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Do Honda Portable Generators have to be grounded?


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#1 Guy Holt

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Posted 01 February 2011 - 12:43 PM

… 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'>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.

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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.

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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 '>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?

Posted Image


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.

Posted Image



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.

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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'>use of portable generators in motion picture lighting.

Posted Image


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
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#2 John Sprung

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Posted 01 February 2011 - 06:47 PM

Guy, a question about the role of capacitance in all this:

What I've observed with a supposedly floating generator and 100 ft. of 12/3 run over moist (but not really muddy) ground is that at the far end there's about 60 Volts between neutral and a probe in the dirt, and also about 60 between hot and the dirt. There may be a couple Volts difference between the two readings. This is with a good digital multi-meter, very high impedance. My theory is that capacitance is creating a voltage divider between the two active conductors in the cable and the earth. Is that right?

While that sort of thing won't produce a sustained continuous current through your body, the initial shock that discharges the capacitance is annoying at best, and if you're working with power tools at the time, potentially dangerous because it causes you to jerk your arm.




-- J.S.
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#3 Phil Rhodes

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Posted 01 February 2011 - 08:19 PM

And strike sparks between BNC shells and the equipment to which you're about to connect it. And make your computer-based video recording equipment brownout. And other fun things.

I'm always twitchy around portable power until I've seen a large man with a sledgehammer pounding a big copper rod into the ground. And frankly, I'm only slightly less twitchy afterward.

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#4 Hal Smith

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Posted 02 February 2011 - 12:32 AM

Guy, a question about the role of capacitance in all this:

What I've observed with a supposedly floating generator and 100 ft. of 12/3 run over moist (but not really muddy) ground is that at the far end there's about 60 Volts between neutral and a probe in the dirt, and also about 60 between hot and the dirt. There may be a couple Volts difference between the two readings. This is with a good digital multi-meter, very high impedance. My theory is that capacitance is creating a voltage divider between the two active conductors in the cable and the earth. Is that right?

While that sort of thing won't produce a sustained continuous current through your body, the initial shock that discharges the capacitance is annoying at best, and if you're working with power tools at the time, potentially dangerous because it causes you to jerk your arm.




-- J.S.


Affirmative on the capacitive divider thought, it might be more complex involving the capacitance of the generator's frame to ground, etc. but you've got the right idea. The amount of capacitance will determine just how much current flow. Modern digital voltmeters (DVM's) usually have input impedances around 10 megohms (1X10^6 ohms). Since the meter's impedance is so high, a very small amount of capacitance will support readings like yours. Unfortunately there's no way of knowing from a DVM's readings just what the capacitance is and whether or not it's large enough to support a dangerous amount of current. Bottom line? If you get any reading assume it's not safe.
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#5 Guy Holt

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Posted 03 February 2011 - 11:10 AM

Unfortunately there's no way of knowing from a DVM's readings just what the capacitance is and whether or not it's large enough to support a dangerous amount of current. Bottom line? If you get any reading assume it's not safe.


Hal is right. Where you can't know if the capacitance is large enough to support a dangerous amount of current - you must assume it is not safe. Most people think that high voltage causes fatal shocks, this is not necessarily so. To paraphrase Harry Box from the 4th Edition of his “Set Lighting Technician’s Handbook”: The amount of current flowing through the body determines the effect of a shock. A mili-ampere (1 mA) is 1/1000th of an amp; a current of 1 mA through the body is just barely perceptible. Up to 8 mA causes mild to strong surprise. Current from 8 to 15 mA are unpleasant, but usually the victim is able to free himself or to “let-go” of the object that is causing the shock. Currents over 15 mA are likely to lead to “muscular freeze” which prevents the victim from letting go and often leads to death. Currents over 75 mA are almost always fatal; much depends on the individual involved; how much muscle mass, body condition and condition of the heart.

Posted Image


If the fault is high resistance (making only loose contact with the housing) the current will create a lot of heat, but it may not be high enough to open an over-current breaker. And, if the grounding conductor is faulty (the grounding pin broken or bad connection) the current may be high enough to cause cardiac arrest.

It is a common misconception that a circuit breaker is there to protect you. 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. An electrical shock current of one hundred milliamps (100mA or 0.1A) is a very serious shock capable of causing paralysis of the lungs and heart muscle. The smallest circuit breaker we use is 20A – that’s about two hundred times more current than is needed to kill you.

To protect against serious harm from electrical shock, the circuit must be monitored by a Class A GFCI (Ground Fault Circuit Interrupter.) This type of device will interrupt the circuit if it detects current leakage that is greater than 6 mA. At 6 mA, almost all adults and children can let go of the source of the shock. At higher currents, people are progressively less able to overcome muscle contractions caused by the shock, and therefore less able to disconnect themselves from the fault source. A GFCI will de-energize the circuit in less time than it takes to receive a harmful amount of current. A GFCI will not protect against short circuits or overloads. The circuit breaker or circuit protector in the control panel, which supplies power to the circuit, provides that protection. A GFCI is not a substitute for grounding or over-current protection – it should be considered a supplemental part of the circuit.

