About Mains

[ricothetroll]

Hi,

After having some issues with my bass amp (http://www.diystompboxes.com/smfforum/index.php?topic=87393.0), I decided to create this topic. I realized that I didn't really know what mains is exactly made of. I read on wikipedia (french) that neutral is connected to earth locally or at the provider's side, that makes sense, as current must flow to it. When I measured earth-line and earth-neutral voltages with my DMM, I read about 130V for both of them. I expected to read OV for the neutral and 230Vac for the line ! Why did I measure 130V ? I must be misunderstanding something.

Best regards.

Eric

[therecordingart]

http://www.school-for-champions.com/science/ac.htm

I'm not trying to be condescending by posting the link, but I'm not good at explaining things. Your assumption would be correct in a DC circuit.

[ricothetroll]

Hi,

Thanx for the link (I wanna be a champion ! Just joking), but I already know the basics of AC electricity. My question was : why don't I have 230V on the hot wire and 0V one the neutral, instead of 130V on both of them ?

After lots of different researches on google I finally typed one that leaded me to an answer. Sometimes it's hard to figure out what words will point to what you're looking for, that time it was "ac hot neutral" 

Found here :
http://www.controlbooth.com/forums/lighting-electrics/7724-how-does-ac-have-hot-neutral.html

In house wiring, there is a bit of a funny legacy issue that kind of set the stage for this odd combination. Houses built early last centaury did not have grounded outlets. They only had two conductors, Hot and Neutral. The problem with this is that wires are not perfect conductors. They are actually like big resistors, that drop voltage if the load is heavy enough. What this means is that if you have a really long run of wire and a heavy load, the neutral conductor at the plug  end will actually have some voltage on it! Because of this, old "two wire" appliances did not connect the frame to either wire. In fact, on older two blade appliances you will see that the blades are the same size so they can get plugged in either way! As the years went by, appliances started coming out with one blade slightly larger than the other. This "larger blade" side of the outlet was suppose to be connected to the white neutral wire, although I often found this not to be the case when refurbishing older homes. When wiring an older lamp, you were suppose to wire the outer shell of the lamp socket  to the wider blade in hopes that the bigger part would be less likely to electrocute people! (Still true on two blade table lamps) The code writers still prohibited any real connection between the "larger blade" side and the case. Finally, the idea came forth to have a separate third prong that would actually be a ground. As this third prong would not be part of the circuit  path, it would always be at "true ground" potential, and could be connected to the case of the appliance. As long as the ground wires are run separate from the neutral wires, no voltage drop  will occur. If it was combined with the neutral, some drop will occur and it will no longer be at ground potential. The only time the ground wire sees any current  is when there is a short in the appliance. In these cases, this current is looped back through the ground and hopefully the overload quickly trips the breaker. Because the ground conductor may have to handle the full circuit current when this happens, it is required to be the full approved gauge for the circuit in question.

When you looked in your circuit breaker box, you saw a buss where the grounds and neutrals came together. This buss also had your service entrance neutral connected to it, and hopefully also had a thick copper wire that was connected to a large metal stake in the ground. It is usually also connected to a water pipe and a gas pipe so that all are bonded together.

In a funny twist of fait, technology is eliminating the "third prong" defense with the introduction of ground fault detectors. These devices work like a bouncer in a club, who only lets the same amount of people enter as are leaving! If any imbalance occurs, they trip.

Thanx, JD !

Best regards.

Eric

[PRR]

> neutral is connected to earth locally or at the provider's side, that makes sense, as current must flow to it.

No, power current does NOT normally flow to earth/ground/dirt.

Power systems "CAN" work without any earth connection. (iPods, aircraft, spaceships.)

Utility systems ARE connected to earth because "things go wrong". Lightning strikes. HV-LV crosses. Accidental earth connections. Accidental earth connections THROUGH people. Utility systems are safer if there is a deliberate path to local ground.

