Ok here's a good one. I have 6 RV pedestals with 12 GFIs. (2 each) All the pedestals are 100 feet from their service disconnect. Three are served by 1 200 amp disconnect, 3 served by another 200 disconnect. All pedestals have seperate neutral and equipment groung. (all wired correctly as a subpanel, neutrals and grounds separated)all have suplimental ground rods connected to the ground bar only. Each pedestal has two 20 amp breakers serving two GFI receptacles (12 total). With no load, nothing plugged in or nothing connected to the load side of the GFIs, they all trip within a few minutes. Yep, all 12 with no load. All 6 problem pedestals are within the same area however, there are other pedestals near by and supplied from the same power co. transformer, wired exactly the same way, and have no issues. Any ideas?

Each pedestal has its own ground rod?

Have you verified the neutrals are routed correctly with the proper hot wire?

The neutrals are within the same underground conduit as the supply conductors and the equipment groung. Each pedestal does have its own ground rod however disconnecting the ground rod makes no difference. I tried that but the pedestal itself is metal and burried 2 feet in the ground too.

You are sure line voltage is connected to the line terminals?

Is there a moisture problem in the boxes?

Verify connections upstream of the subpanel after the 200 A service disconnect. I suspect a loose neutral connection.

MarkD123 I have a similar problem at my shipyard & usually it is due to water even if it is just condensation.

First thought would be incorrect L-N Terminations at the GFCI Receptacle (Line side Grounded Conductor Terminated to the Load Terminal / Load side Grounded Conductor Terminated to the Line Terminal - and/or a similar scenario for the Ungrounded Conductors)

Next would be N-G connection on the Load Side of the Devices; could be from a nick in the Conductor's Insulation - resulting in an N-G "Leak",
could be from bare EGC touching the Silver Screws on the Device,
Etc...

After that would be Wiring Fault - Open Common Neutral issues, Neutrals of the Two Branch Circuits tied together at some remote location past the GFCI Device, etc...
IIRC, the latest and greatest GFCI Devices are supposed to "Crow Bar" (trip and remain non-resettable) if the Load Side has a Wiring issue.

Then there is the possibility of Current flowing via either of the Two Wires of the Branch Circuit - which is causing the Devices' CTs to sense an imbalance...

Last would be defective Devices.

Start with the "Obvious" and easiest, then work your way down the list until you reach "Defective Devices".
If you get that far, exchange with a Device which is known to be functioning properly, then energize the Branch Circuit to see if the properly functioning Device will hold or trip.

To verify if Neutrals for the Two Branch Circuits are tied together "Downstream" of the Devices, turn on One Circuit at a time. If no trip occurs, turn on the Second Circuit.
Trip will indicate a Load Side Wiring issue.

-- Scott (EE)

Thanks guys but keep in mind there is nothing connected to the devices. Nothing pluged in nothing downstream. As in every case the neutrals go to neutral buss which intern is grounded at the disconnect at the service. I have replaced a few devices with new _same result.

If there is no load on the gfi's and they're tripping on their own it's going to be one of three things..

1) Condensation building up within the gfi's themselves.

2) Line voltage disturbance. (What manufacturer made the GFI's? Some GFI's will trip when power is removed or "browned out", so that you must reset them after power has been restored.)


3) You got a run of defective gfi's.

If the gfi's will allow you to reset them and function, even for a few minutes,I don't see it as a line/load mix up. They shouldn't reset at all..

BTW make sure if there are lawn sprinklers in the area that they aren't hitting your pedestals.

P.S. If all else fails, try a different make of GFI, and stay away from any that say "3Grace" or "General Prohtect" anyplace on them. These have false UL labels on them (There's a thread about when I came across these before someplace in the forums) Stick with the known manufacturers (P&S, Bryant, Leviton, Hubbell, etc..)

Speaking of GFI tripping. I just install a lot of Christmas lights and it seems that 2 of my many GFI receptacles trip. OK, now I know that I can replace them. However once I turn on the lights and see these 2 strings aren't working. I go out unplug lights, reset GFI and plug lights back in. They will work all night long. Next night I turn on all outside recpt. and the same 2 strings (which are on different recpt. and different sides of yards.)do not go on. I rest GFI and they work all night long again.

