Wall power terminology

Discussion in 'General Electronics Chat' started by tmac, Nov 17, 2009.

  1. tmac

    Thread Starter Member

    Oct 28, 2008
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    Hi!

    I am curious about the terminology of "hot", "neutral" and "ground" terminology that is used in the USA. Here is how it works in Norway as far as I know:

    Ground: connected through the electrical system in the house to a proper grounding in the soil under or near the house.

    Two "hot" wires: these constitute the one-phase AC power we use, and ideally they fluctuate symmetrically around the ground potensial. It is not very seldom that they fluctuate around a different value if someone in the neighbourhood has a grounding error :) The potential between these two wires is around 230VAC. There is no distinction between these two hot wires here in Norway. They carry the AC electricity into the house from the street. The grounding in the house is not connected the electric cables in the street.

    Is it not the same in the USA? Aren't the "hot" and "neutral" leads equivalent, i.e. both are really "hot" in the same manner with respect to earth?

    Or are the voltages like this?:

    hot - neutral: 110VAC
    hot - ground: 0VAC
    neutral - ground: 0VAC

    And as in Norway, the ground lead is not connected to the street electricity? I.e. it is not as dangerous to touch "neutral" and "ground" at the same time in the USA as it is in Norway when everything is working correctly?

    Best regards
    Torquil Sørensen

    EDIT: Sorry, I didn't remember that this is an electronics forum, so I guess this is a bit off topic... :)
     
    Last edited: Nov 17, 2009
  2. BMorse

    Senior Member

    Sep 26, 2009
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    since in the US we only use single phase 110VAC, we do not have 2 "hot" lines, the Hot is essentially the main AC line coming in and a neutral is almost like the ground where it returns to the mains, and the ground is supposed to be an Earth ground, but I still cant figure out why they have the Neutral and Ground tied to the same bus???? Maybe someone can explain that too......
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    They do and they don't. Ground and Neutral are linked at the pole, to create the single phase setup. If Neutral wasn't linked it would be like an open ended transformer, split phase.

    You have to remember that the 3 wire setup is a relatively recent development in the States. Before that it was two wire, and they wanted at least one of those wires to be safe...
     
  4. BMorse

    Senior Member

    Sep 26, 2009
    2,675
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    I did my own electrical wiring when I had my house built, and it was just confusing on how the "Neutral" was attached to the Ground bus.... I always thought those were separate....
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    They are by code once they leave the pole. A quick quiz, they are connected at the pole, yet it is possible to measure significant voltage on the neutral compared to ground (say 3VAC). Guesses?
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    I'm going to bed, so here's the answer.

    The ground wire should never carry current. The Neutral wire carries the full house load, same as the hot wire, so you're seeing the IR drop in the wire.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    I am not an electrician. We do have several licensed electricians on the board; I hope at least one of them chimes in at some point.

    Here in the USA, high voltage AC (somewhere in the vicinity of 11,000v to 22,000v, 60Hz) is routed to residential neighborhoods.

    Every few homes, there is a step-down transformer that steps this high voltage AC down to "consumer" levels. The secondary winding(s) on this transformer has a center tap.

    The "ends" of the secondary winding are called "L1" and "L2", (for Line1 and Line2, which are "hot") and the center tap is called "N" for Neutral. Basically, it's a single phase 60Hz AC that is "split" in the middle by the Neutral tap. If one places a voltmeter's leads from Neutral to either L1 or L2, 120VAC is measured; between L1 to L2 measures 240VAC.

    The three heavy-gauge wires are routed from the transformer to the service panel (circuit breaker box) in the residence. There is also an earth ground wire, which is AWG 4 or larger, that is connected to two 8' long copper clad ground rods driven into the earth, spaced at least six feet apart.

    The ground wire is electrically connected to the Neutral line at the service panel; this is the only location that Neutral and Ground should meet. This is for safety; if a short should develop between the primary and secondary windings of the step-down transformer, the ground wire will cause a breaker/fuse on the step-down transformer to trip.

    Most lighting and small appliances run from 120VAC. Large appliances such as air conditioning systems, electric clothes dryers, electric ranges/stoves operate from 240VAC.

    120V electrical outlets have a Hot (L1 or L2), Neutral, and Ground connection. The ground connection is connected to the chassis of the device to protect the human using it. The ground is never used to carry current. In areas that may have moisture such as kitchens, bathrooms, and outside locations, the circuits are protected by GFCI (Ground Fault Circuit Interrupt) breakers; if even a small amount of current (about 15mA) is detected in the ground wire, or a difference in the current flow between Neutral and Hot, the breaker will trip.
     
  8. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Thought you needed to be a certified electrician to do home wiring installations in North America.
     
  9. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Much of the electricity supply in North America is overhead, not underground.
    As such it does not posess the armoured and grounded sheath.

    Some members here report what is called a bi-phase or more correctly a split-phase system where the consumer has 2 x 120 volts about a centre tapped local power transformer giving 240 available, across the ends with the centre earthed.