As I mentioned in my post above, simply using a GFCI on a Floating Neutral generator will not ensure a safe system. A GFCI will not operate reliably if one side of the winding is not grounded to the generator frame because 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.

Since the Neutral and ground are bonded in a Transformer, GFCIs will operate reliably on them, even when the power is being generated by a Floating Neutral generator like the EU6500is. To completely comply with the OSHA requirements for the use of a EU6500is on work sites all you need to do is use a transformer, like our Full Power Step-down Transformer/Distro, with a 100A shock block placed inline on the secondary load side of the 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 that are not designed to filter the harmonics generated by dirty lighting loads like non-PFC HMI & Kino ballats (use thishttp://www.screenlig...ard Protection'> link for details.)

Posted Image

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.


Used in-line with our 60A Full Power Transformer/Distro, a 100A shock block will also provide a larger GFCI protected circuit than is available on any other portable generator (by comparison the largest GFCI circuit available on a Honda “Industrial Generator” 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'>use of portable generators in motion picture lighting.

Guy Holt, Gaffer, ScreenLight & Grip, Lighting and Grip Rental & Sales in Boston
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#6 John Sprung

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Posted 03 February 2011 - 02:50 PM

Why does it have to have a transformer? Couldn't you convert a floating generator to grounded just by grounding its neutral?




-- J.S.
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#7 Guy Holt

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Posted 03 February 2011 - 04:14 PM

Why does it have to have a transformer? Couldn't you convert a floating generator to grounded just by grounding its neutral?


The EU generators are not really designed for bonding the neutral to the ground. Inverter generators operate in a completely different manner than conventional AVR generators. Inverter generators use micro-processor control modules to produce AC power with a "true" sine wave from high voltage DC power converted from multi-phase AC power generated by magnetic induction in a multi-pole alternator (see illustration below.)

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The three phases of the inverter generator process: high frequency AC converted to DC; DC inverted to stable clean 120V, 60 Hz AC.


Unlike the simple two-pole alternators of AVR generators, an inverter generator uses a core that consists of multiple stator coils and multiple rotor magnets. Each full rotation of the engine produces more than 300 three phase ac sine waves at frequencies up to 20 kHz, which is considerably more electrical energy per engine revolution than produced in conventional two pole AVR generators. A fixed diode bridge rectifier then converts the more than 300 three phase ac sine waves to a DC voltage (about 200 V). AC Output is then generated from the high voltage DC by a inverter module with voltage and frequency set by micro-processor controlled switches using a PWM control logic (use this http://www.screenlig...ave Generators'> link for details.)

Posted Image

On Honda AVR generators bonding Neutral to ground is as easy as adding a Nuetral Bond wire.


Because of the inverter unit, bonding the Neutral of a Honda EU6500is to the frame is not as simple as in AVR models where you simply add a Neutral Bond jumper from one of the generator winding leads to the frame as in the illustration above from the service bulletin on how to bond the Neutral in a Honda EB5000 industrial generator. In an EU series inverter generator, bonding the Neutral to ground requires removing the main panel and inverter module to get behind the breakers, switches, sockets etc. - not easily done or undone. According to the Honda Service Bulletins, it should only be done by a qualified service technician. In the end, it is much easier to use a tranformer instead. In addition to offering other production benefits (use this link for details), our a transformer bonds the neutral to ground and so meets this OSHA requirement for use of a Honda EU6500is on jobsites.

For more detailed information on using transformers with 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'>use of portable generators in motion picture lighting.

Posted Image


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
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#8 John Sprung

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Posted 03 February 2011 - 07:46 PM

OK, so as I understand this, it's mainly the difficulty of getting access to the neutral ahead of the generator's built-in breaker panel that's the issue. It seems that if you were to take all your power out of the generator through a single 120/240 connection into an outboard panel, much like your transformer box, you could bond neutral to ground there. The only issue with that is that it might violate the letter of various codes and regulations, right?

Anyhow, your discussion of the relationship between AC frequency and the physical rotation of generators reminded me of something you might find interesting:

http://www.dynamicde....co.uk/grid.htm

It's the same thing on a grand scale.




-- J.S.
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#9 Guy Holt

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Posted 04 February 2011 - 10:59 AM

It seems that if you were to take all your power out of the generator through a single 120/240 connection into an outboard panel, much like your transformer box, you could bond neutral to ground there. The only issue with that is that it might violate the letter of various codes and regulations, right?



As John suggests, one can bond Neutral to ground in a distribution panel designed to break out the 120V circuits of the 240V output of the generator. For years, rental houses wired such custom distribution panels, called “Splitter Boxes,” in order to access more 120V power from the 240V twist-lock receptacle on the generators. While this approach does meet the OSHA requirements, and GFCIs receptacles on such a box will work as designed, some inspectors may still want the Neutral to be bonded at the generator.

