ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 2 [All]   Go Down

Author Topic: Permanent Install  (Read 8030 times)

Luke Richison

  • Newbie
  • *
  • Offline Offline
  • Posts: 4
Permanent Install
« on: October 09, 2013, 10:09:40 am »

My church bought an old strip mall and gutted it. We've got a (relatively) blank slate to design our stage, which we'd like to be flexible enough to double as a small venue. I've got a pretty good handle on the audio but none at all on powering it. So, I was hoping someone on here could give some advice on what is ideal for a House of Worship / Small Venue (and if this post belongs in that forum).

Here are a few things I'm pondering:
  • Should we run a sub panel to the FOH and have dedicated circuits for each element (PA, FOH, Lights, Stage / Instrumetns
  • Do we leave the sub panel and run home runs to each element
  • Dedicated 60a service instead of sub panel?
  • Should we group PA, FOH, and Stage on one larger circuit (20a, 30a?)
  • What about a power conditioner or sequencer

I would also appreciate advice on what is practical given our limitations (this is the relatively part of our blank slate):
  • powerwed Mackie HDAs and subs for PA
  • Presonus StudioLive mixer
  • No floor monitors - we use in ear monitors
  • No backline - everything goes direct
  • LED lighting, and we're considering par cans
  • Being a church, the budget is (as always) quite minimal

Thanks in advance
Logged

TJ (Tom) Cornish

  • Hero Member
  • *****
  • Online Online
  • Posts: 4248
  • St. Paul, MN
Re: Permanent Install
« Reply #1 on: October 09, 2013, 01:27:49 pm »

A few non-complete thoughts and suggestions:

Thinking about this now is a good idea.  A sub panel for all audio and video power has some benefit if it shortens the distance between the grounds of the different receptacles in the system, but there's very little noise immunity benefit to separating lighting, unless there's a transformer in-between.  Modern equipment and non-garbage dimmers (and possibly getting rid of single-coil electric guitar pickups) should be all you need to be noise free.

My priorities would be in the following order:
1.  Getting enough power
2.  Getting enough power in the right places - amp room, dimmer room, etc.
3.  Getting modern equipment that doesn't have noise immunity problems
4.  Sourcing all audio and video power from the same panel
5.  Sourcing lighting from a different panel from audio/video

Even if you're going to use a portable PA system now, plan for an install.  Depending on the size of your auditorium, you may want to reserve a few 20A circuits for amplifiers all the way up to a dozen or more in the place your amplifiers will go in the future.

For lighting, LED fixtures for color wash really make a huge difference in usability and power consumption.  In my opinion, white front light is still better done with tungsten fixtures, which take a lot of power.  For larger systems, dimmers are usually done in a monolithic dimmer rack.  For smaller installations, a couple circuits feeding multiple locations of tree-mount or dimmer-bar units is likely more economical.

You can't feed standard receptacles from anything greater than a 20A breaker - multiple circuits is your solution.

Telling us a little more about your space, your plans, and your constraints will help get more relevant and specific advice.
Logged

Kevin Graf

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 298
Re: Permanent Install
« Reply #2 on: October 09, 2013, 07:39:03 pm »

Before you start,  spend some time and read the following papers:
They total about 145 pages, but it's time well spent.

"Power White Paper" from Middle Atlantic.com
http://www.middleatlantic.com/power.htm

The Bill Whitlock of Jensen Transformers Seminar paper
http://www.jensen-transformers.com/an/generic%20seminar.pdf

The Jim Brown of Audio Systems Group white paper
"Power and Grounding for Audio and Audio/Video Systems"
http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

Logged
Speedskater

Tom Young

  • Global Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 620
Re: Permanent Install
« Reply #3 on: October 10, 2013, 02:51:15 pm »

Kevin's reply contains VERY good sources for how to do this right.

I would add that while you do not use stage monitor wedges and backline now, what happens in the future is a question mark..... even if you think it isn't. You would be wise to place a few 15A-20A ckts around the platform and add a few in your amp rack or where amps would be racked if they are used in the future.

