Help Me Understand The N-E Connection

[Daffy D]

In my day back in the Uk house wiring was quite simple. You had three basic wires which were all color coded and each had it's own place in the consumer unit.

Now it seems the new way to do things is to connect the N to the E at the consumer and run your earth grounding rod from there.

This begs the question "why do we need an earth at all" Every unit will automatically be connected to earth through the N terminal. Those hot water shower units that "Must be connected to an Earth" are already earthed through the N. If you really feel the need to do it the old way why not just connect the E terminal (if it has one) to the N inside the shower unit.

This way of earthing may be a little tricky with things like fridge and washing machine that only have two pin plugs but once you sort out which pin is N and always plug it in the wall the same way there should be no problem with connecting the frame to the N within the unit.

Think of all the money saved by not having to run an extra Earth cable from each of your socket outlets all the way back to the consumer unit.

Another thought comes to mind. If you do have the E - N connection testing the Earth by connecting a 15W lamp between L and E is pointless as the lamp will light through the N anyway so not proving anything about the strength of the grounding rod.

And a final thought, if at sometime somewhere down the road they do some line repairs and reverse the polarity the N would become L and go straight to E.

Just some random musings while lying bed this morning in the dark listening to my windows rattling as yet another funeral was taking place at one of the nearby temples.

[Crossy]

What you are talking about is a TN-C system. Whilst this is commonly used by distribution systems it is usually prohibited within buildings, mostly due to the severe danger posed by reversing appliance leads or other accidental polarity reversals.

The modified version where a separate ground lead goes to the appliance and is linked to the neutral in the fixed wiring is called TN-C-S and is what is used in new installations in Thailand with the addition of a local ground stake which makes it MEN (or PME).

The various different grounding systems are described here http://en.wikipedia....Earthing_system

[prefabs]

The poor bugger who died. Was he electrocuted?

[necronx99]

I'm going to request NO acronyms in this thread and SPECIFICALLY no instances of using an acronym and then saying aka as (these other 6 acronyms)

TYVM.

Edited April 2, 2012 by necronx99

[chrisnor]

hey daffy

the conection type in thailand is not the same as you yous in england

they have the same system as scandinavia( norway sweden denmark)

and the same in the us

we dont have a fixt + - cabel and all system is one cabel normal is green with yellow ore yellow with green line this is always ground

this cabel is not conectet to the fuse box

but it vill have a conection pointe in the mane fuse central

and a big ground cabel going out of the central to a minimum of 1.5 meter down inside ore outside your house

the ground cabel is so if you have a brokes system all power will lead out of electronic cabel and you wont get a shock

ore die with hotwater shower

same if you get a smale electric shock wen touching water system in your house then your ground is not good anoff

inn norway we yous copper pipes minimum of 3 pipes we hammer down in the ground if ground wirer isent good anoff

new houses in noway has 30 mm cabel out of house and a 20 mm copper wire in the ground around your house

hope this help you

chris

[Crossy]

Actually Chris, the system in Thailand is mostly the same as the UK, 3-phase 4-wire with a grounded star point.

I believe (and I'm open to correction here) that Scandinavia uses a lot of 3-phase 3-wire (delta) connections for domestic with 2-pole MCBs in the consumer unit.

I did write a long explanation and some history of UK supply architecture, but a crappy internet connection here in India ate it

[dhrobertson]

A separate ground or earth is for two reasons.

Firstly, by connecting all metallic parts to the same reference voltage (0V) it is impossible to get a shock.

Secondly, a separate ground/earth allows a fault to be detected and automatically disconnect the supply.

Neutral is connected to ground/earth at the supply transformer and often at several other locations. However neutral DOES carry current. We're talking ac here. In Thailand the voltage on the phase wire alternates between +/- 220V. Thus, half the time, current is being supplied by the neutral.

As a result, whereas neutral may be approximately at 0V it is still a "live" wire.

Be VERY careful about ground/earth. It is a non-trivial matter. Often, neutral and ground are bonded together at the consumer unit, but then run separately within the building. This is to improve "performance" because any solid ground fault becomes effectively a short circuit and the associated breaker trips quickly. However various afety measures are required. These usually include local ground rod(s) and multiple protective earthing.

[Daffy D]

I hope it was appreciated that my OP was semi humorous though some of the points mentioned do concern me.

It seems that having a N/E (Neutral/Earth) connection or not to have a N/E (Neutral/Earth) connection at your consumer unit depends on the electricity company's set up in your particular area.

As that seems to be difficult to establish I'm going to stick with the old method of not connecting the N (Neutral) to the E (Earth) in the consumer unit and run a E (Earth) to the G (Ground) out the back of the house near the (concrete rings) septic tank where it is always damp.

