Prime power generator grounding

Butch(OH)

Well-known Member
I know, a subject kinda beat to death but
I have looked on line about generator
grounding and all of it is for standby
and I get is more confused. I know there
is expertise on this forum. Here are the
facts, I have a large barn on the
property that used to be grid powered via
sub panel but it was disconnected years
ago. I want to repower the barn with an
old generator I recently purchased. There
will be no grid connection, only
generator as prime power. The generator
is 3 wire, 2 lines and one nuetral, 220
between the lines, 110 line to neutral. I
have that all wired to the panel. The
neutral is not bonded to the frame of the
generator. As I understand it the sub
panel was incorrectly wired as it was
used previously as the neutrals and
ground are bonded and there is a ground
rod with #6 bare copper running to the
neutral buss. So, my question is how do
I, or do I? ground this set up? I
remember reading here that grounding
certain generator installations would
create a hazard. If it makes any
difference the generator has no tags and
Id guess 4KW. Just running a few lights
and occasional power tools.
 
Butch, GREAT QUESTION. Being its legal or electrical, you may get several answers and opinions and that's a good thing, there are a lot of fine gents on here.

I will go ahead and offer my "opinion" but remember I'm longggggggggggg retired as a Power Distribution Design Engineer and rusty as an old nail on the latest codes grrrrrrrrrr fortunately there are several electrical engineers and professional electricians here who can correct me and/or add to this. I'm never to old and willing to learn yet still believe that below to be correct ??????????

I'm proceeding based on your assertion the Genset HAS A FLOATING NEUTRAL and there are three conductors L1 L2 and Neutral configured as true 120/240 Volt Single Phase Three Wire similar to what the utility provides.

1) Since you DO NOT fall under the exemption where if cord and plug connected tools are the ONLY loads served by onboard receptacles in which case a Ground Rod isn't required (but you're feeding a buildings power panel NOT a cord and plug drill to a genset receptacle) IT IS MY OPINION the generator frame should be bonded to a "Grounding Electrode" such as a "Made Electrode" consisting of copper rod or rods driven into earth.......... IE I recommend you drive a ground rod or rods (subject to any local authority or applicable codes when 2 may be required) at the genset and bond to the frame.

2) Being what you're using to provide 120/240 is the same as if the utility transformer were doing the same with the three wires (L1 L2 N) running to your panel which is now your main service entrance and since there should be ONLY ONE NEUTRAL GROUND BOND (and your Genset has a Floating Neutral, no NG Bond)

In the panel I would (if not already) BOND the Neutral and Ground Busses together if there were separate (maybe it only has one common NG buss to which all the White Neutrals and Bare/Green Equipment Grounding Conductors are attached)

In the panel I would attach a "Grounding Electrode Conductor" such as a bare copper conductor to the Neutral Buss (or if it has a single Common NG Buss) and run it out to a "Grounding Electrode" including "All readily available Grounding Electrodes" such as a "Made Grounding Electrode" consisting of a copper rod or rods (subject to any local codes) driven into mother earth.

HERES A KICKER No warranty, but it is my opinion since your Genset HAS A FLOATING NEUTRAL and since all non current carrying conductive enclosures and junction boxes and appliance and tool frames etc etc ect require bonding to the Equipment Grounding Conductor assembly, I would run an extra Equipment Grounding Conductor FROM the panels Ground Buss out to the gensets case/frame. NOTICE Im not near as sure about this as I am paragraphs 1 and 2 above BUT STILL THINK ITS SAFER AND LIKELY CODE COMPLIANT

There ya go if Im incorrect hopefully the other electrical engineers and professional electricians can add to and/or correct this

DISCLAIMER where fire and life safety are concerned consult with local professional electrical engineers and electricians and the utility provider and any other applicable regulatory agencys DO NOT RISK YOUR LIFE OR A FIRE ON ANYTHING POSTED HERE ME SURE INCLUDED.

John T BSEE,JD
 
John T
Between the NFPA and the NEC codes.Then some city codes. I think I lost more than I won.Some inspectors were real idiots.I had one nursing home. That was written up. Because they had no light telling them they were on generator power. The head nurse told him. She didn't care where it came from. As long as it got here.

Another small nursing home. Had a 350kw as a back up unit. They were written up because they had no red colored plug covers. Telling them which plug was an emergency power plug. I tried to tell him. The whole home was on back up.

Don't get me started on Military and OSHA units,
 
Butch, now that I've had my after lunch nap I've decided since you now have an earth grounded system and since the Genset has a FLOATING Neutral I would bond the gensets case/frame to an Equipment Grounding Conductor carried out from the panels Ground Buss. That means carry out FOUR conductors, L1 L2 N and G. If a hot shorts to case frame that way you have a dedicated low impedance fault current return path so a breaker trips not leaving the case frame at 120 volts above earth.

Again if any engineers or electricians or lay persons can cite NEC references to wire this DIFFERENT then I suggested please educate myself and others here !!!!!!

John T Old but still curious
 
ground the chassis of the generator and the ground bar on the power panel Together to the ground rod . Leave the neutral bond open in the generator .
Bond the neutral and ground in only one location , in the barn s electrical panel .
 
