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Author Topic: Simple Generator Grounding Info  (Read 6652 times)

jason misterka

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Simple Generator Grounding Info
« on: April 08, 2015, 09:39:52 PM »

Hello Folks -

I searched a bit and read some but this is a timely issue and we are quite up to our ears right now.

We have an event at one of the Universities that we work at on a regular basis.  The location of this event requires a 45KW generator to power PA.  I have a good bit of experience using generators at festivals (typically with the assistance of a licensed electrician) but I am no expert on all things electrical and electrical theory.

My understanding was that it is proper to ground the generator with a grounding rod and wire.  From my understanding of the situation (from many years of discussions with others in the production business) this is the best operating practice and is appropriate.

The issue I am having is that the head electrician of this University, whom I have had many conversations with for years and hold in quite high regard, has been resistant to us using a grounding rod.  The generator needs to be placed in an area with a lot of underground electrical and telecom, as well as a buried sprinkler system.

However his reason is not logistical.  He has determined that it is unnecessary.

He did eventually give in, and went the extra mile to drive a rod in an appropriate location, with the wire coiled up inside a quazite box to be used each year.  So, I do have a ground now. 

However, I would like to get to the bottom of this for once and for all.  I have been making this same argument for years now I feel like a broken record.  Half the time I have to bring my own grounding rod because many generator rental companies refuse to do it. 

My understanding is the NEC says that you don't need a ground on a generator if using one of the outlets on that generator (ie plugging in your drill to the generator frame).  My understanding is that it is different if you are using the bare wire disconnect and breaking the power out into a PD, with 50amp California outlets going to all your amp racks, and stage power drops throughout the stage.  Is there a difference in the code for these two uses?

Here is what the electrician sent me:
"Please see the attached images citing NEC Article 250.34 regarding the grounding of portable and vehicle mounted generators. Most all rental generators fall under this category, ie. the grounding yoke is connected to the generator frame, which is bonded with the neutral, which provides short-circuit and ground-fault protection for any circuitry attached to the generator. I just don't see an advantage to driving a ground rod for this application, however, if I am missing something in the code, please feel free to bring this to my attention."

Here is NEC 250.34:
250.34 Generators-Portable and Vehicle-Mounted
(A) Portable Generators. The frame of a portable generator is not be required to be grounded to the earth if:
(1) The generator only supplies equipment or cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The metal parts of generator and the grounding terminals of the receptacles are bonded to the generator frame.

(B) Vehicle-Mounted Generators. The frame of a portable generator is not required to be grounded to the earth if:
(1) The generator frame is bonded to the vehicle frame.
(2) The generator only supplies equipment or cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(3) The metal parts of generator and the grounding terminals of the receptacles are bonded to the generator frame.


So, am I wrong? or If I am correct, can someone give me some text to send out when this situation arises again as it does several times a year?  Ideally a bit of NEC or a brief paragraph explaining the difference and necessity of running the grounding rod.

Thanks in advance,
Jason
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Stephen Swaffer

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Re: Simple Generator Grounding Info
« Reply #1 on: April 08, 2015, 10:51:18 PM »



Here is NEC 250.34:
250.34 Generators-Portable and Vehicle-Mounted
(A) Portable Generators. The frame of a portable generator is not be required to be grounded to the earth if:
(1) The generator only supplies equipment or cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The metal parts of generator and the grounding terminals of the receptacles are bonded to the generator frame.

(B) Vehicle-Mounted Generators. The frame of a portable generator is not required to be grounded to the earth if:
(1) The generator frame is bonded to the vehicle frame.
(2) The generator only supplies equipment or cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(3) The metal parts of generator and the grounding terminals of the receptacles are bonded to the generator frame.


I am not sure what more you need?  Are you saying all of the equipment used with the 45 kW genny is cord and plug connected?  Obviously it is not mounted on the genny.  In your example the situation you used does not meet the conditions necessary for the exception from the rule.

If you are supplying a distro (even from a single 50 amp California), that is really a "wiring system" (though it may be portable and more or less temporary), but it does not meet the definition (found in Art 100) of equipment.
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Mike Sokol

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Re: Simple Generator Grounding Info
« Reply #2 on: April 09, 2015, 08:30:29 AM »

If you are supplying a distro (even from a single 50 amp California), that is really a "wiring system" (though it may be portable and more or less temporary), but it does not meet the definition (found in Art 100) of equipment.

Stephen is correct. What allows a "portable" generator to be ungrounded is the fact that tools or appliances are directly plugged into it. So if there's a ground fault created by something like standing in water and touching a drill with a line-to-frame short, then the generator frame will rise to 120-volts, while no current will pass through the guy holding the drill.