My question, these are "newer" style GFI that have to have power on to rest. I still have the old style where you can reset without power. Could a rush of current when the lights go on be tripping the GFI? I am more curious than anything else.

Harold:
Have you considered the morning dew??

Maybe I just live in a swamp but I always suspect water first on a GFCI trip problem.

Apparently transients on the line side can cause GFIs to trip too, even European RCDs with much higher nominal fault currents. Older 100 and even 300 mA RCDs frequently trip in lightning storms. I'd assume that US GFIs with their much lower trip current are even more susceptible to such phenomena (not necessarily caused by lightning activity).

I have not noticed GFCIs tripping here from lightning but I do have a bit of protection on my power.

John,


I haven't thought about Morning Dew, but i do drink Mountain Dew on occasions. Actually, I went out there the other day and I wrapped each and every connection with zip lock bags and taped up the ends to keep moister out. The GFI's still trip. I will look into it this weekend. I also bought a bunch of new GFI recp. in case I have to replace. I am wondering if a GFI breaker inside would be better than 5 GFI recpt. out side.

Greg,

The last time I had a large lightning strike near me, it took out a large tree, several bulbs and dimmers in the house. I also have a small sub station out behind my property. I also have 8 acres of woods behind me and the sub station. Luckily, it didn't get hit when Sandy hit us.

What kind of surge protection do you have?

Greg,

NONE as of now.

I would get a panel protector at a minimum and take a very good look at your grounding system. Make sure everyone is using it. (telco, cable etc)

Have voltage readings been made from G to N / L to N / L to G?
What happens if the GFI Receptacle is pulled out of the box and the ground wire is removed from the receptacle?
Since all of problem pedestals are fed off the same main it seems like the cause is most likely back at the main disconnect.
But then again is could be a mis-wiring at any of the pedestals.
Is the feed to all of the pedestals in conduit the full length? If it’s URD maybe one of the wires are damaged.

Right now I have 6"-7" of snow on top of everything. This may have to wait until spring.

I would check the GFI outlets and make sure that the supply is on the line side terminals not the load side.

Martin,


Let me say Welcome to the board. Don't be a stranger, we are all friendly around here. As for the GFI line/load side, I did that already. It would not be the first time that I was rushing and I screwed that up. Now a days with the new style, they have the tape over the Load side so that I don't make those mistakes anymore. ( At least I hope I don't)

Looks like this is the hot thread on GFCI's this winter which is always the time I get headaches beyond the ordinary because I start to run trough heaters.

Last year I went through agony with stray voltage problems unrelated to the GFCIs. This phenomenon has been around virtually forever but gets worse as buildout continues around us without substantial upgrades in the local grid. (Not ragging on the power company, I think it is a travesty that they have to provide us power in the sticks at the same price as in more densely populated areas. I'd rather be able to pay for a system that works than be stuck in a relationship with them where what they can charge me is limited so they scrape by doing the minimum. Rural electrification was one of those social programs that, if it was ever useful, has long outlived it. But, I digress . . . you better get used it it, that's my middle name.)

So, although I've occasionally seen animals react to trough heaters because of this stray voltage problem, I've been running them for 30 years here and never had trouble tripping GFCIs. (That was why I was doubly mystified by the stray voltage until I realized it was not straying between line and neutral which is the tripping monitor of a GFCI, but rather between neutral and ground.)

But this year, I started plugging in trough heaters in one location and get a loud buzz and then a trip. I'm not sure I have ever heard a GFCI buzz like that. Different GFCI unit from different manufacturer right next to this one on the opposite leg of the 240 connected to the same neutral all on the line side terminals in the box, so I move over and same result. So I plug something else - a hair dryer we keep for thawing stuff - into both of them and it works fine.

So I carry the trough heater to another installation and it works. However the variable is that I have a short (6 foot) extension cord in the location that keeps tripping. I didn't suspect the cord because it doesn't trip with just the cord plugged in, but I plugged the hair dryer into the cord and that causes a trip. So I go back and move the trough closer and low and behold, the thing works without the cord. Cord looks fine and dry, uncut, not old or cracked, but assume this means there is maybe a moisture related minor neutral to ground fault that isn't noticed until there is actually current flowing. This makes sense as I think about it, although not when yours frustrated truly was out in the field.

