Gfci

[Pavlovsky]

I have been told that a GFCI will not protect a worker who isn't grounded. Does this include a worker on a ladder?

 

[charlie b]

You were told wrong. A GFCI device works by comparing the current that leaves the source on one wire with the current that returns to the source on the other wire. If they are not equal, it means that current must be taking some other path, and that path might include a person. So it will trip if it senses a leakage current, regardless of where that leakage current is flowing.

Saying it will not protect a person who is not "grounded" is very deceptive. Consider two persons, each holding a power tool that has an internal failure and that is plugged into a GFCI protected receptacle. One person is barefoot and is standing on a metal deck leaning against a metal pipe. The other person is wearing rubber boots and is standing on a rubber mat close to, but not touching, the same metal pipe. If both power tools short out, both persons might get a shock, and if they do, the GFCI devices will both trip and will protect both persons. How could the person in rubber boots get a shock, if he is "not grounded," you ask? Through capacitve coupling with the nearby metal, I answer. My point, from a safety program standpoint, is that you may think you are not grounded, but you may still be part of a fault current path.

So a better way to look at things is this way: If the non-grounded person starts receiving a shock, the GFCI will protect him. If he does not get a shock, perhaps because of the rubber boots, or perhaps because he is standing too far from the metal pipe to create a capacitive coupling, or perhaps for some other unknown reason, then there will be no need for the GFCI to act to protect him.

Bottom line: regardless of whether a person is grounded or not, if he is subjected to a shock situation, the GFCI will protect him.

 

[Pavlovsky]

Thanks for the response!

 

[al hildenbrand]

I have been told that a GFCI will not protect a worker who isn't grounded. Does this include a worker on a ladder?

Is the ladder conductive or not conductive? And if the ladder is conductive, is the ladder on a non conductive floor while leaning against a non conductive wall?

My point is, if a person has a bare hot conductor gripped in their bare hand and no other point on the person's body is in contact with anything conductive, then there is no circuit that is complete for a GFCI (Ground Fault Circuit Interrupter) to interrupt.

A GFCI protects a person by its presence in the power supply. The protection is not removed because the person is not in a ground fault situation.

 

[marti smith]

I have been told that a GFCI will not protect a worker who isn't grounded. Does this include a worker on a ladder?

Its possible that some are misled when upon installing a gfci that is faulty, experience shock and relate it to the situation instead of checking the device. Its good to always test. They do come blasted-wretched-cursed-faulty out of a new box on occasion.

Charlie, I think that's the best explanation on the subject I've heard.

 

[bobsherwood]

It's Friday and I am thinking crazy..... What if a person gets a hold of both the hot and neutral for a GFCI circuit... he's got enough resistance in his skin to not trip the circuit and the line and neutral are ballanced???? seems he's in for ride!??

 

[480sparky]

It's Friday and I am thinking crazy..... What if a person gets a hold of both the hot and neutral for a GFCI circuit... he's got enough resistance in his skin to not trip the circuit and the line and neutral are ballanced???? seems he's in for ride!??

The GFI simply would see you as a normal load.

 

[al hildenbrand]

seems he's in for ride!??

Yup! But in the middle of that shock, the GFCI, while not tripping, is still protecting you when a current leak out of that hot-person-neutral circuit occurs and exceeds ~5 milliamps.

 

[480sparky]

Yup! But in the middle of that shock, the GFCI, while not tripping, is still protecting you when a current leak out of that hot-person-neutral circuit occurs and exceeds ~5 milliamps.

Yep! All the (not so happy at this point) person has to do is ground himself out.

 

[gar]

091218-1335 EST

A GFCI does not prevent you from getting a shock, but hopefully it prevents you from being killed. If the shock knocks you off the ladder the fall might kill you, but it was not directly the shock that was the killer.

6 MA will produce a substantial shock. Now look at the maximum trip time curve vs current for a GFCI. At 6 MA it could be fairly long. Even look at the 10 MA level for its maximum trip time.

.

 

[zog]

Anyone ever had a GFCI trip when they were getting shocked? 5mA hurts more than you think. Thank God I had one on my Koi pond when my heater broke.

