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#163374 - 05/07/07 11:37 AM Helpful how-to?  
Jim M  Offline
Joined: Aug 2001
Posts: 457
Chestertown, MD, USA
Think anyone checked this before it was posted? Maybe they were trying to boost sales of those slow moving isolated ground receptacles.

Work Gear for Electricians and the Trades

#163375 - 05/07/07 11:48 AM Re: Helpful how-to? [Re: Jim M]  
hbiss  Offline
Joined: Dec 2003
Posts: 886
Hawthorne, NY USA
Sure, those instructions fit all circumstances. Professionals can't even get IGs right what makes them think a homeowner will? Why don't they just say that if you have a dedicated circuit and a regular receptacle fed with 2 wire NM you already HAVE an IG?


#163385 - 05/07/07 02:23 PM Re: Helpful how-to? [Re: hbiss]  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,124
IG is a big bunch of snake oil anyway. IBM removed this requirement/recomendation from their physical planning guide 25 years ago although there are still data center managers and "tech support" guys who insist on it.
In some very "noisy" industrial installations it may have some value to separate the EGC from the building steel down stream of the MBJ but in most places it is simply wasting your money.

BTW how many of you would say a residence has "conditions of maintenance and supervision ensure that only qualified persons service the installation" per 250.119(B)?

Greg Fretwell

#163435 - 05/08/07 02:24 AM Re: Helpful how-to? [Re: gfretwell]  
noderaser  Offline
Joined: Mar 2007
Posts: 404
Portland, Oregon, United State...
They still install "isolated ground" outlets in theatres, for sound equipment... Prevents the buzzing caused by dimmers and shifting/unbalanced phase loads.

#163438 - 05/08/07 06:55 AM Re: Helpful how-to? [Re: noderaser]  
SteveFehr  Offline
Joined: Mar 2005
Posts: 1,213
Chesapeake, VA
You're all forgetting the audiophile market, where IG and gold-plated bus bars all make music sound better!

#163449 - 05/08/07 11:45 AM Re: Helpful how-to? [Re: SteveFehr]  
Luketrician  Offline
Joined: Jul 2006
Posts: 272
Sale Creek, TN USA
That was pretty good Steve, I forgot about that one. laugh

Luke Clarke
Electrical Planner for TVA.

#163452 - 05/08/07 12:52 PM Re: Helpful how-to? [Re: Luketrician]  
ghost307  Offline
Joined: May 2005
Posts: 916
Chicago Illinois USA
I get folks from the POS companies (get your minds out of the means "Point Of Sale" in this context) who tell me that their electronic cash register absolutely HAS to have an isolated ground because it's susceptible to electronic disturbances and electromagnetic fields.

The real kicker is that I know of one in downtown Chicago that is working fine on a regular 20A circuit...despite being direct above one of the double-ended 5kV 2500kVA basement substation transformers.

Susceptible my butt...they just have this silly notion that their dinky little PC has the same power needs as an old fashioned mainframe computer with an air conditioner room and a raised floor.


#163488 - 05/08/07 11:35 PM Re: Helpful how-to? [Re: ghost307]  
noderaser  Offline
Joined: Mar 2007
Posts: 404
Portland, Oregon, United State...
Well, I can speak from experience that having IG circuits on sound equipment is helpful in theatre. You can clearly hear the hum of dimmers in sound and communications equipment, where the difference in loads between phases could be as much as 50A.

As far as the gold-plated connectors and stuff goes, it's all a gimmick to get more money out of basic cabling.

#163492 - 05/09/07 12:49 AM Re: Helpful how-to? [Re: Jim M]  
LK  Offline
Joined: Jan 2003
Posts: 1,429
New Jersey
The problem with isolated ground receptacles, is they are usually installed wrong, we found most of them din't have the isolated ground run back to unity ground, most of them were tied to local ground at the nearest panel.
Noise from other electronic equipment is best supressed with line filters.

#163540 - 05/10/07 12:21 AM Re: Helpful how-to? [Re: LK]  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,124
Cash registers or any other interconnected systems, get blown up because you don't have enough bonding, not because you have ground loops.
In one particular building (actually 3 store fronts opened up to be one) we ended up actually pulling a bonding wire along with the LAN cable to positively bond all the frames together. That is the definition of a ground loop but it was what it took to stop us from replacing system boards and LAN cards a couple times a week in the summer.

Greg Fretwell

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