Now my wife reports that the sans extension cord installation tripped the breaker overnight, so I'm slogging out there momentarily. Not to undermine her logic skills but she infers this from some lights being off rather than from having taken a flashlight and actually checking the kill-o-watt that I keep installed at the trough heater so that we can monitor hours that its on, know that it is working and know if the power is out visually.

It may be that I left one of the other circuits off with all our testing yesterday and that is why the lights are off. But I'll fill in that blank in a half hour. Meantime, I think I have managed to talk myself through what is happening with the extension cord just in writing this out.

I guess the bottom line is, could we get a less sensitive GFCI that would provide some protection in these circumstances but eliminate this constant nuisance tripping in difficult circumstances. There were trough heaters long before their were GFCI, and maybe I don't spend enough time on farm forums, and/or maybe all the old timers with stories of dead cattle, horses and farmers killed by trough heaters gone critical just haven't made the net, but the cost benefit of this safety protection is starting to exceed its utility at the moment.

My other notion is just to try an airstone for a pond and see if that will keep the water open, but thats maybe a more appropriate discussion for a livestock forum, but figured a bunch of handy guys around here might have dealt with other stuff besides wire in their lives -- not that there's anything wrong with that . . . .


thanks,

brian

Brian,

I used to do electrical work for a farm in my town. We would use heater tape around the water pumps in order to get water to the live stock. When I worked near a dock on the lake, we used to use bubblers in order to keep the water from freezing around the dock. I am going to assume that an airstone is like a water bubbler. Maybe they make electric blankets to wrap around the trough to prevent the frozen water.

As for stray voltage, that would be a real hot topic around here. I have seen lots of problems with stray voltage around pools. Sometimes it was caused by pin hole leaks in the Power Co. (POCO) primary underground feeders.
We would get readings between 5-30 volts around a pool. Enough voltage so that you feel a tingle when you touch metal, the pool deck and had bare feet.

I used to wrestle with various techniques for keeping water lines open, but thank god I bought an exacavator and we have buried lines to half dozen hydrants around the farm. Every once in a rare while you can freeze one of those. I'm not even 100% sure I know how but I assume in the cases I've seen they might have had slight leak at the seat that exceeded the drainage capacity of the surrounding soil so you got a water level established up the hydrant, but maybe I'm overthinking this and it was just CTWT.



Right, an airstone is an aquarium and backyard pond aesthetic outlet for pumped air to do the bubbling. With fish, it oxygenates the water as well as keeping it from freezing if it is an outdoor fish pond. I don't know why there isn't more focus on this kind of device for water troughs. It may put the animals off, but I have found that the introduction of stray voltage (see below for more on that) from the standard trough heater approach is highly offputting to livestock - for obvious reasons, i.e. they tend to be well grounded unless you get them rubber horseshoes (mostly kidding although they make rubber boots that are substitute for standard metal horseshoes for riding. Of course, if the horses wore them in the fields this would pretty much frustrate the effectiveness of elecric fences, or you would have to run one or two ground strands as well as hot strands).

So back on the GFCI issue. I rechecked everything. The GFCI stayed on running the heater as long as I didn't use the suspect extension cord. I took the cord inside and warmed it up for 24 hours laying on the warm floor and hoped I might drive out any moisture that might be cause the tripping. My ohmmeter shows infinite resistance between all legs of the cord. But took it back out, plugged it in and it still trips as soon as I plug anything into it, despite the fact that these same appliances will run in the same GFCI without the cord. It is no great loss to need another 6' cord but I'm mystified as to how to really diagnose what the problem with the cord is if anyone has any ideas. The male end is a molded original. I shortened the cord and put a field installed female on it. Same cord was running these heaters last year without any tripping.



