I just searched for and found this newsgroup because I need help
understanding electricity as it applies to a standard, grounded
I purchased a decent digital test meter today at the store. I decided
to test an outlet I have in the kitchen because it's already a
grounded type with three prongs.
I inserted one lead into the hot side and one into the ground opening
(the 3rd hole at the bottom), and the meter reads about 115ish. It
sort of fluctuates as I move the leads around. The instructions on
the tester say that it should read 120 V. Are there variations in the
normal voltage of a standard 120 V outlet, and is this normal that it
is only reading 115 not 120?
Since I am getting a reading at all, I am assuming that this means
that the outlet is indeed grounded. Am I correct that if the outlet
were not properly grounded, then the meter would not read anything at
all? In other words, it would read 000?
I do believe that my house is grounded because I have found what I
believe is the grounding rod near one of the front corners of my house
right by the electrical panel. It's a copperish looking rod stuck in
the ground and extending about 9-12 inches out of the ground. The
cable TV cable is attached to it and it looks like a wire that comes
from the electrical panel is also connected to it. Do you think I am
correct, that this is most likely the grounding rod for my house? If
so, generally, does this mean that all the fuses/outlets for the
entire house are then grounded, regardless if they have a 3 prong
outlet in them? In other words, is the electrical panel itself with
all it's circuit breakers the thing that is grounded? Or is grounding
specific to just one or two outlets or one circuit in the house?
This is long I know, and any help is apprecitated.
I would not be 100% certain. Modern meters are real sensitive and they
can give some spook readings. Stop at the hardware store and get one of
those three dollar outlet testers. They are not so easily fooled.
As for the voltage, don't worry 115 is in the acceptable range and it is
possible you really have 120, try checking across the two power legs of the
Two different things. You home may be grounded but the outlets may not
or even the other way around. In older homes you never KNOW, that's why you
use that little tester.
Likely true. That "It looks like..." has bit more than one electrician.
No. An outlet is only grounded if it is properly connected to a proper
ground. Chances are very good that an outlet with out a ground is not
grounded at all and may need a new wire to make it so.
Yes there are variations in the voltage. Also, your meter may not give
you an exact reading. What you have is normal.
Essentially yes, More likely the meter would read close to 0 than
actually reading 0. So your outlet is grounded at least as far as the
breaker box. But you still need to be sure that the house is grounded at the
breaker box. You'll also want to confirm that the neutral at your outlet is
hooked up so measure the voltage between the two outlet slots. It should be
around 120 V AC
Yes, that's must likely the grounding rod though I'm surprised it looks
copperish. It's often an 8ft steel rod. Your house may also have another
ground rod for lightning rods and one for the telephone, Some houses have a
ground connected to the plumbing, too.
If you have three prong outlets it is likely that they are grounded and
you can check the grounding by using your meter, just as you did above. If
the outlet has 2 prongs it is not grounded.
Your panel is grounded and your neutrals are connected to ground at the
panel but it is unsafe to think that the outlets are grounded unless they
have 3 prongs and the ground prong is wired.
My meter shows 122 by the fridge, except when the compressor is
running and it drops to 118. When the defrost is on, it drops to 115.
I can put the meter on ohms and it reads 1.5 ohm between the ground
plug of the socket by the fridge and the copper water pipe under my
In my electrical circuit breaker box, I have a thick copper ground
wire running from the common bar in the bottom of the box where all
the green ground wires are tied down to a solid bar buried in the
ground. Also on that same solid bar is another copper wire running to
the white buss in my circuit breaker box.
So every outlet has a green wire running to ground. But also there
is a white wire running to the buss bar which also runs to the same
115volts is fine for most things im sure your meter is fine.
is the ground rod you saw 5/8" it beings so far out of the ground
makes me think the cable or phone ppl might of put it there but they
drive a thinner rod than electricians and it should be in the same
area as your service as they are suppose to ground to our system,but
some older houses might not have one or two as we are required to use
today, nothing to sweat if you dont its a crappy ground anyways. your
water ground is your primary ground and a good one if done properly.
just because a service is grounded doent mean your branch circuits
will be grounded but by what you said it appears your outlets are
which wont mean your lighting is cuz back aways they ran grounded
outlets but not lighting.
if you take the cover off your panel look at the wires leaving the
box..do all the cables have a bare or green wire with the black and
white? if so they are grounded.
The copper clad ground rod is part of the grounding system of your service,
a metallic water pipe would be another part.
If you use your tester and measure from the hot slot of a grounding outlet
to the grounding hole, it is a good indication that the outlet is grounded.
For non grounding outlets,(two slots only) test between the hot slot and the
screw that holds the outlet plate on. If you get a 115 volt or so reading,
it's a good indication that the outlet is grounded and all you'd need to do
is replace the non grounding outlet with a grounding outlet
Thank you all very much for your detailed replies. :-)
Alas, this is as I feared, more complicated than I had anticipated. I
think the last post got to the real "meat" of the situation. What I
want to do is replace the two outlets in the bedroom that do not have
3 prong grounded recepticles with ones that do. But I do not want to
do it unless the outlets are actually grounded.
So if I test those outlets by testing the screw and the hot side, and
I get a reading (115V-120V), then the outlet is actually grounded, and
I can proceed to change the recepticles? I am somewhat adverse to
getting electrocuted, so I want to do this correctly. lol
I sincerely apprecitate all your responses.
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