    Others simply have one ( or more) phase of a 120 volt three phase system and neutral (=0).
     
  10. PIC_User

    Member

    Sep 22, 2008
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    See if this looks right.
    -Adam-
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, that's right.
     
  12. BMorse

    Senior Member

    Sep 26, 2009
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    Yo do not have to be certified, but you have to be the "contractor" of the job site and pull a "Home Owners" permit to do the work.... once you do pull a Home Owners permit, you can not have a licensed contractors work on it or they would have to pull their own permits.... at least that's what the county clerk told me when I pulled all my permits (I did the electrical, plumbing, and HVAC saved me a lot of $$$$ doing it myself...) and your work does have to meet specs and pass inspection by a licensed inspector.... (All my work passed with flying colors :cool: !! it was a long 6 months though!:eek:)
     
  13. gerty

    AAC Fanatic!

    Aug 30, 2007
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    One thing to remember, the Neutral is designed to carry current under normal conditions, the Ground is not. The ground is supposed to act as a safety to
    prevent shocks when a device/appliance becomes shorted to the case.

    It prevents shocks by tripping the breaker when the "hot" is shorted to the case or ground. On double insulated tools the case is made of plastic, and that reduces the ability for the tool to shock you, therefore there is no ground wire.
     
  14. BMorse

    Senior Member

    Sep 26, 2009
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    Yeah, I found out that Half of my house is on 1 phase, and the other half on the other, and my X-10 modules didn't work for a while (couldn't control the other half of the house since the X-10 communicates over the power lines...) , until I installed another transceiver module on the second phase then everything worked like a charm.....
     
  15. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
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    Hi, Torquil:

    As usual, SgtWookie's reply is thorough and knowledgeable. I'd like to add the following comments (and I'm also not an electrician, so there could be some factual errors). Here's a sketch I made of the power as it comes into our house in the northwest US:

    [​IMG]

    I can trace this exactly, as it's up on a telephone pole in my back yard. The left side is the high voltage coming in on the power line. This is nothing to play around with, as our next door neighbor has heard the explosion of squirrels that get on the transformer and short between the high voltage line and ground. A bare wire comes down the pole at E and goes into the ground (it appears to be about a 12 gauge (American Wire Gauge) (2 mm diameter) wire). This is also connected to the center tap on the secondary winding at D. The three lines on the right bring power to the house (they're buried about 1.5 m in the ground in a run of about 60-70 m to the house). A and C are called L1 and L2 and B is called the neutral.

    From what I can tell from what you said, the major difference between the US and Norway's power distribution scheme is that Norway doesn't use the center tap on the transformer.

    In the US, virtually every small electrical appliance is run from the 120 VAC lines. It is up to the electrician wiring the house to distribute the legs L1 and L2 approximately equally amongst the 120 VAC circuits around the house (remember, L1 and L2 both have 120 VAC on them with respect to the neutral line). Otherwise, an imbalance can occur and cause too much current on the neutral.

    The 240 VAC power is used for heavier loads such as the stove, clothes dryer, air conditioner, and water heater. It's also popular for power tools in the shop.

    From a wiring standpoint, there's little difference between the 120 VAC and 240 VAC circuits. When I wired my shop 20 years ago, I ran the same wire 12 gauge 2 conductor with bare ground Romex (Romex is a trade name that has become generic for this type of wire) into my outlet boxes for both circuits. I have 8 double-wide boxes around the shop -- the left fixture is a 15 A 240 VAC outlet and the right fixture is the typical 15 A 120 VAC duplex outlet. The other day I came across the somewhat hokey router fixture I made to cut out the hole in the cover plates for the 240 VAC fixture, as there were no off-the-shelf ones available.

    20 years ago we added 100 m^2 (1000 ft^2) onto our house (half of it was my shop). My wife and I did as much of the work as we could to keep the cost down. I did the wiring on weekends and remember two key lessons from that. First, I pulled over 300 m of Romex and other wire; drilling all the holes, climbing up and down a ladder, etc., was lots of physical work (not to mention hot, as it was in August). Second, I had never done any wiring like this before, so I bought a copy of the National Electrical Code and tried to train myself in how to do things. The only thing my wiring job failed inspection on was that I had three junctions that were not in electrical boxes. From where I sit typing, I can look to my left and see two of these boxes I had to add and the lesson makes me smile, as any electrically-experienced person would see them and ask "Why the hell are there junction boxes there?". :)
     
  16. tmac

    Thread Starter Member

    Oct 28, 2008
    10
    0
    Hi again! You guys are really helpful, thanks! This clears up my ignorance in this matter. Interesting to hear about the 120/240VAC possibilities for electrical appliances in the USA.

    Poor squirrels! Once our cat was on top of the telephone/power cable pole because of an angry dog in the street. Fortunately he did not come into contact with any high voltage parts (or at least not more than one...)
     
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