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Title: Portable Generator Grounding
Post by: Mike Sokol on March 13, 2014, 03:51:39 pm
Having followed this thread, it seems that even when using a small, portable Honda 3000 watt genny, a ground rod would be a good idea.
I don't see any ground connection point on these small gennys.
Thoughts or experiences?

OK, I'm splitting out this thread into a generator grounding topic. I just got a phone call back from my Honda Generator contact, and he says that EVERY modern Honda portable generator has a grounding lug, and its location is in the operators manual. So I took the liberty of downloading the EU3000 manual and found its location (though it's not real obvious). He also stated there's no single publication that shows the ground lug locations for ALL Honda generators, but perhaps that would be a good project for an intern.
Title: Re: Portable Generator Grounding
Post by: Ray Aberle on March 13, 2014, 04:33:26 pm
OK, I'm splitting out this thread into a generator grounding topic. I just got a phone call back from my Honda Generator contact, and he says that EVERY modern Honda portable generator has a grounding lug, and its location is in the operators manual. So I took the liberty of downloading the EU3000 manual and found its location (though it's not real obvious). He also stated there's no single publication that shows the ground lug locations for ALL Honda generators, but perhaps that would be a good project for an intern.
Owning three Hondas here, they all definitely have grounding points. Some of them are just a small screw on the back (EU2000i), others (EM3500) has a bolt on the main frame.

... but I never ground them when using them.... my only generator that gets grounded is the WhisperWatt.

-Ray
Title: Re: Portable Generator Grounding
Post by: Lyle Williams on March 14, 2014, 03:03:35 am
It seems to be variable with small generators as to whether the frame is connected to outlet ground.
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 14, 2014, 07:45:40 am
It seems to be variable with small generators as to whether the frame is connected to outlet ground.

I'm not sure that's true. Most small (under 5 KW) generators don't have their Neutral bonded to the outlet ground, but every one I've ever seen DOES have the outlet ground tied to the frame.

But let's find out. Do any of you have an example of a generator that does not have the outlet ground connected to the frame? 

Title: Re: Portable Generator Grounding
Post by: Stephen Swaffer on March 14, 2014, 11:33:51 am
After doing some reading, I come to these conclusions:

Portable generators supplying only cord and plug connected or genny mounted equipment do not need a ground rod if the frame is bonded to the grounding wire-which obviously includes the receptacles.  (NEC 2014 250.34)  If supplying "premises wiring" a ground rod is required.
"
Neutral/ground bonding is only required for "premises" wiring-which is permanent OR temporary distribution-ie panels or distros.  (NEC 250.26, Art 100 definitions)

I see several references to no connections between neutral and ground downstream of the main disconnecting means. A ground neutral bond can be at the source or the main disconnecting means. Is that "or" enough to preclude both?  (NEC 2014 525.31)

I am not seeing a distinction between "less than 5kw" and "larger than 5kw".

Where am I not looking? What am I missing?
Title: Re: Portable Generator Grounding
Post by: TJ (Tom) Cornish on March 14, 2014, 01:11:22 pm
After doing some reading, I come to these conclusions:

Portable generators supplying only cord and plug connected or genny mounted equipment do not need a ground rod if the frame is bonded to the grounding wire-which obviously includes the receptacles.  (NEC 2014 250.34)  If supplying "premises wiring" a ground rod is required.
"
Neutral/ground bonding is only required for "premises" wiring-which is permanent OR temporary distribution-ie panels or distros.  (NEC 250.26, Art 100 definitions)

I see several references to no connections between neutral and ground downstream of the main disconnecting means. A ground neutral bond can be at the source or the main disconnecting means. Is that "or" enough to preclude both?  (NEC 2014 525.31)

I am not seeing a distinction between "less than 5kw" and "larger than 5kw".

Where am I not looking? What am I missing?
I don't have time to follow this through now, but a quick search of some emails on this - the exemption may be in OSHA 1926.404(b)(10(ii).  NEC doesn't have jurisdiction over everything; UL/ETL and OSHA have governance as well when you get closer to a "product" rather than a wiring infrastructure.
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 14, 2014, 03:49:18 pm
I don't have time to follow this through now, but a quick search of some emails on this - the exemption may be in OSHA 1926.404(b)(10(ii).  NEC doesn't have jurisdiction over everything; UL/ETL and OSHA have governance as well when you get closer to a "product" rather than a wiring infrastructure.

