weather earth and ground are same in case of Ac/DC system. when i read article ,they say both are similar.
We know that we measure voltage in dc system w.r.t ground.My question is when power supply connected to passive or active device it has two postion positive or negative . Can i call -ve position has ground terminal or not??
If common ground not connected, How can measure voltage w.r.t closed path system.
What is major difference between neutral , ground and earth
It is the Common reference point in a multiphase AC system. Measuring each phase in a US mains electrical feed will give you 110V on each leg when measured against "neutral"
Earth and Ground "should" be the same thing. Sticking an 8 foot rod in the ground will provide a good literal "ground" reference point for electrical fields, including lightning.
Ground is what all other voltage potentials are measured against.
So, -ve is in reference to GND... +15V is 15 above GND and -15V is 15 Below GND for a 30V range.
On a mains supply the PE (protective earth) wire has one function - to blow a fuse or breaker should
fault currents flow down it.
There are two cases - massive current due to live shorting to an earthed metal case - here the main
fuse in the live phase will blow rapidly.
Secondly if there is enough leakage current to earth (perhaps the device got damp?) then any
residual current breaker fitted will detect this current and trip out the live and neutral.
The PE wire should never have high voltages on it for more than a few milliseconds, and usually
will be close to local earth (but can vary by several volts).
PE is usually bonded to any metal structures in a building like pipework to ensure they cannot
become dangerous in the case of a stray live wire touching them.
Neutral is the return current from the phase or phases - it can regularly have large voltages on it
in a mis-balanced system (this is not desirable), and is to be treated as live from a safety perspective.
Modern systems always switch both live phases and neutral when isolating a section of mains wiring
for this reason.
Neutral is usually grounded to earth (and the actual ground) at the transformer secondary for
each substation, to stop it floating arbirarily - you never earth or ground it anywhere else since
high currents can flow on the neutral leading to corrosion/heating of the grounding stakes.
Neutral would be better termed 'mains common' I think. In a balanced 3-phase installation it is
intended to be pretty neutral, but for domestic single-phase installation it carries the same current
as the live phase.
Local ground depends on where you are - in a room in a house it is basically defined by the potential
of the floor, furniture, people, and can be floating well above the potential of the ground outside since
rooms are surrounded by mains wiring and tend to pick up mains waveform at several 10's of volts.
Most modern electronic equipment uses isolated supplies, so that the ground in the equipment is
independent of mains earth. Metal-cased appliances though still use mains earth as their ground
to provide protection should the live touch the case - these days that tends to mainly be heaters,
boilers, kettles (and computers that have kettle leads!)
In the U.S., ground and neutral are normally connected together at the breaker box. But throughout the house, the lights and electrical boxes are wired so that current flows through neutral. o current flows through the ground wire under normal conditions. Although ground & neutral are wired together, the current-flow through the neutral wire's resistance may result in a small voltage on the neutral (relative to ground).
Metal electrical boxes are grounded so if the box somehow gets connected to hot, the voltage is grounded-out, the circuit breaker blows, and nobody gets hurt.
There is also a ground-fault interrupter (a special circuit breaker) ifor bathrooms & kitchens (where there is water). If the current through the hot & neutral are not equal, that means current is flowing through ground and that's a fault condition.... That current-to-ground could be flowing through someone's body, and the GFI breaker prevents that. (Sometimes the GFI is built-into the outlet.)
Ah it looks like I'm wrong about earth and neutral links - that does make for a better local earth
of course, but it also implies considerable currents flowing through the ground in parallel with the
neutral conductor in a single phase system. I beleve in 3-phase systems domestic properties on
the same circuit are parcelled out in rotation between the three phases to balance the load.
In the UK I've seldom seen an earthing stake on new-build property (other than for lightning conductor),
but on older properties I have, I think the incoming water utility pipes are used for that purpose?
The term ground is a bit width. But if you talk about a (low voltage) circuit it reference only to a reference point for all measurements. And if the circuit is power via a isolated supply battery, USB charger, most (but not all) wall warts etc) GND isn't PE isn't Neutral.
pwillard:
Earth and Ground "should" be the same thing.
Don't agree. If you talk about a AC distribution you're right but the term GND is more general just the reference for voltage measurements. And as long as the meter and system are isolated you can pick the GND how you like.
