Why is a ground wire required from a generator?

[Billy_Bob]

Why is a ground wire required from a generator to a building's main electric panel, yet no ground wire is provided from the electric company's transformer?

Why does the electric company not provide a ground wire either with a pole mounted transformer or a pad mounted transformer on the ground? (I was thinking that the electric company reason was that their transformers are up high in the air and no one can touch these (except qualified persons). But then there is the case of pad mount transformers which are on the ground...

I see with the following that pad mount transformers are grounded using a special method...

"Provide a 1/0 bare copper-ground girdle around transformer. Girdle shall
be buried 305 mm one foot deep and placed 915 mm 3 feet laterally from the
transformer enclosure. Connect girdle to enclosure at two opposite places
using 1/0 copper. Exothermically weld joints."

http://www.wbdg.org/ccb/DOD/UFGS/UFGS 26 12 19.20.pdf

Picture...

Then another difference would be the wiring from a generator to a building. The wiring from a generator would tend to be temporary - perhaps strung on the ground. The electric company's wiring would be high in the air or far underground in well protected conduit.

Then people would tend to have their hands all over a generator, especially if there is an electrical problem. For the electric company transformer, only qualified persons would work on these.

And is the neutral bonded to ground at a pad mounted transformer? Or is just the case grounded?

 

[Speedy Petey]

Where in the world did you get those specs??? And that image?

I saw "USACE / NAVFAC / AFCESA / NASA" at the top of that .pdf and quit reading.

How big is the generator in the image above that it requires a 1/0 or 2/0 grounding wire that is Cad welded???


Portable generators do NOT require any connection to a grounding electrode.

 

[Sponsor]

 

[CodeOne]

Portable generators do NOT require any connection to a grounding electrode.

What about this code section in the NEC.

702.10 Portable Generator Grounding.
(A) Separately Derived System. Where a portable optional
standby source is used as a separately derived system,
it shall be grounded to a grounding electrode in accordancewith 250.30.
(B) Nonseparately Derived System. Where a portable optional
standby source is used as a nonseparately derived
system; the equipment grounding conductor shall be
bonded to the system grounding electrode.

 

[Speedy Petey]

Yeah, I forgot about that one. Poor wording on my part.

By portable I meant cord connected. It is pretty rare to find a portable unit that is genuinely hard wired to a system like a pad mount standby unit typically it.



250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable generator shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by the generator under the following conditions:
(1) The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The normally non–current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are connected to the generator frame.


Even a genset connected to a Gen-Tran type panel via a twist-lock plug and cord is still "cord-and-plug-connected equipment through receptacles mounted on the generator".

 

[CodeOne]

Yeah, I forgot about that one. Poor wording on my part.

By portable I meant cord connected. It is pretty rare to find a portable unit that is genuinely hard wired to a system like a pad mount standby unit typically it.



250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable generator shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by the generator under the following conditions:
(1) The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The normally non–current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are connected to the generator frame.


Even a genset connected to a Gen-Tran type panel via a twist-lock plug and cord is still "cord-and-plug-connected equipment through receptacles mounted on the generator".

No problem, We (me espically) all have ram problems with memory espically when it comes to the NEC. No one can know it all or remember it all. The closest one can come is someone like JWElectric who eats, sleeps and breathes the NEC. However I have caught him once in a while on something obscure that rarely comes up.

 

[Billy_Bob]

Something which is of interest is the OSHA requirement for GFCI's to be on portable generators and with these the neutral is bonded to the outlet ground connection prior to the GFCI outlet at the generator...

Ok....

THEN someone uses a regular transfer switch to connect one of these generators to a home. And the home main electric panel of course has the neutral bonded to ground...

Then part of the current returns to the generator via the neutral wire and part of the current returns via the ground wire...

Then the GFCI on the generator has a fit and trips!

There are two solutions to this as provided by generator manufacturers...