I believe you're correct about the 5KW threshold being a UL and/or OSHA thing rather than an NEC thing. I initially found out about this 5KW neutral bonding exemption from a generator manufacturer during one of my yak sessions. IIRC there was an official online PPT presentation discussing the drill in the water scenario. I'll look through my saved files and see if I can find the source.
Title: Re: Portable Generator Grounding
Post by: Keith Broughton on March 15, 2014, 08:07:40 am
Owning three Hondas here, they all definitely have grounding points. Some of them are just a small screw on the back (EU2000i), others (EM3500) has a bolt on the main frame.

... but I never ground them when using them.... my only generator that gets grounded is the WhisperWatt.

-Ray
Thanks Mike.
I will look a bit closer next time I have to use one of these.
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 15, 2014, 11:12:52 am
I don't have time to follow this through now, but a quick search of some emails on this - the exemption may be in OSHA 1926.404(b)(10(ii).  NEC doesn't have jurisdiction over everything; UL/ETL and OSHA have governance as well when you get closer to a "product" rather than a wiring infrastructure.

Correct. Here's the OSHA reference. Note that when they say the circuit conductors are insulated from the frame, that's a floated neutral. That does NOT imply that the safety ground is isolated from the generator frame.

1926.404(b)(1)(ii)

Ground-fault circuit interrupters. All 120-volt, single-phase 15- and 20-ampere receptacle outlets on construction sites, which are not a part of the permanent wiring of the building or structure and which are in use by employees, shall have approved ground-fault circuit interrupters for personnel protection. Receptacles on a two-wire, single-phase portable or vehicle-mounted generator rated not more than 5kW, where the circuit conductors of the generator are insulated from the generator frame and all other grounded surfaces, need not be protected with ground-fault circuit interrupters.
Title: Re: Portable Generator Grounding
Post by: Stephen Swaffer on March 15, 2014, 12:59:20 pm
The OSHA reference specifically applies to construction sites-which of course would be a major market for genny manufacturers. And a 2 wire floated neutral would be safe, in that you really don't have a neutral per se.

If you floated the neutral on a 3 wire 240 volt system, a hot to ground fault could result in parts of the system being 240 volts to ground-obviously a much more hazardous situation.
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 15, 2014, 01:37:52 pm
The OSHA reference specifically applies to construction sites-which of course would be a major market for genny manufacturers. And a 2 wire floated neutral would be safe, in that you really don't have a neutral per se.

If you floated the neutral on a 3 wire 240 volt system, a hot to ground fault could result in parts of the system being 240 volts to ground-obviously a much more hazardous situation.

That's correct. But the OSHA reference is what drives the generator manufacturers to float the neutrals on their gennys under 5KW, even though I don't consider that safe for RV power or music stage power. And I do believe that's why there's so much confusion on the subject of floated neutrals and no ground rods for portable generators. Because ground rods are not required for construction generators, and are too much trouble for RV camper sites, it's assumed that they're not required for anything else. And because generators under 5KW can eliminate GFCI protection if their float the neutral, then that's the design default. Again, I don't consider floated neutrals without an earth ground on a portable generator to be safe for distributed power systems used for a music stage. There's just too many ways it can go bad in a hurry.   
Title: Re: Portable Generator Grounding
Post by: Stephen Swaffer on March 16, 2014, 05:58:59 pm
Somehow my post was incomplete.

It seems that the intent of OSHA and the NEC is to allow cord and plug connected equipment to be run on a 2 wire non-bonded genny without a ground rod.  Cord and plug connected being what you can go down to your favorite store buy, and literally plug and play with virtually no interconnections.  This scenario might fit a very small gig-2 speakers on a pole etc.

IMO a bonded neutral is always safer for A/V work and a ground rod is a good idea especially in wet or damp conditions.

