Touching ground wire to metal box trips breaker

Old 07-22-14, 02:39 PM
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Touching ground wire to metal box trips breaker

I'm extending an existing outlet in my garage (finished walls and box is plastic) and adding an outlet --> switch --> outlet. These new outlets and switch will be on the outside of the walls and Im using metal boxes and wiring in flex conduit.

I added the first outlet and grounded the metal box and outlet with a pigtail (wire to screw in box, pigtailed to 3 other wires with one of those going to outlet). Using a 3 pronged tester it showed normal.

I then extended the wiring to a switch (that will control the next outlet) using a metal box. I wired up the switch (whites pigtailed off), black wires to both screws. Green wire to screw on box and pigtailed to 3 other green wires with one of those going to switch.

With switch off, all is fine.

Flip the switch and the GFI and breaker get tripped. I checked there were no wires touching (elect taped off each wire too).

After some testing, i removed the ground to the box and the problem went away when turning switch on. I put the box ground wire back in but did not have it touch anything. No trips. Then turning switch on i touched the ground wire to the box and breakers tripped.

Very weird. When I installed the last outlet with the ground wire to the box it also tripped the breaker.

So, I have 2 metal boxes without a ground to their box and everything tests normally. The box is not charged.

There was an electrician next door doing some work and I asked him. He came over and said that shouldn't be right and did some initial testing and verified the box was not hot but didn't have an answer without further investigation.

Any ideas on what I did wrong or should look at. Don't all the metal boxes need to be grounded or just the first one in line????

Thanks for any help.
Old 07-22-14, 03:30 PM
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Why is there a switch and what is the wiring in that box?
Old 07-22-14, 03:59 PM
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It sounds like you have a fault between the switch and the last receptacle.

All the metal boxes should be bonded to ground.
Old 07-22-14, 06:20 PM
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Welcome to the forums!

Is the breaker a GFCI breaker (it will have a "test" button) or is it a standard breaker?

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