… a faculty member…. advised that we ground the generator. (And) it seems like a ground fault interrupter (GFI) is recommended in any situation where you're potentially mixing water and electricity but …. been told that it's not necessary and will trip too easily or too often. I've never worked with a GFI or shot very much in snow so I put it to you, the experts: are GFIs absolutely necessary, just a good idea or a waste of time?
You do not need to Ground the gensets... The Gensets are "grounded" thus the 3 prong receptacle.... ground can be the earth or in the case of portable generators, the frame of the generator which will serve as a large conducting body that serves in place of the earth.
A question came up in another thread, “How to enjoy snow and not let it kill you” (http://www.cinematog...showtopic=49830) that, I feel, warrants being addressed alone. That questions is whether Honda portable generators should be grounded with a grounding electrode (ground rod.) Some technicians believe that Honda portable gas generators, like Crawford Studio units, do not require grounding and that GFCIs will function regardless of the grounding arrangement. What fuels the debate is a general ignorance that there are two distinct types of portable gas generators – those with Floating Neutrals and those with Bonded Neutrals. Which type of generator you are using determines whether it should be earth grounded with a ground electrode and what grounding arrangement is required to make GFCIs operational.
“Floating Neutral”, “Grounded Neutral”, “Bonded Neutral”, “Floating Ground”, “Earth Ground”, “Ground Fault”: if you are unfamiliar with the meaning of these terms I would suggest you first read an article I wrote for our company newsletter on the http://www.screenlig...ard Protection' class='bbc_url' title='External link' rel='nofollow external'>use of portable generators in motion picture lighting before proceeding further.
Neutral Bonded generators have their Neutral bonded to the frame of the generator. Neutral Bonded generators offer a high degree of protection against Ground Faults (if there was a fault to the frame via the Equipment Grounding System, the generator’s circuit breaker would trip eliminating the fault), and so they can be operated without an Earth Ground in what is called a Floating Ground condition. Crawford Studio generators are Neutral bonded, but most Honda portable gas generators are not.
In most Honda portable gas generators the neutral circuit is not bonded to the frame of the generator or to the earth ground lead; and are commonly called Floating Neutral generators. The floating neutral configuration is common for applications such as connection to a recreational vehicle and connection to home power where the transfer switch does not switch out the neutral to ground connection. When used as a stand-alone power source (a “Separately Derived System” in NEC parlance), Floating Neutral generators require that at least the frame of the generator to be bonded to earth ground for reasons we will explore shortly. This involves putting a rod 8’ into the earth and attaching a ground cable from the rod to the generator frame.
There is no question that a generator system with a Floating Neutral requires grounding with a grounding electrode. Remember that OSHA guidelines for the grounding of portable generators does not allow for isolating the generator from ground when the Neutral conductor is not bonded to the frame along with the equipment grounding conductors. The reason being, over-current breakers offer no protection in the event of a double ground fault when the Neutral is not bonded to the equipment grounding system. To understand why this is the case, it helps to understand first why technicians are not endangered by electrocution from current going to ground if there is only one fault in the system.
In a Floating Neutral system, technicians are not endangered by electrocution from current going to ground as long as there is only one fault in the system. Since the ground wire and the neutral wire are not bonded at the generator bus, the equipmet grounding wire does not offer a path for the fault current to complete the circuit back to the generator windings. In effect an open circuit, current will not travel it and so the fault current does not even go to ground. The figure below, illustrates why that is the case.
1) A fault in a metal fixture energizes the entire housing as soon as the circuit is turned on.
2) Since the ground wire and the neutral wire are not bonded at the generator bus, and the generator is not grounded to earth by an grounding electrode, the equipmet grounding wire does not offer a path for the fault current to complete the circuit back to the generator windings. Therefore, the fault current does not go to the equipment ground wire.
3) If the generator frame is completely insulated from the ground (a Floating Ground), an individual making contact with the energized housing does not present an alternate path for fault current back to the generator windings. An open circuit, the fault current does not go through the individual and ground back to its source.
But, in the event of a double ground fault - one on the Hot, and a second in the Neutral - a path (circuit) can be created for fault current to return to the generator windings through an individual making contact with the energized housing and through the ground if the generator frame becomes grounded (either through moisture or contact with the ground.) Since the equipmet ground wire is not bonded to the generator windings, it does not offer in the event of a double fault an alternate path of lower resistance. Where the individual/ground route is now the path of least resistance, the fault current travels through the individual and the ground back to the generator windings through the second fault - delivering a shock to the individual. If either of the faults is high resistance, the current will not be high enough to open the breaker, and the individual will receive a sustained shock that can be potentially fatal. The Figure below illustrates why an individual receives a shock when there are two faults.
