Shop vac trips gfci

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  #1  
Old 04-25-16, 02:17 PM
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Shop vac trips gfci

shop vac stopped working while I was using it. GFCI tripped. Turned off tried it again and it pops the GFCI immediately upon inserting the plug into the outlet... with the vac turned OFF.

Tried it on 2 other GFCI's on 2 other circuits and it does the same thing.

Whats up with that? Bad vac right? Not wiring issue?
 
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  #2  
Old 04-25-16, 02:21 PM
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Most likely you have a short in the cord to the vac. Is this a well used vac?
 
  #3  
Old 04-25-16, 02:22 PM
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Yeah I beat the heck out of it.

Do the GFCI's outlet weaken or go bad once tripped like that?
 
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Old 04-25-16, 02:25 PM
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Over time GFCI outlets can go bad. But one tripping will not kill or weaken it.
 
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Old 04-25-16, 02:31 PM
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if its a short, why wouldn't the breaker trip instead?
 
  #6  
Old 04-25-16, 02:36 PM
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It's most likely a short from the neutral to the ground. A small amount of current is flowing back on the ground but not enough to trip the breaker. If it was a dead short from the hot to neutral or to ground it would trip the breaker. And you'd see sparks fly where shorted.
 
  #7  
Old 04-25-16, 02:45 PM
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A GFCI receptacle can trip as low as 0.005 amps of current leakage whereas the smallest household breaker won't trip until at least 15 amps. As patten said it also depends on which wires in the cords or motor are shorted out as to whether the GFCI receptacle or the breaker will trip first.
 
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Old 04-25-16, 03:16 PM
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Since the OP says it trips the GFCI with the vac switched off I'm thinking the cord is the culprit vs. the motor. Plugs seem to get pulled out by the cord and shop vacs get pulled around by the cord causing damage to the cord and plug.
 
  #9  
Old 04-25-16, 05:03 PM
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Is that an actual three prong plug type vacuum ?

A two wired appliance should not be tripping a GFI device.... unless it's wet.
 
  #10  
Old 04-25-16, 05:47 PM
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yeah its 3 prong. And indeed it was tripping with the switch off. So quickly in fact that it snapped the outlets off before I had the plug fully inserted.
 
  #11  
Old 04-25-16, 05:54 PM
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Could be in the power cord. Could be a the brush on the neutral side touching ground. Since it's not tripping a breaker.... the problem is a leak or short from neutral to ground.
 
  #12  
Old 04-25-16, 07:04 PM
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It was a small Stanley 1 gallon vac I got for 15 bucks on sale a few years ago. So its going to the trash instead of the workbench.

Just for the sake of knowing... say the vac was fine, no short but the outlet still tripped. What type of miswiring issue can cause a GFCI to "phantomly" trip?
 
  #13  
Old 04-25-16, 07:22 PM
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None that I know of. Even if you had the hot and neutral connected to the receptacle backwards.... it would still work normally.

The GFI trips when it detects an inbalance between hot and neutral which would indicate a short or leakage to ground.
 
  #14  
Old 04-25-16, 08:26 PM
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If you have a dead device with a suitable power cord you could salvage you could open it up and see how hard it would be to replace the power cord.
 
  #15  
Old 04-27-16, 12:32 PM
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just for kicks I put my multimeter on the cord prongs and I have continuity between all combinations of the prongs. about 4ohms.

I assume that means the windings opened or something? Don't know anything about motors... enlighten me please.

ps- Im afraid to plug it into a standard outlet to see if its completely dead.
 
  #16  
Old 04-27-16, 09:16 PM
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If you check it with the switch on.... then yes.... you'll see something across the pins.

The vacuum will work fine in a standard receptacle as the neutral will still only be touching ground and that won't cause a short.

I question your measurement of 4 ohms. That sounds a little low.
 
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