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Author Topic: Mixing Street Power and Generator Power  (Read 1552 times)

Art Nadelman

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Mixing Street Power and Generator Power
« on: September 06, 2019, 11:40:00 am »

I am NOT an electrician.  So I need to ask you experts for some advice here.

I have an outdoor show next weekend where the power source is about 125 feet from the stage.  That's a lot of new expensive extension cords to purchase to run this show.  So I recommended to the promoter that they get a generator for the show.

They contracted for a 6500 Watt generator.  The 5-piece band I'm running sound for is going direct with all instruments (no amps) and all use IEMs, so no wedges.  The only major power consumers on the stage will be my 4 main speakers and 2 subs.  So this is plenty of power.

My concern comes from my mixer/wireless rack. I always run it on a UPS, but I remember that UPS's and generators don't always play nicely with each other.

So I've considered 3 different options.  Option 1 is to run everything off of the generator as I normally would.

Option 2 is to run everything off of the generator, but instead of running a UPS in the rack, use a power conditioner in the rack.

Option 3 is to run the rack off of city power and run everything else off of the generator.  By doing this, am I causing a grounding or other issue?

What are your recommendations?

Thanks.

Art
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Jonathan Johnson

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Re: Mixing Street Power and Generator Power
« Reply #1 on: September 06, 2019, 12:34:48 pm »

If you are using a digital snake, with no analog interconnects between the stage and the mixer, you probably don't have much to worry about.

If you do have analog interconnects between the components on different power sources, then I recommend bonding the ground of the generator with the ground of the utility power. The reason is that, if you don't, you could get undesirable currents on the shields of your interconnects; this is especially problematic if any of them are not true balanced. The other option is to use isolation transformers in the interconnects.

Bonding can be done with a #6 AWG wire connected between the grounding point of the generator and a grounding point of the utility power supply. That probably means buying at least some wire.
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Stephen Swaffer

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Re: Mixing Street Power and Generator Power
« Reply #2 on: September 06, 2019, 12:47:18 pm »

I agree with Jonathan on bonding the grounds-but the main reason being safety anyone in the area.  Undesirable currents may or may not occur-but they are easier to fix than people.

Technically, bonding wire size is determined by breaker size involved-so if only 20 amp circuits, a #12 is Ok, 30 amp breakers need a #10.  Larger is better-and obviously more robust/dependable.
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Tim Hite

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Re: Mixing Street Power and Generator Power
« Reply #3 on: September 06, 2019, 04:43:02 pm »

Option 1a: Bypass UPS and run off the generator.
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Luke Geis

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Re: Mixing Street Power and Generator Power
« Reply #4 on: September 06, 2019, 11:42:21 pm »

You don't know till you try, but If you are that worried about the UPS then nix it and run off the Genie power. If you are using a digital snake and no analog connections are going to anything connected to the Genie, you should have little to worry about. I would use a network cable that has its shield lifted though as a fully shielded network cable can carry ground current between the two halves of the systems.
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Tim McCulloch

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Re: Mixing Street Power and Generator Power
« Reply #5 on: September 07, 2019, 01:26:25 am »

You don't know till you try, but If you are that worried about the UPS then nix it and run off the Genie power. If you are using a digital snake and no analog connections are going to anything connected to the Genie, you should have little to worry about. I would use a network cable that has its shield lifted though as a fully shielded network cable can carry ground current between the two halves of the systems.

Uh... If there is an X/M32 involved you're inviting problems without shield continuity.

I think once the OP hears how loud the genset is, he'll wish for extension cords.
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Scott Holtzman

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Re: Mixing Street Power and Generator Power
« Reply #6 on: September 08, 2019, 08:16:33 pm »

Uh... If there is an X/M32 involved you're inviting problems without shield continuity.

I think once the OP hears how loud the genset is, he'll wish for extension cords.

Yes what do you mean "contracted for a 6500 watt generator", who is providing it and who wrote the specs?  If not done properly you will end up with a noisy ass construction generator as Tim pointed out as nobody understands power.  You have to spec Honda (or equivalent) inverter generator with a continuous operating capacity of 6500watts.  It must be inverter, period.  Unless you spec a larger diesel generator that have large mechanical flywheels to maintain regulation. 

Don't buy extension cords.  They are not rated for this use and very unprofessional.  Nothing screams amateur like an orange extension cord.  No matter what you do you should have a small case of 12GA SOOW rated feeder cable.  I keep ours cut to 50's lengths, you may find 25' more convenient.  Make your own with this cable using high quality industrial ends.  Don't forget to gaff the couple.  You need to route to not have trip hazard.  Rubber matts, Gaff tape and cable trough are all tools that you may need. 

If there is a 240v volt 4 conductor (2 hots, neutral and ground) with 125' of the stage just rent 150' of feeder, cable ramps and a lunchbox distro from a local production house.   You should have a relationship with a local house to rent additional capacity as needed anyway.
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Tim McCulloch

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Re: Mixing Street Power and Generator Power
« Reply #7 on: September 08, 2019, 08:48:27 pm »

Yes what do you mean "contracted for a 6500 watt generator", who is providing it and who wrote the specs?

My Inner Cynic translates that to: "6500 watt contractor generator."  The kind the snow cone concession trailer uses to drown out the ice grinder...

I'd love to be wrong about this.  Art N. has been around long enough but his client may not have been. ;)
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Dave Guilford

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Re: Mixing Street Power and Generator Power
« Reply #8 on: September 08, 2019, 09:05:24 pm »

Option 4-

Ensure its a whisper INVERTER generator or the show is ruined.  Straight up.

Once youve formed that up, just put mixer near stage and go with a tablet. 
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Jamin Lynch

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Re: Mixing Street Power and Generator Power
« Reply #9 on: September 08, 2019, 09:16:41 pm »

How much available power is 125ft away?  1 20amp circuit or 200amp 3phase? Or something in between?

Maybe you could borrow or rent a distro. with a long enough feeder cable that will handle your application.
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Re: Mixing Street Power and Generator Power
« Reply #9 on: September 08, 2019, 09:16:41 pm »


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