.2 volts between neutral and ground

[Dave Botsch]

I have noted on some outlets between .1 and .2 volts from the neutral to
the equipment ground. One outlet was showing .4 when the AC was on and
nothing when the AC was off (but, it's on the same circuit as the AC,
hence the load on that circuit).

In the past, I hadn't noted any voltage btwn neutral and ground and hot to
neutral and hot to grnd was the same (it's off, now, by the amounts above).

I'm guessing this is bad and is something I should have looked into as
soon as possible?

I am going to check again tonight after people have gone to bed and
electric usage in the area should have gone down.

thoughts?

 

[George Pontis]

I have noted on some outlets between .1 and .2 volts from the neutral
to the equipment ground. One outlet was showing .4 when the AC was on
and nothing when the AC was off (but, it's on the same circuit as the
AC, hence the load on that circuit).

In the past, I hadn't noted any voltage btwn neutral and ground and
hot to neutral and hot to grnd was the same (it's off, now, by the
amounts above).

I'm guessing this is bad and is something I should have looked into as
soon as possible?

I am going to check again tonight after people have gone to bed and
electric usage in the area should have gone down.

thoughts?

If there is enough current flowing through the circuit to develop the
..1 to .2 volts across the neutral wire, then this is a normal reading.
To simply things you could just measure from neutral to ground.

For a real-world example, consider a single 100W light bulb, 65 feet
from the breaker panel. 12 gauge wire has about .0019 ohms per foot. So
with the drawing .833 amps and 65 feet of wire, one could expect .1
volt drop in the neutral line. So your measured numbers of .1 to .2
volts are very reasonable. With a heavy load you could see 1 to 2 volts.

Geo.

--

 

[Michael A. Terrell]

I have noted on some outlets between .1 and .2 volts from the neutral to
the equipment ground. One outlet was showing .4 when the AC was on and
nothing when the AC was off (but, it's on the same circuit as the AC,
hence the load on that circuit).

In the past, I hadn't noted any voltage btwn neutral and ground and hot to
neutral and hot to grnd was the same (it's off, now, by the amounts above).

I'm guessing this is bad and is something I should have looked into as
soon as possible?

I am going to check again tonight after people have gone to bed and
electric usage in the area should have gone down.

thoughts?

--
********************************
David William Botsch
[email protected]
********************************

You are measuring the voltage drop on the neutral wire from an
outlet, back to the breaker box. Do you understand Ohm's law?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Dave Botsch]

So, it's much more complicated, then, than the neutral and ground are
connected together at the breaker panel, thereby equalizing the
potential between the two, so, there shouldn't be a voltage differential
between the two (this only works if it's the same wire, same current, and
same length run)? And that the voltage between hot and neutral and hot and
ground should be the same because of that?

 

[Dave Botsch]

Wouldn't that be from one wire on the outlet, back to breaker box, then
back over the other wire back to the outlet?

So, it sounds like there is more current on one of the neutral, ground
since I last measured (I wonder if hooking up the tv upstairs to the cable
line could have some effect on this).

 

[lsmartino]

Dave Botsch ha escrito:

Wouldn't that be from one wire on the outlet, back to breaker box, then
back over the other wire back to the outlet?

So, it sounds like there is more current on one of the neutral, ground
since I last measured (I wonder if hooking up the tv upstairs to the cable
line could have some effect on this).

The readings you are obtaining are normal. The neutral wire carries the
current of the circuit back to the breaker box, while the ground
conductor is unloaded. The load in the neutral causes a slight voltage
drop in the conductor, and your reading is just showing that.

If you measured a difference of 1 - 3 volts between neutral and ground,
you should worry, but a 0.20 V difference is meaningless. Probably
there isn´t even a difference and you are just obtaining an spurious
reading caused by the DMM itself.

