Question about AC from The Wall Outlet

[Tybe]

I have searched the internet for this, and forums, but haven't managed to figure it out.

I'm getting some readings. I have pictures here to illustrate:






I'm getting 400V peak to peak from my 230VAC Wall Outlet on my oscilloscope. I believe I have power from a TN-System, but not sure. I live in Nothern Europe.

Link to the grid system I might have; http://en.wikipedia.org/wiki/Earthing_system#TN_networks

It maby makes sense that I measure 400V because I think I get 400V from the "L2" wire? But what I don't understand is why I'm measuring 400V peak to peak from the Neutal "N".
And what about the math if its correct. What are the calculations we will have to make for getting 400VAC to 230VAC that the Wall Outlet is delivering?

And here are the readings from a multimeter,







That's a cheap multimeter, so the voltage may appear a bit too high or low maby.

If anyone want to share some time to help and answer me it's highly appreciated.

-Tybe

[G7PSK]

You either have a poor earth at the house and no bond wire back to the substation or you have an old type ELCB which has a high resistance coil in the earth to measure an earth current. The result is that you have an emf induced into your neutral. What sort of current can you draw from the neutral to earth connection use a small light bulb say about 15 watt and see if that lights even dimly on the neutral to earth, I suspect that it wont as a scope and a dvm respond to so small a current that even a moving coil meter will not see.

[Kremmen]

OK; i'll bite.
The only measurement that makes sense is the last one: between phase and neutral (L and N) you should have nominally 230 V RMS so the indicated 243 is a bit high but OK.
The 400V could be a main voltage between live phases but 3 reasons why i don't think so: 1) You already measured a normal phase voltage between L and N; 2)a single phase Schuko outlet would _never_ be wired that way. It would be a shooting offense from an electrician to do so; 3) Your scope voltage is too nicely reading 400.000 volts for both L and N to PE. You sure about that?
The other meter readings would indicate a floating PE conductor. The exposed wire colors do not necessarily indicate L and N correctly (a Schuko plug enters both ways) but one of those measurements should be the same 243 V and the other a firm 0 V. Because they are both same it looks like the PE is not connected to anything.

[Kremmen]

You either have a poor earth at the house and no bond wire back to the substation or you have an old type ELCB which has a high resistance coil in the earth to measure an earth current. The result is that you have an emf induced into your neutral. What sort of current can you draw from the neutral to earth connection use a small light bulb say about 15 watt and see if that lights even dimly on the neutral to earth, I suspect that it wont as a scope and a dvm respond to so small a current that even a moving coil meter will not see.

The OP said he lives in Northern Europe. So do I and the current code around here mostly calls for TN-S distribution system in the premises. In a TN system there really should not be a case of totally missing PE since the premises PE is connected to grid N at the supply entry in the main panel. Additional to that there are the local grounding rods, cables and whatnot. So if the wiring is at all according to code, there will be a connection between PE and N somewhere. However the wall outlet grounding prongs are another matter. They might be totally floating (no actual PE wire at all behind the outlet) or it could be unconnected at the distribution panel. This is known to happen.
The newest code requires RCDs in all outlets. Connecting N and PE at the wall outlet and introducing a load should make the RCD trip if PE is connected.
In a properly wired house connecting anything between N and PE won't do anything since they should already be together at the panel end. If PE is floating there again won't be any current of course. Only if N or PE are actually connected to some other potential than ground (a grievous error!) will there be any current in this circuit. Let's hope that is not the case.

