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Author Topic: Generator question  (Read 29465 times)

Guy Holt

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Re: Generator question
« Reply #90 on: September 24, 2015, 04:55:42 pm »


Over a beer I think you and I would agree on far more things than we would disagree.…  What I hope you will concede based on significant experience between several posters is that the typical situation many of us run into in the course of this industry … is somewhat different than what you're used to.  While it would be great for every poster to own their own EU7000 that is internally bonded and/or a transformer like you describe that may assist with some other factors (with some disadvantages, too) complete with 10' ground rods, that's not the reality for many of us in these particular trenches, nor is it required by code or practical efficacy.  Asking users to do too much may have the opposite effect of what you desire, in that users may end up being deterred based on perceived complexity or effort, whereas practical solutions are more likely to be implemented, even if they don't meet certain letters of the code in some circumstances. Where the rules are different, I expect the players know them and adapt accordingly.

What I run into in my line of work is not as dissimilar to what you encounter as you may think.  We provide power generation to a number of outdoor theatre productions, music videos, as well as rock shows large and small (see the speaker stack in the rap video below.) Since many lighting effects are tied to music we are quite familiar with dynamic loads. 

2010 BET Hip Hop Awards “Director of the Year” Nahala Johnson, aka "Mr. Boomtown", directing his latest Rap Video: an outdoor dance party with DJ and dancers on top of a speaker stack (upper left.)

I am not suggesting the use of small portable transformers with portable generators because I sell them, but because as a working gaffer I find that they solve a number of issues related to the use of portable generators in production in general.

A modified Honda EU6500is supplies power to set (far left.) A 60A Full Power Transformer/Distro compensates for line-loss of 300’ cable run (left center) to assure 120V line level to 4K HMI (far right), Speaker Stack, Amplifiers, Set Monitors, Battery Chargers, & DIT station (Center.) 60A Bates Splitters, Extensions, and Gang boxes distribute power from Transformer around set (right center.)

I would hate to see someone be deterred from using them when they offer a solution because of a false perception obtained in this thread. For this reason I would like to address several false assumptions and misleading statements that have been posted.

Running all of your loads on a single 120 V circuit doubles your voltage drop compared to running the same load on a 240 volt circuit.

This argument doesn’t really apply to the use of step-down transformers because  transformers are 240V loads, and since in this application they would be used next to the amp rack, far from the generator as possible, there is no more line-loss than if the amps were powered at 240V.

Of course, a 120/240 volt circuit requires an extra wire.  So your pro's/con's would be to compare cost of 3 wire vs 4 wire vs cost of transformer.

Because transformers return no current, the neutral conductor can be dropped. Which means that you can use 10/3 SO cable which is lighter and cheaper than the 10/4 SO cable you would use with a L14-30 120/240 distro.

Yes you can add a transformer at the end of the run-but that adds complexity to distribution plus potential issues with getting a ground rod vs with a genny typically parked outside away from production.

A step-down transformer actually simplifies distro.  You can use off-the-shelf and straightforward 120V distro panels rather than more complicated custom panels that combine 120V and 240V receptacles. And as previously noted you don’t have to worry about balancing your loads on the two legs of a generator because a 240V-to-120V transformer splits whatever load is placed upon it (which is why there is no return current.)

As for the floating neutral-it is my understanding that can be fixed with an appropriate bonding jumper.  I simple low cost solution.

The simple  low cost solution may not pass inspection (see above for details.)

If the generator has voltage drop under load, transformer taps would work well for a steady load - under a dynamic load such as audio, the voltage would rise, perhaps to unacceptable levels when the generator was lightly loaded- making transformer taps a less than ideal solution.  The longer (higher impedance) your run, the greater your variation as the load varies.

Actually the opposite is true.  The magnetizing current of a step-down transformer puts a “phantom” load on a generator that buffers dynamic loads like power amps without adding to the overall loading of the generator. The net effect is that the generator sees a more consistent load with less wide disparities. As a result, there is less fluctuation of voltage when dynamic loads are powered through a step-down transformer than when they are powered directly off a generator.  Why this is the case is more complicated than I have time to get into here – I will try to put together a more detailed explanation in the near future.

If you see material safety issues with a presented option, then let's talk about it, ….

I do see safety issues with the statements below,  but it is more complicated than I have time to get into here – I will try to put together a detailed response in the near future.

... again, in this type of operation, with ground/neutral bonded, and GFCIs, a ground rod doesn't add any safety to the setup.....

... Get two inline GFCI devices like these: and plug them into the two NEMA 5-20 receptacles on the generator....

Guy Holt, Gaffer
ScreenLight & Grip

Mike Sokol

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Re: Generator question
« Reply #91 on: September 24, 2015, 10:05:56 pm »

This thread has run its course so I'm locking it. We'll continue discussion of the various topics later.

Mike Sokol
Mike Sokol

ProSoundWeb Community

Re: Generator question
« Reply #91 on: September 24, 2015, 10:05:56 pm »

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