 

[[email protected]]

Draw a picture showing three wires going from the outlet back to the
fuse box. There is the hot lead, usually black wire, the return or
neutral lead, usually white wire, and the safety ground which connects
to the outlet box and the outlet grounding pin. Connect the safety
ground and the return/neutral lead together at the fuse/circuit breaker
box. Now have a 1-ampere current flowing between the hot lead and the
return/neutral lead. The current flowing back to the fuse box will
have the voltage drop the previous poster described. When you connect
a voltmeter between the safety ground and the return/neutral point at
the outlet you see the drop in the return wire.

Hope this clarifies the previous post which was right on.

H.R. (Bob) Hofmann

 

[JANA]

What you are reading is normal. The heavier the load, the greater the
reading. You are seeing the differential voltage difference between the load
return side and the neutral side. The wiring has some electrical resistance,
and you are measuring this along the neutral to ground return path.

--

JANA
_____


I have noted on some outlets between .1 and .2 volts from the neutral to
the equipment ground. One outlet was showing .4 when the AC was on and
nothing when the AC was off (but, it's on the same circuit as the AC,
hence the load on that circuit).

In the past, I hadn't noted any voltage btwn neutral and ground and hot to
neutral and hot to grnd was the same (it's off, now, by the amounts above).

I'm guessing this is bad and is something I should have looked into as
soon as possible?

I am going to check again tonight after people have gone to bed and
electric usage in the area should have gone down.

thoughts?

 

[[email protected]]

So, it's much more complicated, then, than the neutral and ground are
connected together at the breaker panel, thereby equalizing the
potential between the two, so, there shouldn't be a voltage differential
between the two (this only works if it's the same wire, same current, and
same length run)? And that the voltage between hot and neutral and hot and
ground should be the same because of that?

<snip>

Please Dave, tell me you're not an EE professor. As others have said,
200mV is completely normal for a modest load. I'm always amazed when
people discover there is a voltage drop (courtesy of Mr Ohm) on BOTH
wires supplying the load. Run a hair dryer on that circuit and measure
the drop again. If it stays low (<1) everything is good. Elsewise,
start looking for physically loose connections. Personally, I never use
the quick-connects (those push-ins) but prefer to use the screw
terminals and make them TIGHT.

GG

 

[George Pontis]

So, it's much more complicated, then, than the neutral and ground are
connected together at the breaker panel, thereby equalizing the
potential between the two, so, there shouldn't be a voltage
differential between the two (this only works if it's the same wire,
same current, and same length run)? And that the voltage between hot
and neutral and hot and ground should be the same because of that?

At the breaker panel their potential is equal. But as you go farther
from the panel, your "neutral" wire is not at the same potential as the
neutral in the panel because of the load current and resistance of the
wire. The ground wire never has current flowing though it under
non-fault conditions, so what you measure on any ground wire is the
potential of the neutral / ground bus at the panel.

Geo.

 

[Michael A. Terrell]

Wouldn't that be from one wire on the outlet, back to breaker box, then
back over the other wire back to the outlet?

So, it sounds like there is more current on one of the neutral, ground
since I last measured (I wonder if hooking up the tv upstairs to the cable
line could have some effect on this).

You have to remember that there is not supposed to be any current
flow in the safety ground, so it will have the same voltage as the
ground buss bar in your breaker box. So, when you connect the meter
between neutral and ground, you are measuring the voltage drop on the
neutral conductor, only. The higher the load on that circuit, whether
at that outlet, or another will show on your meter. Your meter should
have a 10 Megohm input impedance, so the ohm or so resistance of the
ground wire won't affect the reading.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Dave Botsch]

Haha, no, I'm not (actually, I'm not a professor at all).

Believe it or not, a lot of the information out there tells you that you
should measure zippo between neutral and ground, but, clearly not taking
into account what we've talked about in this thread. Hence, my confusion.

 

[ftlqed]

That's called an earth battery, either the earth at 50 amps is powering, or the wire is corroding in the earth to create the battery. You can add some salt to your earth ground connection to figure out how much potential the ground has, which should be constant. If you could, not saying I could, but the voltage current power shifts towards the weaker of the root mean square, then you would know the actual earth voltage, which is around 1V per square meter.