:-)

[Crossy]

I hope it was appreciated that my OP was semi humorous though some of the points mentioned do concern me.

It seems that having a N/E (Neutral/Earth) connection or not to have a N/E (Neutral/Earth) connection at your consumer unit depends on the electricity company's set up in your particular area.

As that seems to be difficult to establish I'm going to stick with the old method of not connecting the N (Neutral) to the E (Earth) in the consumer unit and run a E (Earth) to the G (Ground) out the back of the house near the (concrete rings) septic tank where it is always damp.

Yup, that would be my broken record Daffy

If in doubt TT and RCD.

[sirineou]

I'm going to request NO acronyms in this thread and SPECIFICALLY no instances of using an acronym and then saying aka as (these other 6 acronyms)

TYVM.

I echo this sentiment, If we knew what these acronyms mean , we are probably educated in electrical maters and know all about grounds.

[Daffy D]

I'm going to request NO acronyms in this thread and SPECIFICALLY no instances of using an acronym and then saying aka as (these other 6 acronyms)

TYVM.

I echo this sentiment, If we knew what these acronyms mean , we are probably educated in electrical maters and know all about grounds.

Please see my post No. (number) 8

:-)

[Pib]

What you are talking about is a TN-C system. Whilst this is commonly used by distribution systems it is usually prohibited within buildings, mostly due to the severe danger posed by reversing appliance leads or other accidental polarity reversals.

The modified version where a separate ground lead goes to the appliance and is linked to the neutral in the fixed wiring is called TN-C-S and is what is used in new installations in Thailand with the addition of a local ground stake which makes it MEN (or PME).

The various different grounding systems are described here http://en.wikipedia....Earthing_system

Yeap, my 4 year old house here in western Bangkok uses a single phase TNC-C-S system, like shown on the right hand side of below image. Wiring/sockets within the house is the 3 wire hookup with Line, Neutral and Safety Earth wires.

[Pib]

I'll take back what I said above about my house having a TNC-S system. In closer examination of my main circuit box and grounding system today I have a single phase TT system like shown on the right hand side of below image. In my jam-packed Square D circuit box with one double poled main breaker which the 2 incoming main power wires (L & N) hook to, 16 single pole circuit breaker outputs, one heavy gauge Earth wire going from the Earth bar to grounding stake in/through the concrete floor, 16 outgoing Line wires, 16 outgoing Neutral wires, and 16 outgoing Earth wires I thought I had seen a connection between my Neutral and Earth bar but closer examination revealed there is no connection. Wiring/sockets within the house is the 3 wire hookup with Line, Neutral and Safety Earth wires.

[electau]

I'll take back what I said above about my house having a TNC-S system. In closer examination of my main circuit box and grounding system today I have a single phase TT system like shown on the right hand side of below image. In my jam-packed Square D circuit box with one double poled main breaker which the 2 incoming main power wires (L & N) hook to, 16 single pole circuit breaker outputs, one heavy gauge Earth wire going from the Earth bar to grounding stake in/through the concrete floor, 16 outgoing Line wires, 16 outgoing Neutral wires, and 16 outgoing Earth wires I thought I had seen a connection between my Neutral and Earth bar but closer examination revealed there is no connection. Wiring/sockets within the house is the 3 wire hookup with Line, Neutral and Safety Earth wires.

It would appear than you have a typical Thai electrical installation. Neutral is not earthed ie TT. One notes that this installation is 4 years old so there is is an option not to use TN-C S ( neutral earthed) and the TT option has been used instead.

The earth conductor is probably 10sqmm to an electrode or equivalent in the concrete.

Can you access the connection to the electrode?

As the installation is TT all circuits should have RCD protection.

16 final circuits seems a lot of circuits for a residential house any reason for this?

[Crossy]

16 final circuits seems a lot of circuits for a residential house any reason for this?

We have 18:- 6 air conditioners, 3 water heaters, 4 lighting, 4 power, 1 water pump.

[bankruatsteve]

"16 final circuits seems a lot of circuits for a residential house any reason for this?"

You've got to be kidding!? I have 13 circuits and only 1 A/C, oven, water pump. The rest are lights, 5 receptacle, outside, etc. And this is a "small" house.

Anyway... if you get a box (CU) with x number of slots, you might as well fill it. (I have a 4x and a 10x so I left one empty dam_n it).