To tread on questionable ground here, I wonder what the best grounding scheme is for portable A/V.  For installs we drive 2 8 foot ground rods, an 8 foot rod is a pain to pull out  (OK 7 foot 6 inches is a pain-when you hit an old foundation!)  I wonder, especially when wet if multiple 4 or 6 footers might be easier and just as effective?  Just thinking in print here-so don't get too upset with me!
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 16, 2014, 06:54:07 pm
Somehow my post was incomplete.

It seems that the intent of OSHA and the NEC is to allow cord and plug connected equipment to be run on a 2 wire non-bonded genny without a ground rod.  Cord and plug connected being what you can go down to your favorite store buy, and literally plug and play with virtually no interconnections.  This scenario might fit a very small gig-2 speakers on a pole etc.

IMO a bonded neutral is always safer for A/V work and a ground rod is a good idea especially in wet or damp conditions.

To tread on questionable ground here, I wonder what the best grounding scheme is for portable A/V.  For installs we drive 2 8 foot ground rods, an 8 foot rod is a pain to pull out  (OK 7 foot 6 inches is a pain-when you hit an old foundation!)  I wonder, especially when wet if multiple 4 or 6 footers might be easier and just as effective?  Just thinking in print here-so don't get too upset with me!

Last year I came up with a design for a temporary ground that might be quite good for portable A/V work. This was a plate about half a meter square (19" x 19" for the yanks) with 100 metal spikes about 2" (50 mm) long pointing down into the ground. The idea was to place it in front of your vehicle tire and drive over it, thus spiking it into the ground. This was made out of perforated (expanded metal) so you could dump a jug of water over it to wet the soil, and had a lug to attach the generator ground. It also had a place to insert a handle to lever it up out of the ground once the gig was done. I never built one, but it would be an interesting experiment to see if it would pass the NEC 100 ohm max impedance listed for 8-ft ground rods before you needed a second rod. I have a fall-of-potential ground rod tester so if I did build one I could get a reading in my back yard to see if it works at all. Of course, this would drive inspectors crazy unless it had official NEC sanction, but you get the idea. 
Title: Re: Portable Generator Grounding
Post by: TJ (Tom) Cornish on March 16, 2014, 10:34:10 pm
Thinking out loud, I suspect that a multiple shallow spike solution like your "bed of nails" would work really well - sometimes.  If the ground is wet, you've likely got a nice low-impedance path.  However, a couple dry days and the top layer of soil dries out quickly.  When I dig on my property, I'm always amazed at how much moisture there is 12" down - even when it has been really dry.  I suspect a deep ground rod would have more reliable contact with the earth since it taps soil that is relatively unaffected by day-to-day weather conditions.
Title: Re: Portable Generator Grounding
Post by: Jonathan Johnson on March 17, 2014, 01:08:28 am
It seems that the intent of OSHA and the NEC is to allow cord and plug connected equipment to be run on a 2 wire non-bonded genny without a ground rod.  Cord and plug connected being what you can go down to your favorite store buy, and literally plug and play with virtually no interconnections.  This scenario might fit a very small gig-2 speakers on a pole etc.

IMO a bonded neutral is always safer for A/V work and a ground rod is a good idea especially in wet or damp conditions.

Thing to remember is that nearly all handheld power tools marketed in the U.S. -- except for some very old ones -- are double insulated and have two wire cords with no ground conductor. Many pieces of A/V equipment are NOT double insulated, and should be grounded.

With two-wire equipment, having ground and neutral non-bonded may be irrelevant -- especially if only one tool is in use at a time. A two-wire power tool used in wet conditions could have a ground fault, and if the ground and neutral are not bonded there will be no complete circuit and the user should (theoretically) not receive a shock.

However, most genny's have at least a duplex receptacle, so one must assume that two pieces of equipment could be used at a time. Under certain conditions -- such as the example of two drills in the water -- the possibility of a ground fault shock hazard exists even without bonded neutral and ground.
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 17, 2014, 01:47:06 am
Thing to remember is that nearly all handheld power tools marketed in the U.S. -- except for some very old ones -- are double insulated and have two wire cords with no ground conductor. Many pieces of A/V equipment are NOT double insulated, and should be grounded.