FWIW
Logged
Tom Young
Electroacoustic Design Services
Oxford CT
203-888-6217

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3342
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Permanent Install
« Reply #4 on: October 10, 2013, 10:56:39 pm »

Kevin's reply contains VERY good sources for how to do this right.

Agreed.... So while I'm teaching seminars in Texas this week (and not at my desk) I don't have a lot of time to thing about your questions this week. However, I would suggest that to future proof your system you add at least one "house power" connection. In the old days (before LED lights and Class-D power amps) I would have suggested camlocks and a 200-amp circuit breaker. However, I think it's time to revisit a trick I first used some 40 years ago in my misspent youth at the Old Mill Inn. A 50-amp/240-volt Range Outlet (NEMA 14-50) fed by a double-pole 50-amp circuit breaker in the service panel would allow most any medium size act to plug in their own power distro and run quite a large sound and lighting system. Unless you are doing major shows, then 100 or 200-amp camlocks seem like expensive overkill. But a 50-amp/240-volt range outlet located near the stage would give you a lot of future expansion options since that's 100 amperes of 120-volt power which is sufficient for a 10,000 watt PA system and a pretty large LED lighting system. I'll have to double check with my code monkeys, but this should be perfectly code compliant and WAY more legal than letting a visiting band hang some camlock pigtails out of your open circuit panel.

I would appreciate some input from the other sound pro's here. Does this seem like a reasonable distro power idea for a small/medium church or club, or is it too simple/crazy to work? Of course, really big productions need really big power from camlocks, but how much room do you have on stage for potential acts?
« Last Edit: October 11, 2013, 05:39:21 am by Mike Sokol »
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Tom Bourke

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1564
    • http://www.cwalv.com
Re: Permanent Install
« Reply #5 on: October 11, 2013, 01:31:32 am »

  • Do we leave the sub panel and run home runs to each element
  • Dedicated 60a service instead of sub panel?
  • Should we group PA, FOH, and Stage on one larger circuit (20a, 30a?)
That is not even CLOSE to enough power to have in reserve.  Admittedly that will cover most normal church productions it leaves you NO room to grow. Here are some reference points:
An Aqua2000 dry ice fogger for  that special Christmas, Rapture, wedding, other big production will eat 2 20A circuits on stage.
That same production may also have a couple of full size moving lights, that's another 20A circuit or two per pair of lights. 
A decent sized amp rack will need two or three legs of 20A to 30A.

Also when sizing an entertainment power system you need to plan for closer to 100% peak power use than a regular house.  During the climax your going to have every light full plus sound rocking.

With out knowing the size of your venue I would want to see a MINIMUM 100A to 200A single phase service for production with plenty of spare room in the breaker panel for expansion or small cams.

As soon as you want to add the option for flying truss it goes to 200A 3 phase minimum. The chain motors will most likely need 3 phase.

Contact a few of the local production companies to come and see your space.  Ask them what power they would need and expect to do a medium to large show in your space.  Then at least prep for that kind of power.  If they want 400A 3phase and you have no intention of ever going that big, at least get an appropriate sized conduit in place so you can pull a feed, put in a camlock disconnect and set a transformer with out breaking into cement to do it.

Edit: Forgot to add that the last theater power upgrade I was in charge of was a 600 seat high-school auditorium.  We had a 400A feed to the main dimming system plus 2 circuits on stage and 2 in the booth that was shared with the "scene shop."  I think we may have had a couple more available in the house.  It was a nightmare.  We would end up running a couple of dimmers in constant on mode to get power for any extras.

We added a 200A 3phase panel with dedicated transformer.  For circuits we added:
8 20A quad boxes near stage floor.
2 L21-20 circuits (3 phase) on 6 connectors in the ceiling for chain motors and breakout stringers for LED's.
7 20A circuits spread threw out the FOH lighting positions for movers and video projectors.
4 circuits in the booth for various needs.
a few more 20A circuits in the scene shop they desperately needed.

