GFCI related question

[mr horsepower]

i was doing some reading on another electrical site and came across something in an article that didn't seem correct to me.

the article -

http://ecmweb.com/grounding/electric_case_floating_dock/

what didn't seem correct -

"A ground wire provides a safe return path to ground for any leakage or fault voltages. An internal motor short would result in tripping the circuit breaker, or leakage imbalance would trip the GFCI circuit. However, with the ground wire severed at the house, electricity could not flow on this wire. Therefore, there would not be a GFCI sensed voltage imbalance at the lift motor to trip the unit. Both GFCI circuits were on the up side of where the short to ground was located. Effectively, this said the GFCI became unusable as soon as the ground wire became severed."

my question -

if i understand GFCI's correctly, they don't require a ground path to function as they operate/trip by sensing a current imbalance between the hot and neutral. so........

- how was the broken ground at the house responsible for not allowing the GFCI protected circuit(s) to not function properly?

- how could the current flow to the lake, and therefor not be seen on the neutral side, and not trip the GFCI?

.

 

[kwired]

i was doing some reading on another electrical site and came across something in an article that didn't seem correct to me.

the article -

http://ecmweb.com/grounding/electric_case_floating_dock/

what didn't seem correct -

"A ground wire provides a safe return path to ground for any leakage or fault voltages. An internal motor short would result in tripping the circuit breaker, or leakage imbalance would trip the GFCI circuit. However, with the ground wire severed at the house, electricity could not flow on this wire. Therefore, there would not be a GFCI sensed voltage imbalance at the lift motor to trip the unit. Both GFCI circuits were on the up side of where the short to ground was located. Effectively, this said the GFCI became unusable as soon as the ground wire became severed."

my question -

if i understand GFCI's correctly, they don't require a ground path to function as they operate/trip by sensing a current imbalance between the hot and neutral. so........

- how was the broken ground at the house responsible for not allowing the GFCI protected circuit(s) to not function properly?

- how could the current flow to the lake, and therefor not be seen on the neutral side, and not trip the GFCI?

.

You are correct.

After reading that my opinion is this investigation was not very thorough.

But how was I supposed to do this? The motor was hanging 15 ft to 20 ft over the water, with no means to place a ladder up to it and no way to prove that the water-filled plastic junction box was the conducive path (

You would think if you were investigating a death this would not be that big of a problem, the installer had to get it there somehow, it can be reached.

A would guess that he never did find where the fault actually occured, that would have made things a lot more clear. He never did identify the source of fault current in the article just a couple of assumptions. It was likely ahead of the GFCI protection that is why it never tripped.

Using a megohmeter on the conductors to the unreachable hoist motor would have been a good start at finding out if it was a contributor or not to the accident.

 

[kwired]

OK I read it again and maybe he did eliminate the motor as the source but he did not really confirm what the source was either.

If the GFCI was located after the junction box where he assumes the problem is and from what I can understand it was, the GFCI would not have tripped even with a good equipment grounding conductor.​

 

[glene77is]

. . . If the GFCI was located after the junction box where he assumes the problem is . . .

Kwire,
If I touched the ground-faulted equipment/conduit/wire ,
would I be in the path of leakage ?
Would that trip the GFCI (per its design) ?

 

[kwired]

If the GFCI was located after the junction box where he assumes the problem is ..

Kwire,
If I touched the ground-faulted equipment/conduit/wire ,
would I be in the path of leakage ?
Would that trip the GFCI (per its design) ?

In the incident this thread is about no. The fault is ahead of the GFCI and it will never see an imbalance of current and will not trip.

As was mentioned in the article There should have been GFCI protection at the house or at least on shore someplace before the circuit was run to the dock. That would have provided protection for everything on the dock that could energize the water or objects in close proximity to the water.

 

[mr horsepower]

The fault is ahead of the GFCI and it will never see an imbalance of current and will not trip.

it seems to me that the lift motor was after the GFCI protection but he's not real clear on a few things for sure.

anyway....

my theory i came up with today is the there was a short from the hot to the grounding circuit in the water filled junction box which -

a. didn't trip a breaker due to the open grounding circuit at the house

and

b. bypassed the GFCI protection completely (energizing the motor case and boat lift metal parts) allowing for the boy to become a path to ground from the lift to the lake.

i don't know if thats correct, but it let me stop thinking about it and get on with my day.


so.....
my new question -

if my theory (the possibility of the hot shorting to grounding circuit bypassing the gfci) seems reasonable, wouldn't the only 'truly safe' way to provide power to the dock be from a gfci breaker vs. gfci protection outside the box?

.

 

[kwired]

it seems to me that the lift motor was after the GFCI protection but he's not real clear on a few things for sure.

anyway....

my theory i came up with today is the there was a short from the hot to the grounding circuit in the water filled junction box which -

a. didn't trip a breaker due to the open grounding circuit at the house

and

b. bypassed the GFCI protection completely (energizing the motor case and boat lift metal parts) allowing for the boy to become a path to ground from the lift to the lake.

i don't know if thats correct, but it let me stop thinking about it and get on with my day.


so.....
my new question -

if my theory (the possibility of the hot shorting to grounding circuit bypassing the gfci) seems reasonable, wouldn't the only 'truly safe' way to provide power to the dock be from a gfci breaker vs. gfci protection outside the box?
.

The fact that the equipment ground was lost in the supply is the whole problem here plus the fact that there maybe should have been GFCI protection installed someplace before the circuit went onto the dock instead of on the dock. This was mentioned in the article. I have not found a NEC requirement but think it is a good idea.

