From someone who thinks electrity is magic...


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Old 10-17-13, 10:26 AM
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From someone who thinks electrity is magic...

I am totally unable to wrap my head around how electricity works, so I'm lost on this one. I have an older (90 years) home with a detached garage. I noticed a very slight feeling of current a couple of times when I flicked the light switch inside the garage. At first I thought I was imagining it. Finally, I figured something wasn't right so I called up one of my old Marine buddies who is a GC and told him to come over for a couple of beers cuz we hadn't hung out in awhile. Coincidentally, I happened to mention this problem while we were rehashing old times and he volunteered to take a look at it. He said, to paraphrase an old Marine saying, "This wiring looks like it was done by two monkeys 'doing something' to a football". He came over the next week and rewired the whole garage for me. Ok, the problem is this: Since then, I happened to be using a heat gun next to a 3" exposed exterior aluminum conduit. I briefly touched the metal tip to the conduit and got a pretty significant arc and a loud pop. Then, last week, I was cutting a timber with a circular saw using an aluminum speed square as a guide. (something I've done hundreds of times) As soon as I touched the saw to the square, my saw tried to electrocute me. Both of these tools were plugged into the garage outlet at the time, connected by 2-3 three prong extension cords. My questions are, "Are these two things related?" and "Would some issue with the electric in the garage cause this, or is it more likely to be with the saw and heat gun, or maybe the extension cords?" The saw is a good one, so I'd have it repaired, but I don't want to spend the money if that's not the problem. Any advice would be appreciated.
 
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Old 10-17-13, 10:54 AM
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Yes, you have an issue that should be addressed immediately. While I can't tell you exactly what it is...you should describe exactly what kind of wiring you have.

How is the house connected to the garage? How many wires and breakers feed the garage. Is there a sub-panel in the garage?
 
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Old 10-17-13, 12:44 PM
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In addition, certainly the receptacles are protected by GFCI's, right? Uh-oh. Plan B. Install a GFCI breaker for the garage or install a GFCI receptacle at the first box and protect all the downline receptacles from that one on the LOAD side.
 
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Old 10-17-13, 02:17 PM
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The building, a 2 unit duplex I own, has original knob and tube with any additions done with modern wiring in conduit. Most new work (since I've owned the place) has been added on completely new circuits. Both units have breaker boxes. The connection to the garage is by an overhead wire which I had raised several years ago. The garage does not have a panel of its own and does not have its own circuit from the house. I suspect it is just patched into the existing knob and tube inside the house.
 
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Old 10-17-13, 03:20 PM
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The connection to the garage is by an overhead wire which I had raised several years ago. The garage does not have a panel of its own and does not have its own circuit from the house. I suspect it is just patched into the existing knob and tube inside the house.
The feed for the garage can remain overhead or go underground. A detached structure can have no more than one power feed. So long as you don't need more than two 20A circuits, your garage can be served with a multiwire branch circuit (MWBC) - two hots and a neutral. If you only need one circuit for everything, fine. Either way, the first stop in the garage must be a disconnect that cuts off all the power. For one circuit that's an on/off switch. for the pair of circuits, it's a double-throw, double-throw switch that will open both circuits at once.

If you need more circuits or more amps, You'll need to install and feed a subpanel. And regardless of what you run to it, you need to feed it from overcurrent protection devices - fuses or breakers - inside the panel for your unit. The feed should have three or four wires: one or two hots, a neutral, and an equipment grounding conductor (a ground wire). Although it may not be required by Kane County or Cook County (depending on which you're in) for a single or multiwire circuit feed, I would drive a ground rod next to the garage and add that to the grounding for all of the outlets there.

Right now, immediately, make sure all of the receptacles in your garage are GFCI protected, as Chandler suggested.

It sounds like your saw may have lost its built-in protection (isolation) somehow. It could be as simple as some damage to the cord. You might want to drop it off at your favorite repair shop for a look-see.
 
 

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