Ditch the bed..

[AgAuMoney]

The high impedance connection of the earthing mat should protect the people from electrical system problems ONLY to the extent that the mat will not make such problems worse.

The outlet ground testers are questionable.

The style pictured earlier in this thread are typically trivially easy to fake out.  (Get a false 'good' reading.)  This is done by simply connecting the ground terminal of the outlet to the neutral terminal and thus to the neutral wire.  The simple neon bulb circuitry in the typical outlet checker cannot detect the subtle differences between the correct wiring and the very common fake done when someone who does not understand or care replaces a 2 wire receptacle with a 3 wire.  (Scummy contractors.)

This is bad because the ground is connected to any external metal appliance housings (e.g. the computer case or washing machine shell).  My 'office' with all the computers has a 8-10volt difference between ground and neutral in the room in spite of the two being connected at the breaker panel.  This is because of E=RI -- Ohms Law -- because of the normal current thru the neutral between that room and the breaker panel.  That voltage is enough to feel and could be dangerous if you are wet or bleeding and/or contact a good ground while touching the miswired ground.

A slightly better style has the same three lights plus a GFI test button that only works on GFI circuits.  A GFI does NOT require a ground and is allowed by code to protect 3 wire receptacles with no ground connection.  (Such a receptacle will NOT ground ala 'earthing'.)  The GFI tester works by allowing a small current to flow from hot to ground when the button is pushed.  This will trigger the GFI except if ground is not connected or is connected to neutral then the GFI will not activate.


Side note:  My last house I purchased new.  It had several wiring errors including one which connected the metal range to 120V.A.C. (within 4 feet of the kitchen sink).  My present house was built ca. 1975.  I tested every outlet before I moved in.  Several were miswired and some of them, judging by the layers of paint, had been that way for a very long time.  The previous owners had also made several changes, additions and repairs, wrong.  For example the outlet on the front of the garage was wired so that the three-way switches for the garage lights had to be both correct relative to each other (not to the light) for the outlet to operate.  Fixed.  The outlet on the patio was reversed hot and neutral.  I fixed that, and now the GFI blows every time it rains (splashing on the wall/windows runs down and into the box).  The 5hp pump should have been on 6ga wire and a 60amp breaker.  It requires over 100amps to spin up and is wired with 10ga.  Blew the 30amp breaker frequently when I first moved in but almost every time by 2 or 3 years later (breakers wear out).  It's on a 50amp breaker now and I replaced the wire in the house but not underground.  And I could go on and on...


I wonder how people with no electrical knowledge get by.  And then I see an electrocution or electrical fire article in the paper. 

[Kriegsspiel]

I sleep on a J-life futon on a platform bed, it's great.  I can sleep 'ok' on soft beds, but the futon is really where it's at.

[Gumby]

The style pictured earlier in this thread are typically trivially easy to fake out.  (Get a false 'good' reading.)  This is done by simply connecting the ground terminal of the outlet to the neutral terminal and thus to the neutral wire.  The simple neon bulb circuitry in the typical outlet checker cannot detect the subtle differences between the correct wiring and the very common fake done when someone who does not understand or care replaces a 2 wire receptacle with a 3 wire.  (Scummy contractors.)

Got it. So, how does one test the difference between a real ground and a neutral on a digital multimeter? I'm guessing one can run a real ground out the window and see if there's a difference between the neutral line and the ground hole. Or, perhaps comparing two 3rd ground holes versus a 3rd hole ground to neutral with the multimeter. Is there a better/easier way?

[AgAuMoney]

Got it. So, how does one test the difference between a real ground and a neutral on a digital multimeter? I'm guessing one can run a real ground out the window and see if there's a difference between the neutral line and the ground hole. Or, perhaps comparing two 3rd ground holes versus a 3rd hole ground to neutral with the multimeter. Is there a better/easier way?

If there is a load on the circuit (amount of load needed depends on how far it is to the breaker panel) then the voltage difference between the neutral and a real ground will be measurable.  No difference detected means you don't know.  If you do detect a voltage difference between neutral and ground, then you know it is almost certainly correct.