And that's the primary reason I believe that ALL generators (portable or otherwise) powering outside stages with A/V equipment should be both Neutral-Ground bonded as well as earthed via a ground rod of some sort. Plus the stage structure and any stairs should be connected to this same G-N-E bonding point. I don't see why a small (2 or 3 KW) generator should be treated any differently than a 50 or 100 KW generator doing a show. The amount of current required to kill somebody is extremely small (20 or 30 mA) compared to the load currents available from ANY generator. Certainly a 2KW generator can kill you just as dead as a 100KW genny. I think we professionals in the music industry are so used to getting shocked, that we sometimes forget just how dangerous it can be.

Now note that I'm not trying to make extra trouble for anyone doing a show, nor do I want restrictive legislation put in place by suits in some office who have no idea how this all really works. But I can only report what the data points out, and I just don't like this floaty-ground generator thing. There's too many ways for it to go wrong in a hurry.
Title: Re: Portable Generator Grounding
Post by: Jonathan Johnson on March 17, 2014, 03:00:06 pm
But I can only report what the data points out, and I just don't like this floaty-ground generator thing. There's too many ways for it to go wrong in a hurry.

Going back to my previous post (in which I was kind of thinking "out loud" and not sure where I was going with it), I suspect one reason for the "floaty-ground generator thing" is to avoid nuisance tripping of breakers and GFIs on construction sites. Especially here in the Pacific Northwest, builders often end up working out in the rain. Having to go reset the GFI every time you pull the trigger on your skilsaw because there's a little moisture in the motor gets old REAL QUICK. This leads to people bypassing GFI -- which in a bonded G-N-E and damp environment situation makes things dangerous. If you can eliminate the need for a GFI on a single power tool without significantly decreasing safety** ("I know! Instead of a GFI, let's float the neutral! Then there's no complete circuit and nobody gets shocked!") there will be a market for that, and market pressure will drive public policy to allow these small gensets to have floated neutrals.

I'm not advocating for floating neutrals; but I can see where they're coming from.


** In somebody's mind.
Title: Re: Portable Generator Grounding
Post by: frank kayser on March 17, 2014, 04:02:21 pm
Ok.  Floating neutral solves a PITA.  Except in R/V where floating neutral is a PITA.


Let's look at it from a different angle:  Is there ANY situation where a floating (un-bonded neutral) is SAFER than a bonded neutral?
Is a genset with a floating neutral SAFER or less safe with a GFI?
and the opposite

Is a genset with a floating bonded SAFER or less safe with a GFI?


frank

Title: Re: Portable Generator Grounding
Post by: TJ (Tom) Cornish on March 17, 2014, 04:07:23 pm
Ok.  Floating neutral solves a PITA.  Except in R/V where floating neutral is a PITA.


Let's look at it from a different angle:  Is there ANY situation where a floating (un-bonded neutral) is SAFER than a bonded neutral?
Is a genset with a floating neutral SAFER or less safe with a GFI?
and the opposite

Is a genset with a floating bonded SAFER or less safe with a GFI?


frank
G->N bonds are better in every situation where there isn't a second G->N bond.  In other words, as long as the generator is not feeding a structure with an existing bond, the generator should be bonded.  The trouble comes in home backup power situations - the panel already has a G-N bond, and if you create a second one, you now have made your ground between the service panel and the generator a current carrying conductor.  This could potentially become energized, and will goof up GFCI operation for generator receptacles.
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 17, 2014, 04:21:50 pm
G->N bonds are better in every situation where there isn't a second G->N bond.  In other words, as long as the generator is not feeding a structure with an existing bond, the generator should be bonded.  The trouble comes in home backup power situations - the panel already has a G-N bond, and if you create a second one, you now have made your ground between the service panel and the generator a current carrying conductor.  This could potentially become energized, and will goof up GFCI operation for generator receptacles.

I agree 100%. And because any power distro you might have for your sound system WILL, by NEC code, have a separated Ground and Neutral, then all generators used for outside stage power SHOULD provide the G-N bond. Since generators under 5KW, by OSHA specs and practical GFCI reasons, DON'T have a G-N bond to begin with, adding a simple bonding kludge plug is perhaps the easiest way to do this, especially for rental situations where they don't want you messing around inside the generator wiring.

