Bar are linked together, and the Earth Bar is connected, via the Main Earthing Conductor to the Earth Electrode (Earth Spike in our case), it is also connected to the case of the switchboard (obviously) and there is a separate conductor from the Earth Bar to the water pipe system etc to provide Equipotential Earthing for exposed metal surfaces etc around the building.

2. Another section of the same drawing surrounded by a dotted line is named "Separate MEN Installation Distribution Board in Outbuilding or Detached portion of Installation". This is basically the same as described above, with it's own Earth Spike. The Neutral is connected from the Sub-Board Neutral Link back to the Main Switchboard Neutral Link of course, but the Earth Bar in the Sub-Board is only connected to it's own local Earth Spike, and there is no cable connection between the Earth Bar in the Sub-Board and the Earth Bar in the Main Switchboard. The Neutral Bar and the Earth Bar in the Sub-Board are linked.

Hope the gobbledegook above helps clarify the picture...it's a little difficult to put a schematic into words..

Greer

Edited June 19, 2005 by Greer

[chownah]

I know this topic was pretty much comatose.....but I emailed my brother-in-law who is a retired electrical engineer in the US and I wrote:

"I told them it [the residential wiring in the US] was three wires with two being (more or less) 120 volts 180 degrees out of phase and a neutral which was grounded. A couple of them (who haven't been in the US for many many years) thought that it was 208 volts which derived from two 120 volt lines 120 degrees out of phase and a grounded neutral. Now I know for sure (I'm pretty sure on this) that in Seattle I'm right....but....I have no experience elsewhere in the US.....I've looked on the internet but don't seem to be able to find information about this so I'm turning to you ...my electrical expert....can you fill me in on what the standard residential service is across the US and does it change from place to place? Also there is some question if the ground wire...the one that connects to the ground rod...is also connected to the neutral supply wire in the service panel....do you know about this?"

And he wrote back:

"You are correct about the 120/240 Vac (180 degrees) with a grounded neutral for RESIDENTIAL wiring and distribution. This type of service is properly called an "Edison three wire service". Both sides of the 120 volt to neutral (ground), 240 Vac line to line, circuit are used through individual single pole circuit breakers (or fuses in older homes) for lamps, small appliances, etc. and the heavy drain type equipment such as electric ranges, clothes dryers, water heaters and electric furnaces use double pole circuit breakers from the two out board (120 Vac) conductors to obtain 240 Vac connections. This residential stuff is all SINGLE Phase. Residential wiring always connects the center tap of the Edison three wire system to earth ground (usually via a water pipe of ground rod for safety) at the main circuit breaker panel. In the entire U.S. and Canada too, all residential service is the 240/120 Edison three wire kind. But the distribution of higher voltages has many variations. As you know the frequency is 60 Hz in the U.S. and Canada. I am not sure of Mexico or South America residential service, but believe that it is like the U.S. too, but maybe at 50 Hz. In the U.S. some electric railroad service is at single phase 13.8 kV and 25 Hz and street cars are usually 600 Vdc."

[paulfr]

IMO, the only reason for a home to have a ground stake in the earth is to attach to a lightning rod on the roof to provide a path for the transferred charge away from the house. Connection of this stake (or your metal pumbing pipes) to your electrical system is unnecessary and very possibly could cause a fire if connected multiple times.

I would love for someone to refute this with a rational explanation. I am always willing to learn.

<{POST_SNAPBACK}>

Believe you are talking about neutral ground rather than the requirement to have a three wire ground system. Obviously you want that refrigerator case to lead directly to ground and that is what the electric ground wire and a ground stake provides.?.

<{POST_SNAPBACK}>

Lop

The point of my implied question is that a stake in the ground does nothing unless it hits a conductive water table AND the neutral at the house input breakers and/or the Power company neutral at the pole feed also connect to the water table AND the water table is continuous. Otherwise, making a floating connection does not alter the circuit at all and is pointless. There is no return path for current to flow.

So is the stake(s) hitting the conductive water table the unstated assumption ??

[chownah]

IMO, the only reason for a home to have a ground stake in the earth is to attach to a lightning rod on the roof to provide a path for the transferred charge away from the house. Connection of this stake (or your metal pumbing pipes) to your electrical system is unnecessary and very possibly could cause a fire if connected multiple times.

I would love for someone to refute this with a rational explanation. I am always willing to learn.

