Thjis is incorrect. A GFCI detects a difference in current between the “hot” and the “neutral” wires and trips is the difference is greater than a set point, generally 30 mA. The ground wire has noting to do with it and GFCI are often installed in circuits with no ground wire.
It seems to me that the logical thing to do is you have installed a 3 hole outlet in a circuit with no ground is to simply plug the ground hole thus converting the outlet to a 2 hole outlet. A sticker on the outlet saying “no ground” would add even more security.
The earth-ground prong is needed because it mechanically opens the other two. In my travels I have found out that you can push a screwdriver or a key into the upper hole and then insert (or rather, force) a European plug with two round pins into the other two. I was doing this at Hong Kong airport when someone saw me and I had some explaining to do. “NO, I am not trying to blow up the airport, I am only trying to plug in my laptop.”
As for things which are not protected by earth; earth protection makes sense for things like a dishwasher, refrigeartor, which have large exposed metal parts. Those parts should be grounded. But now think of a laptop. The mains voltage only goes to the external power supply which is all plastic outside. There is really nothing to ground there. Past the high voltage switching part everything is isolated from the mains and there is no need to ground it just like there is no need to ground something that works with batteries. If you have serious insulation from the mains AND there are no metal parts which can be accidentally made “hot” then grounding is nor necessary.
One of the most hazardous conditions we were facing in the fire service is our truck mounted generators. None of them came with GFCI’s.
And there was never a earth ground implemented.
There is always more to do in the name of safety!
With double-insulated appliances, it isn’t really an issue. Nonetheless they need something to open up the sliding safety sheet alluded to above.
When my late father paid a couple of men to run an armoured cable up to the shed at the top of the garden, they didn’t connect the earth wire for some reason, just cut it short. When I was getting a slight shock of my lathe, I investigated. There was just enough connection left to be able wire it to an earth lead, then bolt that to a piece of studding which I got from work and hammered several feet into the ground.
You can buy short extension cords with a gfci built right in.
Chances are, though, that there will be no potential difference between your gen and ground. Could be, though. So use a gfci.
If it’s a truck-mounted generator, it’s isolated from earth ground, is it not? If it’s isolated from earth ground, then a GFCI won’t be of much benefit. In addition, the system would be inherently safe, since most electrocution incidents occur when a person (who is grounded) comes in contact with a ground-referenced voltage (e.g. the hot conductor in your home wiring). If the truck-mounted generator is isolated from earth ground, and a person touches the hot or neutral on the generator, then (theoretically) they won’t get zapped, even if they’re grounded. The only way they could get zapped is if they touched the generator’s hot and neutral.
Again, this all assumes the truck-mounted generator is isolated from earth ground. If there’s a chance the generator’s hot or neutral could come in contact with earth ground, a GFCI would probably be a good thing.
I am yet another person who has worked on GFCI design and I believe the wording in this sub-thread has become a bit inaccurate. I believe the following is a more exact description;
The GFCI protects (i.e. shuts off the Hot lead) whenever either/both of the following two conditions occur;
1.) If the difference in current between the Hot and Netutral is about 30ma.
2.) If the Ground and Neutral are shorted (less than about 2 ohms IIRC) on the ‘load’ side of the GFCI.
#2 is called a ‘grounded neutral’ condition and the reason for protecting against it is that it will impair or eliminate the GFCI’s ability to perform protection #1. (I can describe why if you really want to know)
IIRC the GFCI does not need to be connected to the Ground lead in order to perform protection #2 or protection #1.
Its been a while since I worked on GFCIs but, unless there has been some significant technological breakthrough, I believe the above shouild still be accurate.
Your analisys is "sorta"wrong because condition #2 implies #1 which is all the GFCi detects.
A GFCI, all it is is a detector of differential current between the two conductors. There is no more to it.
But if neutral and ground are shorted on the load side, then there will be no problem as long as there is no load as there will be no current. But as soon as you start applying a load the return path splits between the (correct) neutral and the (faulty) earth and therefore as the load increases the imbalance between the two feed wires also increases until the GFCI trips when the difference reaches the set point.
Isolation is not guaranteed and in practice is very hard to achieve. Get enough wet mud on the tires and you could have a path to ground, for example. Or what if someone leaves an aluminum ladder leaning up against the truck?
The power cable I use on my generator has a NEMA twist-lock plug on one end and a plastic wiring box at the other holding two GFCIs. (The genny puts out two ~17 amp, 120 volt circuits or 17 amps of 240.) If there’s any current imbalance, the GFCI will trip, regardless of whether or not there’s an earth ground. The receptacles are also labeled “No Equipment Ground” as any actual earth ground would be unintentional and unpredictable.
No, wait, this is a bit more copmplex. First off we take it as a given that the meutral wire is grounded at the generator or, in this case, transformer. In that case a metal rod is a perfectly good earth. Note I am not saying according to code because codes differ, some will accept in and some will not. See TT network.
The GFCI WILL trip if you provide a ground fault. It is very easy. The GFCI measures the difference in current between the two conducting wires and trips when it exceeds a certain setpoint. That is all there is to it. If a ground fault exists then it WILL trip. But if no ground fault exists then it will NOT trip. You can electropcute yourself so long as you do not create a ground fault.
The protection to persons lies in that if the external metal parts are all grounded then a ground fault would be created before the voltage could reach a live person and this would make the GFCI trip.
In that wikipedia page you can see different grounding systems and they are all used somewhere. American code requeres very different things than European codes where the TT system is used and only a local earth is used.
Following a code does not mean it is automatically safe nor does it mean anything not in compliance is automatically dangerous. I have seen codes accept multistranded, flexible, conductors which I consider bad practice and which I would avoid in my home. American plugs are polarized which I consider a good thing while European plugs are not. Some European codes require double breakers such that both hot and neautral are interrupted. I am not sure if this may have become part of American code recently but it did not use to be necessary and interrupting only the hot wire was enough. Besides following the code it is even more important to understand the issues and what you are doing.
Crafter_Man, thanks for your welcome message. I tried to send you a message but the software seemed to be glitchy and I had to try many times. I think it finally went out but just in case I repeat my thanks here.
A GFCi is a good thing anyway because for the purposes of this example the body of the truck is “earth” and it can still be touched and a ground fault created.