> I read on wikipedia (french)
> I measured earth-line and earth-neutral voltages with my DMM, I read about 130V for both

As far as running lamps or bass-amps, what you want is Line To "Neutral". That;s where you take power.

Where are you? USA/Canada or in France?

In the USA etc, we normally have 120V on "Hot" and nearly zero voltage on "Neutral", 120V available. We have a few 240V outlets, mostly for single large loads, as two "hot" leads 120V from ground or neutral but out-of-phase thus 240V from each other.

In most of the rest of the world, power is used at 230V. I think this is usually delivered as zero and 230V. But it could also be delivered as 230V center-tapped, 115V each side of ground or neutral.

In any case, the wiring is critical yet simple. In the US there is no "neutral" in a 120V outlet. One prong is probably tied to neutral, via a white screw and wire; in fact many outlets are wired randomly (60% of outlets in my kitchen had white/black reversed). So the two flat prongs are both "live". This goes to transformer primary via switch and fuse. The U-shape ground pin goes to chassis, very secure.

In other areas the pins and wires are other shapes and colors, but the idea is the same. The GROUND pin/wire is clearly different from the two "live pins". On your side of the wall outlet, you do not care which wire might or might not be "neutral".

[darron]

Topics like this frustrate me. Here in Australia, unlike other parts of the world, EVERY power point has an Earth, and YES that Earth is always connected to the physical ground under your house. Neutral is always connected with Earth at the power box (test before assuming still). In some rural areas there isn't even a neutral line and power is returned to the station through the dirt/ground/Earth so houses only need the one active line to be powered.

This being the case there must always be near perfect continuity from neutral to Earth, and the voltage between the two must always be zero.

Your points remain valid, Eric.

[PRR]

> In some rural areas there isn't even a neutral line and power is returned to the station through the dirt/ground/Earth so houses only need the one active line to be powered.

Yes. SWER. One wire working at 20,000V with ground return. A guy in NZ did the development and promoted it. It is used in parts of Canada and Alaska, and has been used in mainland USA.

http://en.wikipedia.org/wiki/Single-wire_earth_return

However "YOUR" 230V side of the power transformer is 2-wire or 3-wire, and transformer-isolated from the SWER line.

> Neutral is always connected with Earth at the power box (test before assuming still).

As you say.... professional electricians sometimes slip-up, inspectors can't see/test everything, homeowners do their own repairs and damage (mower into the dirt-rod is popular), rust never sleeps.

> frustrate me. Here in Australia

Here's an observation. The earlier an area or market was electrified, the nastier the electric system.

The USA had residential power very early. Earlier than good rubber. Edison used 100V to ground (+ and - 100V to a common neutral which was grounded) believing that to be reasonably safe despite poor insulation. BARE-wire installations were common in factories and home attics. On smaller 100V-only services, no distinction was made between grounded and hot wires. Fuseboxes (IF used) were often live-front behind wood door.

England had various local standards very early; probably you too. But by the time electrification swept across European markets, good insulation was available and the US experience emphasized the need for much safer systems than the US had installed. With good insulation the balance shifts to higher voltage and lower current. Less copper and often less fire-hazard.

US houses started with one circuit. As loads increased this meant either over-wiring or under-fusing, so we went to multiple circuits. There was once a 20-breaker limit on residential boxes; we had to drop that limit because even my simple house has 17 active circuits; 12-13 if I brutally rationalized. That's a lot os 20 Ampere cable. OTOH in the UK they run one ring-main around each storey, and sub-fuse at each load. That's a lot less wire (even before you consider voltage).

That's not to say the US is horribly un-safe. Houses built 99% in compliance with post-1975 code are very safe. Older work may be safe as far as it goes, or may be falling apart in odd ways.

[ricothetroll]

Hi,

Thanx for your answers ! Once again, I'll go to bed a little less ignorant thanx to this forum ! 

I'm in Belgium. I might receive the mains center tapped, as my measures suggest.

Best regards.

Eric