<{POST_SNAPBACK}>

Believe you are talking about neutral ground rather than the requirement to have a three wire ground system. Obviously you want that refrigerator case to lead directly to ground and that is what the electric ground wire and a ground stake provides.?.

<{POST_SNAPBACK}>

Lop

The point of my implied question is that a stake in the ground does nothing unless it hits a conductive water table AND the neutral at the house input breakers and/or the Power company neutral at the pole feed also connect to the water table AND the water table is continuous. Otherwise, making a floating connection does not alter the circuit at all and is pointless. There is no return path for current to flow.

So is the stake(s) hitting the conductive water table the unstated assumption ??

<{POST_SNAPBACK}>

When I redid my electrical panel I wondered about how the stake could work unless it contacted liquid water so I read a bit and asked the electrical inspector and the basic answer is that I was required to have two ground stakes both 8 feet long and seperated by some distance...probably about 8 feet and the reasoning is that there is enough moisture in the soil and there is enough surface area of the combined stakes that there is a path for electricity to follow and the resistance to this current is low enough to give protection. By the way I was also required to have a ground wire attached to my water pipe on the street side of my water heater. So anyway they say it works even if the stake doesn't touch the liquid water table do to soil moisture and large contact area.

[lopburi3]

Lop

The point of my implied question is that a stake in the ground does nothing unless it hits a conductive water table AND the neutral at the house input breakers and/or the Power company neutral at the pole feed also connect to the water table AND the water table is continuous. Otherwise, making a floating connection does not alter the circuit at all and is pointless. There is no return path for current to flow.

So is the stake(s) hitting the conductive water table the unstated assumption ??

<{POST_SNAPBACK}>

Talk about a mail delay.

If your hypostasis were correct there would be no need for any ground as nobody who was not standing in water would be in any danger. That is just not true. The idea is to provide stray electric a better path to ground than your body. It does not have to be into water to do that.

Edited June 26, 2005 by lopburi3

[lopburi3]

I know this topic was pretty much comatose.....but I emailed my brother-in-law who is a retired electrical engineer in the US and I wrote:

"I told them it [the residential wiring in the US] was three wires with two being (more or less) 120 volts  180 degrees out of phase and a neutral which was grounded.  A couple of them (who haven't been in the US for many many years) thought that it was 208 volts which derived from two 120 volt lines 120 degrees out of phase and a grounded neutral.  Now I know for sure (I'm pretty sure on this) that in Seattle I'm right....but....I have no experience elsewhere in the US.....I've looked on the internet but don't seem to be able to find information about this so I'm turning to you ...my electrical expert....can you fill me in on what the standard residential service is across the US and does it change from place to place?  Also there is some question if the ground wire...the one that connects to the ground rod...is also connected to the neutral supply wire in the service panel....do you know about this?"

And he wrote back:

"You are correct about the 120/240 Vac (180 degrees) with a grounded neutral for RESIDENTIAL wiring and distribution.  This type of service is properly called an "Edison three wire service".  Both sides of the 120 volt to neutral (ground), 240 Vac line to line, circuit are used through individual single pole circuit breakers (or fuses in older homes) for lamps, small appliances, etc. and the heavy drain type equipment such as electric ranges, clothes dryers, water heaters and electric furnaces use double pole circuit breakers from the two out board (120 Vac) conductors to obtain 240 Vac connections.  This residential stuff is all SINGLE Phase.  Residential wiring always connects the center tap of the Edison three wire system to earth ground (usually via a water pipe of ground rod for safety) at the main circuit breaker panel.  In the entire U.S. and Canada too, all residential service is the 240/120 Edison three wire kind.  But the distribution of higher voltages has many variations.  As you know the frequency is 60 Hz in the U.S. and Canada.  I am not sure of Mexico or South America residential service, but believe that it is like the U.S. too, but maybe at 50 Hz.  In the U.S. some electric railroad service is at single phase 13.8 kV and 25 Hz and street cars are usually 600 Vdc."

<{POST_SNAPBACK}>

I agree that the 240 cheap transformer option seems to be the norm now for residential use. This is a quote listing the various voltages currently in use within the US:

Standard voltages in the US are 120/240 volts single phase 3 wire, 277/480 volts 3 phase 4 wire, and 120/208 volts 3 phase 4 wire. There are some medium duty industrial facilities that will have 240 volt delta 3 phase 3 wire, and even less of 5 wire 2 phase, which has been removed as much as possible. Heavy industrial can use 550 volts 3 phase and even higher voltages. 4160 is very common in large wood and paper industrial plants.