No underground feeders around here lighting up manhole covers and frying dogs, or the like. We're in the sticks. It's all overhead. But I did some fairly extensive research on this last year. The Stray voltage to which I refer is the relatively ubiquitous Neutral to Earth Voltage, i.e., the line loss or voltage drop between of the return to the substation - which is exacerbated in rural climes because of the distance to the substation and a grid that was sized based on electric demands before exurban buildout.

Because the voltage drop is based on current, it varies around here from about 3 volts at low usage times to as high as 7 or 8 volts when a lot of power is being drawn first thing in the morning and early evening.

This potential is introduced to the exterior of any grounded appliance because of the bonding of neutral to ground at the box. And more ground rods or pounding them deeper, etc. is marginally helpful. The one thing I learned about this, that is the most helpful analytical tool, is current takes all paths to ground relative to resistance, as opposed to my earlier misconception that it takes the easiest path.

If I had any doubt what horses were experiencing, I've had some good bouts myself running electric drills and angle grinders with diamond blades in concrete where we are using water as a lubricant and to control dust. We obviously run the tools on GFCIs but once everything is thoroughly misty, I can get some goddamn good, i.e. painful, tingles off the casing of the tools when I am grounded but this doesn't throw the GFCI.

This is because the same amount of current is going out the line and back the neutral as far as the GFCI measures. The current that is zapping me is the small but potent potential (guess that is redundant but for emphasis) between the neutral and the ground which is not measured by the GFCI.

This is a subject I really like to talk about but it is only tangentially related to GFCI. If there is a stray voltage thread here I'll try to stray onto it.

Brian

There are some faults that trip a GFI but don't show up at very low voltage, i.e. with a multimeter. This is where a megger gets really helpful, because its test voltage is much higher.

got it, of course. i usually think about voltage . . . eer amperage I mean when I think about it . . . as breaking down continuity. so you can test and get continuity on a circuity but apply load and the continuity breaks down at a corroded or loose connection somewhere.

and of course with very high voltages I think of faults -- , i.e continuity to ground as becoming more likely, but, of course, 110V is well more than the testing voltage on standard tester.

unfortunately the meggers are well more than I can spend to confirm that there is a fault at 110V on this $5 extension cord, so I guess I will have to accept that trying this on several GFCIs and getting the same result is definitive. unless and until I find a friend who has one, my mind is whirring on that. You see, I know this linesman . . .

thanks for the note

brian

For tingle voltage problems one of the solutions the local power co uses is a Ronk Block isolation device at the transformer. http://www.ronkelectrical.com/blocker.html

Regarding the GFI, I remember when I bought my Black and Decker electric lawnmower 5 years ago it came with a warning note that certain brands /model numbers of GFI's that were know to trip if thelawnmower was used.

They advised to change to a brand not on the list to prevent problems.

"As for stray voltage, that would be a real hot topic around here. I have seen lots of problems with stray voltage around pools. Sometimes it was caused by pin hole leaks in the Power Co. (POCO) primary underground feeders.
We would get readings between 5-30 volts around a pool. Enough voltage so that you feel a tingle when you touch metal, the pool deck and had bare feet."

Primary (loop or star) Poco Feeders are those conductors that function on the line side of Poco transformers -- pad mount or pole mount. Hence, they operate at "Medium" voltages -- i.e. beyond 2,000 VAC.

Service Laterals to homes and their common Secondary Tap run should best be termed Secondaries.

Pocos can deliver juice at both Primary and Secondary voltages to Service customers. -- And, obviously, will only provide Medium Voltages to industrial and major commercial ratepayers.

(Las Vegas casinos famously draw only Medium Voltage/ Primary (Distribution) Circuit power. The casinos own and operate all of the utilization transformers, themselves.)

When overhead, the Primary Distribution is unshielded. Any car parked near High Voltage transmission lines will have an induced ( capacitive coupling ) voltage ranging into the hundreds of volts. The actual charge quanta will be very low. It can be tested by a high impedance meter -- like our common DMM -- with one lead stuck in the ground and one on the bodywork.

This phenomena can't happen with buried Primary conductors -- because they are Shielded with a braided neutral -- looking like a massively oversized co-axial cable wire.

Even pin hole leaks in Secondary insulation would vent so much current that the heat would open up the fault until even a Primary transformer fuse would blow. (Pocos don't fuse their secondaries -- as a rule.)

