ProSoundWeb Community

Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Dave Guilford on January 30, 2020, 01:20:35 pm

Title: School me on generators.
Post by: Dave Guilford on January 30, 2020, 01:20:35 pm
 I have my own small Multiquip 7000 generator that puts out 50amps which is great for many of my
Smaller-medium gigs.  Sometimes I rent a larger 25kVA , and sometimes I rent a EU3000 to be used solely for a beer truck. So I’m thinking about buying an EU3000 so I don’t have to keep renting.

 Years ago I did a small outdoor gig where they had loud gasoline generators. One wasn’t enough to run the whole show, so I used one for backline and one for sound system.   I made sure that they were separate and none of one “touched” the other. I did this by putting a Mac on the bass can (no di), and running acoustic guitar pedals off power allocated to sound system.  Show went fine.

 Since then he crosses my mind if that was even a proper thing to do.  Would it have been fine for them to share a grounding rod? Did I do it the smart way by keeping them isolated from each other?
Title: Re: School me on generators.
Post by: Stephen Swaffer on January 30, 2020, 07:43:58 pm
The NEC, in general, requires anything that is "likely to be energized" (pretty much anything using AC power, or having cords or powered equipent touching it) to be bonded and it requires all "separately derived" services (each genny is a separately derived service) to be bonded to the same grounding electrode system.

If everything metallic that can be touched by a person is connected together, then there can never be enough voltage difference between to two objects to create a hazard.  If two items have no connection, a volt meter connect between them will read a fluctuating voltage-and there is no guarantee that a fault won't occur that couldcreate a lethal voltage difference.  Isolation, in theory, should be safe-but isolation is almost impossible to guarantee.  Isolation is used in the electrical industry for energized work-but under carefully controlled and tested conditions.  Moisture easily circumvents many insulators-a lot of people think of rubber as an insulator-but some common rubber hoses used for compressed air or water or very conductive.
Title: Re: School me on generators.
Post by: Dave Guilford on January 30, 2020, 08:35:52 pm
Excellent and thank you. Pardon my ignorance- what exactly is “bonded” in this situation?
Title: Re: School me on generators.
Post by: Stephen Swaffer on January 30, 2020, 10:13:54 pm
"Bonding" is defined as an intentional metallic connection.  The size of the bonding wire is determined by the size of the breaker protecting the circuits.  For generators the size you are talking, #12 would usually be OK (up to 20 amp breakers), #10 is good up to 60 amp breakers.

One common misconception is that you can set a genny in one location with a ground rod and another in another location with a ground rod and , since they are both "grounded" all is good.  Unless you have a metal bond, you still have a potential hazard.  Run a wire between the two ground rods and now you are "bonded" and have a correct situation.
Title: Re: School me on generators.
Post by: Dave Guilford on January 31, 2020, 09:09:32 am
"Bonding" is defined as an intentional metallic connection.  The size of the bonding wire is determined by the size of the breaker protecting the circuits.  For generators the size you are talking, #12 would usually be OK (up to 20 amp breakers), #10 is good up to 60 amp breakers.

One common misconception is that you can set a genny in one location with a ground rod and another in another location with a ground rod and , since they are both "grounded" all is good.  Unless you have a metal bond, you still have a potential hazard.  Run a wire between the two ground rods and now you are "bonded" and have a correct situation.

Excellent info!  So to bond 2 generators, it’s a nice thick wire beteeen the ground rods, and that’s it?

Does that make things safe for “crossing lines” on the stage?  In my Original post I mentioned that bass was via mic and not DI.  Bonding generators as described eliminated potential?

And I also saw someone mention bonding to a metal stage.  Like a stageline or we get type trailer stage?  I would bond the ground rod to the metal stage?
Title: Re: School me on generators.
Post by: Jonathan Johnson on January 31, 2020, 01:29:26 pm
"Bonding" is defined as an intentional metallic connection. 

The key word here is “intentional.”

That is, the bonding is deliberate, designed to ensure connectivity between objects, in such a way as to be obvious to trained personnel and unlikely to be defeated by untrained personnel.

That means your bonds are secured by bolts, not spring clamps or cord and plug connections where accessible by the public.