It may sound extravagant but ALL our power problems went away!  No more hum from the powered speakers on stage being on a different panel and transformer from the FOH console.  No more rolling ground loop waves in the projectors because now they were all on the same power.  Director wants 2 huge foggers? no problem, I made sure we had 2 locations with plenty of power up stage for foggers.  Flying stuff got much more safe since we could now use chain motors for the heavy lifting.

Something else to watch for if you DO get real power is other places may "need it."  I had the clout to keep them from putting a computer lab on our panel.  You may not be able to keep them from using your panel to also feed the concession stand with a pile of nesco rosters eating 100A.
« Last Edit: October 11, 2013, 01:57:40 am by Tom Bourke »
Logged
I have a mild form of Dyslexia that affects my ability to spell.  I do use spell checking to help but it does not always work.  My form of Dyslexia does not affect my reading.  Dyslexics of the world untie! <a href="http://www.cwalv.com" target="_blank">http://www.cwalv.com</a>

TJ (Tom) Cornish

  • Hero Member
  • *****
  • Online Online
  • Posts: 4248
  • St. Paul, MN
Re: Permanent Install
« Reply #6 on: October 11, 2013, 08:34:18 am »

Agreed.... So while I'm teaching seminars in Texas this week (and not at my desk) I don't have a lot of time to thing about your questions this week. However, I would suggest that to future proof your system you add at least one "house power" connection. In the old days (before LED lights and Class-D power amps) I would have suggested camlocks and a 200-amp circuit breaker. However, I think it's time to revisit a trick I first used some 40 years ago in my misspent youth at the Old Mill Inn. A 50-amp/240-volt Range Outlet (NEMA 14-50) fed by a double-pole 50-amp circuit breaker in the service panel would allow most any medium size act to plug in their own power distro and run quite a large sound and lighting system. Unless you are doing major shows, then 100 or 200-amp camlocks seem like expensive overkill. But a 50-amp/240-volt range outlet located near the stage would give you a lot of future expansion options since that's 100 amperes of 120-volt power which is sufficient for a 10,000 watt PA system and a pretty large LED lighting system. I'll have to double check with my code monkeys, but this should be perfectly code compliant and WAY more legal than letting a visiting band hang some camlock pigtails out of your open circuit panel.

I would appreciate some input from the other sound pro's here. Does this seem like a reasonable distro power idea for a small/medium church or club, or is it too simple/crazy to work? Of course, really big productions need really big power from camlocks, but how much room do you have on stage for potential acts?
Mike, in my opinion the 14-50 is a very reasonable choice - still a good chunk of power, and inexpensive components.  Somewhere on one of the forums a few folks mentioned that there were potentially regional restrictions on using a 14-50 for general use and that a CS connector would be more appropriate, but in my region 14-50's are fine, and as you mentioned, infinitely better than panel spelunking.

The other way to go would be a "built-in" distro -  4-6 20A circuits on or near stage that would allow for extra tree-pack dimmers, or whatever.  I believe this is better for the other 51 weeks a year that production isn't brought in - the church wouldn't have to dig out the portable distro just to plug in a couple lights.

I suppose someone with a big amp rack that has a rack pack inside might be loathe to un-patch their amps from the rack pack, meaning a 14-50 would still be desirable, but then it gets to a cost/benefit question, and just how often that would be a problem.
Logged

Jerome Malsack

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1322
Re: Permanent Install
« Reply #7 on: October 11, 2013, 08:52:32 am »

With some of the larger power amps for items like subs looking at 30 amp  should one consider having one or two 30 amp plugs installed in the amp and at the performance area??
Logged

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3342
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Permanent Install
« Reply #8 on: October 11, 2013, 09:50:28 am »