[Tybe]

G7PSK
What sort of current can you draw from the neutral to earth connection use a small light bulb say about 15 watt and see if that lights even dimly on the neutral to earth

I tried to connect a 25W lightbulb, But since I dont know witch one is neutral I just picked one. A little flash from the bulb then the fuse (10A) went off. I have to tell, This leaded to a good thing because my motherboads smd network card in my pc came alive after the power shortcut Thats just great! and strange, It has been dead for a month :p cheers:)

And Kremmen, I still reading your inputs and try to understand, I'll give a feedback after some more reading:)
Thanks for the answers so far

[Tybe]

BTW I checked the peak to peak again. I got 400.0 Vp-p and also I got 398.0 Vp-p. Nothing in between. So the reason It's showing 400.000 must be that the scope has a resolution of 2.0 Voltage on that level. It's and Owon SDS7102 so You know.

[G7PSK]

A 25 watt bulb should no way blow a 10 amp fuse there is something wrong here to say the least.

[nixxon]

Hi!

I also live in Norway. Based on http://no.wikipedia.org/wiki/TN-nett ,  most of the existing low voltage power grid in Norway is based on IT (Isolated Terra). 

The power line into a small house in Norway usually consists of 3 wires (L1, L2 and L3) with 3-phase Delta. You should read approx. 230-240 VAC RMS between any 2 of the L's. The electrician that mounts all the sockets is responsible for distributing the power equally throughout the house (between L1-L2, L2-L3 and L3-L1). Newer buildings and developement areas utilize the TN-system.

In my citchen, I read 242.6 Volts between the two leaders in a socket, using a Fluke 83V. Between each leader and ground, I read 141.8 and 136.6 Volts respectively. I thought I would read approx. 242.6 divided by 2 = 121.3, but no!? I hooked up my Rigol DS1052E and made a screenshot, as seen below. Each probe in its own L, Ground clip not connected.

I expected to see a Vpp of 141.8 Vrms / 0.707 = 200.6 * 2 = 401.2 Vpp and 136.6 Vrms / 0.707 = 193.2 * 2 =  386.4 Vpp, but not exactly so.

Now it's dinner time...

[IanB]

The power line into a small house in Norway usually consists of 3 wires (L1, L2 and L3) with 3-phase Delta. You should read approx. 230-240 VAC RMS between any 2 of the L's. The electrician that mounts all the sockets is responsible for distributing the power equally throughout the house (between L1-L2, L2-L3 and L3-L1). Newer buildings and developement areas utilize the TN-system.

In my citchen, I read 242.6 Volts between the two leaders in a socket, using a Fluke 83V. Between each leader and ground, I read 141.8 and 136.6 Volts respectively. I thought I would read approx. 242.6 divided by 2 = 121.3, but no!? I hooked up my Rigol DS1052E and made a screenshot, as seen below. Each probe in its own L, Ground clip not connected.

I expected to see a Vpp of 141.8 Vrms / 0.707 = 200.6 * 2 = 401.2 Vpp and 136.6 Vrms / 0.707 = 193.2 * 2 =  386,4 Vpp, but no.

In three phase systems you divide by the square root of 3 to find the voltage to the "star" point at the centre between the three phases. So for instance 240 V / 1.732 = 140 V.

Since the earth potential will usually be at the star point between the three phases this is why you read what you see between L and E.

To explain the observations at the top of the thread, 140 V RMS would have a peak voltage of 140 x 1.414 = 198 V, and then the peak to peak voltage would be twice this, i.e. ~400 V.

[vk6zgo]

So the system at your house & some others in Norway is another of the exceptions like the USA split transformer system.
Well,we have learned something...

[Monkeh]

240V three-phase. Well, that's different.

[HardBoot]

3-phase for residential?

Damn, I need to move to Norway.

[Monkeh]

3-phase for residential?

Damn, I need to move to Norway.

Yeah, but only 240V. I'll take my 415V, thanks.

[HardBoot]

3-phase for residential?
Damn, I need to move to Norway.

Yeah, but only 240V. I'll take my 415V, thanks.

3-phase has more cool factor than fat single/split phase.

Although... HVDC, yum, I wish it was more popular.

[Tepe]

3-phase for residential?

Of course:

If I remember correctly, it is, from left to right, N, L1, PE, L2, L3.