1) Current goes out on the hot (black conductor) to the light housing fault.
2) Even though Current travels on the ground wire (if it is in good condition), Current also travels through the worker's body into the earth back to the generator windings, because there is no clear return path because of the un-bonded condition.
3) Current enters the generator frame and goes back to the generator winding through the second Fault
on the Neutral side. If either of the faults is high resistance, the current will not be high enough to
open the breaker. However, the currrent will be high enough if the grounding conductor is faulty (the grounding
pin is broken or there is a bad connection) to give the individual touching the housing a shock.
4) The generator’s circuit breaker may trip in response, but only if enough current flows through the
second fault to create an over-current situation.
5) The worker, however, is exposed to electrical shock until the breaker operates because no GFCI is present.
The inherent risk in using Floating Neutral generators lies in the fact that the neutral of the generator winding is neither grounded to the generator frame nor to the grounding pin of the receptacle. This deficiency makes operation of the protective device (breaker or fuse) unreliable because in a two Fault situation, fault current has no definite path as it does in a Bonded Neutral generator. For example, a fault current that, under these circumstances, is too low to trip a breaker or blow a fuse will also travel through an individual making contact with the energized housing and deliver a potentially life threatening shock. Since all equipment leaks some current, it is not uncommon to have two Faults in a system. A defect in the generator, a poorly insulated or defective extension cord, defective insulation in a lamp housing, or defective plug, can all produce Faults - to name just a few causes. And, since it is difficult to completely insulate a portable generator from ground (wet ground, rain, or even high humidity can cause a generator to be inadvertantly grounded) the risks of shock greatly increases (see the study by The Construction Safety Association of Ontario (CSAO) below). Floating Neutral generators are deceptive because they give the appearance of a safely grounded system when, in fact, they are not. Their receptacles accept a plug with a grounding pin, but in the receptacle the grounding pin is connected only to the generator frame and not to the generator winding (neutral). The user is given a false sense of security.
Grounding Floating Neutral generators to earth with a grounding electrode offers some degree of protection from electrical shock in the event of a double ground fault – and for this reason it is mandated by OSHA (use this link for the complete guidelines.) When the equipment grounding conductor is earth grounded with a grounding electrode, the equipment grounding conductor offers a path of lesser resistance then the individual/ground route for the current to travel back to its’ source through the second fault. The individual making contact with the energized housing will receive a lesser shock, because the bulk of the fault current will now travel through the equipment grounding wire instead.
Simply using a GFCI on a Floating Neutral generator will not ensure a safe system, and can in fact lead to unnecessary and costly production delays. Tests recently conducted by The Construction Safety Association of Ontario (CSAO) uncovered significant problems in using GFCIs on ungrounded portable generators with Floating Neutrals (use this link for the complete report.) A GFCI will only operate reliably if one side of the winding is grounded to the generator frame because otherwise fault current has no path back to the winding to complete the circuit. Only when Neutral is bonded to ground, will current go to ground to complete the circuit when there is a current leak. In other words, a complete circuit is required to create an imbalance and cause the GFCI to trip. GFCI test circuits can also be misleading when they are used on Floating Neutral generators. On a Floating Neutral generator, the test button will draw power from the Hot through the toroid and back to the Neutral without going through the toroid again and the sensor will initiate the GFCI to trip. The false positive received by GFCI test circuits on ungrounded Floating Neutral generators does nothing to eliminate faulty equipment and only causes unnecessary and costly production delays. A combination of grounding the generator winding (grounding the Neutral) and adding a GFCI is necessary. For this reason OSHA requires both on worksites.
For the reasons illustrated above, OSHA requires that all portable generators on work sites have their Neutral bonded to the equipment grounding system and be equipped with GFCI protection. So that they can provide an industrial generator that will pass OSHA job site inspections, manufacturers like Honda provide special industrial generator lines that meet these requirements. The EB generators are Honda’s “Industrial Generators.” The EB3800, EB5000, and EB6500 generators are neutral bonded and GFCI protected to meet OSHA jobsite regulations. Unfortunately the Honda EB generators are AVR type (prone to voltage waveform distortion from dirty loads) and quite load because of their open frame design. For example the Honda EB6500 is more than twice as load (72 dBA sound level) as the comparable Honda EU6500is (60 dBA) under full load. Since the Honda EU6500is is an Inverter type, it is less susceptible to voltage waveform distortion, and quite a bit quieter than the EB6500 under less than full load because its’ speed is load dependent (use this link for details about http://www.screenlig...horInverter Gen ' class='bbc_url' title='External link' rel='nofollow external'>Inverter generators .)
