fog37 said:
Why doesn't it represent a dangerous situation if the frame becomes the ground?
The Osha leaflet imposes conditions
The significant one is that the portable generator power
only things connected to it by three wire extension cords.
that "Bond" the load to the generator via their green wire.
Always plug electrical appliances and tools directly into the generator, using the appliance manufacturer’s supplied cords. Use heavy-duty extension cords that contain a grounding conductor (3-wire flexible cord and 3-pronged cord connectors).
So any fault that connects metal to hot will trip the breaker in the generator.
It would be very unwise to use a 'Ground Buster"
fog37 said:
The ground is a connection so that, in case of malfunction, the current chooses that path instead of your body.
KCL dictates that current goes back to the source from which it came.
If the path back to its source doesn't include ground then current won't go there.
This requirement assures that the only place current wants to get back to is the generator frame.
OSHA said:
... The generator supplies only equipment mounted on the generator and/or cord and plug-connected equipment through receptacles mounted on the generator, § 1926.404(f)(3)(i)(A), . (emphasis mine - jh
fog37 said:
If we touch the generator's frame, don't we become also the ground and get zapped?
Not unless there's a source of current between ground and the generator frame.
Your whole mini-grid consisting of generator and its extension cord connected loads "floats" with respect to ground .
There is no connection to ground so it won't exchange current with ground.
Unless somebody has made a connection to ground and you become the second one. That's how you get hurt.
That's why they require a ground rod if you connect the generator to a building - the building's distribution panel is connected to ground.
OSHA said:
Thus, rather than connect to a grounding electrode system, such as a driven ground rod, the generator’s frame replaces the grounding electrode. If these conditions do not exist, then a grounding electrode, such as a ground rod, is required. If the portable generator is providing electric power to a structure by connection via a transfer switch to a structure (home, office, shop, trailer, or similar) it must be connected to a grounding electrode system, such as a driven ground rod.
Observe they used verb "replaces" not "becomes". The return path for fault current becomes the green wire not Mother Earth.
fog37 said:
The generator has plastic wheels which insulate it from earth...
Hmm i don't know if that's a requirement but it's a good idea. Same function as rubber shoe soles.
