Open-ground hazard

[hedgehopper]

My AC Line Meter indicates "Open Ground." What are the dangers associated with this condition?

Note added: My system is 30 amp and connected to shore power. Shore power is grounded. The AC Line Meter is plugged into a newly added 120v outlet. The indication is "Open Ground" not "Open Neutral."

[MEXICOWANDERER]

Wanna hoot? Connect a scope to a microwave that is loading a MSW >50%

140 volt tops would be classified "pipe dream"

[road-runner]

MSW peaks vary from model-to-model, and with the DC input voltage. Having said that, after looking at a few of them I think a good generalization for the peak voltage is 140-ish, which is why microwaves run at less than full power with MSW.

[time2roll]

Actually MSW 120v RMS is likely lower than 177 at peak.
Sine Wave 120vac is 177 at peak.

[Harvard]

I am with Ktmr, 120V RMS Voltage goes from about +177V peak to -177V peak each cycle....

[Harvey51]

Ktmr wrote:
120V RMS Voltage goes from about +177 v to -177V each cycle as a sine wave.

I think you mean peak, rather than root Mean square.

[ktmrfs]

hedgehopper wrote:
ktmrfs and wa8yxm,

Based on the input from you two, I have determined that the outlet is not connected to a ground wire and is not protected by the adjacent GFCI. The technician who did the installation has promised to correct the problems.

Thank you for your assistance.

glad to see you got it figured out and on the way to a fix.

[MEXICOWANDERER]

With our tropical salt air, GFCI's malfunction (false trip) all the time. One outside receptacle continued to trip even with a NEMA flapper in place. The bottom line is total sealing. A plug gooped with silicone dieletric grease stuffed into each socket. Life in the tropics.

[hedgehopper]

ktmrfs and wa8yxm,

Based on the input from you two, I have determined that the outlet is not connected to a ground wire and is not protected by the adjacent GFCI. The technician who did the installation has promised to correct the problems.

Thank you for your assistance.

[wa8yxm]

hedgehopper wrote:

wa8yxm wrote:
EXCEPTION: If the outlet is GFCI protected.. The ground may be open on purpose as the GFCI will provide protection.

Pls say more. I think the new outlet is on the same circuit with an outlet with GFCI protection.

It not only has to be on the same circuit it has to be PROTECTED By the GFCI.. How to test for that.

Plug in your 3LT (3 light tester) and note the light comes on, Now go to the GFCI and press the TEST button,,, Are the lights still on. NO Good protected YES not protected.

Now press the Reset (Got to go back in a sec)

Now if it IS down-line from the GFCI (Protected) then here is how GFCI's work

Imagine a Teeter Totter perfectly balanced The weight (Current) on each end is identical One end has a black wire, the other white.. Now so long as the current (Weight) is the same in both wires. it nethier Teeters nor totters it remains flat

But if you add even a single drop of water (Tiny fraction of an ounce or in this case tiny fraction of an ampere) that end goes down and the GFCI is tripped...

So if you go back to my last post.. Had that Skill Hand grinder shorted I would never have felt a ting.. Just tripped the GFCI because it is far more senistive to that imbalance than I am to shock.

That is why they require GFCI in "Wet" places (Kitchen, Bath, Patio)

[ktmrfs]

hedgehopper wrote:

myredracer wrote:
OP needs to provide a bit more info

What additional information would you like?

ok,
1) do other outlets on this breaker or other breakers also indicate open ground?
2) when you say shore power, is that connected to 120V at your house or 120V at a campground pedistal?
3) have you verified that on the new outlet that the ground wire is connected to the outlet properly.

[hedgehopper]

myredracer wrote:
OP needs to provide a bit more info

What additional information would you like?

[MEXICOWANDERER]

Its worth pursuing to the point of asking readers for their opinions on this. Thank you road-runner.

[road-runner]

MEXICOWANDERER wrote:
Why aren't phase failures discussed more often? Could it be? Neutral bus and conductors are more vulnerable? How would that be possible? Or the succinct question How Would That Be Permissible?

Just a guess here. When we hear of a neutral failure it's usually in the context of fired equipment from too high voltage. A phase failure never results in voltage being too high, drastically reducing the risk of fried equipment. It's more likely for somebody to post "The park power fried my equipment", rather than "The power wasn't right so we had to move to another space". And the subject of the thread, open ground, usually goes undetected until somebody feels a tingle from the RV body.

[MEXICOWANDERER]

Dang I can't pull one over on you guys 😞

My next step would have been phase phrased differently for simplicity then ktmrfs' succinct reply but I'll press ahead with the fun...

"A shared neutral is a connection in which a plurality of circuits use the same neutral connection. This is also known as a common neutral, and the circuits and neutral together are sometimes referred to as an Edison circuit.

In a 3-phase system it is legal in some jurisdictions to share a single neutral wire between all three (3) phases*. One neutral may not have two “hot” wires from the same phase. It is good practice to use four (4) pole Circuit breakers (as opposed to the standard three pole) where the fourth pole is the neutral phase, and is hence protected against over current on the neutral conductor. Please remember that some jurisdiction prohibit the use of shared neutrals and/or require that the neutral conductor be substantially larger than the phase conductors"

OK, so far so (good) but using circular mil ampacity as a guide how do various (regional) jurisdictions compare? I do not know the answer to this question so I am asking.

There is a method to my madness of being purposefully oblique. Another question must follow -- the ratio, the % of neutral failures in relationship to L1 and L2 failures with regard to terminals and fixtures.

Nothing is "by accident". Predominance of one factor over two others, all thing being (supposedly) equal is illogical when large sampling has been conducted.

On one extreme there is ktmrfs whom I must beware of in trying to pull future "fast-ones" on the other hand there is the majority who may need to have this spelled out plainly.

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You have read numerous accounts of pedestal and cord failures. You have heard innumerable accounts discussed in person (I would imagine). Failures involve connections and integral wire terminations. why neutral? Why aren't phase failures discussed more often? Could it be? Neutral bus and conductors are more vulnerable? How would that be possible? Or the succinct question How Would That Be Permissible? We have NEMA we have NEC. Then we have differing regional neutral ampacity regulations.

Fascinating...

*This is completely dependent on transformer configuration. A DELTA 3-phase transformer can more easily support a single neutral. We have WYE transformers here and the neutral issue is much more prevalent. Part of the reason my SOLA ferroresonant line regulator creates its own neutral via a 2 to 1 step down.