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#84177 - 03/14/03 10:24 AM Isolated Grounds  
mvrandazzo  Offline
Member
Joined: May 2002
Posts: 110
I am planning on running isolated ground circuits for a new church audio system. Does the isolated ground circuits need to be in a separate sub-panel or can I run the circuits into a panel for general circuits? Of course taking into consideration keeping the isolated ground conductor isolated back to the service location and connecting it at the bonding point. Is it preferable to install a sub panel? I'm sure there are plans at the church for adding more circuits for computers and the like. Thanks for your oppinions.
Blessings. Mark


2017 / 2014 NEC & Related Books and Study Guides

#84178 - 03/14/03 12:29 PM Re: Isolated Grounds  
ccdave  Offline
Member
Joined: Jan 2003
Posts: 59
culver city,calif. usa
if the system is real touchy, i used to isolate the conduit bond also by using a pvc coupling/connector.


#84179 - 03/14/03 12:39 PM Re: Isolated Grounds  
steve66  Offline
Member
Joined: Mar 2003
Posts: 25
How does isolating the conduit help? And do you mean that you left the conduit ungrounded, or did you run a bonding jumper back to the service panel? Isn't it a violation to leave the metal conduit and boxes ungrounded?


#84180 - 03/14/03 01:06 PM Re: Isolated Grounds  
mvrandazzo  Offline
Member
Joined: May 2002
Posts: 110
Good point! If it is touchy enough to isolate the conduit then should I not run any circuits that have isolated grounds in the same raceway as general circuits? Of course being sure to have a separte ground wire for the isolated outlets only. Just asking.
Blessings, Mark


#84181 - 03/14/03 02:39 PM Re: Isolated Grounds  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
If one gets "creative" with raceway isolation, then two equipment-ground conductors are needed—one for the box and one for the receptacle.

These O-Z fittings seem to have been around decades before the "isolated ground" concept went mainstream, and they are specifically intended for conduit applications...no PVC-plumbing kludges here! http://www.o-zgedney.com/PDF/DA1thru6.pdf page 6 for ICC-series couplings.

I think the whole I-G voodoo noise-suppression thing is way overrated. I-G stuff will not fix poor-workmanship signal-ground loops, but I think some expect it to.


#84182 - 03/14/03 08:16 PM Re: Isolated Grounds  
WebSparky  Offline
Member
Joined: Feb 2003
Posts: 138
Cleveland, Ohio
I agree with Bjarney. Most of the times a isolated ground system is specified, it is designed eroniously and has little effect.

Past experiences with "touchy" equipment has always resulted in installing an after market surge protector and line filters that simply plug in before the equipment.

Check with the supplier of your equipment for recommendations.

IMO

Hope this helps.
Dave


Dave

#84183 - 03/14/03 11:57 PM Re: Isolated Grounds  
Scott35  Offline

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Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
I also agree with Bjarney - all the IG work in the world will not help if some clown has set things up already, which create ground loops!

Along with an attempt to reduce the possible noise being brought in from utilizing the common equipment grounding schemes (transmission of noise via conduit systems), the complete IG design criteria should focus around TVSS devices, Isolating equipment with different characteristics, and to attempt to eliminate the possibilities of ground loop currents.

For simple situations, (where the connected equipment is not crucial), adding the IG bus in an existing subpanel will work fine. Be sure to derive the IG "Feeder" from the point of system ground bonding (where the grounded conductor for the system of use, is bonded to the grounding electrode system).
The "IG Feeder" may be as small as #12 cu (if no larger than 20 amp OCPD on IG circuits), or could be #6 cu - which is normally used on my designs and projects.

After this, things become a little more in-depth, but not to the point of flat-out sillyness! (don't get me started on some of the crazy crackpot IG "Interpretations I have seen from some quack EEs!!!).

Feel free to ask more Q's, or contact me directly via E-mail. This IG stuff deserves a much more detailed section in the Technical Reference Area.

Scott35 S.E.T.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#84184 - 03/14/03 11:58 PM Re: Isolated Grounds  
zstarch  Offline
Junior Member
Joined: Mar 2003
Posts: 3
Charlotte, NC. USA
What else is on the panel? If there are motors or other heavy loads,or noisy loads like lighting ballasts, I would try to put in a separate panel. Noise can be caused by voltage spikes on the line as well as grounding.
Be sure all your audio wiring is BALANCED (two wires under a shield. Connect all shields (except mike cables) at one end only to avoid loops.
John (audio engineer for 32 years)


#84185 - 03/15/03 08:53 AM Re: Isolated Grounds  
mvrandazzo  Offline
Member
Joined: May 2002
Posts: 110
Thanks for all the responses. I understand the possibilities of over concern in installing IG's. This is a new building and I am overseeing the electrical installation. I am also the sound tech. For this reason I feel the need for a "clean install". The cost would be minimal to avoid the posibilities of complicaitons down the road. As for the audio, our pastor has made it clear that we will try to do it on our own. I know this is not recommended, but that is a conversation for another forum. Thanks, John. The audio would be all balanced lines. We installed 2 sets of 2" GRC in the floor for the runs.

The only circuits on the subpanel would be lighting, plugs and maybe the feed to a baptismal heater/motor. All HVAC would have its' own subpanel. Right now I am working with a local lighting design firm to come up with a layout for the sanctuary. No HID's, no florecents, no hanging fixtures. The pastor only wants recessed downlights.

Thanks for the replies.
Blessings, Mark


#84186 - 03/15/03 08:59 AM Re: Isolated Grounds  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I too agree with Barney, we work for many well known dot coms (some now dot gones) and tech manufactures.

Some use IG in the Data centers and some do not it seems to make no difference.

Power Quality seems to be the important thing


Bob Badger
Construction & Maintenance Electrician
Massachusetts


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