The most simple commercial tester does a large momentary load and looks for the difference between ground and neutral.  There should be some but it depends on how far from the breaker panel (increased distance increases the R in the wiring).  I'm not sure your DMM will be fast enough to capture a large momentary transient.  Does it latch?  You will probably need a few seconds at least, and that means a smaller load so you don't overload the circuit, which means a less discriminating test.  A 1500w space heater or blow dryer or hot plate (as large wattage as you can) run on your circuit long enough to test will likely put a measurable voltage difference unless you are very close to the breaker panel.


I don't think I'd trust comparison with other ground pins.  I'd rather try metal plumbing, metal duct work, large permanent appliances, etc.  This part gets more risky!  --  You can identify if other things that are supposed to be grounded really are by trying to run several watts of load between the hot of the outlet and the supposed ground while measuring the voltage drop across that load - should be the same as measuring voltage hot to neutral. (I prefer an incandescent light, and typically use a 100w or bigger trouble light.  A 7w CF is probably sufficient but harder to measure accurately since they are not a linear load and they also do not give a good visual indication of low voltage.)  The load is necessary because your digital meter is so sensitive that just measuring the voltage between hot and the appliance can appear like the full line voltage is there when really the appliance is just floating, perhaps with a capacitive ground coupling.

The way a sophisticated tester (rare and expensive, only used on hospital and other sensitive circuits) does the most accurate testing is they trail a long wire either from the circuit breaker panel or the system ground bond point so they know it is connected to the system ground.  (you could use a heavy duty, long extension cord)  This known good "ground" wire is connected to the tester as the reference ground.  The plug on the tester is plugged into the outlet.  One of the tests imposes a very heavy (could be 50+ amps) but very short duration (fraction of a second) load on the outlet and statistics are recorded.  Some of them have a screen (like a 'scope) and/or a strip recorder so the results can be instantly seen either or both as numbers or a graphic and newer units can upload the results to a computer when testing is done for the day.  Stats include voltage drop on the hot and voltage increase on the neutral (that's your test).  Other tests include longer-term (minutes) loads to measure stability and temperature increase at the outlet, load spikes into the outlet ground, etc.  Some testers can even do multiple outlets simultaneously to test for isolated grounds (required for some hospital and industrial safety circuits) by inducing a large ground fault on each outlet and watching for the effect, if any, on other outlet grounds.

[Gumby]

If there is a load on the circuit (amount of load needed depends on how far it is to the breaker panel) then the voltage difference between the neutral and a real ground will be measurable.  No difference detected means you don't know.  If you do detect a voltage difference between neutral and ground, then you know it is almost certainly correct.

Thanks again for your help AgAu.

So, it sounds you're are saying I can test an outlet by having one probe in the hot and the other probe testing for a voltage comparison between the 3rd hole and the neutral (compare Hot/Neutral vs. Hot/Ground and look for a measurable difference when a load is on the circuit). Correct?

One of the outlets is near the circuit breaker. The other is very far away from the breaker. If I understand you correctly, it should be easy detecting a problem in the outlet that's far away from the circuit breaker (i.e. the farther away it is, the smaller load on the circuit required to sense a difference?).

The most simple commercial tester does a large momentary load and looks for the difference between ground and neutral.  There should be some but it depends on how far from the breaker panel (increased distance increases the R in the wiring).  I'm not sure your DMM will be fast enough to capture a large momentary transient.  Does it latch?

I have to dig it out, but it's an Equus 3320 Auto-Ranging Digital Multimeter. I believe it's nearly just as fast as a more expensive Fluke. However I don't think it has latching. It has an audible continuity tester (is that what you mean?).

You will probably need a few seconds at least, and that means a smaller load so you don't overload the circuit, which means a less discriminating test.  A 1500w space heater or blow dryer or hot plate (as large wattage as you can) run on your circuit long enough to test will likely put a measurable voltage difference unless you are very close to the breaker panel.

So, just turn on the appliance and run the test to look for a difference between Hot/Neutral vs. Hot/Ground? If I overload the circuit, I assume the breaker just kicks in, correct?

How does one test an outlet that is very close to the breaker panel? Are you saying that outlets near the breaker panel require expensive and sophisticated testers? Or does it just require a higher load, such as a window air conditioner on the circuit?

[Gumby]

For what it's worth, the Wikipedia article on those little receptacle testers seems to have similar advice to what you are saying...