While Honda’s EB generators meet OSHA requirements, they are too loud and too susceptible to voltage waveform distortion to be used in motion picture production. Unfortunately, Honda’s generator line that meets the noise and power quality requirements for motion picture production, the EU series of Inverter generators, are not Neutral Bonded and do not offer GFCI protection and so do not meet OSHA guidelines for use on work sites. Honda doesn’t even make an Inverter generator that meets OSHA guidelines (the EM5000is is not Neutral Bonded and does not offer GFCI protection.) So what should a film electrician do when filming will take place in wet hazardous conditions?
One approach that meets OSHA requirements is to use a Floating Neutral generator with a grounded Transformer. Since Transformers bond the Neutral to Ground on the secondary load side they provide a low resistance path (illustrated below) for fault current back to the Transformer windings. And, if the Transformer has a breaker wired into it ( like our 60A Full Power Transformer/Distro) that will trip from the over-current situation, it offers more protection against faults than does the generator used alone.
1) A fault in a metal fixture energizes the entire housing.
2) Since, electricity seeks the path of least resistance back to its’ source, the bulk of the fault current will travel through the grounding wire, instead of a individual making contact with the housing, because it is of a much lower resistance than the individual.
3) Because the ground wire and the neutral wire are bonded on the secondary side of the transformer, the current carried by the ground wire back to the transformer creates a dead
short (over-current situation).
4) If enough current flows through the ground wire, the circuit breaker on the transformer pops in response – shutting off power to the distribution system.
Since a Transformer bonds the Neutral to Ground, to completely comply with the OSHA requirements for the use of a EU6500is on work sites all you need to do is use 20-Amp GFCI protected cords. Since the Neutral and Ground are bonded in the Transformer, GFCIs will operate reliably even when the power is being generated by a Floating Neutral generator like the EU6500is.
The ability to use GFCI protection in wet conditions or locations has got to be one of the greatest benefits to using a Transformer/Distro with a Honda EU6500is Generator. Not only can you use a generator that is quiet and produces clean power, but it also makes it possible to use GFCI technology, like a 100A shock block pictured below, that is specifically designed for motion picture applications.
A single 100A GFCI "Shock Block" can provide ground fault protection on wet locations for the entire distro system of a Honda 6500 portable generator when used in-line with a Step-Down Transformer/Distro.
To prevent the nuisance tripping that electronic Kino & HMI ballasts can cause with standard GFCIs, film style shock blocks like the one pictured above sense on an "Inverse Time Curve." And, to deal with the harmonics that non-PFC Kino & HMI ballasts kick back into the power stream (that will cause other GFCIs to trip), our 100A GFCI includes a harmonic filter with a frequency response up to 120 hz. 3rd harmonics are attenuated by 50%, and by 500 Hz are down to 20%. Attenuated by the filter, the harmonics generated by dirty loads such as non-PFC Kino & HMI ballasts, pose less of a problem. Placed immediately after the secondary load side of a Transformer, a 100A shock block will provide safe and secure ground fault interruption for the entire distribution system – eliminating the need for finicky individual 20A GFCI outlets. Used in-line with our 60A Full Power Transformer/Distro, a 100A shock block will provide a larger GFCI protected circuit than is available on any other portable generator (by comparison the largest GFCI circuit available on a Honda EB6500 is only 30Amps.) In fact, it enables the operation of even 4k HMIs with GFCI protection. Specifically tailored to the type and size loads used in motion picture production, a film style 100A shock block provides reliable ground fault protection for larger lights, or more smaller lights, than has ever been possible on a portable gas generator when used on our modified Honda EU6500is with our 60A Full Power Transformer/Distro.
For more detailed information on using shock blocks to provide ground fault protection with portable Honda generators, I would suggest you read the article I wrote for our company newsletter on the http://www.screenlig...ard Protection' class='bbc_url' title='External link' rel='nofollow external'>use of portable generators in motion picture lighting.
This article is cited in the just released 4th Edition of Harry Box's "Set Lighting Technician's Handbook" and featured on the companion website "Box Book Extras." Of the article Harry Box exclaims:
"Great work!... this is the kind of thing I think very few technician's ever get to see, and as a result many people have absolutely no idea why things stop working."
"Following the prescriptions contained in this article enables the operation of bigger lights, or more smaller lights, on portable generators than has ever been possible before."
The article is available online at http://www.screenlig...generators.html.
Guy Holt, Gaffer, ScreenLight & Grip, Lightng & Grip Rental in Boston