1. A neutral switching transfer switch...
http://www.briggsandstratton.com/pdf/owners_manual/101/071014_0_om-Domestic.pdf

2. This manufacturer says to remove the ground / neutral bond connection at the generator and re-label it...
http://www.gen-tran.com/assets/pdfs/HondaGeneratorServiceBulletin20.pdf

 

[JWelectric]

Billy Bob

A read of 250.34 will tell us that a portable or vehicle mounted generator is to be used for equipment mounted on the generator or cord-and-plug-connected equipment through receptacles mounted on the generator, or both.

Once we connect one of these type generators to a building which is not equipment, then the generator is not longer portable and must comply with 250.35.

 

[CoreyF]

portable generator ground rods, neutral bonding, NEC, OSHA

I recently had a new High Efficiency natural gas furnace put in, and the owner of the HVAC company mentioned that he had put a plug on his own furnace's power supply in order to power the furnace ignition/blower from a portable generator in an emergency. At no extra cost he put a 120V outlet and plug on my furnace (located at the furnace) so that I could do the same--directly unplugging the furnace from the home's wiring system and then plugging it into an extension cord to a generator. I then purchased a 7000 watt Generac (GP7000E) generator so that I could be prepared for any winter power outages. My further intention was to purchase a 25 ft generator cord which had the L14-30 plug on the generator end, and two 120V GFI outlet boxes on the end I would use inside the house to power the furnace/refrigerator/TV.

I was very much surprised to then read the generator owner's manual and find the statement "The National Electrical Code requires that the frame and external electrically conductive parts of this generator be properly connected to an approved earth ground (Figure 9)" , and which then referred to a diagram and description of the location of the grounding lug provided on the frame,wire guage, and earth-driven ground rod. It also stated that this was to prevent electrical shock in the event of a ground fault condition in the generator, connected electrical devices, and for dissipating static electricity. My generator has a sticker on it stating that it is "neutral bonded to the frame", and this is visibly done at the location of the lug used to attach a grounding rod.

I have since spent hours on the Internet trying to sift through the conflicting opinions on the use of grounding rods, neutral grounded to frame, and other issues regarding the use of portable generators. I have learned much from reading some of the posts in this forum from people like JW Electric, and I wanted to say thank you. I think I finally feel secure in operating my generator without a ground rod as long as I am just using power cords directly from the generator to the equipment I will plug into those power cords, and not even dealing (at this time anyway) with the issues of disconnecting neutrals via the correct transfer box and other such things.

I also intend to contact Generac and try to determine why their instructions (and those in other manufacturer's manuals) to use a ground rod seem to actually be a contradiction of NEC and OSHA code, and in fact could possibly increase my risk of electrocution (the link I've provided to the OSHA paper of John Gryzwacz is particularly well illustrated, and explained in terms a lay person can understand).

I'd appreciate a heads up if anyone sees a flaw in my current plan. Thanks in advance for any feedback, and I've listed some of the results of my research so that others in my position might find some helpful information :

Billy Bob's previous post's discussion of NEC code 250.34 regarding portable generators with neutral grounded to frame (like the Generac 7000E has) supplying power to a house, link to a comprehensive owners manual of a 'switching neutral manual transfer switch' by Briggs and Stratton which describes safely hooking one of these to a house system to isolate the neutral bonds of the generator and the home wiring, and if the appropriate 'switching neutral' transfer switch is not used, a Honda generator link regarding GFI trips when hooked to the house unless using a transfer switch or the generator neutral bond is disconnected within the generator itself (and then discussing that it will no longer be OSHA compliant and would need a sticker stating the neutral is NOT bonded to the frame). https://terrylove.com/forums/showthread.php?p=240008

The Washington State Dept of Labor and Industries, Aug 2009 Electrical Currents Newsletter, from the Office of the Chief Electrical Inspector, regarding not grounding portable gens which are already frame grounded, and which includes the link to the OSHA paper by John Gryzwacz explaining and diagraming the dangers of using an external ground with portable generators:
http://74.125.95.132/search?q=cache...s/currents/elc0908.pdf+NEC+250.34&hl=en&gl=us