That often means jumpers across joints. Your metal lighting truss sitting on a metal stage is not bonded by virtue of merely being in contact with the stage, for that is incidental, not intentional. The truss must either be bolted to the stage or jumpered to the stage.
Title: Re: School me on generators.
Post by: Dave Guilford on January 31, 2020, 09:04:26 pm
Your metal lighting truss sitting on a metal stage is not bonded by virtue of merely being in contact with the stage, for that is incidental, not intentional. The truss must either be bolted to the stage or jumpered to the stage.

And this is done in practice?  Obviously supposed to.  Do most large productions adhere to this strictly, or loosely?
Title: Re: School me on generators.
Post by: Tim McCulloch on January 31, 2020, 10:58:48 pm
And this is done in practice?  Obviously supposed to.  Do most large productions adhere to this strictly, or loosely?

It's as tight as the contractor performs the work the inspector insists upon.  On world-class touring (Rolling Stones level) the stage superstructure is bonded to generator compound's Grounding Electrode System and metalic sub-structures are bonded to the superstructure.  Been there, built that with StageCo Belgium.

On a local or regional level?  Eh... *something* is grounded/bonded but how much of the structure/sub structure is?  Metallic hand rails?  Aluminum steps?  Metal edges of stage decks?
Title: Re: School me on generators.
Post by: Jonathan Johnson on February 01, 2020, 09:29:01 pm
That often means jumpers across joints. Your metal lighting truss sitting on a metal stage is not bonded by virtue of merely being in contact with the stage, for that is incidental, not intentional. The truss must either be bolted to the stage or jumpered to the stage.

And, I might add, the bonding must be bare metal to bare metal. If there's paint or coating in the way, it's not a proper bond.
Title: Re: School me on generators.
Post by: Jonathan Johnson on February 01, 2020, 09:31:25 pm
It's as tight as the contractor performs the work the inspector insists upon.  On world-class touring (Rolling Stones level) the stage superstructure is bonded to generator compound's Grounding Electrode System and metalic sub-structures are bonded to the superstructure.  Been there, built that with StageCo Belgium.

On a local or regional level?  Eh... *something* is grounded/bonded but how much of the structure/sub structure is?  Metallic hand rails?  Aluminum steps?  Metal edges of stage decks?

I imagine the big tours employ their own electricians who handle bonding, rather than depending on the stagehands and engineers to do that when they're plugging in mics and amps.
Title: Re: School me on generators.
Post by: Tim McCulloch on February 01, 2020, 09:54:49 pm
I imagine the big tours employ their own electricians who handle bonding, rather than depending on the stagehands and engineers to do that when they're plugging in mics and amps.

It appeared on the Stones stage and set I was working on that the bonding was engineered into the build process - IIRC the bonding points were welded to the steel and there were multiple jumpers between primary structure and stage subassemblies.  Whether or not StageCo used electricians or their stage techs, I don't know.  I'm fairly certain that local hands did not perform this task.
Title: Re: School me on generators.
Post by: John Sulek on February 01, 2020, 11:15:36 pm
And this is done in practice?  Obviously supposed to.  Do most large productions adhere to this strictly, or loosely?

As one of the production managers I know well has said to folks providing temporary stages/power...

Are you going to bond the stage to the genny grounding stake?

No..we never do.

Ok, can I get a business card?

Sure, why?

I need to make sure we get your name spelt correctly for the lawyers.

I'll go get some wire and clamps.
Title: Re: School me on generators.
Post by: Robert Piascik on February 02, 2020, 08:56:46 am


 Years ago I did a small outdoor gig where they had loud gasoline generators. One wasn’t enough to run the whole show, so I used one for backline and one for sound system.   I made sure that they were separate and none of one “touched” the other. I did this by putting a Mac on the bass can (no di), and running acoustic guitar pedals off power allocated to sound system.  Show went fine.

 Since then he crosses my mind if that was even a proper thing to do.  Would it have been fine for them to share a grounding rod? Did I do it the smart way by keeping them isolated from each other?

I always thought the danger here was holding onto a guitar and lips touching a microphone. Wouldn’t that be no longer isolated?
Title: Re: School me on generators.
Post by: Rob Spence on February 02, 2020, 02:12:07 pm
For the OP

To be clear, when using generators, one should BOND the neutral to ground. Also, one should BOND metallic structures to ground. Also, the ground should be BONDED to Earth.

There should only be ONE ground. All ground leads should connect together.