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#216049 - 09/18/15 10:10 PM Portable Generator Question  
renosteinke  Offline
Cat Servant
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Joined: Jan 2005
Posts: 5,316
Blue Collar Country
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?


2017 / 2014 NEC & Related Books and Study Guides

#216050 - 09/19/15 04:00 AM Re: Portable Generator Question [Re: renosteinke]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
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.


#216051 - 09/19/15 02:38 PM Re: Portable Generator Question [Re: renosteinke]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,117
Estero,Fl,usa
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?

[Linked Image]


Greg Fretwell

#216052 - 09/19/15 05:22 PM Re: Portable Generator Question [Re: renosteinke]  
renosteinke  Offline
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Posts: 5,316
Blue Collar Country
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.

xxxxxxxxxxxxxxx

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!


#216053 - 09/19/15 05:29 PM Re: Portable Generator Question [Re: renosteinke]  
renosteinke  Offline
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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.


#216055 - 09/20/15 12:40 AM Re: Portable Generator Question [Re: renosteinke]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
(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.



#216057 - 09/20/15 04:30 AM Re: Portable Generator Question [Re: renosteinke]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,117
Estero,Fl,usa
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

Quote
Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.


These are not much of an issue with portable generators.


Greg Fretwell

#216058 - 09/20/15 03:14 PM Re: Portable Generator Question [Re: gfretwell]  
renosteinke  Offline
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Joined: Jan 2005
Posts: 5,316
Blue Collar Country
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).


#216060 - 09/20/15 08:50 PM Re: Portable Generator Question [Re: renosteinke]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,864
Brick, NJ USA
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??



John

#216063 - 09/20/15 09:09 PM Re: Portable Generator Question [Re: renosteinke]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,117
Estero,Fl,usa
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.


Greg Fretwell

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