Now, we just need a simple way to provide an earth ground rod (or bed of nails) and tie the generator G-N bond point to a ground lug on the metal stage. I can't think of a single outdoor situation where that would be more dangerous than floating everything, simply because there are too many everythings to float for an outdoor live show. Whew!  :o
Title: Re: Portable Generator Grounding
Post by: Benjamin Gingerich on March 17, 2014, 04:23:40 pm
It also had a place to insert a handle to lever it up out of the ground once the gig was done. I never built one, but it would be an interesting experiment to see if it would pass the NEC 100 ohm max impedance listed for 8-ft ground rods before you needed a second rod.

The thing i feel people often forget is as the humidity changes so does the resistance to the ground, if it is not driven not below the point where the air above earth affects the moisture below the earth.

The only way to know if you or your equipment is safe is to test it with a vibro-ground, and some would argue that 100ohms may not be suitable for equipment thatís as sensitive as audio and video. The Airforce's "Tops and Blue" require a 25ohm resistance or less before they will hook up anything.  ( I think itís a bit ridiculous but safe)
With that said I think it would be cool to test your concept and see how it would do for very short term uses.

We always use 3 3ft ground rods that thread together to give us a total of 8ft underground and 1ft on-top of the ground.
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 17, 2014, 04:29:24 pm
The thing i feel people often forget is as the humidity changes so does the resistance to the ground, if it is not driven not below the point where the air above earth affects the moisture below the earth.

With that said I think it would be cool to test your concept and see how it would do for very short term uses.


Hey, it could be important like the Ufer grounds: http://www.psihq.com/iread/ufergrnd.htm (http://www.psihq.com/iread/ufergrnd.htm) I just need to weld up my "bed-o-nails" ground and stick it in the ground.

See below: NOT

I know that it's not a long term building ground because of the dry soil thing, but perhaps dumping a gallon of water on it once a day would be sufficient. I'm just spit-balling here, so who knows? But I've got the test equipment to measure the impedance, so it's worth trying an experiment once the snow goes away.  >:(
Title: Re: Portable Generator Grounding
Post by: Jonathan Johnson on March 17, 2014, 07:10:16 pm
I know that it's (bed-of-nails) not a long term building ground because of the dry soil thing, but perhaps dumping a gallon of water on it once a day would be sufficient. I'm just spit-balling here, so who knows? But I've got the test equipment to measure the impedance, so it's worth trying an experiment once the snow goes away.  >:(
Better yet -- two beds-of-nails, with individual conductors going back to the genset, and a monitoring circuit that sounds an alarm if the resistance between the to BONs gets too high. Hey, while we're at it, let's hook up the monitoring circuit to the lawn sprinkler system to give it a good dousing if it gets too dry!

Oh, yeah. We're trying to keep this simple.
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 17, 2014, 07:43:38 pm
Hey, while we're at it, let's hook up the monitoring circuit to the lawn sprinkler system to give it a good dousing if it gets too dry!

My grandfather was a machine gunner in WWI and he told me that when the gun barrel got too hot they would take turns pee'ing on it so it wouldn't melt. I'm pretty sure that urine would have the proper electrolytes for a good ground. Seems like a simple solution to the dry earth problem. 

Just sayin' ;D
Title: Re: Portable Generator Grounding
Post by: Frank DeWitt on March 18, 2014, 10:14:55 am
Spring is coming and I am starting to think about old engine shows.  I show a 1947 Kohler light plant  The common side of the 120 VAC is grounded to the generator frame as is the negative side of the 24 volt battery  When the generator is running it puts out 120 VAC  I have installed a GFI outlet.

When the generator is not running it puts out 24 Volts DC is series with a high resistance relay on what was and will be the hot side of the AC.
When a light is turned on current flows through the light switch and the light bulb and pulls in the relay.  When the relay pulls in the  generator starts.  When it comes up to speed it transfers power to the outlet and monitors the current.  When the light is turned off, the generator shuts off and goes back to watching for a load.
http://www.oldengine.org/members/frank/kohler1.htm

I have used it with a skill saw, and with a sound system.

