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#128395 - 02/23/03 10:33 AM Grounding a 3 prong Range/Dryer Outlet?  
AeroSKI5150  Offline
Junior Member
Joined: Feb 2003
Posts: 4
Boston, MA
Question for those who work on these situations professionally... I run sound and lights for band and commonly work in clubs where the only quality power available is an older style 30A to 50A "range" or "dryer" style outlet with 2 hots and a neutral. I have used some "distros" built by others where they split each hot through a 20A breaker to an Edison quad box. The grounds are then simply "tied off" inside the distro box, without any real ground connection. Interestingly, the typical outlet tester shows this combo as valid but I wonder about the safety! Would it be better to bond the Edison outlet grounds to the Neutral line, as I think was done with appliances until the code changed to the newer 4-prong outlets? Or, should I make my own ground connection to available cold water pipe, etc.. ?? None of this optimal, but looking for the safest most logical thing to do for temporary hookups... thanks!


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#128396 - 01/20/07 01:50 PM Re: Grounding a 3 prong Range/Dryer Outlet?  
Theelectrikid  Offline
Member
Joined: Apr 2004
Posts: 810
Levittown, PA
Hmm, I don't have a reply for this post, but I find it interesting enough to bump up.

Ian A.


Is there anyone on board who knows how to fly a plane?

#128397 - 01/21/07 07:26 AM Re: Grounding a 3 prong Range/Dryer Outlet?  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Ian the post is four years old, I doubt that the poster is still out there.

That said the answer is simple, they can not legally power a 120/240 volt portable distribution panel from a 3 wire receptacle.

They need a 4 wire receptacle with two hots, neutral and ground.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#128398 - 01/24/07 11:09 PM Re: Grounding a 3 prong Range/Dryer Outlet?  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,198
Chesapeake, VA
GFCI would make it safe.


#128399 - 01/26/07 04:55 PM Re: Grounding a 3 prong Range/Dryer Outlet?  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
A functional GFCI may make it safe.

I point that out as GFCIs have a very high faliure rate. (OR they had, I am not sure how they are doing now)

However it will not make it code compliant.

For what it's worth protecting a Feeder with a GFCI is not a great design.

The cumulative leakage current of all the branch circuits will likely lead to nuisance tripping of the feeder.

And having a feeder nuisance tripping is much more than a nuisance. [Linked Image]


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#128400 - 01/27/07 09:26 AM Re: Grounding a 3 prong Range/Dryer Outlet?  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Quote
The grounds are then simply "tied off" inside the distro box, without any real ground connection. Interestingly, the typical outlet tester shows this combo as valid but I wonder about the safety!


If the tester is just one of the types with three neons connected across each permutation of the wires, this wouldn't be entirely unexpected. Neons draw only a tiny current, so it's likely the ones tied to the "floating" ground could have a sufficiently low-impedance path to glow via either capacitive coupling or leakage through the various equipment connected to the distro board.


#128401 - 01/27/07 09:58 AM Re: Grounding a 3 prong Range/Dryer Outlet?  
Roger  Offline
Member
Joined: May 2002
Posts: 1,716
N.C.
Quote
Ian the post is four years old, I doubt that the poster is still out there.


I hate to think poor AeroSKI5150 had been checking in everyday to see if his post had been addressed. [Linked Image]

I could see him telling the band "no, we will have to do acoustic sets with out lights again this week, I'm still waiting for some advice, it should be any day now. [Linked Image] [Linked Image]

Roger


#128402 - 01/27/07 11:02 AM Re: Grounding a 3 prong Range/Dryer Outlet?  
Theelectrikid  Offline
Member
Joined: Apr 2004
Posts: 810
Levittown, PA
Bob, I wanted to see out of curiosity what the answer/solution would be.


Is there anyone on board who knows how to fly a plane?

#128403 - 01/27/07 11:59 AM Re: Grounding a 3 prong Range/Dryer Outlet?  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,198
Chesapeake, VA
I have a similar question- when backfeeding a portable generator into a 3-prong range/dryer outlet, should the generator chassis be grounded to the neutral or just left to float?

(ducks)


#128404 - 01/27/07 01:21 PM Re: Grounding a 3 prong Range/Dryer Outlet?  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Quote
For what it's worth protecting a Feeder with a GFCI is not a great design.

The cumulative leakage current of all the branch circuits will likely lead to nuisance tripping of the feeder.


And this is a problem in Britain where an RCD (GFI) can protect an entire distribution panel or an entire installation, even though the trip current is 30mA rather than 4 to 6mA.


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