The equipment grounding conductor and all bonded metal enclosures became energized but they did not really bypass the GFCI. The GFCI simply does not have anything to do with the EGC. If it becomes energized by anything that is not connected to the load side (hot and neutral) the GFCI does not do anything, because all it is looking for is current leaving one side (hot)to return on the other (neutral).

The fault occured before the GFCI so there was no imbalance of current through the GFCI.

Another problem I see is a violation of 555.9

..All electrical connections shall be located at least 305 mm (12 in.) above the deck of a fixed pier but not below the electrical datum plane.

 

[hurk27]

I can see how there would be enough current pass between the hot and EGC in the water logged J-box under the deck, but how much would depend upon the conductivity of the water inside the box.

First because the EGC is bonded to the boat lift which would provide a path to earth, the small amount of water in the box would have built up contamination of copper sulfide from the electrolysis that would have occurred over time, this would be no different then what happens to a damaged UF under the ground, at first the circuit doesn't trip, but after a couple weeks enough copper sulfide is expelled to make a conductive path between the hot and EGC that would trip the breaker if the EGC was connected.

this same thing could happen if the underground portion of the UF was ever damaged and the EGC was not connected at the source but bonded at the load.

In both the above cases only a GFCI at the house upstream of the fault would have provided protection even without an EGC connected

The reason of my opinion is a case where I had a post light that was being heated up, a neighbor hood boy was shocked by the post, and I helped the insurance company investigator determine the cause, but this case wasn't because someone did something wrong, the install was to code, what happened was a ground hog had chewed into the uf exposing the hot to the earth, this started the electrolysis that produced some heat, this exposed the EGC to the hot which was a lower impedance path then the earth the home owner experienced the living room breaker trip after a good rain, unknowing that the post light was also fed from this circuit the breaker was reset, after a few times the EGC opened but enough copper sulfide was buildup between the hot and EGC still going to the post light that the post light was at 120 volt potential, since the EGC was opened toward the house the breaker didn't trip anymore, it was kind of interesting as after marking the run and locating the break with my RDF, we dug about a foot on both side of the break and like an archaeologist carefully digging down to recover a bone, we uncovered the bad section of the UF being careful to not disturb the damaged section, we noted the green copper sulfide path between the hot from the house and the EGC to the lamp post.

In short the investigator showed in court that the cause of the live post was an act of nature, and the the installation was code compliant, and after this the plaintiff dropped the suit, think we got lucky.

Oh and the boy was ok, but he was rushed to the hospital via chopper and kept over night to make sure, these bills was what they were suing for.

after we received the ok to repair the feed, we found that the aluminum post had almost completely electrolysis off at the ground, one little push and it fell right over, and the new feed was not only put into PVC but also GFCI protected at the home owners request, we got a lot of work as other home owners who also heard of the case wanted theirs done the same way.

 

[mr horsepower]

thanks for the feedback guys.

 

[glene77is]

Huck/Hurk,

Should change your name to Sherlock.
Really appreciate seeing your methods and rational approach.

 

[kwired]

I can see how there would be enough current pass between the hot and EGC in the water logged J-box under the deck, but how much would depend upon the conductivity of the water inside the box.

First because the EGC is bonded to the boat lift which would provide a path to earth, the small amount of water in the box would have built up contamination of copper sulfide from the electrolysis that would have occurred over time, this would be no different then what happens to a damaged UF under the ground, at first the circuit doesn't trip, but after a couple weeks enough copper sulfide is expelled to make a conductive path between the hot and EGC that would trip the breaker if the EGC was connected.

this same thing could happen if the underground portion of the UF was ever damaged and the EGC was not connected at the source but bonded at the load.

In both the above cases only a GFCI at the house upstream of the fault would have provided protection even without an EGC connected

The reason of my opinion is a case where I had a post light that was being heated up, a neighbor hood boy was shocked by the post, and I helped the insurance company investigator determine the cause, but this case wasn't because someone did something wrong, the install was to code, what happened was a ground hog had chewed into the uf exposing the hot to the earth, this started the electrolysis that produced some heat, this exposed the EGC to the hot which was a lower impedance path then the earth the home owner experienced the living room breaker trip after a good rain, unknowing that the post light was also fed from this circuit the breaker was reset, after a few times the EGC opened but enough copper sulfide was buildup between the hot and EGC still going to the post light that the post light was at 120 volt potential, since the EGC was opened toward the house the breaker didn't trip anymore, it was kind of interesting as after marking the run and locating the break with my RDF, we dug about a foot on both side of the break and like an archaeologist carefully digging down to recover a bone, we uncovered the bad section of the UF being careful to not disturb the damaged section, we noted the green copper sulfide path between the hot from the house and the EGC to the lamp post.

In short the investigator showed in court that the cause of the live post was an act of nature, and the the installation was code compliant, and after this the plaintiff dropped the suit, think we got lucky.

Oh and the boy was ok, but he was rushed to the hospital via chopper and kept over night to make sure, these bills was what they were suing for.

after we received the ok to repair the feed, we found that the aluminum post had almost completely electrolysis off at the ground, one little push and it fell right over, and the new feed was not only put into PVC but also GFCI protected at the home owners request, we got a lot of work as other home owners who also heard of the case wanted theirs done the same way.

Just asking, where does the sulfur come from to make the copper sulfide you mention?

 

[glene77is]

As was mentioned in the article

kWired,
Right. You were right.
I was simplifying the issue, with a question.