The 2005 OSHA paper/guidelines of Professor John 'Grizzy' Gryzwacz of the OSHA National Training Institute in Arlington Heights, IL, which trys to clear up the "much misunderstood" regulatory issues concerning the use of portable generators like those used at construction sites: http://oshaprofessor.com/Portable Generators and OSHA Construction Standards 3-05.pdf Includes cross-references to OSHA and NEC code, simplified diagrams and explanations of situations referenced (including why using a grounding rod on a portable generator that is already grounded to its own frame can be an electrocution risk). Explains the three distinctly separate regulatory references pertinent to the use of portable generators (which 'should not be confused or combined'): 1) Grounding electrode, 2) GFCI exemption requirements for some small portable generators under 5000 watts (and that this exemption may no longer even exist) , and 3) Neutral Bonding requirements.


A section of a 2003 Army Corps of Engineers manual, particularly section 11C, regarding grounding rods for portable gens (usually not required), but including how to lay an 8 ft ground rod in a trench if it can not be driven in vertically, for those situations in which equipment must be grounded: http://www.elcosh.org/record/document/92/SECTION11-V2-final.pdf

A link I found to the government's 2007 Federal Register regarding the proposed elimination of the GFCI exemption for some small portable gens, including those under 5000 watts :
http://ftp.resource.org/gpo.gov/register/2007/2007_07159.pdf

 

[Billy_Bob]

Thank you for posting that!

Interesting reading and the Grzywacz article was a big help by clearly discussing grounding as being for...

-Poco transformer insulation breakdown and primary to secondary short.
-Lightning.
-Personnel protection.

So in answer to my own question above, it appears that in the case of a generator being connected to a building and a ground wire being run from the generator to the building...

It is actually more of a case of the ground wire being run from the building to the generator!

You are providing an earth ground TO the generator FROM the building wiring. And could consider the frame of the generator as an "appliance" (if you will) which could be a shock hazard. Thus you are providing "personnel protection" at the generator via that ground wire!

So power is from the generator to the building.
Grounding is from the building to the generator.

[Then you could look at it another way.* (See below)]

And this would not be necessary with a poco transformer high in the air. And the pad mount transformer has its own grounding system.

Then something of interest is that a "transfer switch" would also be a "NEC code rule switch" depending on if you used a neutral switching transfer switch or not!

Use a neutral switching transfer switch and the generator becomes a separately derived system and the neutral must be bonded to the generator frame per the Grzywacz article.

But use a transfer switch which does not switch the neutral, and you have a non-separately derived system!

Then contrary to the "not grounding a generator for added safety under certain circumstances" as discussed by Grzywacz, the last link above stirs up a whole new set of problems with the following statement...

"Bonding one of the circuit conductors to the generator frame provides a path outside the circuit conductors for ground-fault current to flow. Such current will be detected by a GFCI. If the circuit conductors are insulated from the generator frame, it is more likely that any ground fault current will return through the circuit conductors and go undetected by a GFCI."

So it seems to me for the "personnel protection" part of the grounding equation, if using a GFCI, it would be desirable to bond the neutral to the frame of the generator and to ground the generator frame! Else the GFCI will not work!

Are we all totally confused now?

*I think all the confusion is because grounding a generator has not one, but multiple purposes...

-Personnel protection.
--By touching the frame of the generator.
--By a ground fault when using a hand held appliance or electric tool.
--By a short from hot to a metal electrical raceway or enclosure.
--By the capacitive coupling problem.
--By use of a GFCI.
--By causing the circuit breaker to trip in the case of a hot short to a metal object.

(And it seems to me that when you provide a solution to some of the above, it is contrary to others of the above.)

 

[JWelectric]

Rule one in current flow.

There must be a complete path from the source back to the source. The earth or ground if you please in not part of this path

Rule two in current flow.

At low voltages of 120 volts current will not travel through earth or ground if you please enough to open a 15 amp breaker nor blow a 15 amp fuse.

Rule three in current flow.

The earth or ground if you please plays no role what so ever in protecting anything from electrocution.

Rule four of current flow.

If one thinks that earth or ground if you please plays any role what so ever in the protection of someone from electrocution please refer back to rule one.

 

[Speedy Petey]

Rule one in current flow.