Note also that simple three light testers cannot detect two potentially serious house wiring errors: (1) neutral and ground reversed at the receptacle. (2) a "bootleg" ground, where the neutral and ground pins have been connected together at the receptacle. (Done by someone to attempt to fool the three light tester, typically if 3-prong outlets have been retrofitted to an old house with only two physical wires in the conduit.)

However by using the receptacle tester first, then a multimeter, these two errors can be detected: With the meter, look for low (but not zero) resistance and volts between neutral and ground. (Zero ohms is a sure sign of a bootleg job.) For the neutral-ground reversal test, next put some load on the same outlet circuit (e.g. a 100w incandescent lamp plugged into the other socket of the outlet), the meter should show a higher voltage between hot and ground, than between hot and neutral. This is because of the voltage drop due to the load. If it is the reverse situation, then you likely have a receptacle with neutral and ground reversed.

External Links:
Ways a receptacle tester can mislead (by an electrician)
How to do more accurate testing with voltmeter


Source: https://en.wikipedia.org/wiki/Receptacle_tester#Safety

Sounds like that matches up with what you were saying. But, I still don't understand what I will need to do to properly test the outlet that's near the circuit breaker.

[AgAuMoney]

So, it sounds you're are saying I can test an outlet by having one probe in the hot and the other probe testing for a voltage comparison between the 3rd hole and the neutral (compare Hot/Neutral vs. Hot/Ground and look for a measurable difference when a load is on the circuit). Correct?

One of the outlets is near the circuit breaker. The other is very far away from the breaker. If I understand you correctly, it should be easy detecting a problem in the outlet that's far away from the circuit breaker (i.e. the farther away it is, the smaller load on the circuit required to sense a difference?).

Usually for this precision all you need to test is for voltage between neutral and ground.  The load will cause the neutral to present a voltage (E) offset from ground due to the current (I) flowing in the neutral wire and the resistance (R) of that wire.  With no current flowing in the ground, it will stay at ground potential.  The voltage offset can be roughly predicted:  E = R x I  but the R is going to be fairly low in most code compliant wiring.  (If I remember, code requires a general purpose circuit to have a drop no more than about 10% at full load, and you will normally see only half of that on the neutral.  Also these are A.C. circuits so accurate analysis is more complex.)

If you don't see a voltage develop on the neutral, either your load is insufficient, or your ground is the neutral, or your meter is not sensitive enough (pretty unlikely with any DVM).

The most simple commercial tester does a large momentary load and looks for the difference between ground and neutral.  There should be some but it depends on how far from the breaker panel (increased distance increases the R in the wiring).  I'm not sure your DMM will be fast enough to capture a large momentary transient.  Does it latch?

I have to dig it out, but it's an Equus 3320 Auto-Ranging Digital Multimeter. I believe it's nearly just as fast as a more expensive Fluke. However I don't think it has latching. It has an audible continuity tester (is that what you mean?).

No, by "latch" I meant a function which will capture a transient reading.  Maybe known as "peak hold" or similar.  Some meters have a "hold" button which freezes the readout as long as you hold the button.  That won't help since if you can see the readout change you know something is happening.

You will probably need a few seconds at least, and that means a smaller load so you don't overload the circuit, which means a less discriminating test.  A 1500w space heater or blow dryer or hot plate (as large wattage as you can) run on your circuit long enough to test will likely put a measurable voltage difference unless you are very close to the breaker panel.

So, just turn on the appliance and run the test to look for a difference between Hot/Neutral vs. Hot/Ground? If I overload the circuit, I assume the breaker just kicks in, correct?

Again, the primary indication is a voltage between neutral and ground.

And you want the load plugged into the same outlet that you are testing.  For a normal duplex outlet, no problem.  If you have an outlet that is split in any way (1 switched, 1 always on; or an edison circuit where each half is on opposite sides of the 240v; etc) then I use a 1-to-2 (or 3) outlet adapter to make sure the load and the test are testing the same thing.

I like this kind:


Not this:

How does one test an outlet that is very close to the breaker panel? Are you saying that outlets near the breaker panel require expensive and sophisticated testers? Or does it just require a higher load, such as a window air conditioner on the circuit?

If you can get a large enough load, and if you can capture transients, you can test an outlet right next to the breaker panel.  That is what the expensive testers do.  It's worth a try with your meter.  As I said before, the test will either tell you it is good (difference between neutral and ground) or be inconclusive.  So you end up better or no different than now.  Do test your distant outlet first to get a feel for the behavior. 