 

[ELA]

Gar, Zog,
I have always been curious just how much a 5 ma shock would hurt. How do you know?
Did you have an ammeter in the circuit when you got shocked?

As I am sure you know a GFCI does not limit the current of the shock, just the duration, so I am curious... just not enough to run my own experiment.

 

[480sparky]

Gar, Zog,
I have always been curious just how much a 5 ma shock would hurt. How do you know?
Did you have an ammeter in the circuit when you got shocked?

As I am sure you know a GFCI does not limit the current of the shock, just the duration, so I am curious... just not enough to run my own experiment.

1mA : minimal perception level.
5 mA : GFCI trip level.
10 mA : Average Adult "Let-Go" Threshold.
15 mA : Muscles 'freeze' in 50% of the population.
30 mA : Difficult breathing, fibrillation in a small child.
0.05A to 0.1A : Possible ventricular fibrillation.
0.1A to 0.2A : Certain ventricular fibrillation
4A + : Heart paralysis, tissue and organ damage.

I'd say between 1mA and 10mA, you're going to know you've been zapped.

 

[ELA]

What electrical person has not seen these charts many times? There are many different flavors of this chart and many explain that the levels are different for each of us.

My point was.... how many of us know first hand how much 5 ma of current affects us personally?

To say that 5ma hurts because you tripped a GFCI by being part of the circuit is not very accurate. You most likely do not know what the current level was.
Of course you know if it hurt.

 

[480sparky]

What electrical person has not seen these charts many times? There are many different flavors of this chart and many explain that the levels are different for each of us.

My point was.... how many of us know first hand how much 5 ma of current affects us personally?

To say that 5ma hurts because you tripped a GFCI by being part of the circuit is not very accurate. You most likely do not know what the current level was.
Of course you know if it hurt.

I understand. But I doubt most normal, intelligent folk aren't too keen to allowing themselves to get shocked just to prove or disprove whether 5mA smarts.

 

[gar]

091219-0728 EST

ELA:

I can not tell you how a specific current feels.

Indirectly I believe, from experience, that 5 MA for several seconds would be a very substantial shock.

Also, if my reaction time is quick enough, then I should get a substantial shock and never trip a GFCI.

My skin resistance is about 500k hand to hand squeezing as tight as possible on Simpson 260 test probes. On Fluke 27 the same test reads OL.

Years ago. On a car with a 6 V battery, a metal horn ring that was hot to 6 V thru the horn relay coil, and I was sweaty from humid air, I felt a slight tingle to the door frame when touching the door frame and the horn ring. Assume 10,000 ohms and 6 V the result is 0.6 MA.

In earlier years I mostly played with vacuum tube circuits. These were typically 300 to 400 V DC and maybe 450 mfd capacitors. Under dry skin conditions I got some very substantial shocks of a fractional second duration. 500,000 ohms, probably actually higher because of light contact, and 400 V is 0.8 MA.

There are stories I have heard of electricians measuring voltage with their fingers. Obviously these were persons with high skin resistance.

Not on the shock problem, but in the vacuum tube days, I heard stories that end of line car radio troubleshooters at Zenith did much of their testing with a screw driver. Voltage could be estimated by the arc from shorting a high voltage wire to chassis, also effectively checked the capacitance of a high voltage filter capacitor. Also note the screw driver was a good probe to introduce a noise signal to an input.

.

 

[ELA]

Yes I have received my share of shocks in my nearly 40 years of working in various electrical/electronics jobs.

Some hurt and some tingled.

I often knew what the voltage level of the circuit that got me was.
I cannot remember a time when I knew what the current level was.

Sorry for being picky ... I only wanted to emphasize that the GFCI does not limit the current amplitude and so assumptions of the current level would be only that.

 

[LarryFine]

Years ago. On a car with a 6 V battery, a metal horn ring that was hot to 6 V thru the horn relay coil, and I was sweaty from humid air, I felt a slight tingle to the door frame when touching the door frame and the horn ring.

You might have been quite surprised had you honked the horn while touching the ring, from the inductive kickback.