I have recently purchased a 6500W portable generator. You know the type; wheels on one end, handles on the other, move it around like a wheelbarrow.

The instructions tell me to connect this generator to the building ground bus, GEC, or ground rod.

Huh?

Can someone please explain just what this is supposed to accomplish? The generator is designed only for the use with cords. It has receptacles. Just what will a connection to the service ground do when everything is powered by an extension cord?

Any thoughts?

IF, and this a only an if, there is some sort of surge suppression network built into the generator, the connection to the "building ground bus, GEC, or ground rod" is to provide a reference for the surge suppression network.

Do you know, or can you tell if any of the output power wires are connected to the generator frame, i.e. neutral to frame bond.

If neither of these conditions are true, then the only two things I could guess, is the desire to prevent the voltage of the generator frame from rising significantly above "earth" and to minimize EMI/EMC emissions from the generator itself.

Lawyers and misunderstanding.

Usually these do bond the neutral and ground (except the little Hondas in my experience)
Personally I think grounding them is giving up the safety you have from isolation. That is particularly true in a wet situation like after a hurricane.

When you connect this to the building wiring, that all changes and then you need to follow the NEC (SDS or not SDS etc)

Is this what they have in mind?

Thank you, Greg- that's the picture that came to mind as I read the instructions!

They're pretty clear, though, that they intend the genny to be bonded to the service ground. There's even a lug provided for this use, with a note specifying #8 or larger GEC. It seems they really want the genny frame to be bonded to the building ground - the neutral did not come into the discussion.

As I've pondered this issue, a few things come to mind...

I assumed that the ground wire on the cord would, together with the case grounding within the appliance, provide protection against any faults. What if, I wondered, someone used a 2-wire cord? Attaching the system to the building ground would provide a redundant ground path.

Next, I realized that I had assumed the use of the genny only when there was no electrical service available. What if that were not the case? What if there was another source of power available- be it PoCo or another generator? Hmmm...

A situation where there were multiple sources COULD result in a voltage difference between the different "grounds." This is why the NEC requires all grounds to be bonded together.

So, maybe that specified #8 wire is not such a bad thing.

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John Peters, author of the famed "In Search Of Excellence" management series, once tried to find out where product manuals actually came from. He never did find out - somehow the things magically arrived whenever the factory supply ran low. No one knew who ordered them, or where from. With that sort of oversight, perhaps the manuals are as good as they are!

As for 'surge suppression" ....

This genny is of an exceptionally reputable make .... Think "Mercedes-Benz truck" rather than "economy car" in terms of construction.

(Had I wished, I could have purchased a Chinese import of supposedly similar ratings for about 1/3 the price ... and I got a deal!)

This implies an integral alternator, rather than an inverter. As a quality make, the voltage regulation is likely to be a lot better than that on an economy generator. Does this mean some manner of surge suppression? I don't know. I'm more inclined to think along the lines of diode bridges and capacitors, rather than transistors. I'm not about to open it up and look.

(Straw grasping in progress)

Maybe it is not about the generator. By bonding to an approved earthing network, would that protect the 300 V wire insulation rating of whatever is plugged into the generator?

Based on the idea that a voltage charge could build up and puncture insulation.

Bonding provides the protection that operates the over current device. Grounding has nothing to do with it.
In fact grounding a generator increases the hazard potential because a fault to earth, grounded objects etc, through your body can kill you. If the generator is floating, you are a bird on a wire.

Article 250 says this about grounding



These are not much of an issue with portable generators.

I suppose it's time to be precise ...

The model-specific manual that the manufacturer provided says:
"Grounding the Generator: The National Electric Code (NEC), as well as many local electrical codes, require the generator to be connected to an earth ground before operating. Before starting the generator, make sure it is connected to earth ground by connecting the ground terminal on the control panel (See Figure 12) to earth ground using copper wire (minimum 10AWG). Consult a qualified electrician for local grounding requirements."

(OK, so my earlier statement about #8 wire was incorrect).

Now, what else is in the manual?

Well, I see that they describe the wheels as an "accessory." I also see a section about connecting the generator to a transfer switch.

Let's pause and think about that for a moment. Is it possible that some variants of this generator are permanently installed?

I think we may have found the electrician's equivalent to "one size fits all" clothing.

I see absolutely no benefit to bonding this generator to "Mother Earth." I do see some (marginal) benefit to having a redundant bond to the equipment grounding network of the building.

Using the generator as I intend .... physically unplugging the furnace from its' receptacle on the wall, then powering the furnace with a (3-wire) cord that runs straight to the generator ....., well, I don't see any way making a 'permanent' ground connection improves things.

Of course, we've had our discussions about having a flexible cord on a permanently installed appliance, such as a furnace. That's another topic. personally, I'd rather see a cord on a furnace than find a 'suicide cord' for the dryer receptacle.

How will I get the cord out to the generator? Well, I'm going to try something new. Garvin makes an "extension ring" that takes screws on BOTH sides. That means I can place a device ring on both sides, making an opening right through the wall. I could mount an "inlet" on one side and a receptacle on the other, or I can simply pass multiple cords out the hole, stuffing it with fiberglass to stop drafts and bugs.

(I plan to use a similar arrangement for my phone / data / CATV services).

Reno:
Does your 6.5KW gen have a 120/240 4 wire twistlock?

Why not an inlet, and a interlock kit w/2 pole cb and choose your loads?

No 'cords' except one, no holes to stuff w/'glass

As to the ground issue; an acorn clamp & piece of #8 or what you have can't hurt can it??

I am willing to be called wrong but I would like to see the NEC requirement for a cord connected portable generator to be grounded.

Yes, it has the twist-loc. It even comes with a very nice, fat cord ... 30A, 4-prong twist-loc on one end, and FOUR 120v 15A plugs on the other. It is protected by the generator's main breaker.

For that matter, a 'power inlet' (with weatherproof cover) costs less than $20. As long as I only use "one circuit" worth of power I'll be OK. Plenty enough for a furnace blower and a few lights. Can't accidentally overload things if I have to swap plugs

Acorn? My rods are ... as code requires ... completely buried. I'll run the ground wire either to my 'inter-system grounding bridge,' or maybe even straight to the panel bussbar.

I specifically do NOT want to have a permanent connection. Choose loads? It's a bit too easy to mess up - and, before you know it, you might as well put in a proper transfer switch, etc. No, this is a PORTABLE generator, and will be used as such.

Keep in mind that this genny won't just sit there ... it also serves as my jobsite genny when I need one.

I put an inlet and a breaker interlock kit in here but I have never actually used it.
It is piped in PVC and I thought about putting a couple "T" conduit bodies in with a little loop for one of the ungrounded conductors so I could easily check the current but I never bothered.

I bet that is why the Instructions ask for the Genny to be Bonded to the Local GES... for a Standby Genny situation, semi-permanently connected via an ATS.
Kind of a ---CYA--- inclusion for the Manufacturer, even if the device is used for Temporary Power / not used as a Standby source.

OTOH, the Manufacturer might really feel strongly about creating a GES for ALL their Gennys - low Power included, and the Grounding Specifications became "Boiler Plate Text" in every Manual - for whatever reason


--Scott (EE)