MarkT:
Neutral is usually grounded to earth (and the actual ground) at the transformer secondary for
each substation, to stop it floating arbirarily - you never earth or ground it anywhere else since
high currents can flow on the neutral leading to corrosion/heating of the grounding stakes.
True, but you cannot be sure your PE is a line from the "place neutral is connected to earth" (TN) or another "rod into the ground" (TT).
MarkT:
Neutral would be better termed 'mains common' I think.
I find it a okay name because it still should be pretty voltage neutral with respect to PE.
MarkT:
In a balanced 3-phase installation it is intended to be pretty neutral, but for domestic single-phase installation it carries the same current as the live phase.
Still find it amusing/baffling a big nation like the US keeps using 2-phase... In most of Europe, 3-phase = domestic....
MarkT:
(and computers that have kettle leads!)
What's a kettle lead :o Ahh, IEC C16 but you probably mean C14. Just, a (regular) desktop should be connected to PE, yes! And it's indeed common for computer power supplies to connect PE to secondary GND. Some laptop supplies do this as well but not all.
And to add to Doug, in Europe:
TN (like he described) and TT are both widely used.
Non conductive electrical boxes/pies are used (at least modern, metal can be found in old houses).
in a lot of countries it's standard nowadays to have GFCI aka RCD for every outlet in the house (but a GFCI may be shared between multiple breakers)
I'm not an Electrician but have been told by Electricians that in the U.S., the Neutral is tied to Earth GND at the transformer (that round grey thingy up on the power pole , or that big rectangular green box on the ground). As a result, you should see little or no ac voltage from EGND to Neutral.
More correctly, the center tap of the transformer, house Neutral, and house Ground are all tied together at the breaker box and attached to a 4 foot ground rod hammered into the actual Earth ground.
And ground loops are why you don't want to consider Neutral in a mains feed the same as ground. You could measure some serious induced voltage difference between the two. With the Neutral wire being grounded far away and the Earth/GND being a more local grounding rod into the earth.
On that topic, I have seen the result of induced "lightning" voltage difference in two buildings that were 400 feet apart coupled by copper first hand. I'm glad I was not there when it blew the 66 racks off the wall and used the wiring liked a fuse.
In the US, per the NEC (National Electrical Code (at least the 1993 version I have)), in residential wiring, neutral and ground wires are connected together BUT only at the breaker panel. Then the Ground/neutral bus bar is grounded with heavy wire to a big ground rod driven into the ground just outside the breaker box. One thing that confuses many people working with both DC and AC (house wiring) is the colors. For residential house wiring, the HOT wire is usually BLACK and the NEUTRAL is WHITE. Ground is either bare or green. That can (literally) bit folks that are used to DC systems in cars etc. since they typically use BLACK as the ground wire. There are also many special circuit breakers these days - there are both GFCI (Ground Fault) as well as the ARC FAULT (which sense an arc likely to start a fire - typically outlets that get loose and the contacts arc or a wire broken inside the insulation). GFCI breakers work by measuring the current in the hot and neutral legs - if the current is different by something like 5ma, the breaker will trip. Last I heard, they were required on kitchen, bathroom, basement, garage and all exterior outlets less than 8 feet above grade with exceptions for outlets say in the garage behind a freezer or something that were dedicated to the freezer. Watch the colors though between DC and AC wiring (no idea how black = hot in AC and black = ground in DC systems evolved other than nobody was talking to nobody :o )
raschemmel:
Agreed . But anyone who is strictly AC OR DC should know enough to stay in their own ball park.
True, but be aware of the differences. Friend of mine bought a house some years ago where the previous owner had done a bunch of wiring in finishing the basement and some other stuff up. He was obviously used to the DC (car) side and half the house was wired with the black being "neutral" and the white being the "hot" wire. Came as a rude awakening to my friend when he started to do some remodeling (some of the breakers were wired odd too) so it is good to be aware of the differences even if you don't normally work that side of the fence. I do need to buy a newer copy of the NEC - 1993 is just a bit dated
gpsmikey:
Then the Ground/neutral bus bar is grounded with heavy wire to a big ground rod driven into the ground just outside the breaker box.