There must be a complete path from the source back to the source. The earth or ground if you please in not part of this path

Rule two in current flow.

At low voltages of 120 volts current will not travel through earth or ground if you please enough to open a 15 amp breaker nor blow a 15 amp fuse.

Rule three in current flow.

The earth or ground if you please plays no role what so ever in protecting anything from electrocution.

Rule four of current flow.

If one thinks that earth or ground if you please plays any role what so ever in the protection of someone from electrocution please refer back to rule one.

Well said.

 

[Orlando29]

I don't find John Gryzwacz's explanation convincing at all. I've shown it to a couple of electrical inspectors who also don't find it convincing.

He states that grounding the generator is dangerous. Sorry, I just don't get it.

In the diagram Gryzwacz provides, if the hot touches the metal body of a tool, the voltage is going to return to it's source by by the path of least resistance. In this case, it will travel through the person holding the tool and return to earth.

Pounding a grounding rod into the earth at the generator isn't necessary, but I don't see how the diagram proves that it is dangerous.

I also intend to contact Generac and try to determine why their instructions (and those in other manufacturer's manuals) to use a ground rod seem to actually be a contradiction of NEC and OSHA code, and in fact could possibly increase my risk of electrocution (the link I've provided to the OSHA paper of John Gryzwacz is particularly well illustrated, and explained in terms a lay person can understand).

 

[Dav hamm]

Yup digging up an old thread. Bought my first generator after 1 day of what turned out to be 5 days without power. Its a Honda EB3000c so neutral bonded to ground.

Furnace is hard wired in but there is an outlet at it for the condensor pump. I threw the main and all the circuits (cause when the electrician upgraded our panel he didn't label anything). Disconnected the ground coming from the line(house) (so the furnace was then basically an appliance (or so I thought) but plugged it in and the GFCI blew, there must have been ground another way (ductwork, conduit??) so I disconnected the ground from the outlet to the furnace and things worked. But with a Freezer or Ref plugged in (having ground) and the furnace (ungrounded) the GFCI would pop.

Still not sure why but did read somewhere that can happen if you plug in grounded and ungrounded devices into GFCI. So I found the 3 to 2 conversion plugs and effectively eliminated the ground from the freezer and ref. Then everything worked.

Generator has neutral bonded to Ground but in effect there is no ground from generator to appliances (given its GFCI figured shock was not an issue) got us through the storm. But I am wondering is there a safety risk I am missing, or in the future can I just do this and run only the Hot and Neutral into the house to power the devices (note I am not backfeeding the house, I would be the furnace circuit but will turn that circuit (11 checked when power came on ) off at the panel (and the main just to be safe) Or I might wire a transfer switch in at the furnace.

Thanks for any comments can not find anyone who has done this or discussed this option.

 

[Reach4]

Interesting comments.

Some furnaces use the ground to complete the circuit for the flame detector. It is a very very small current involved, so I doubt that would be the cause of the GFCI tripping.

 

[Stuff]

Furnace is bonded/grounded to the gas line. That may be bonded to ground directly near the main panel or indirectly through a gas stove, dryer, grill, or water heater. Maybe even through neighbor's house if all metal pipe.

Were the freezer and refrigerator ever plugged into GFCI receptacles before? Lots of complaints about old ones tripping GFCIs and people losing their food. Solution is to get new appliances, not disconnect safety ground.

 

[Dav hamm]

Stuff,
Freezer is currently plugged into a GFCI in the basement and runs fine pretty sure replacing them is not going to solve the problem. Please educate me what is are the risks of running on the GFCI without a ground?

 

[Stuff]

As with most things a single failure/misconfiguration normally doesn't show up as a problem. It is the multiple failure case that shocks. People have been cutting ground plugs off for decades but only a few get killed. What is your risk level?

Re-reading comments still not clear what is going on or what how the wiring is configured. You say you disconnected the house ground. Ground and neutral are only supposed to be connected at the first disconnect but you may have them connected intentionally or accidentally elsewhere. A neutral touching a grounded metal box anywhere in your house would cause the generator's GFCI to trip as soon as a load was turned on.

