2 wire upgrade

Discussion in 'Electrical Forum discussion & Blog' started by nedjinski, Dec 25, 2007.

  1. nedjinski

    nedjinski New Member

    Messages:
    5
    I have 50 year old house that is a 2 wire house - that means the utility pole brings in 2 hots and 1 neutral.
    the hots (blacks) go to the breakers ( 1 hot for each side of the breaker layout) and the neutral (white) goes to a buss bar.
    all the circuts are 1 black and 1 white - no ground.

    how do I retro the whole system to make a 3 wire / grounded system? at least for the plugged outlets anyway.
  2. markts30

    markts30 Commercial Plumber

    Messages:
    630
    Location:
    Phoenix, AZ
    I hate to say it, but the correct answer is to hire an electrician...
    If you don't know how to add a ground to the existing system, you should not be messing with it...
    After 50 years - probably time to re-wire it fully anyway depending on the type and condition of the existing wires and insulation....
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,251
    Location:
    Cave Creek, Arizona
    wires

    50 years ago it was probably wired with BX cable, in which case the outer sheath will provide grounding if it is connected properly.
  4. nedjinski

    nedjinski New Member

    Messages:
    5
    the house was wired with what was like Romex today - 2 wire sheathed in an outer fabric cover. if it was fmc then I could use that for the ground.

    as far as doing the work it's not a problem. I have already added / changed circuits / wiring in this house to code and with permits.
    I am more interested to know how it's typically done - the neutral buss is connected to the cold water pipes with #6 solid copper, but that's it for grounding.

    in new construction are the neutral and ground circuits isolated from each other - meaning the ground has it's own buss and is connected to a ground rod, and the neutrals are connected to the neutral buss. if thats the case how do you retro and old 2 wire system? add a ground rod, add the ground wires, then move the existing grounds from the neutral over to the new ground buss?

    etc etc
  5. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    The ground and neutral are isolated ONLY AFTER the service point; not AT the service point.

    The power company supplies only the two hots and a neutral such as you already have.

    The ground for what you call a "3-wire" system is connected to the neutral bus at the location where the service is connected.

    That ground/neutral buss is connected to the water service pipe or to ground rods or both. The code now requires ground rods in addition to the water service pipe.

    The neutral and ground of all of your grounded branch circuits that are connected to that main service panel are ALSO connected to that ground/neutral bus.

    The ground and neutral are thereafter NOT connected to each other and the neutral is not connected to ground at any sub-panel that you may install.
  6. nedjinski

    nedjinski New Member

    Messages:
    5
    thanks Bob -

    that clarifies things quite a bit.

    in terms of theory - if the grounds and neutrals are tied together at the sevice point, what is the difference if they stay tied throughout the whole system? ie, why even have a separate ground wire? why not tie the neutral wire to the ground lug on a 3 way outlet, for example?
  7. BrianJohn

    BrianJohn DIY Senior Member

    Messages:
    151
    Location:
    VA
    Because then you set up parallel paths and can end up with circulating ground current.

    If you are not willing to rewire the whole house.

    1. Hire an electrical contractor and have him megger all the branch circuits to verify the integrity of the neutral and hot conductor.
    2. Replace the panel and utilize GFCI circuit breakers for all branch circuits with receptacles on them.
    3. Replace all wiring that tested with low resistance.
    4. Replace the easy branch circuits and do the difficult circuits one at a time as remodeling dictates.
  8. construct30

    construct30 New Member

    Messages:
    590
    Location:
    NorthWest PA
    How does a GFCI breaker help if there is no ground wire? I know GFCI outlet won't help at all, but what makes the GFCI breaker work? You sound like you should know. I'm just looking for info.
  9. 480sparky

    480sparky In the Trades

    Messages:
    149
    GFIs do not require a ground wire to provide protection. It does not matter whether you use a GFI breaker or GFI receptacle, they operate the the same.

    An ungrounded receptacle is allowed to be replaced with a grounded receptacle if GFI protection is provided. (National Electric Code 2005, Article 406.3(D)(3)(c). You can also install a GFI receptacle per 406.3(D)(3)(b).
  10. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,713
    Location:
    Central Florida
    A GFCI detects any difference between the current going out the hot wire and that returning via the neutral. If that difference is greater than .006A or so, for .025 seconds, the breaker trips. The "missing" current must be going somewhere, and since the most likely place it's going is to ground, they call it a "ground fault" circuit interrupter.
  11. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    The GFCI (whether breaker or receptacle) measures the difference between the current on the hot (black) wire and the return current on the neutral, and trips if they are different by 0.006 amp or more. That is supposed to be small enough that it won't electrocute you if there is a ground fault through you, as if the hair dryer you are using in the bathroom has a fault and you simultaneously touch a grounded faucet.

    The GFCI will not work if the neutral and the ground are connected beyond the GFCI because it will produce a false trip for the following reason. If the ground and neutral are connected beyond the GFCI device, then some of the current that should be returning through the GFCI via the neutral will return through the ground wire that is connected to the neutral. THAT IS A GROUND FAULT and will trip the GFCI. That is often one of the things that trip a GFCI and people have trouble figuring out why it is tripping because they check only the hot wire.
  12. construct30

    construct30 New Member

    Messages:
    590
    Location:
    NorthWest PA
    Good info thanks. I know some code, but not the reasons why. I like knowing why especially when troubleshooting.
  13. BrianJohn

    BrianJohn DIY Senior Member

    Messages:
    151
    Location:
    VA
    IMO the two important issues here are meggering and the GFCI, IF he is not going to do complete replacement.
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