Portable generator - grounding or not?

[fog37]

Hello,

I have read of someone being electrocuted using a generator. I noticed that portable generators don't need to be Earth grounded with a grounding rod. Why not? In the households, all appliances are grounded and directly connected to the ground through the main panel.

However, if the generator is permanent, an Earth ground connection is necessary...

Thank you,
Fog37

 

[berkeman]

I have read of someone being electrocuted using a generator.

Did they grab the Hot/Line lead in their left hand and the Neutral lead in their right hand? That would certainly result in a Darwin Award...

 

[anorlunda]

Ground or not? Do exactly what the owners manual says, including restrictions on the kinds of things to use it for.

 

[jim hardy]

https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf

 

[fog37]

Thanks everyone.

Jim, this is from the pdf link you sent me: "Thus, rather than connect to a grounding electrode system, such as a driven ground rod, the generator’s frame replaces the grounding electrode"

Why doesn't it represent a dangerous situation if the frame becomes the ground? The ground is a connection so that, in case of malfunction, the current chooses that path instead of your body. If we touch the generator's frame, don't we become also the ground and get zapped? The generator has plastic wheels which insulate it from earth...

 

[Guineafowl]

Thanks everyone.

Jim, this is from the pdf link you sent me: "Thus, rather than connect to a grounding electrode system, such as a driven ground rod, the generator’s frame replaces the grounding electrode"

Why doesn't it represent a dangerous situation if the frame becomes the ground? The ground is a connection so that, in case of malfunction, the current chooses that path instead of your body. If we touch the generator's frame, don't we become also the ground and get zapped? The generator has plastic wheels which insulate it from earth...

The generator has plastic wheels which insulate it from earth... if we touch the generator’s frame... the current chooses that path instead of your body... in the case of malfunction.

Almost! Your question, rearranged, is almost your answer.

Only your instruction manual knows how to wire up your generator properly. Generally, the neutral and Earth are tied to the genny frame, providing a low impedance path for fault current in the event of a phase to neutral fault. An accidentally live appliance’s chassis will pass lots of current down the Earth lead, where it joins up with the neutral to complete the circuit and trip the MCB or RCD/GFCI.

For more permanent, larger and multiple-feed applications, a ground rod is used to keep everything grounded/earthed equipotential.

 

[anorlunda]

For more permanent, larger and multiple-feed applications, a ground rod is used to keep everything grounded/earthed equipotential.

I liked your reply except this last sentence. Portable generators should not be used for those purposes. We do not want to confuse permanent home generators with portable generators. That is why I (and you) pointed toward the owner's manual. That manual should explicitly say, for example, that they should not be used for permanent installations such as supplying backup power to home wiring.

 

[jim hardy]

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"

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.

... 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

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.

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.

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.

 

[Guineafowl]

I liked your reply except this last sentence. Portable generators should not be used for those purposes. We do not want to confuse permanent home generators with portable generators. That is why I (and you) pointed toward the owner's manual. That manual should explicitly say, for example, that they should not be used for permanent installations such as supplying backup power to home wiring.

Yes, good point, I meant for standby generators versus portable.