So every house has a separate ground rod AND a PE Neutral connection ::o Doesn't that give serious ground loops?
gpsmikey:
One thing that confuses many people working with both DC and AC (house wiring) is the colors. For residential house wiring, the HOT wire is usually BLACK and the NEUTRAL is WHITE.
Yeay, AC colors can be confusing.
gpsmikey:
There are also many special circuit breakers these days - there are both GFCI (Ground Fault) as well as the ARC FAULT (which sense an arc likely to start a fire - typically outlets that get loose and the contacts arc or a wire broken inside the insulation).
Interesting, never seen a arc fault circuit breaker before here.
gpsmikey:
GFCI breakers work by measuring the current in the hot and neutral legs - if the current is different by something like 5ma, the breaker will trip.
The default value here in the Netherlands is 20mA and the max for residential is 30mA.
gpsmikey:
Last I heard, they were required on kitchen, bathroom, basement, garage and all exterior outlets less than 8 feet above grade
Here in the Netherlands they are required for every new (or changed) installation.
gpsmikey:
with exceptions for outlets say in the garage behind a freezer or something that were dedicated to the freezer.
Wait, why would you want to to specifically not have a PE outlet for a freezer... I would really want a device with big metal panels to have PE...
alnath:
Here, in Europe, NFC15-100 says :
hot wire (called 'phase' in France) may be any colour but blue or yellow/green
neutral must be blue
earth must be yellow/green
I think it's the same here although I never saw a (modern) installation with a different color then brow for line. Except black as switch wire and black or gray as 3-phase L2 and L3... (Or a brown striped wire).
Fun fact, before the unification of mains wiring in Europe the colors where:
Red for Neutral
White or gray for PE
And green as line (together with black and blue for L2 and L2)
Talking about confusing Still found in older houses... And when mixed it still doesn't feel right to connect blue and red together
" Then the Ground/neutral bus bar is grounded with heavy wire to a big ground rod driven into the ground just outside the breaker box.
So every house has a separate ground rod AND a PE Neutral connection ::o Doesn't that give serious ground loops?"
No - every house has one (or more) ground rods that tie to the ground/neutral bus in the breaker panel. Essentially, ground and neutral are the same but they only connect together at the breaker panel. Neutral is supposed to carry the current while ground is there for protection (unless you are using a double insulated device which does not have a ground pin on the plug).
Arc fault are still fairly new, but are being required in many new situations (I don't have a copy of the current NEC, so I can't say exactly when they are required). They look for the "signature" in the current that is typical of an arc and will trip. I believe this was initially triggered by the number of fires cause in bedrooms etc. where things (beds etc.) have been pushed into the plugs in the wall too many times either breaking the wires or bending the sockets so there is a poor connection and you get an arc. Hey, at least we got rid of that da***d aluminum wire they had for some years back in the 70's or so. That stuff was bad news in a typical residential wiring situation.
I don't want to oversimplify this issue but I'm not an Electrician and I learned many years ago that Neutral is WHT (USA) and Line is BLK, and Earth GND should be Green with yellow stripe but sometimes appears as just solid Green. Line and Neutral are the current carriers so clearly the difference between Neutral and Earth ground is that Neutral is a current carrier and Earth Ground is not. The colors are clearly not the same so there's no confusion there. The only issue seems to be the whole ground - Neutral connection issue and what that means to the home owner. I would think that the NEC code requiring the Earth GND-Neutral connection to be at the breaker panel would offer the most protection for the enduser.
When you read the OP's question carefully , some things become obvious:
We know that we measure voltage in dc system w.r.t ground.
(TRUE, obvious)
My question is when power supply connected to passive or active device it has two postion positive or negative .
(ONLY TRUE FOR DC circuits when discussing wiring)
Can i call -ve position has ground terminal or not??
(obviously this could only apply to DC since there since "-Ve" is a DC designator. It stands for Voltageemitter), which only appears in DC circuits, (-Ve can also be NEGATIVE.
If there is no NEGATIVE supply voltage then -Ve would refer to GND.
If common ground not connected, How can measure voltage w.r.t closed path system.
(Really ? Is this a serious question ? There are only 2 wires in a "closed path system" ! Where ELSE are you going to put your meter ?