On BOTH the HV (tens of thousands of volts) Primary Distribution system and the LV (480, 240, 120 etc) Secondary Distribution system in order to protect against lightning and surges PLUS to keep the grid at a common low voltage reference (Mother earth) the Neutral (LV and HV) is bonded to a Grounding Electrode such as copper rods driven into the earth. Its to tie all the grid to a common low voltage reference. In your home its similar intending to bring everything down to earth potential. The NEC requires bonding the incoming utility service Neutral to "All readily available Grounding Electrodes" including but not limited to "Made Electrodes" such as copper rods driven into earth. This might be done at the service entrance riser orrrrrrrrrr the meter base orrrrrrrrrrrr the main distribution panel.

NOTE its wayyyyyyyyyyyyy more complicated then that, but for a short general purpose answer on a Tractor Forum here you are.

John T No warranty Im too darn long retired
 
Here's another example for you. If you were standing on the ground and touched a metal object which was for whatever reason at a voltage potential higher then earth YOU WILL GET SHOCKED. If you bonded that metal object to say a rod driven into earth that tends to bring it back down to the same potential as earth so you may not get shocked.

HOWEVER don't bet your life on that since it only takes like 0.030 to 0.050 amps of current to cause heart fibrillation. It depends on how well its grounded and the resistance and voltage drop in the grounding electrode conductor

Got it ???

John T
 
Butch

I was in a signal unit in the Guard.As motor sargent it was my job to check. All our power units for proper grounds.We would drive a metal rod into the ground. Pour water into the space where the rod was. Hook the genset frame to the rod before starting the unit.In 17 years we never had a problem.
 
Because the main panel is the first place that any power is being drawn from, and according to code at the main panel the ground and neutral are one and the same, tied together, I would think that neutral and ground would be one and the same at the generator, only one conductor.

This is only a guess on my part.

Been retired long enough that many fine parts are becoming foggy. And the coed gets up dated, changed every three years.


Dusty
 
Hey there Dusty, to your question " I would think that neutral and ground would be one and the same at the generator"

INDEED THATS OFTEN TRUE IN THE MANY GENSETS THAT USE A BONDED NEUTRAL

HOWEVER the poster indicated his genset has A FLOATING NEUTRAL and this is another fairly common type of portable genset. Based on if its
configured as a "Separate Derived Source" and in cases where a Transfer Switch is used and IF it switches the Neutral or not determines
when a Bonded or a Floating Neutral genset is used. Based on if its a Floating or a Bonded Neutral determines how things get wired. I
answered the posters question based on his statement his had a Floating Neutral but if it were Bonded things would be different

In RV applications if the genset has a Floating Neutral (like some small Hondas and Yamahas) and an EMS is used IT WILL THROW AN ERROR
CODE, however if a genset uses a Bonded Neutral it sees it the same as the utility and will say all is okay.........

I will try to post a link that identifies which gensets have a Floating and which have a Bonded Neutral

Hope to see you again my sparky friend

John T
Generator with Floating Neutrals
 
Billy my occupation was portable rock crushing and everything ran on generators. The mines run there own set of electrical regs and for a long time we were not allowed to have an earth ground due to the generator configuration. Everything was 3 phase and we ran 4 wire SO cables with the 4th wire connecting the motor frame to the generator frame as that was code. Then we had an inspection and found the regs changed and because we had a 4 KVA transformer to supply 110V for lights and such it was determined that we needed an earth ground. We were sitting down in the hole on solid limestone and had the blasting driller drill 4 6"holes about 25 foot deep for a mat. We dropped the rods in and back filled with fines but it would not megger to code so we drilled 4 more but after we set the rods in we mixed rock salt with dampened fines and it meggered out so MSA let us go back to work, LOL
 
Butch I hated working on Cement and Gravel pit plants. Dust was everywhere. You would end up covered in dust. Your white service truck was now. A whiter shade of white. Or red depending which pit you were at. Wife would hose me down in the back yard. Before she would let me in the house
 
Here is my view on this: If your generator is PERMANENTLY installed, and not mobile, and has a floating neutral (meaning the neutral and equipment ground are NOT connected at the generator), then three wires directly to the panel (NO automatic switch), and the neutral and equipment ground bonded in the panel. AND a ground rod driven near the panel and connected to the neutral/equipment ground buss bar. You should probably have another ground rod driven near the generator, and the generator frame (NOT neutral) connected to it. This is an equipment ground. I am not a qualified electrician, by any stretch of the imagination, but have a similar scenario at my residence. Review your situation with a knowledgeable electrician as to the applicable code requirements. YMMV. Don't take the above as gospel; it could be inaccurate in your situation. zuhnc
 
Thanks again for all the replies. For someone like me who is NEC ignorant it is nice to have this great source of knowledge to lean on. We have no local code or inspection retirements here and I have learned much about proper wiring just from reading posts here over the years.
 
You're welcome. That's my best recollection of how the NEC requires it be done (even though you have no local authority) but again I'm long retired from power distribution design and rusty, codes can change over the years.

John T
 

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