Once you distribute power to multiple locations (the stage, FOH mixer, amp racks, etc....) if there's a line-to-ground short anywhere, then all other equipment chassis connected to the EGC (virtually everything at a sound gig) will be biased to 120-volts above earth potential. So in the case of a metal stage, an extension cord that's partially cut through by a stair riser can have a line-to-stage short. Without a properly neutral bonded and grounded stage, this failure could bias the mixing board and all its racks to 120-volts AC. Then if you're standing on the damp grass mixing the show, you could create a path for the ground fault current through your own body and be killed.

Note that many (or even most) of these small generators don't have GFCI protection because there's an exception in UL allowing the elimination of GFCI breakers on generators under 5KW as long as their neutral is floated. But once you're over 5KW and distributing power to multiple locations via a distro of sorts, then you not only do you require an earth ground and a bonded G-N connection, you should also supply GFCI protection on your stage branch circuits.
« Last Edit: April 09, 2015, 08:52:31 AM by Mike Sokol »
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jason misterka

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Re: Simple Generator Grounding Info
« Reply #3 on: April 09, 2015, 10:42:59 AM »

Stephen is correct. What allows a "portable" generator to be ungrounded is the fact that tools or appliances are directly plugged into it. So if there's a ground fault created by something like standing in water and touching a drill with a line-to-frame short, then the generator frame will rise to 120-volts, while no current will pass through the guy holding the drill.

Yeah, and that is how I read the NEC portion as well, and what I explained to him.  I just wish there was a portion that positively asserted the specifics of the opposite situation so I can have an "official" and "easily read" item to email when this situation arises.  Instead of having to say, "well we don't do the things that allow the exception" ":)  Which is what I do say and doesn't seem to sink in with everyone.



Once you distribute power to multiple locations (the stage, FOH mixer, amp racks, etc....) if there's a line-to-ground short anywhere, then all other equipment chassis connected to the EGC (virtually everything at a sound gig) will be biased to 120-volts above earth potential. So in the case of a metal stage, an extension cord that's partially cut through by a stair riser can have a line-to-stage short. Without a properly neutral bonded and grounded stage, this failure could bias the mixing board and all its racks to 120-volts AC. Then if you're standing on the damp grass mixing the show, you could create a path for the ground fault current through your own body and be killed.

So I understand properly, aren't you saying here that the STAGE needs a ground connection (which I understand, though it is often difficult to do properly given the design of a trailer stage (plywood, metal frames, heavy paint, etc).  Would a ground at the generator prevent the stage from becoming energized?

Any easy spots to properly grounding the Stageline?  We work on 100,250/260 and 320 all summer (we do not own any).  Are they designed with easy to use grounding bolts in the frame?




Note that many (or even most) of these small generators don't have GFCI protection because there's an exception in UL allowing the elimination of GFCI breakers on generators under 5KW as long as their neutral is floated. But once you're over 5KW and distributing power to multiple locations via a distro of sorts, then you not only do you require an earth ground and a bonded G-N connection, you should also supply GFCI protection on your stage branch circuits.

Understood.

Thanks Mike I appreciate the insight.

Jason
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jason misterka

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Re: Simple Generator Grounding Info
« Reply #4 on: April 09, 2015, 10:44:52 AM »

I am not sure what more you need?  Are you saying all of the equipment used with the 45 kW genny is cord and plug connected?  Obviously it is not mounted on the genny.  In your example the situation you used does not meet the conditions necessary for the exception from the rule.

If you are supplying a distro (even from a single 50 amp California), that is really a "wiring system" (though it may be portable and more or less temporary), but it does not meet the definition (found in Art 100) of equipment.

That was my take as well but it has been a constant fight, and not just with this electrician (whom I have a lot of respect for).

Jason

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Guy Holt

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Re: Simple Generator Grounding Info
« Reply #5 on: April 09, 2015, 02:00:40 PM »

If you are supplying a distro (even from a single 50 amp California), that is really a "wiring system" (though it may be portable and more or less temporary), but it does not meet the definition (found in Art 100) of equipment.

Not according to the Safety Committee of the Contract Service Administration Trust Fund (CSATF), an industry wide administrative body (governed by the collective bargaining agreement by and between Motion Picture Producers, The International Alliance of Theatrical Stage Employees ("I.A.T.S.E."), the Moving Picture Technicians Artists and Allied Crafts of the United States, its Territories, and Canada ("M.P.T.A.A.C."); as well as the collective bargaining agreements by and between the Producers and the Basic Crafts Locals (Article 18)) According to their Safety Bulletin #23:

"Generators mounted on trucks or trailers shall be completely insulated from earth by means of rubber tires, rubber mats around metal stairways and rubber mats under any type of lift gate or jacking device. Metal supports for trailers shall be insulated by means of wooden blocks. Safety tow chains shall be secured so as to not touch the ground. If complete insulation is not possible, a grounding electrode system shall be installed per the National Electrical Code, Article 250.52."

