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Can I ask some electrical questions?

  1. Dec 29, 2006 #1
    I've done some googling on some questions I had and came to this site. I see poeple like Averagesupernova are pretty dagum knowledgable.

    A few questions I have in regards to installing a subpanel. My subpanel is about 100' away from my house, I will be coming off a 200a main panel.

    1) In the main panel, the nuetral and ground will be attached as normal to the busses, perhaps the same bus, but in the subpanel, they are not to touch, correct? This is due to not wanting the possibly energized white conductor touching the ground beyond the main panel which could zap you when you touch equipment, etc, correct? So, there is a bus that I could attach in the subpanel that isolates the nuetral from touching the metal?

    2) For the equipment ground at the subpanel, I still need to pound in a ground rod, or two, and attach them with a #6 to the equipment ground bus in the subpanel along with the ground coming from the main panel, correct?

    hopefully I'm not being confusing..

    thanks for any help!
     
  2. jcsd
  3. Dec 29, 2006 #2
    Do a search on this forum. Alot of what you are asking has been discussed many times. I think it would be worth your while.
     
  4. Dec 29, 2006 #3
    I've done searches, I don't understand them completely, so I just want to confirm what I'm thinking is correct....
     
  5. Dec 30, 2006 #4
    Neutral the white wire is the "grounded conductor" and ground the green wire is the "grounding conductor" as described by NEC. Not to sound disrespectful but from reading your post you do not have enough knowledge for wiring. Especially around your house where loved ones are at rest and play. My advise is to hire a licensed electrician for your installation.
     
  6. Dec 30, 2006 #5

    berkeman

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    And even if a licensed electrician does the work, s/he will still need to get a building permit from the city that you live in, and have the final work inspected by one of the city's building inspectors. When you sell your home, for example, one of the questions on the sales contract is whether you have done any work on your home, and if the work was done with the applicable building permits.

    Even if you do the work yourself, getting the building permit and having the work inspected afterwards helps you to be sure that you are following the NEC rules and any other city rules. Those rules are there for your safety, and the safety of your family and any other families that end up buying your home later on. Building permits and inspections are generally required for new electrical work, new plumbing work, and any structural work involving load-bearing walls.

    Stay safe, and do the work right. o:)
     
  7. Jan 3, 2007 #6
    Neutral (white) and Ground (green) are some-what the same thing. The only difference being neutral is the current carrying conductor back to the power source. Ground is used as a safety mechanism, only to conduct current under fault conditions.

    There shouldn't be a voltage difference between Neutral and Ground. In that sense Neutral is not really energized. It will appear to be energized only with respect to the hot (black) wire when it (the hot wire) dips below 0 VAC on it's voltage sine wave. When this happens current changes directions and you will get an AC voltage with respect between hot and neutral.

    You shouldn't get shocked by touching a neutral lead and ground.

    I also agree that you probably shouldn't work on anything past your own capabilities. I would hire an electrician, who will gladly answer any of your remaining questions.
     
    Last edited: Jan 3, 2007
  8. Jan 4, 2007 #7

    Whoa... Let's keep the spread of misinformation to a minimum. By defintion, you cannot have less than zero volts AC. It's like saying you have an absolute value that is less than zero.
     
  9. Jan 4, 2007 #8
    If you look at an Oscilloscope with your "hot" being positive and your "neutral" being common, the sine wave (voltage) will go negative. How else would the current change directions? The neutral should stay at 0 V with respect to ground. When the "hot" reaches it's minimum at let's say -170 V, the neutral will be the most positive with respect to the hot wire (It will appear to be energized). The hot wire oscillates between -170v to +170v giving us 120 VAC RMS.

    Sorry my first post wasn't very clear. I didn't mean to put "... wire when it (the hot wire) dips below 0 VAC...". I meant V not VAC.
     
    Last edited: Jan 4, 2007
  10. Jan 4, 2007 #9

    berkeman

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    Okay, *Safety Stop*

    Nobody go checking AC Mains voltages with an oscilloscope unless you *really* know what you're doing. And preferably use an isolation transformer, like you should be doing if you are working inside equipment that has AC Mains exposed (like if you're troubleshooting a TV for example).

    The "ground" cliplead on your 'scope probes really is hard grounded to the 3rd prong in the power cord, and if you go clipping it onto some AC Mains line that is not exactly staying at ground potential, you can have problems. I've seen more than one oscilloscope damaged by a newbie exploring an AC receptacle (luckily no injuries yet!).

    If you're using a battery-powered oscilloscope and are *very* careful about what you do with the return clips on the scope probes, you can poke around AC Mains voltages relatively safely. But be sure to read and understand the safety information that comes with battery-powered oscilloscopes before trying to use them in that way.

    I've spent a lot of time with exposed voltages in front of me and my instruments, from 120Vrms AC Mains up to 30kV color CRT supplies, and you do not want to be making mistakes in how you connect things up. Please be careful with this folks.
     
  11. Jan 4, 2007 #10

    berkeman

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    Oh, and don't ask me about the surprise 30kV arc incident. I'm sworn to secrecy on that one. :blushing:
     
  12. Jan 4, 2007 #11
    Agreed, an easier way to see this is to use software such as MultiSim.
     
  13. Jan 4, 2007 #12
    And to add my 2 cents. The only time the neutral wire has zero potential in reference to the "hot wire" is at the OV crossover on the sign wave. This gets a lot more complicated when you figure in the inductive and capacitive effects of the load and wire.
     
  14. Jan 4, 2007 #13

    berkeman

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    I think people are referring to the US National Electric Code (NEC) requirement that Neutral and Earth Ground be tied at the distribution/breaker panel. There Neutral really is equal to ground. Farther out in the house or building as you get away from the panel, then Neutral will have the (normally small) return voltage drop on it.
     
  15. Jan 4, 2007 #14
    Not really. Neglecting source impedance of the transformer the voltage does not shift phase due to reactive loads. The current is what shifts in the case of a reactive load, not the voltage.
     
  16. Jan 5, 2007 #15
    I was responding to an earlier post by HuskerEE post #6 that seemed to imply that the neutral is only energized when the sine wave is negative going. It would also be energized when the sine wave is positive going. Although the neutral would not shock you if it is properly installed. I have found out the hard way what happens when it is not properly installed on more than one occasion. You don't feel the full potential because it is being dropped through the designed load and of course your body. You are right Averagesupernova, I thought about that after I made my post
     
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