With some of the larger power amps for items like subs looking at 30 amp  should one consider having one or two 30 amp plugs installed in the amp and at the performance area??
I do have a pair of MacroTech amps at the school with 30-amp connectors so that's a reasonable idea if you regularly roll out the BIG AMPS for certain gigs. However, I really don't like the TT-30 30-amp/12-volt outlet format since it's easily confused with a 30-amp/240-volt dryer outlet. See my NoShockZone article at http://www.noshockzone.org/accidentally-plugging-into-240-volt-outlet/ Now I'm not suggesting you can accidentally plug a TT-30 plug into a an old NEMA 10-30 outlet, but I have dozens of emails from RV owners who paid an electrician to wire up a TT-30 outlet for their 120-volt camper, but found it was miswired with 240-volts since it looks a LOT like a dryer outlet. Of course, plugging your 120-volt RV into an outlet miswired with 240-volts will destroy all the electrical gear in seconds. I still think that every good sound tech should meter all outlets before plugging in any sound gear. 
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Luke Richison

  • Newbie
  • *
  • Offline Offline
  • Posts: 4
Re: Permanent Install
« Reply #9 on: October 14, 2013, 03:30:24 pm »

Thanks for all the replies. I really appreciate the advice and knowledge shared. Even though a lot of it seems like overkill for my needs, I enjoy learning the ideal / theoretical applications. I'd really like to learn more about where to place certain elements in the supply chain (sorry if this is detailed in the resources listed in the first reply - I'm still working through them). For example: 200A service >> conditioner / limiter (at FOH?) >> PA mains, or service directly to PA?

Kevin, thanks for those resources. I had stumbled across the Mid-Atlantic paper (probably from the resources section of this forum) but found it a little daunting. I will give it and the others a read. I really appreciate it!

Mike, I really like the idea of pulling that 50A line to the stage. Thanks for the tip!

TJ, thanks for the quick reply. Sorry I couldn't respond sooner. Here's some more specifics about our space and current setup:

  • Space (all measurements approximate)
    • 250 seats max
    • Wedge shaped, 115°
    • 2500 sqft
    • 12' drop ceiling
    • seating area (front of stage/PA to back wall)
      • 30 feet wide at stage, 85 feet wide at back wall
      • 40 feet deep
    • stage
      • 11 feet wide at back wall, 30 feet wide at front
      • 18.5 feet deep
      • We will use floor pockets to minimize cords and clutter
  • A/V equipment (with specs found in owner's manual)
    • 2 Mackie HDA's - power requirements: 100-120 VAC, 50-60Hz, 200W; AC Connector PowerCon A 20A, 250 VAC, Max input 800W
    • 1 Mackie HD1501 subwoofer - power requirements: 100-120 VAC, 50-60Hz, 300W; AC connector: 3-pin IEC 250 VAC, 15A male
    • Presonus StudioLive 24.4.2 - input voltage range: 90 to 240 VAC, power requirements: 100W
    • iMac
    • on stage equiment / instruments: no floor monitors or amps
    • Video: 1 projector, 2 60-inch monitors
  • lighting (not purchased yet)
    • Our church subscribes to "less is more" - we won't be doing anything too extravagant with lighting
    • House lighting (recessed can lighting) grouped in zones, dimmable
    • color wash on stage walls
    • front lights (white tungsten, as suggested by TJ)
    • This section of the budget would probably be the first to be postponed to a "phase 2"
    • We would rather spend the money to have the right power and audio setup, then buy proper lighting gear when more money is available, rather than scrimping on power & audio to make room in the budget for lighting

Thanks for all the advice.
Logged

Jonathan Johnson

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2961
  • Southwest Washington (state, not DC)
Re: Permanent Install
« Reply #10 on: October 15, 2013, 01:54:52 am »

Electrical codes require there be only a single service entrance -- the point where the utility lines enter the building -- for each structure. In a typical strip mall, you'll see a bank of meters and switches/breakers serving the individual suites with a single, common utility connection. (If you see multiple service entrances, there may be double firewalls between sections of the structure, which in code terms means they are considered separate buildings.) In your case, you're repurposing the entire structure, removing the "suites" and creating a large, single-occupancy space. That means you're probably planning to completely redo the electrical infrastructure.