[Pib]

I'll take back what I said above about my house having a TNC-S system. In closer examination of my main circuit box and grounding system today I have a single phase TT system like shown on the right hand side of below image. In my jam-packed Square D circuit box with one double poled main breaker which the 2 incoming main power wires (L & N) hook to, 16 single pole circuit breaker outputs, one heavy gauge Earth wire going from the Earth bar to grounding stake in/through the concrete floor, 16 outgoing Line wires, 16 outgoing Neutral wires, and 16 outgoing Earth wires I thought I had seen a connection between my Neutral and Earth bar but closer examination revealed there is no connection. Wiring/sockets within the house is the 3 wire hookup with Line, Neutral and Safety Earth wires.

It would appear than you have a typical Thai electrical installation. Neutral is not earthed ie TT. One notes that this installation is 4 years old so there is is an option not to use TN-C S ( neutral earthed) and the TT option has been used instead.

The earth conductor is probably 10sqmm to an electrode or equivalent in the concrete.

Can you access the connection to the electrode?

As the installation is TT all circuits should have RCD protection.

16 final circuits seems a lot of circuits for a residential house any reason for this?

2 breakers/RCBOs used by the two heaters, 7 used by the 7 split A/Cs (4 bedroom house with and A/C in each bedroom and then 3 A/Cs downstairs...the home builder/developer threw-in the 4 bedroom A/Cs as part of the house deal...then we installed 3 more downstairs on our dime...wish I could afford to run all of them), 1 used by the water pump, 1 used by the outdoor yard lights...that adds up to 11 and I haven't even started talking about the lights, outlets, kitchens (indoor and outdoor), washer/dryer, etc., in all the rooms. Heck, I wish I had a main circuit box with some spare holes for possible future expansion, but they are all used up in my 100A box.

Yes, I expect the Earth bar to ground rod wire is around 10sqmm as its diameter is larger than a pencil's diameter/about the same size as a fat writing pen. The main circuit box is mounted approx 6 foot up on the wall, with metal wall mounted conduits leading to the floor and ceiling. The conduit going up from the floor to the circuit box has the large diameter (fat thumb size 35sqmm sized) incoming L & N leads and the grounding lead enclosed in it...the main L & N wires run underground in metal/PVC piping from the soi pole for about 10 meters and come up through the concrete foundation up the conduit to the box. This rectangular shaped conduit would not be easy to open-up the way it has been secured to the wall, baseboard, and circuit box...in fact, the white baseboard is built around the conduit...yeap, itwould take some effort and follow-on baseboard repair to open up the conduit. Then the conduit leaving the top of the box into the ceiling is carrying all my outbound wires to circuits.

I've never actually seen "my" ground point connection at the bottom of that conduit, but while they were building other houses on my street (they had around 8 under construciton) I saw that the grounding point is metal tab that sticks a few inches above the concrete foundation...but I didn't get a chance to see how they bond the ground wire to that tab....welded, bolted, I don't know. And as to whether that tab is attached to a ground rod and/or rebar in the concrete I couldn't say. I don't know if the amount of stray/N-E voltage I measure is an indication of anything other than common mode noise, but I get 1.1VAC between the neutral bar and earth bar....my Googling seems to indicates that is fine, maybe even very good....and it's only when it gets up around 5VAC you may start having some noise issues.

Edited April 17, 2012 by Pib

[electau]

With reference to Pib, post #17.

It would appear that your main earthing complies with the minimum requirements, the conection may be to an electrode that is buried under the concrete, makes it very difficult to test the continuity of the main earth.

A voltage above 1.0V is perfectly normal for a TT system . in some cases of long distribution the voltage will be above 5 volts. depends on the earthing of the distribution system neutral conductor. It is nothing to be concerned about.

30mA RCDs should be installed on all final circuits, lights, socket outlets, airconditioners etc. this will ensure that in the event of an earth fault the RCD will operate in less than 0.3/0.2 seconds.

[electau]

There is a very good reason to try to minimise the number of final circuits originating from a switchboard. Cost. A saving in the number of circuit breakers and cable.

Eg . lighting points, 0.5 per point. socket outlets 1 A per outlet, a twin outlet is 2 outlets.

Airconditioners, waterheaters and hotplate units, 1 circuit each.

Thus on 1.5 sqmm 16A MCB one can have up to 32 lighting points as long as the total connected load does not exceed the rating of the MCB.

On 2.5sqmm 20A MCB one can have up to 20 x 10A socket outlets as long as the total connected load does not exceed the rating of the MCB.

In practice one would install up to 80% of the above points and sockets, thus allowing for possible additions in the future.

Source AS3000.

[Pib]

electau, Good information...thanks. If I do need to add a circuit breaker in the future I'll first evaluate my current circuits/loads to see if I could combine some current circuits currently on two breakers down to one breaker...like for some of the upstairs lighting/outlet circuits. Cheers, Pib