Remote Subpanel on a 2-Wire Feed?

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  #1  
Old 07-18-04, 07:59 PM
mlodahl
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Remote Subpanel on a 2-Wire Feed?

It seemed like a simple idea: I have a 30A 240V circuit to the pumphouse, feeding two pumps which draw 6A each at startup, and would only start together by malignant chance. Why not put in a subpanel in the pumphouse, and extract a pair of 15A 120V circuits for lights and a couple of GFI-protected plugs in the adjacent barn? Well, here's the punchline: this wiring's been there a long, long time, and only has two conductors, so the subpanel would have no access to the house common or ground windows. I tried wiring the subpanel as a main service panel, with common connected to ground and and the panel grounded to a ground rod, recognizing that my only connection to the transformer center tap would be through ground. Initial indications are none too good. It all looks just fine with no load, but even light loads drop the voltage drastically. Is there something I can do (short of running a new feed from the house), or is this a lost cause?

- Martin
 
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  #2  
Old 07-18-04, 08:36 PM
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How many feet is it between panels? What is the gauge of the wires? Is the third wire smaller? Are all three wires insulated, or is one bare? Do the pumps run on 240 volts? Is there any metallic connection between the buildings other than these wires?
 
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Old 07-18-04, 09:11 PM
mlodahl
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As a guess, John, I'd say 150 to 175 cable feet, panel to panel. 10 Ga. 2-conductor direct bury Romex. There is no third wire or any other metal; if there were, I'd be in tall cotton. It's perhaps a hundred feet from the nearest building I could run a ground in from. The pumps run on 240V. As nearly as I can determine, the history of this circuit is that about the time California outlawed open wells in '54, The existing well was capped and a pump installed, fed by aerial wiring. Sometime (much) later, some energetic soul dug a trench and put in the present Romex. In the middle 1970's they drilled a new well, and wired it to the existing service cutoff in the old well house, in place of the old pump. It was at that point they put in the only nod to an equipment ground the circuit ever had, grounding the cutoff to a water pipe. That's how it was when I moved in, in '78. I added the cistern and pressure pump in '88.
 
  #4  
Old 07-18-04, 09:44 PM
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You're trying to use the earth as a conductor. Well, the earth has about a billion times more resistance than copper. So you have achieved the lucky double: an installation that is about as unsafe as they come, combined with an installation that performs poorly.

Sorry, but you must undo this work immediately. Not only will you never get it to work right, it's dangerous as hell. That 15 amp breaker won't trip even if you create a dead short across the 15-amp receptacle. How's that for safety?
 
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