All of which is to say that you're operating under a false conception of where the mystery current is coming from.

----------------

Speaking from experience:

The impressed voltage witnessed in swimming pools and hot tubs that are not well grounded can have two sources.

Either the slightly salty pool is experiencing capacitive coupling to some nearby high voltage, high power current -- or it's experiencing the Faraday effect.

http://en.wikipedia.org/wiki/MHD_generator

In the current age, swimming pools and hot tubs have filtration and agitation circuits built entirely of PVC. The pump impellers are typically plastic, too. It's also very, very common for the field windings to be wrapped in a PLASTIC enclosure, too. The only metals are within the field windings and stator.

Because everyone exudes salt from their skin, and such salt does not evaporate out, swimming pools turn into weak salt baths -- every last one.

Making them conductors of electricity, too.

When such a fluid is forced to pass through the unshielded electric fields of the pool pump, by that pump, both the Faraday effect and the Hall effect kick in: the first being dominant.

If the 'salt bath' is well insulated -- it is possible to lift the voltage of the bath into the tens of volts. I have tested it as high as 45 Volts with a DMM.

Once it's sweetly grounded, this voltage bleeds off.

So, the voltage is being built up by magnetic field effects.

While the voltage can build up to dangerous levels -- the discharge current travels through your groin while stepping into the pool, one leg at a time -- the contained energy is easily bled by a ground wire.

Factory built hot tub assemblies specify that they need a grounded plug. They don't explain, even to their tech reps, the above reason. If you're unlucky enough to plug into an exterior receptacle in a home built to 1960 standards -- (no grounding conductor) you'll get a shock.

If the Heating Elements of the Trough Heaters are similar to Heat Trace Cable (i.e.: Self-Regulated Heater Cable), using a Class A GFCI (Trip Threshold = 6ma) would result in repeated Trip Issues under normal / correct operation.

In the case of Heat Trace Cables, instead of using the Class A, 6ma Trip Threshold GFCI Devices for controlling excessive "Leakage", Ground Fault Protection for Equipment ("GFPE") Devices are used. The standard Trip Threshold for these GFPE Devices = 30ma (0.03A).

GFPE Branch Circuit Breakers look exactly the same as GFCI Branch Circuit Breakers, only the Catalog Numbers differ...
Example:
GE's THQB 240VAC Class 10KAIC 1 pole 20 Amp GFCI (5ma) Breakers are Product Number "THQB1120GF", whereas the THQB 240VAC Class 10KAIC 1 pole 20 Amp GFPE (30ma) Breakers are Product Number "THQB1120GFEP".
Both look exactly the same, except when viewing the Billing Statements from the Wholesale House;...
the GFPE Device is at least 2x the cost of its GFCI counterpart!!!

--Scott (EE)

Tesla,

The one instance there was stray voltage around a pool was when this fiberglass pool was installed. It never had water in it and I asked the EC if he ever had trouble with stray voltage. He said "NOPE! Never had problems." I said , OK. A week later I get a call from the EC asking me what I know about stray voltage and I said WHY? It seems as he was hooking up the ground wire in the wet niche, he got whacked with current. He knew that there was no power to the pool, it wasn't even ready to be filled up with water.

Long story short, he installed 8' ground rods all around the pool 10' apart and exothermically connected all the rods together. Once he got to the back of the pool, the voltage dropped from 25-30 v down to 2-3 volts. You couldn't feel the stray voltage anymore.

That is why I like concrete pools. Between the pool, the 2000 sq/ft deck, Ufer in the the foundation ring under the screen cage, Ufer under the addition and a bunch of 8' rods, I am will grounded.
Everything is well bonded too.

Greg,

I have only seen the problem of stray voltage with the fiberglass pools. No others. However a long time ago in a far away place... I was working with my old boss ( back in 1977?) We were working with an old built in pool and there was problems with voltage I believe. However being a 1-3 year apprentice, I did not know what was going on. Some of the old pools around here were concrete but no rebar. Most didn't have bonding wires around them either and they also use to use brass conduit to go to the wet niche.