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Author Topic: Grounding recommendations using generators.  (Read 15230 times)

Mark Cadwallader

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Re: Grounding recommendations using generators.
« Reply #10 on: May 08, 2017, 11:25:21 AM »

Will there be any problems with using the output of two non-sync'ed generators if (when) the systems are electrically connected?  (Will there be a problems with the AC sources not generating power on the same cycle?)
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Stephen Swaffer

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Re: Grounding recommendations using generators.
« Reply #11 on: May 08, 2017, 12:50:23 PM »

Could someone clearly explain the exact purpose of the ground rod other than lightning protection?
It obvious that if genny chassis and other metal structures are bonded, then there is a path for faults to trip a breaker.
Unlike the power grid, the genny has no reference to earth, right?

The purpose would be to create that earth reference and ensure that all the stuff bonded to the frame of the generator is at the same potential as the earth.  Admittedly, more important as the ground moisture content/conductivity increases.

Debbie, the interpretation hinges on your definition of "equipment".  Some would argue that a "distro" doesn't meet the definition of equipment.  As your "electrical system" becomes more complex, having an earth reference becomes more of a concern.

The output of non-synced generators shouldn't affect anything-unless you have synchronized motors that need to stay synced  ;D.  Seriously, is anyone using any sound gear that doesn't convert the power to DC immediately on entering the cabinet?
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Mike Sokol

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Re: Grounding recommendations using generators.
« Reply #12 on: May 08, 2017, 01:12:49 PM »

I just did some reading and according to an OSHA fact sheet Doc : DSTM 10/2005,  a grounding rod is not necessary for my purposes - if I am reading it right???
 I cannot find a more up to date document than 2005 so not sure if this has been superseded since its publication.

"Grounding Requirements for Portable and Vehicle-mounted Generators Under the following conditions, OSHA directs (29 CFR 1926.404(f)(3)(i)) that the
frame of a portable generator need not be grounded (connected to earth) and that the frame may serve as the ground (in place of the earth):
• The generator supplies only equipment mounted on the generator and/or cord- and plug-connected equipment through receptacles mounted on the generator, § 1926.404(f)(3)(i)(A), and
• The noncurrent-carrying metal parts of equipment (such as the fuel tank, the inter- nal combustion engine, and the generator’s housing) are bonded to the generator frame, and the equipment grounding con- ductor terminals (of the power receptacles that are a part of [mounted on] the genera- tor) are bonded to the generator frame,
§ 1926.404(f)(3)(i)(B).
Thus, rather than connect to a grounding electrode system, such as a driven ground rod, the generator’s frame replaces the grounding electrode."

Once you go through a power distro you're no longer connecting gear to "cord- and plug-connected equipment through receptacles mounted on the generator". So anytime we run power through a distro, we also bond the generator frame to a grounding rod. In your case, if everything is plugging directly into a pair of inverter generators, as long as you bond the two generators together, and bond the generator frames to the metal stage, then all should be well. I also add a G-N bonding plug to one of the generators to create a bonding path back to the generator neutral in case of a line-to-frame short. All of those small inverter generators have a floating neutral, so if there's a hot-to-frame short, then the entire power system will be upside down, with the line at frame/ground potential, and the neutral at 120-volts above the frame ground. The equipment should still operate, but if you get your fingers inside of a box and expect the neutral to the at frame-ground voltage, you can get a big shock or even be killed.

Jonathan Johnson

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Re: Grounding recommendations using generators.
« Reply #13 on: May 08, 2017, 01:33:34 PM »

Any time you have separately derived power services serving the same venue (separately derived means different power sources such as two generators, generator and utility power, or power from two different utility services), the grounding systems of the two services must be intentionally bonded.

Otherwise you can get damaging currents flowing through the shield of audio interconnects, or through staging, or structural steel, or whatever other incidental bond there might be. Or, heaven forbid, through personnel.

Even if you don't drive a ground rod, you can still get currents flowing due to incidental grounding such as when the chassis of the generator or some other equipment comes in contact with the soil. Driving a ground rod can increase these currents.

This bonding of separately derived services is something that is rarely talked about, but it's especially important in the audio realm. In other fields such as construction you almost never have an interconnect, so it's not so much of a worry.
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Tim McCulloch

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Re: Grounding recommendations using generators.
« Reply #14 on: May 08, 2017, 02:02:54 PM »

I just did some reading and according to an OSHA fact sheet Doc : DSTM 10/2005,  a grounding rod is not necessary for my purposes - if I am reading it right???
 I cannot find a more up to date document than 2005 so not sure if this has been superseded since its publication.

