Definition of "Dead short"

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  #1  
Old 09-03-06, 10:10 AM
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Question Definition of "Dead short"

Someone told me I have a dead short on a circuit in my house. What does that mean? Thanks
 
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Old 09-03-06, 10:28 AM
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I will try my best to explain.

Your house is feed from the utility transformer with three wires. Two of those wires come off the ends of the coil from the transformer. The third is a center tap off the middle of the same coil. The two outer wires give you your 240 volt power. If either of the two is used with the center tap you get the 120 volt.

The center tap wire is grounded at the transformer and again at the house. It is commonly called the neutral, although that term is not always correct. The code calls it the grounded conductor.

If any of these three wires contacts any of the other three without having a load in the middle, that is a short. This can happen by accident sometimes when we miswire something, or forget to turn off the power while working and touch the two together by mistake.

A dead short is one that stays connected because we have not found the problem yet, therefore we have not cleared the short.
 
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Old 09-03-06, 12:35 PM
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Technically, any path for current flow which is not an inteded load...light bulb, motor, etc. is a short. The resistance between conductors should be infinite, but that is theoretical and never achieved in practive. But resistance in the megohm region would result in an insignificant current flow. Tens or hundreds of megoms...even better. If the resistance were to drop into the hundreds or tens of k-ohms, now the current flow starts to matter, but will still not pop a breaker.


At some point, low enough resistance represents a safety and fire danger, and circuit breakers will pop. SO, it is all relative. When someone uses the term "dead short" they usually mean a resistance probably in single digit ohms, and also a continuous problem, rather than a momentary or intermittent problem.
 
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Old 09-03-06, 01:54 PM
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Thanks for that explanation. I have been checking all the switches and outlets and they are all backstabbed so I've been pulling them out and wiring them to the scews while looking for the bad connection that is causing the short. I have found two recepticles that don't have screws and there are holes in the back for eight wires and there were three black and three white wires pushed into the holes. This recepticle is wider than the one with screws. Are these made for convenience sake, so all the wires from pigtails don't take up so much room in the box?
 
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Old 09-03-06, 04:37 PM
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Certainly the qwikwired devices are for convenience and speed. Because of their reputation for getting loose, I recommend replaceing with the "backwire" type where up to 2 wires are inserted into an opening on the back, and when the screw is tightened, it clamps the wires . Very reliable, and you can use # 12 wire, and you can get 4 blacks and 4 whites on the device,
 
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Old 09-04-06, 05:10 AM
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When searching for a short circuit the first setp should be to un plug everything on that circuit and turn off all the lights. Then try to turn the breaker back on. Nine out of Ten times the short is in a bulb, or appliance.

Outside gfi outlets are the next place to look.
 
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Old 09-04-06, 12:47 PM
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I replaced those two backstabbed recepticles on the circuit and that solved the problem. Now, time to do the rest of the house. Thanks for the help.
 
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