Even if the inspector is satisfied, you may still encounter problems using HMIs & Kinos on a Splitter Box. Splitter Boxes worked well enough when the lighting load placed on generators consisted predominantly of incandescent lights (a linear load), but they are inherently unsuitable in this case to carry non-linear loads consisting predominantly of non-Power Factor Corrected HMI, Fluorescent, & LED Lights. But, that is a topic for another post. Here I would like to stress (I think this is what John was suggesting) that using Bonded Neutral Splitter Boxes on Dryer & Range Plugs is a clear violation of the National Electrical Code. To quote Mike Holt, of Mike Holt Enterprises (a leading electric code training program): “The National Electrical Code (NEC) requires a neutral-to-ground connection to be made at service equipment only and there shall not be any neutral-to-ground connection on the load side of service equipment [250-23(a), 250-24(a)(5)]” (full excerpt is available online at his website) Which means, the only safe way to pull power from a three wire 240V wall outlet that meets the requirements of the National Electrical Code is to run your lighting load through a 240v-to-120v step down transformer. Where a transformer acts as an impedance, the NEC permits the bonding of Neutral to Ground on the secondary or load side of a transformer.

Amoung the many benefits to using Transformers to access more house power (use this link for details), the ability to use film style GFCIs, like Shock Blocks has got to be one of the greatest. GFCI protection is a must when working around water in doors – whether it is a bath scene, a kitchen scene, or a scene washing a car in a driveway. In any situation where people and equipment are likely to get wet, there needs to be ground fault protection for the reasons discussed above. If you are using tungsten lights, the hardware store variety of GFCIs will work just fine. But, if you plan to use HMI or Kinos you need film style GFCIs, like Shock Blocks, that are specifically designed for motion picture lights. To prevent the nuisance tripping that electronic Kino & HMI ballasts can cause with standard GFCIs, film style GFCIs 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), film style GFCIs include 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.

Posted Image

A single 100A GFCI "Shock Block" can provide ground fault protection for an entire distro system derived from a 240V Dryer or Range circuit with a Step-Down Transformer/Distro.


The problem with Shock Blocks is that they don’t come smaller than 100Amps. So, unless you want to tie-in to the location service head, the only way to use them is on a Range or Dryer plug with a step-down transformer like the 60A Full Power Transformer/Distro we make for our modified 7500W Honda EU6500is generator. A transformer will step the 240V of a 50/30AmpRange/Dryer down to a single 100/60A 120V circuit. If you wire the transformer with a Bates receptacle on the secondary load side, a 100A GFCI used inline can provide safe and secure ground fault protection for an entire distribution system consisting of Bates Extensions, Splitters, and Break-Outs to Edisons – eliminating the need for hardware store 20A GFCIs that are prone to tripping when used with harmonic generating loads like non-PFC HMI & Kino Ballast, & LED Power Supplies. Used in-line with our 60A Full Power Transformer/Distro, a 100A Shock Block will provide a larger GFCI protected circuit than is commonly available in homes. In fact, it enables the operation of even 4k HMIs on wall outlets with GFCI protection.

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Master shot of an iRobot commercial lit with a 4kw HMI Par (outside) & 1.8kw HMI Par (inside) powered from a 30A/240V dryer outlet through a step-down transformer/distro. Note: Sunny feel created by 4k Par on an overcast day.


I used this approach on a recent commercial for iRobot (see production stills attached.) The spot contrasted the iRobot Scooba designed to clean kitchen floors to the old mop and bucket approach. For the mop and bucket approach we had a haggard looking Mom slopping water all over the kitchen floor as kids ran slipping and sliding across the floor.

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Left: Transformer/Distro plugged into a 30A/240V dryer outlet. Right: 4K HMI Par under rain protection powered by Transformer/Distro


Because we knew water would get everywhere we used one of our 60A Transformer Distros on a Dryer Plug to power a 4K HMI, a 1800W HMI, and some Kinos. We put a 100A Shock Block like the one pictured above on the load side of the transformer/distro to provide Ground Fault protection inside around the wet kitchen floor. It was a good thing that we did, because it ended up pouring rain that day and so the Shock Block did double duty for the 4k that was outside the kitchen window.

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Left: Arri AS18 1800W Par powered from Transformer/Distro. Right: 4Kw and 1800W HMI ballasts powered from Transformer/Distro.


For more detailed information on using Shock Blocks to provide Ground Fault protection on Dryer/Range plugs or with portable Honda generators, I would suggest you read the article I wrote for our company newsletter on the http://www.screenlig...ard Protection'>use of portable generators in motion picture lighting.

- Guy Holt, Gaffer, ScreenLight & Grip, Lighting and Grip Rental & Sales in Boston
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