[Monkeh]

3-phase for residential?
Damn, I need to move to Norway.

Yeah, but only 240V. I'll take my 415V, thanks.

3-phase has more cool factor than fat single/split phase.

Although... HVDC, yum, I wish it was more popular.

Who said anything about split phase? I can get 415V 3-phase here if I ask nicely. And dig the drive up. (needs doing..)

[Tepe]

I can get 415V 3-phase here if I ask nicely.

What kind of outlet do you use for that in the UK?

[nixxon]

240V three-phase. Well, that's different.

The 3-phase voltage is higher than the 1-phase tap of 240 volts. I believe around 400V. (230 * 1.732 = 398 V)

Just found this info:
http://power.apitech.com/engineering-tools.aspx

3 Phase Delta (?)A 3 Phase-Delta connected system consists of three hot lines, commonly referred to as X, Y, Z, and a ground wire for a total of four wires in a power distribution cable.
In North America the most common 3 Phase-? voltages are either 208VAC or 240VAC, while internationally the most common 3 Phase voltage is 230 VAC. These phase voltages are measured Line-to-Line and are typically the country’s standard utilization voltage.
Since there is no neutral line in a Delta-connected system, there is no Line-to-Neutral voltage! However, the line current in a Delta-connected system is 1.732 times the phase current supplied to the load(s).
Proper care must be taken to correctly size cables in a Delta system because the line currents are much higher than the load (or phase) currents.
Delta systems typically have lower line voltages but higher line currents than Wye-connected systems

[Monkeh]

240V three-phase. Well, that's different.

The 3-phase voltage is higher than the 1-phase tap of 240 volts. I believe around 400V. (230 * 1.732 = 398 V)

Please look at his readings. He's phase to phase at 240VAC.

I can get 415V 3-phase here if I ask nicely.

What kind of outlet do you use for that in the UK?

IEC 60309.

[G7PSK]

[/quote]
What kind of outlet do you use for that in the UK?
[/quote]

Like these Red 415 volt cee form either 3 pin and earth or 4 pin and earth the four pin ones have 3 phase and neutral.

[Kremmen]

[...]
And Kremmen, I still reading your inputs and try to understand, I'll give a feedback after some more reading:)
Thanks for the answers so far

You are welcome but please note that i didn't realize you were a Norwegian as you mentioned TN system (and didnät have the small flag visible at first ). No?way TT is different as the rest of the replies show, so what i wrote is not really valid for you.
There was a reason why Norway uses TT system but i cannot recall it right now. Something to do wit geography maybe?

[Monkeh]

Like these Red 415 volt cee form either 3 pin and earth or 4 pin and earth the four pin ones have 3 phase and neutral.

Don't forget 5 pin. Three phases, neutral, earth.

[Kremmen]

Like these Red 415 volt cee form either 3 pin and earth or 4 pin and earth the four pin ones have 3 phase and neutral.

Don't forget 5 pin. Three phases, neutral, earth.

Well, he didn't "...or 4 pin and earth.." = 5 pins, right?

[Monkeh]

Like these Red 415 volt cee form either 3 pin and earth or 4 pin and earth the four pin ones have 3 phase and neutral.

Don't forget 5 pin. Three phases, neutral, earth.

Well, he didn't "...or 4 pin and earth.." = 5 pins, right?

Yeah, his post is.. kinda unclear.

[Tybe]

[...]

You are welcome but please note that i didn't realize you were a Norwegian as you mentioned TN system (and didnät have the small flag visible at first ). No?way TT is different as the rest of the replies show, so what i wrote is not really valid for you.
There was a reason why Norway uses TT system but i cannot recall it right now. Something to do wit geography maybe?

You are correct Kremmen, I put on my flag because it may be significant. And thanks

And Nixxon and Ianb Your information are just the one I need to figure this out so great thanks! This thread has now alot of good information about understanding the wall outlet and the threephase systems