You'll probably want to place the electrical service entrance closest to the greatest load. If you have kitchen facilities, it may be near the kitchen. Otherwise, it will probably be the stage. Either way, you'll probably end up with one or more subpanels throughout the building. In a large commercial installation, the main panel will be a bank of large (100A or greater) breakers feeding multiple subpanels.

I would recommend installing a subpanel at the stage. That's where most of the load in the sanctuary/auditorium will likely be, since you'll probably be placing the amps and dimmers near the stage. It's also where visiting acts will expect to find power to connect their distros.

For FOH, you can either do home run to the stage panel, or install a subpanel there. If you install a subpanel, feed it from the stage panel to reduce ground currents and other interference.

In order to get the best value for your money, involve these professionals, in this order, prior to putting a job out for bid or beginning construction:
  • A reputable acoustics engineer and audio system designer (since sound is the most important part of worship) before you even sketch a design
  • A licensed architect with experience in church design
  • A reputable lighting designer
  • A licensed structural engineer (to ensure the structure will support the hanging loads)
  • A licensed electrical engineer (to ensure adequate and safe power for all loads in the building)

Note that the subsequent engineering may require revising earlier engineering. The entire team needs to work together.
« Last Edit: October 15, 2013, 05:30:40 pm by Jonathan Johnson »
Logged
Stop confusing the issue with facts and logic!

Gary Creely

  • Newbie
  • *
  • Offline Offline
  • Posts: 29
Re: Permanent Install
« Reply #11 on: October 15, 2013, 08:47:52 am »

Electrical codes require there be only a single service entrance -- the point where the utility lines enter the building -- for each structure. In a typical strip mall, you'll see a bank of meters and switches/breakers serving the individual suites with a single, common utility connection. (If you see multiple service entrances, there may be double firewalls between sections of the structure, which in code terms means they are considered separate buildings.) In your case, you're repurposing the entire structure, removing the "suites" and creating a large, single-occupancy space. That means you're probably planning to completely redo the electrical infrastructure.

You'll probably want to place the electrical service entrance closest to the greatest load. If you have kitchen facilities, it may be near the kitchen. Otherwise, it will probably be the stage. Either way, you'll probably end up with one or more subpanels throughout the building. In a large commercial installation, the main panel will be a bank of large (100A or greater) breakers feeding multiple subpanels.

I would recommend installing a subpanel at the stage. That's where most of the load in the sanctuary/auditorium will likely be, since you'll probably be placing the amps and dimmers near the stage. It's also where visiting acts will expect to find power to connect their distros.

For FOH, you can either do home run to the stage panel, or install a subpanel there. If you install a subpanel, feed it from the stage panel to reduce ground loops and other interference.

In order to get the best value for your money, involve these professionals, in this order, prior to putting a job out for bid or beginning construction:
  • A reputable acoustics engineer and audio system designer (since sound is the most important part of worship) before you even sketch a design
  • A licensed architect with experience in church design
  • A reputable lighting designer
  • A licensed structural engineer (to ensure the structure will support the hanging loads)
  • A licensed electrical engineer (to ensure adequate and safe power for all loads in the building)

Note that the subsequent engineering may require revising earlier engineering. The entire team needs to work together.

I agree this is certainly the best way to go, however we are talking about a guy who has maybe 10k in gear and the aforementioned team would be well into the 6 figure range.

Luke,

It sounds to me like the budget for AVL is really low- too low. The entire system will likely need to be revisited down the road, but in the mean time I have a few suggestions that will be very helpful.

1. Get a good conduit plan and have it installed. Often in these projects you can slide that under the electrical budget rather than the AVL one.

2. Get an architectural dimmer! Do not put a ridiculous bank of rheostats on the wall.

Here is a suggestions (one of my favorites)  http://www.lightronics.com/architectural_wallmount_dimmers_ar602.html
About $2000

This is 6 20amp channels of dimming, made in the USA, rock solid, and I have used many of them. There are various remotes available, and this will control your house lighting. Besides architectural remotes you would then have control of the house lights via your DMX lighting board.