The CSATF, as well as the Inspectional Services of the City of Los Angeles, deem 1200A Distribution Systems supplying large sets using 4 Ought Feeder Cable as "cord & plug connected equipment" and do not permit driving of ground rods as long as the conditions in the safety bulletin can be met. Proponents of Floating Ground systems (I am not one of them) argue that if you have a Bonded Neutral, and you can effectively isolate the distribution system from earth ground, there is good reason not to drive a grounding electrode or ground rod. It is a common misconception that ground rods are there to protect you (the same is true of circuit breakers.) A circuit breaker is there to prevent fire created by heat from an over-current or short-circuit and protect the equipment. The amount of current it takes to electrocute a person is much smaller than the amount needed to trip a circuit breaker. Add the fact that a ground rod will never pass enough Fault Current to trip an over current device and you realize that they are not there for personnel safety.

... you're standing on the damp grass mixing the show, you could create a path for the ground fault current through your own body and be killed.

Proponents of Floating Ground systems will also argue that the installation of a ground rod decreases safety. Their arguement is that installing a rod for a generator with Bonded Neutral only provides a path for a person to get in between the source and return.  Short of two Ground Faults (one in the Hot conductor and one in the Neutral), there is no potential to the earth without the rod, so fault current will not use the tech standing on damp grass  to return to its' source because it is in effect an open circuit. But, as soon as you bond the system to the earth there is potential to earth when the ground is bonded to the Neutral.

Note that many (or even most) of these small generators don't have GFCI protection because there's an exception in UL allowing the elimination of GFCI breakers on generators under 5KW as long as their neutral is floated. But once you're over 5KW and distributing power to multiple locations via a distro of sorts, then you not only do you require an earth ground and a bonded G-N connection, you should also supply GFCI protection on your stage branch circuits.

While that may be true of UL, it is no longer true of the NEC. In the 2014 code revision all portable generators that have a 240V receptacle must be equipped with GFCI protection on all 120V outlets.  Generators manufactured before the code change are exempted, but the user must use GFCI pigtails if they are using the 240V receptacle.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
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Stephen Swaffer

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Re: Simple Generator Grounding Info
« Reply #6 on: April 09, 2015, 03:10:09 PM »


So I understand properly, aren't you saying here that the STAGE needs a ground connection (which I understand, though it is often difficult to do properly given the design of a trailer stage (plywood, metal frames, heavy paint, etc).  Would a ground at the generator prevent the stage from becoming energized.


Grounding the stage would be correct, but far more important is bonding the stage.  Do a youtube search on "Mike Holt" and grounding or bonding for an excellent explanation.  Grounding has certain technical benefits-bonding has some critical safety benefits.

While, I have not researched the exception Guy mentions-completely insulating the generator form earth-that seems to make sense.  My concern in a concert/gig situation is an insulated genny is no longer insulated the first time someone leans a folding chair/speaker stand/mic stand/lighting truss/etc. against the genny.  To me an insulated condition is much more difficult to ensure than is a grounded setup.  As for the concern with a grounded system increasing the hazard, my answer would be to use GFCI technology to mitigate the hazard.
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Steve Swaffer

Guy Holt

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Re: Simple Generator Grounding Info
« Reply #7 on: April 09, 2015, 04:57:07 PM »

Yeah, and that is how I read the NEC portion as well, and what I explained to him.  I just wish there was a portion that positively asserted the specifics of the opposite situation so I can have an "official" and "easily read" item to email when this situation arises.

Unfortunately, a lot of issues are not cut and try in the NEC.  Always bare in mind that the NEC is a national code that a municipality can elect to adopt or not. For instance, as mentioned above the City of Los Angeles does not permit earth grounding of a generator except under special conditions, where as the City of Boston requires the earth grounding of generators under all conditions.  It ultimately comes down to the Authority Having Jurisdiction and what they want you to do. The local electrical inspector has the final say, so it is worth finding out ahead of time what they want and don't bother trying to argue with them. It is a complicated issue, especially when it comes to the use of GFCIs. If you are interested in getting into it in more detail I have posted online a workshop that I developed for IATSE Local 481 on ground fault protection.  A summary of the workshop is available at www.screenlightandgrip.com/html/481_GFCI_Workshop.html.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
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Re: Simple Generator Grounding Info
« Reply #7 on: April 09, 2015, 04:57:07 PM »


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