The generator is mounted on a steel trailer.  When I arrive at a show I push a 18 in screw driver into the ground and connect it to the frame of the generator.

If people are not touching things they shouldn't there is no current flowing through them and all is well.
If people touch something they shouldn't and they are sufficiently grounded and the generator is sufficiently grounded then there is current flow and the GFI trips (and BTW the generator senses there is no load and stops.)
If people touch something they shouldn't and either they or the generator are not grounded well enough to draw current then no one knows they did it including them.
I never run the generator unless I am next to it to make sure no one touches something they shouldn't

I think one of the light fixtures I have connected to it meats code but I am trying to get rid of that one.

Don't try this at home.

http://lbpinc.com/light%20board.jpg
Title: Re: Portable Generator Grounding
Post by: Stephen Swaffer on March 18, 2014, 10:19:32 am
I am not seeing how a second G-N bond in a genny would affect GFCI operation?  I certainly do not know all of the reasoning behind only having one bonding point, but one reason certainly is that grounds are typically smaller than neutrals-and with mutliple bonds a lost neutral results in the ground carrying neutral current-which would lead to overheating, etc.

In a "typical" 5kw to 10kw backup situation, we usually use SO cord between genny and premisis-so ground and neutral are the same size.  Ohms law says in this situation, both wires will carry the same current-a violation of the NEC rule against "objectional current" on a ground.

However, if you draw the circuit out, the ground and neutral are in fact parallel conductors, so you really have a 3 wire system from the genny to the house-not unlike the 3 wire system from the POCO transformer to your house.  POCOs often feed multiple homes with 3 wire from a transformer and GFCIs still function on the home.  Since the genny GFCIs will get neutral and ground from the common G-N bond in the genny, each receptacle would act like a receptacle in a different home on the transformer.

There would be somewhat of a safety hazard if both the neutral and ground conductors had a bad connection, in that the genny frame could become energized to a level above ground, since they are typically sitting on rubber/pvc wheels and pads.

As for grounding electrodes, keep in mind that if a ground rod does not measure less than 25 ohms to ground, a second rod or electrode is required.  Curiously, if two electrodes exist, code doesn't care what the resistance to ground is.  Also, Mike, code does allow "plate" electrodes min of 2 square feet exposed to soil,  must be 1/4" thick, and buried below permanent moisture level "if practicable" .  I would argue that for a temp service -ie weekend, burying is impracticable and surface mounting with artificial (if needed) moisture should be equivalent?  Plate electrodes also require 2 unless resistance to ground measures less than 25 ohms. (NEC 2011 250.52 (A) (7) and 252.53 (A)(1) and (2))
Title: Re: Portable Generator Grounding
Post by: Frank DeWitt on March 18, 2014, 10:24:29 am
Floating grounds.   I am against them.    In the early days of house wiring there was a lot of controversy about grounding.  In some areas grounding a electrical system was forbidden. Some cities required a pair of light fixtures to be installed between each side of the power wires and ground so that if there was a accidental grounding of the system the home owner would know it and could fix it quickly.

Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 18, 2014, 03:25:43 pm
Code does allow "plate" electrodes min of 2 square feet exposed to soil,  must be 1/4" thick, and buried below permanent moisture level "if practicable" .  I would argue that for a temp service -ie weekend, burying is impracticable and surface mounting with artificial (if needed) moisture should be equivalent?  Plate electrodes also require 2 unless resistance to ground measures less than 25 ohms. (NEC 2011 250.52 (A) (7) and 252.53 (A)(1) and (2))

