I know this has probabaly been discussed before, but I wanted some
opinions for a problem I discovered.
The other day, I go to open my garage door barefoot and I got a slight
electrical shock from the handle. I checked the voltage from the door
handle to ground and found 20 VAC. What I discovered is that the
outlets in my garage are not grounded, and since one of the walls in my
garage is metal studs, I guess the stray voltage made its way from the
metal studs to the garage guide rails and to the door. I put a test
light from the studs to ground, but the light did not work and the
residual voltage dropped to 0.
I just had a new panel installed last year with some GFCI breakers
since some of my wiring has no ground. I thought the GFCI breaker would
trip in this situation, but it did not. Basically I guess the right
thing to do is run a ground wire, or new grounded circuit to the
garage. Unfortunately its a pain to do this. Since the neutral and
ground are tied together in the panel, isn't it the same electricallly
if I tied one of the neutrals in the outlet to the metal stud in my
garage, which would ground it? Also why didn't the GFI breaker trip
when I got shocked?
Is this an attached garage? Run a ground wire to it from the main
panel. You cannot use the neutral as a ground because they are not the
same thing -- except at the one point where they are connected back at
the main panel. You shouldn't have to run all new grounded cable, just
a #12 green wire. It's usually not all that hard to do.
If it's a detached garage, you need to install a grounding electrode
(ground rod) or two, and you can connect the grounds and neutrals (and
the metal building) together at the point where you connect the
grounding electrode -- it should be the first box where the circuit
This is an oversimplified description and therefore probably not 100%
accurate, but I hope it helps.
This is an attached garage. But can I just run a piece of #12 green to
a nearby outlet in my den that I know is grounded, instead of running
it to the panel? (which is on the opposite side of my house in the
Well, some things are beyond the scope of the NEC.
It's entirely up to him whether he decides to make an effort to "ground"
most of the exposed metal in his garage or just let it "float."
Were I getting shocks, I damn well would certainly starting grounding stuff.
I would also start looking very hard for the leakage paths. I might
replace the outlet where a powered door opener in plugged in to a GFCI type.
Unfortunately, many "electronic" packages such as a radio receiver have a
network that connects HOT and NEUTRAL and GROUND (frame/chassis) together.
The leakage from this network is supposed to be well below the threshold to
trip a GFCI but ...
Certainly, he should "ground" metal that gives him a shock.
I suspect that you are getting induced current. That happens when there
is no direct connection. A small amount of current flows as in a
transformer across an opening without any direct connection. This only
happens with AC current and in general even a high resistance (light bulb)
will drain it off quickly.
The GFI did not trip because the current because it was not a direct
I do suggest that you prooerly ground your outlets in the garage. Are
all your garage circuits GFI protected?
In addition to grounding your electrical outlet the metal frame (studs) of
the garage should also be grounded to prevent them from becoming
accidentally electrified or even the problem that you have. I don't know if
it is code to ground metal stud walls but in structural steel buildings the
steel frame must be grounded. However if you install a grounded line with
metal boxes, the electrical ground will be connected to the steel studs
through the steel box.
Do you get 20VAC from the wall studs to ground too?
No, NEVER attach use the neutral as a ground. If it ever becomes
detached, the whole garage goes live.
The fact that the residual voltage drops to zero when you put a low
impedance device (the test light), means that the current available is
If the GFCI's don't trip when you run a wire from the stud to ground,
it's most likely _not_ an electrical leak, and is instead static or
induced voltages in the frame of the garage.
According to electrical code, major metal "systems" in buildings need
to be grounded - ie: metal studs. You don't have a ground. If a ground
is too difficult to install, you might want to consider simply driving
in a ground rod and grounding the building frame to it. While
this is normally somewhat of a no-no (multiple unconnected
grounding/single panel), the GFCIs _will_ detect hot-frame shorts
and trip - without GFCI, you'd need to push >>15A thru the dirt
to trip - that won't happen. The GFCI's work on just a few ma and
won't have a problem.
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
There is a very unusual thing that happens if a GFI gets defective. I
know because I had it happen. I had a GFI on the side of the house
and am on a farm. I put some horses on the rear lawn to mow the lawn,
when the weather suddenly turned to cold (November). Their water
trough froze up, so I put a tank heater into the tank and plugged it
into an extension cord and into the GFI. What I did not know was the
GFI was defective. For some reason the 3rd prong (ground) on the face
of the GFI was not connected to the circuit. The extension cord
apparently picked up a capacitance putting a slight tickle of
electricity into the water. The horses would not drink out of the
plastic tank. They kept kicking it and making a fuss everytime they
went to it. I finally decided to test it. First I touched the water
and felt nothing (rubber boots). Then I touched the ground with my
other hand and got a tickle. My meter showed around 15 volts to
With my meter I eliminated the extension cord as being defective and
discovered the GFI had no ground coming out, even though it was well
grounded in the box. I replaced the GFI and the electrical leak was
gone. However, the horses continued to fear the water. One of them
got sick from lack of water and cost me $400 in vet bills and he
almost died, but survived. I had to spend another $70 on a new water
trough that looked different, and move it to another place in the
yard. (Horses remember things like that, but when things change then
they are ok again).
So, $500 later and several sleepless nights everything was back to
normal. All because of a faulty GFI.
IF the GFCI "passes" the push button self test, then it would still provide
protection even if the ground lead was not connected. With the ground, it
might have tripped just from the bad cord, of course, and your animals would
be somewhat better adjusted now.
Sorry about your experience. You may want to invest in a combination
outlet tester/GFCI tester. (It plugs into the outlet: two of three neon
lamps should light. It has a test button which should TRIP the GFCI
protected circuit. They sell for less than $20 (and cost about $1 to
Thanks. I bought one of those GFI testers after that, and regularly
test all of the GFIs used near the animals. I almost had a horse
electricuted from a shorted tank heater years ago. So I installed
GFIs for every heater and any possible place I might use one of those
heaters. I thought I was safe after that. What happened to that GFI
was a very rare and weird thing. I even had the electric company
puzzled when I called them before I did any testing, because I assumed
the farm had a bad ground (called stray voltage on farms). They came
out, tested the electrical system, and could not explain the problem.
I never expected a bad GFI and to this day I still can not totally
understand what happened internally to cause that. If I recall
correctly, the button did trip, but no ground coming out. I'm just
glad that no animals died. I should note that when I was younger I
worked as an electrician for several years, and this really had me
puzzled since I had never heard of such a thing happening.
I'd like to hear from anyone else that had this happen, but somehow I
have a feeling no one else on here has had this problem. I spoke with
another electrician after it happened and they said they never seen it
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