220 wiring for spa

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"> If two points are at the same potential, it is _impossible_ for there

"By this principle, no shorted conductors can carry current. "
Did you even take basic high school science? If you take a short piece of wire and connect a dead short from hot to neutral, the conductors are then not at the same potential. The huge current flow through the wire equals the potential difference. If we had a perfect 120V voltage source that could supply any amount of current and connect a short piece of wire to it, the voltage across the wire will be 120V for the brief time until it melts. In the real world, the voltage would be less, but still substantial. And the remaining voltage which would still add to 120V would be distributed along the supply wires due to their resistance. Class dismissed!
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snipped-for-privacy@optonline.net wrote:

Cut poor Richard some slack. He's not from around here. Richard comes from a planet with some really unusual chemistry, where (according to his posts) it's safe to drink gasoline and breathe carbon monoxide, but common household borax is a deadly poison. Apparently, electricity doesn't work quite the same way on his planet as it does here, either.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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I skipped high school physics class. Actually, they kicked me out and gave me credit for it, because I was a know-it-all-show-off. I got sent to the principal's office for arguing with the math teacher about whether the empty-set symbol was a phi or zero-slash. I was right, but respect for authority was more important than truth. Eventually they took me out of the last two years of math class, too. Over time I must have calmed down, because the big research U's gave me three engineering degrees, and industry some flattering job titles.

And my point remains unanswered, herr professor.
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On Wed, 04 May 2005 17:12:53 -0500, Richard J Kinch

Dude, you're babbling. Putting the breaker in the wrong position will not and can-not cause a dead short. If you *HAVE* a dead short, then putting the breaker in the wrong position, in systems where that's possible, causes nothing to happen, where loud and exiting things would happen were the breaker in the RIGHT place.
In OPs case, there's a breaker at the service panel, and a disconnect in some other box downstream. When the disconnector is open, nothing happens. When the disconnector is closed the first breaker pops.
Now at this point, a description of this second disconnector would be useful, But if it's built like a DPST switch, then the most likely explanation is that it's wired sideways, with the high and low feeds from the service panel connected to the input and output of the same arm in the breaker. The other possibility is that the output side of at least one arm on the breaker is connected to the nuetral or safety ground, or shorted out somewhere. You can figure out which by disconnecting everything except one of the hots, and putting a voltmeter from the terminal that the OTHER hot was connected to to ground, with the disconnect closed. If you get voltage, you know that that's the OUTPUT of the currently hot leg.
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Goedjn writes:

Leaving aside from the quibble about "short", only with a single-fault hypothesis, which hasn't been tested.
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Let's see your explanation for this howler.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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It sounds like a short somewhere. Helpful, eh? :)
Since the house breaker didn't trip until you threw the final disconnect, my guess would be the run of wire between the Spa GFI and the disconnect, or maybe the the final dangling wire at the end for the hot tub. (I assume the exposed ends aren't touching the ground or anything else?)
If you have a continuity meter, you should be able to disconnect the wires at each end and check for a short.
Assuming you have the circuit wired correctly (hot leads to breakers, ground to ground, neutral to neutral, ground bus is separated from neutral bus in the "spa pack"), my guess would be damaged wire insulation. Probably under a cable clamp at one of the boxes, or possibly under a cable staple or where it passes through an opening.
I had this happen once when I overtightened a cable clamp and damaged the wire insulation. This caused a short to the metal box and it tripped the breaker. Everything looked fine till I pulled the thing apart and really inspected the cable.
Easy to find with a meter, virtually impossible without one.
Anthony
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