Jonathan's suggestion is the right way to go, and realize even my suggestions fall pretty short of being adequate, but they will help to have some of the infrastructure that is difficult to do after the fact.
Logged

Jonathan Johnson

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2961
  • Southwest Washington (state, not DC)
Re: Permanent Install
« Reply #12 on: October 15, 2013, 11:41:43 am »

I agree this is certainly the best way to go, however we are talking about a guy who has maybe 10k in gear and the aforementioned team would be well into the 6 figure range.

You're right, of course. Sometimes budgets mean you can't afford a highly qualified team of experts. Nevertheless, the same principles still apply: the architecture needs to be driven by the physics of sound propagation throughout a space; proper lighting is important and can't be determined until the design is roughed out; you need to know what loads you'll be suspending in order to design an adequate structure; and proper infrastructure to power everything can't be determined until you know what you're powering.
Logged
Stop confusing the issue with facts and logic!

Scott Wagner

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1020
  • Richmond, VA
Re: Permanent Install
« Reply #13 on: October 15, 2013, 11:57:33 am »

You're right, of course. Sometimes budgets mean you can't afford a highly qualified team of experts. Nevertheless, the same principles still apply: the architecture needs to be driven by the physics of sound propagation throughout a space; proper lighting is important and can't be determined until the design is roughed out; you need to know what loads you'll be suspending in order to design an adequate structure; and proper infrastructure to power everything can't be determined until you know what you're powering.
The other side to this coin is that hiring the proper team is usually cheaper than trying to fix whatever mess you've made by not hiring them.  "Fixes" after the fact are always more expensive (if they're even possible).  All of these areas of study are complicated.  Add them together, and they get exponentially more so.  The chances of unexperienced people getting all of this correct is almost zero.
Logged
Scott Wagner
Big Nickel Audio

Tom Bourke

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1564
    • http://www.cwalv.com
Re: Permanent Install
« Reply #14 on: October 15, 2013, 12:00:16 pm »

For example: 200A service >> conditioner / limiter (at FOH?) >> PA mains, or service directly to PA?
I think you may be misunderstanding the relationships between AV equipment and power distribution.  That is OK because you really should not have to worry about it.  You need to come up with what equipment your using and where.  What potential upgrades and alternate uses may happen.  This is pie in the sky time.  No one ever regrets having too many outlets and circuits!

When I did the theater system described above I did not design the actual system.  I had a meeting with the electrical contractor and described my needs with a walk threw.  Granted I could talk on their level because I do have an electrical back ground but it was not necessary.  The basic meeting was describing our problems and goals. "We needed more power and for it to all be on the same transformer/sub-panel.  We need 3 phase available for chain motors."  We also went into some detail on  proper grounding for audio systems but they were already on the ball and that was more of side conversation.  Then we did a walk threw and I pointed out where I wanted outlets and circuits.  We discussed potential loads for each location.  I let them decide how big of transformer and panel to put in. I did request we have plenty of empty breaker positions for future expansion.  Together we decided on a location for the panel and transformer based on cost and convenience.  Keep the transformer out of the main space, they buzz or hum!  I think total cost was around $25k.  This included a transformer and a tie in to a very funky 600V building distribution system in a tunnel 3 stories down.

In your case I really hope the electrical is being done by a competent and licensed commercial electrical firm.  This kind of system design is nothing like a house or even an apartment building.
Logged
I have a mild form of Dyslexia that affects my ability to spell.  I do use spell checking to help but it does not always work.  My form of Dyslexia does not affect my reading.  Dyslexics of the world untie! <a href="http://www.cwalv.com" target="_blank">http://www.cwalv.com</a>

David J. Thomas

  • Newbie
  • *
  • Offline Offline
  • Posts: 20
Re: Permanent Install
« Reply #15 on: October 16, 2013, 10:58:38 am »