"Grounding Requirements for Portable and Vehicle-mounted Generators Under the following conditions, OSHA directs (29 CFR 1926.404(f)(3)(i)) that the
frame of a portable generator need not be grounded (connected to earth) and that the frame may serve as the ground (in place of the earth):
• The generator supplies only equipment mounted on the generator and/or cord- and plug-connected equipment through receptacles mounted on the generator, § 1926.404(f)(3)(i)(A), and
• The noncurrent-carrying metal parts of equipment (such as the fuel tank, the inter- nal combustion engine, and the generator’s housing) are bonded to the generator frame, and the equipment grounding con- ductor terminals (of the power receptacles that are a part of [mounted on] the genera- tor) are bonded to the generator frame,
§ 1926.404(f)(3)(i)(B).
Thus, rather than connect to a grounding electrode system, such as a driven ground rod, the generator’s frame replaces the grounding electrode."

OSHA regs cover safety for WORKERS who are engaged in their jobs.  The Electrical Code, as adopted by your locale, is universal in that it covers the installation, materials, methods and uses of electricity.  IOW, you only researched part of the issue here.
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Jeff Bankston

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Re: Grounding recommendations using generators.
« Reply #15 on: May 08, 2017, 05:03:43 PM »

If there is rebar or structural steel embedded in the concrete, that is potentially a better ground than a ground rod.

yep and concrete also retains water.
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Debbie Dunkley

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Re: Grounding recommendations using generators.
« Reply #16 on: May 08, 2017, 06:33:04 PM »

OSHA regs cover safety for WORKERS who are engaged in their jobs.  The Electrical Code, as adopted by your locale, is universal in that it covers the installation, materials, methods and uses of electricity.  IOW, you only researched part of the issue here.

It isn't that I only researched part of the issue - but that this was one of the few things I could find or understand that I felt related to my situation. The reason I quoted it here was to get some further insight.
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Tim McCulloch

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Re: Grounding recommendations using generators.
« Reply #17 on: May 08, 2017, 06:53:15 PM »

It isn't that I only researched part of the issue - but that this was one of the few things I could find or understand that I felt related to my situation. The reason I quoted it here was to get some further insight.

No problem, Debbie.  Quote what you don't understand about the NEC and one of the Gurus will explain.

Not grokking the NEC is pretty common - some folks here swear that their local inspector doesn't understand it!  Mike Sokol's reply is the higher priority reading as are Stephen's comments about "grounding" and "bonding" and Jonathan's discussion of "separately derived service".

At one of my festival gigs we've done "forever", the code enforcement inspector makes sure the feeder is protected, that the distros have the appearance of care and maintenance (he's never checked for UL sticker), that there are fire extinguishers on stage and that the "temporary demountable entertainment structure" is bonded to earth ground.  He spends more time looking at food vendor tents than the festival's 4 stages.

You're doing good, Debbie, and you get points for being proactive and caring about electrical safety.
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Stephen Swaffer

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Re: Grounding recommendations using generators.
« Reply #18 on: May 08, 2017, 09:45:43 PM »

A key to understanding both OSHA regs and the NEC is to pay careful attention to the section a given quote is in-our corporate safety director catches me on this from time to time as OSHA regs for construction are different than for industrial maintenance.  The particular quote Deb referred to is part of the construction regs.

Another key is term definitions-chapter 100 in the NEC, and often part of OSHA regs.

Grounding is covered in depth in chapt 250 of the NEC-but the recomendations in this thread will get you to the same place and are more down to earth for the laywoman.
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Debbie Dunkley

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Re: Grounding recommendations using generators.
« Reply #19 on: May 08, 2017, 10:50:28 PM »

No problem, Debbie.  Quote what you don't understand about the NEC and one of the Gurus will explain.

Not grokking the NEC is pretty common - some folks here swear that their local inspector doesn't understand it!  Mike Sokol's reply is the higher priority reading as are Stephen's comments about "grounding" and "bonding" and Jonathan's discussion of "separately derived service".

At one of my festival gigs we've done "forever", the code enforcement inspector makes sure the feeder is protected, that the distros have the appearance of care and maintenance (he's never checked for UL sticker), that there are fire extinguishers on stage and that the "temporary demountable entertainment structure" is bonded to earth ground.  He spends more time looking at food vendor tents than the festival's 4 stages.

You're doing good, Debbie, and you get points for being proactive and caring about electrical safety.

Thanks Tim....

I always try to find the answers myself to any questions I have but sometimes it is overwhelming just to know where to look.
And as I have proven today, can be rather misleading if taken out of context.
I am so happy and fortunate to have such a wealth of knowledge available to me on this forum and folks who are so generous with their time.
The advice I get here has never led me down the wrong path yet.....
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ProSoundWeb Community

Re: Grounding recommendations using generators.
« Reply #19 on: May 08, 2017, 10:50:28 PM »


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