I thinking that an inverted bed-o-nails and a jug of water could be a pretty simple ground. One thing that's VERY important to worry about when driving any 3 ft or 8 ft ground rod is the possibility of underground utilities. I would think that 2" spikes on a plate would NEVER (hopefully) penetrate anything critical like underground electric, data, water or gas. I sort of think it would be worth an experiment just for grins. It's really nothing more than a 18" metal plate with a bunch of holes and nails welded to it and a lug to clamp a heavy copper wire. I've got a welding buddy who owes me a favor, so perhaps I can get this built for six-pack of beer (our normal method of payment for little projects). As I noted earlier, I have a fall-of-potential tester and could stick this in my yard and measure earth impedance over a few days with varying amounts of dryness. My guess is that on damp ground it would have a reasonable low earth impedance, but dry ground would raise the impedance to unacceptable limits. Perhaps heavy-gauge expanded metal would give me a good place to pour a gallon of water through to wet the soil. I'm in uncharted territory hear, so I'm just WAG'ing.   
Title: Re: Portable Generator Grounding
Post by: Frank DeWitt on March 18, 2014, 04:08:36 pm
I thinking that an inverted bed-o-nails and a jug of water could be a pretty simple ground.

Here you go.  A bed of 4 nails
I spotted this at a old engine show. It is a reel with an extension cord on it. It is 2 wire cord, and the reel has 4 spiked feet coated with silver solder so they won't rust. Run out the cord, stick the reel in the ground, and plug in a 25 ft 3 wire cord to ground your tools.

The same company sold a generator attachment for there Rototiller

 I am not making this up.
http://lbpinc.com/ground1.jpg
http://lbpinc.com/grounded.jpg
http://lbpinc.com/ground2.jpg
Title: Re: Portable Generator Grounding
Post by: Frank DeWitt on March 18, 2014, 04:12:44 pm
As I noted earlier, I have a fall-of-potential tester and could stick this in my yard and measure earth impedance over a few days with varying amounts of dryness. My guess is that on damp ground it would have a reasonable low earth impedance, but dry ground would raise the impedance to unacceptable limits. Perhaps heavy-gauge expanded metal would give me a good place to pour a gallon of water through to wet the soil. I'm in uncharted territory hear, so I'm just WAG'ing.

Mike, You could make a progressive test bed with a piece of 1/4 in plywood, a roll of copper window screening and a box of 2.5 in nails.  lay the plywood on the ground, the screen on top and put a nail  in each corner. then keep nailing and testing.
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 18, 2014, 04:48:08 pm
Here you go.  A bed of 4 nails


Wow, is that scary.... I don't think this would do much to save you from a hot-to-chassis short. Perhaps it would shunt out a small current leakage, but that's only going to give you false confidence that you can stand in a puddle of water and operate an ungrounded appliance. I'm assuming no double-insulation back in the day. Yikes!!!  ???

Title: Re: Portable Generator Grounding
Post by: Jason Phair on March 23, 2014, 12:53:50 pm
I thinking that an inverted bed-o-nails and a jug of water could be a pretty simple ground. One thing that's VERY important to worry about when driving any 3 ft or 8 ft ground rod is the possibility of underground utilities.


I did a show a few years back in a town park type deal...municipally provided generator.  Metered everything before firing up, everything's great.  Several hours later, we're getting shocked by racks.  Pull out the tick tester....everything's hot...touch it to the ground, also hot.  They had driven the ground rod through a power line for a light that was on a timer, which is why it was fine for most of the day.
Title: Re: Portable Generator Grounding
Post by: Mike Sokol on March 23, 2014, 04:05:42 pm

I did a show a few years back in a town park type deal...municipally provided generator.  Metered everything before firing up, everything's great.  Several hours later, we're getting shocked by racks.  Pull out the tick tester....everything's hot...touch it to the ground, also hot.  They had driven the ground rod through a power line for a light that was on a timer, which is why it was fine for most of the day.

I just need to say one thing - Miss Utility: http://www.missutility.net/

I can't believe that a municipal crew would drive a ground rod without consulting Miss Utility. If someone would have been electrocuted during the show, just think of the lawsuits. That's why I think a bed-of-nails ground plate would be better for this sort of temporary gig.
Title: Re: Portable Generator Grounding
Post by: Stephen Swaffer on March 23, 2014, 06:39:52 pm
In Iowa it is One Call, they contact local utilities to do the locates, but when I went to do a service upgrade on city hall for a local municipality, they asked ME to locate the city water line going into the building-they had no way to do so!?

Also around here, they only locate utility owned lines-a light on a timer is likely not a "utility"-so make sure you know what is covered by  the locate service in your area.