It is also possible that the freezer/refrigerator alone isn't leaking that much but something else in the wiring is just enough to add up to the generator's GFCI trip point. 4-6 ma is the normal trip point. The GFCI in the generator also could be more sensitive that the wall GFCI.

Dav - Regardless what you are doing is dangerous and illegal in most areas. A transfer switch or other lockout is required when attaching a generator to house wiring.

 

[Dav hamm]

@Stuff, and that is where the miscommunication is. I am not attaching to the house wiring anymore. I have the furnace disconnected it is on an extension cord, with no ground (cause as you explained its probably grounded through the gas line, so If i connect a ground the generator GFCI trips), the freezer chest and the ref/freezer were both plugged into extension cords all 3 cords go to the generator. If the ref and freezer are plugged in without the furnace, everything is fine, if the furnace is plugged in by itself it runs fine. If either the Ref/Freezer combo or the freezer chest are plugged in with the furnace the GFCI blows instantly (furnace is not even running yet so its not a load issue). But if i disconnect the grounds on the extension cords running to the ref/freezer unit and the Freezer chest all three worked fine.

On cutting grounds off, if they are plugged into a GFCI outlet I don't see where the risk is i mean sure the GFCI could fail, but the ground line could fail also.

 

[Jadnashua]

One does not need a ground for a GFCI to function properly at all. If it only trips when a ground is installed, you have a leak and it's just doing its job. A GFCI trips when the current going out on one line (L1 or L2) does not equal what is coming back on Neutral (or, if a 240vac GFCI, the other half). Since most furnaces' motors are 240vac devices, if something else is out there that is sharing one of the lines, at least on the 240vac lines, depending on where the GFCI is located in that path, there will be an imbalance, because some of the current is returning via the neutral or ground . A GFCI will trip if the power out does not equal the power return within about 4-5ma. Something is leaking to ground. Removing the ground allows the GFCI to not trip because it then takes the easiest way back, via the other power lead. Many 240vac furnaces do not have a neutral connection, and only would be protected with a GFCI when you use a 240vac one. In that case, whatever runs on that L1 line, must return on the other hot line verses neutral.

Somewhere, there's either a loose or corroded, or high resistance short to or between ground and neutral on one of the power leads, allowing enough current to leak to ground that is causing the GFCI to trip. Got a smart thermostat that charges an internal battery from the 24vac line (not sure if that might cause it, would have to think more, but not all of the power going out would be going back as some would be charging the battery). In a properly working system, there should not be any current in the ground line...it is there mostly to provide an alternative path to trip the overload circuit should something go wrong with the actual power conductors, as I said, a GFCI will work perfectly fine without it (not saying that the stuff connected would if it has an internal problem). But, depending on the connection between the power lines, it can take a parallel path, and thus divert some power from returning on the path it is supposed to, which is what a ground fault is - a path for power going through that protection path (or you!) verses the neutral or other leg (if a 240vac) of the circuit.

 

[Stuff]

With a generator cutting off or isolating the ground you have a mixed bag. It makes the GFCI ineffective as the GFCI only trips when the hot and neutral are different. Without a ground connection there will not be current on the ground line so the GFCI should always see hot and neutral being equal - no leakage possible. Without a ground you should theoretically not be able to get shocked if you touch the hot wire (the same as when a bird lands on an electric line). As long as everything is in good working order you should be fine.

It is all what if failure scenarios that sound like they won't happen. When you read the investigations of how people get electrocuted when it is not readily apparent there are usually multiple things that went wrong. e.g. If you have a power tool that has neutral shorted to ground you won't trip a breaker or your groundless generator GFCI. Say you also have a pinched cord that is touching hot to your storm door where your ran a cable for another appliance - nothing trips as there is no path to ground. But then three days later when you carry the plugged in drill through the storm door you get the full 120 volts of the generator with nothing tripping.

Thinking about that - is it possible you have a bad extension cord? Last thought is that it could be that the refrigerator/freezer are touching the floor which conducts ground back to the furnace which has it's neutral touching case ground.