[AgAuMoney]

For what it's worth, the Wikipedia article on those little receptacle testers seems to have similar advice to what you are saying...

Whew! 

With the meter, look for low (but not zero) resistance and volts between neutral and ground. (Zero ohms is a sure sign of a bootleg job.)

Be VERY careful with that.  I would STRONGLY recommend turning off the breaker before doing any "resistance" measurements on your house wiring!

For the neutral-ground reversal test, next put some load on the same outlet circuit (e.g. a 100w incandescent lamp plugged into the other socket of the outlet), the meter should show a higher voltage between hot and ground, than between hot and neutral. This is because of the voltage drop due to the load. If it is the reverse situation, then you likely have a receptacle with neutral and ground reversed.

Now THAT is clever!

[Gumby]

With the meter, look for low (but not zero) resistance and volts between neutral and ground. (Zero ohms is a sure sign of a bootleg job.)

Be VERY careful with that.  I would STRONGLY recommend turning off the breaker before doing any "resistance" measurements on your house wiring!

Understood. Turn the breaker off.

But, not sure I understand why we would want "low (but not zero) resistance and volts between neutral and ground." Obviously "zero" resistance and volts would be a sign of a bootleg job. But, wouldn't "low (but not zero) resistance and volts" imply that the neutral and ground were somehow completing a circuit? I would think we'd want the multimeter to say "OL" overload, which as I understand it, would mean that the circuit between neutral and ground wasn't completed and had no continuity. I mean, aren't the neutral and ground supposed to not have any continuity when the breaker is off?

Usually for this precision all you need to test is for voltage between neutral and ground...If you don't see a voltage develop on the neutral, either your load is insufficient, or your ground is the neutral, or your meter is not sensitive enough (pretty unlikely with any DVM).

Thanks so much, AgAu (and pumpkin too). You're a lifesaver — literally. Sounds like everyone should be testing all of their outlets for proper wiring — regardless of what they are using them for.

Due to time constraints and a busy schedule, I won't have time to check the outlets throughout house until late next week. (I will start a new thread on the topic when I get started.)

[AgAuMoney]

But, not sure I understand why we would want "low (but not zero) resistance and volts between neutral and ground." Obviously "zero" resistance and volts would be a sign of a bootleg job. But, wouldn't "low (but not zero) resistance and volts" imply that the neutral and ground were somehow completing a circuit? I would think we'd want the multimeter to say "OL" overload, which as I understand it, would mean that the circuit between neutral and ground wasn't completed and had no continuity. I mean, aren't the neutral and ground supposed to not have any continuity when the breaker is off?

In U.S. wiring the neutral is tied (or bonded) to ground where the supply enters the building and also at the distribution transformer supplying that building.

This is typically done at the very first breaker panel (the one with the master breaker) or in the meter panel.  (Sub panels are not supposed to bind neutral and ground, but non-code compliant installs do exist and may or may not be safe.)  Outbuildings without their own meters have more complex rules.)

Because these two wires do go to the same place, there will be low resistance between them (the sum of the length from the outlet to the panel and back to the outlet) unless the outlet only has the one wire connected to both places, then the resistance will be essentially unmeasurably low.

The reason why there are two wires that go to the same place is because the neutral will be carrying current and so will be above ground potential.  If that potential can find an alternate path to ground rather than by going all the way back to the main panel, it will take that second path in addition to or instead of going back to the panel.  If that second path is thru a person, hopefully hilarity ensues.

The ground wire will never be carrying current during normal operation. Thus it will never have any potential difference and so is safe to tie that ground wire to the chassis of equipment where people will touch it, to your plumbing, etc. and any current that leaks from an internal short will hopefully most or all to go via the ground wire instead of via a person.

The increased safety is shown in how dryers and ovens used to be 3 wires (HOT1, HOT2, Neutral) but now add Ground as the fourth wire.  The heating element is 240v between the two hots, doesn't even need a neutral so the neutral was tied to the chassis essentially being used as a ground, not a neutral.  A little motor or two or three didn't put significant current in the Neutral to raise its voltage above ground, but modern appliances add a bunch more Neutral current (and it is A.C. circuits so the impulses can be higher than immediately obvious on most meters) and so for safety's sake the code now requires a ground.