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Ground VS Neutral

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  • Ground VS Neutral

    I'm a gas guy, so I've come to you experts in a wiring question.
    After rebuilding my shop that got wiped out by a flood I'm planning to run the wire for my welder and compressor, both 50 amp circuits so I can interchange the locations of the 2 if needed. My welder and compressor have the same type of 3 prong 220 volt plug. I'm familiar with older 2 prong 110 volt house circuits that were ungrounded, so they must be running a hot and neutral. On my new 220 volt 3 prong circuit does the 3rd prong connect to the nuetral (a # 6 wire) or the ground (a # 12 wire). In the sub panel the ground and neutral are not bonded, but they are in the main panel both have passed inspection in my jurisdiction. (NEC?)
    Thanks for your input and subsequent education!
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  • #2
    It goes to the ground bar.

    240v does-not use a neutral

    The circuit travels through both hot legs

    120v : the circuit travels through the hot leg and the neutral

    The neutral ground bond in the main panel causes confooosion when wiring sub panels because people think the since they're bonded at the main panel why not just do the same in a sub panel?

    When a ground fault occurs it is looking for the quickest path back to the Transformer up on the pole, not actual Earth. If you bond at a sub panel then you create alternate paths i.e. Neutral runs from the sub panel, for a fault.
    Last edited by Broccoli1; 03-09-2013, 02:50 PM.
    Ed Conley
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    • #3
      This is gonna be simplified, so it's not technically 100% accurate, but it's close enough:

      Common single-phase 220VAC (alternating current) has an AVERAGE voltage of 220V from the high side of the wave to the low side. (It's actually closer to 350, but that doesn't matter.) Voltage is like pressure - it has to be measured at one location RELATIVE to another; so the nominal voltage is the high relative to the low. In actuality, it comes out of the street transformer 110VAC above ground on one leg, and 110VAC below ground on the other, and the legs are in-phase so one is reaching its peak while the other remains neutral (0V). The house neutral goes back to the transformer's center tap, and the house ground goes to the ground rod, which links the house's voltage to the power company's. Without it, a house could theoretically develop a static charge like a balloon, which could damage appliances or cause injuries.

      So if you plug in a toaster from one hot leg to neutral, it gets 110; a TV on the other hot leg also gets 110; it doesn't matter if it's above ground or below - they work the same.

      But the stove/dryer/furnace/welder/compressor are connected from one hot to the other, so they each get the FULL 220V wave. Like everything else, they're grounded for safety thru the 3rd prong. They don't actually need a neutral for their primary functions, but many modern 220V devices also have 110V sections (for displays, lights, on-board outlets, etc.), so the modern standard is for all of them to be connected to the neutral by the 4th prong.

      If you ever look in a breaker panel with no breakers, you'll see the 2 hot legs coming in at the top (sometimes thru a set of main breakers) going to the 2 bars that zig-zag down the center of the panel to feed the breakers that are snapped in. Adjacent breakers therefore connect to opposite legs, which is why double-wide breakers are used for 220V circuits.

      So you have 220V all over your house - just not (usually) available at the same outlet. You may have one room's outlets wired to a breaker on one leg, and another room (or the same room's lights) wired to a breaker on the other leg. Depending on local codes & the original builder's specs, it's possible to wire a common 110V duplex outlet to both legs (one leg for the top outlet; the other for the bottom). All duplex outlets are built with a tab joining their terminals that's easy to break away for that purpose. With a 110V outlet wired that way, it would be easy to make a 220V adapter plug, but you'd still be limited to the LOWEST current rating in the contraption. If you used a 20A duplex, 20A plugs on your adapter, and wires capable of carrying 20A, you'd have 220VAC @ 20A. But most duplexes are rated for 15A; many plugs, even less.

      Never poke around inside a breaker panel or outlet unless you know what you're doing. It's safer to pay a licensed pro, and always check the local electrical codes.
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