As electronics developed, the common return paths of various circuits were also referred to as
“ground,” regardless of whether or not they were eventually connected to earth. In addition, a
single ground circuit most often serves, either intentionally or accidentally, more than one
purpose. Thus, the very meaning of the term ground has become vague, ambiguous, and often
quite fanciful. Some engineers have a strong urge to reduce these unwanted voltage differences
by “shorting them out” with massive conductors — the results are most often disappointing. [8]
Other engineers think that system noise can be improved experimentally by simply finding a
“better” or “quieter” ground. Many indulge in wishful thinking that noise currents can somehow be
skillfully directed to an earth ground, where they will disappear forever! [9] Here are some
common myths about grounding:
Logged

Kevin Graf

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 298
Re: Permanent Install
« Reply #16 on: October 16, 2013, 11:29:28 am »

David, your link to the 'grounding myths' didn't stick,  but here are some from Henry W. Ott's new book:

3.1.7  Grounding  Myths

More myths exist relating to the field of grounding than any other area of electrical engineering.  The more common of these are as follows:

1.   The earth is a low-impedance path for ground current.  False,  the impedance of the earth is orders of magnitude greater than the impedance of a copper conductor.
2.   The earth is an equipotential.  False,  this is clearly not true by the result of (1 above).
3.   The impedance of a conductor is determined by its resistance.  False,  what happened to the concept of inductive reactance?
4.   To operate with low noise,  a circuit or system must be connected to an earth ground.  False,  because airplanes, satellites, cars and battery powered laptop computers all operate fine without a ground connection.  As a mater of fact,  an earth ground is more likely to be the cause of noise problem.  More electronic system noise problems are resolved by removing (or isolating) a circuit from earth ground that by connecting it to earth ground.
5.   To reduce noise,  an electronic system should be connected to a separate “quiet ground” by using a separate, isolated ground rod.  False,  in addition to being untrue,  this approach is dangerous and violates the requirements of the NEC (electrical code/rules).
6.   An earth ground is unidirectional,  with current only flowing into the ground.  False,  because current must flow in loops,  any current that flows into  the ground must also flow out of the ground somewhere else.
7.   An isolated AC power receptacle is not grounded.  False,  the term “isolated” refers only to the method by which a receptacle is grounded,  not if it is grounded.
8.   A system designer can name ground conductors by the type of the current that they should carry (i.e., signal, power, lightning, digital, analog, quiet, noisy, etc.),  and the electrons will comply and only flow in the appropriately designated conductors.  Obviously false.

Henry W. Ott
« Last Edit: October 16, 2013, 11:32:02 am by Kevin Graf »
Logged
Speedskater

Jonathan Johnson

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2961
  • Southwest Washington (state, not DC)
Re: Permanent Install
« Reply #17 on: October 16, 2013, 02:49:46 pm »

The earth is a low-impedance path for ground current.  False,  the impedance of the earth is orders of magnitude greater than the impedance of a copper conductor.

How I learned this:

First, some background. I grew up on a farm. An electric fence charger has one lead connected to the fence wire which is supported on insulators, and the other lead is connected to a ground rod. The fence charger provides a high voltage (typically 3kV-7kV), high impedance pulsed direct current energy energy source to the fence wire. An animal coming in contact with the electric wire completes the circuit between the wire and earth ground, and receives a nasty shock. Because of the high impedance of the charger, the amperage is too low to cause harm.

Anyway, one day during a rather dry spell, I happened to touch the ground rod and received a shock. Because the soil was dry, the connection between the rod and the soil was high resistance. My body provided an alternate, complementary current path between earth ground and the "ground" terminal of the charger.

If the earth were a low-impedance current path, there might be a lot less lightning and nearby lightning strikes could be less deadly due to lower "step potential."

(By the way, when an electric fence has a short circuit, the arc generates an RF signal. I've used a de-tuned AM radio to detect and find faults in electric fences. As you approach the fault, the pulse becomes louder in the radio.)
Logged
Stop confusing the issue with facts and logic!
Pages: 1 2 [All]   Go Up
 


Page created in 0.112 seconds with 21 queries.