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#128395 - 02/23/03 06:33 AM Grounding a 3 prong Range/Dryer Outlet?
AeroSKI5150 Offline
Junior Member

Registered: 02/23/03
Posts: 4
Loc: 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 09:50 AM Re: Grounding a 3 prong Range/Dryer Outlet?
Theelectrikid Offline
Member

Registered: 04/30/04
Posts: 854
Loc: 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?

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#128397 - 01/21/07 03:26 AM Re: Grounding a 3 prong Range/Dryer Outlet?
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: 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

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#128398 - 01/24/07 07:09 PM Re: Grounding a 3 prong Range/Dryer Outlet?
SteveFehr Offline
Member

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
GFCI would make it safe.

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#128399 - 01/26/07 12:55 PM Re: Grounding a 3 prong Range/Dryer Outlet?
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: 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.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#128400 - 01/27/07 05:26 AM Re: Grounding a 3 prong Range/Dryer Outlet?
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: 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.

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#128401 - 01/27/07 05:58 AM Re: Grounding a 3 prong Range/Dryer Outlet?
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: 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.

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.

Roger

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#128402 - 01/27/07 07:02 AM Re: Grounding a 3 prong Range/Dryer Outlet?
Theelectrikid Offline
Member

Registered: 04/30/04
Posts: 854
Loc: Levittown, PA
Bob, I wanted to see out of curiosity what the answer/solution would be.
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#128403 - 01/27/07 07:59 AM Re: Grounding a 3 prong Range/Dryer Outlet?
SteveFehr Offline
Member

Registered: 03/19/05
Posts: 1192
Loc: 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)

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#128404 - 01/27/07 09:21 AM Re: Grounding a 3 prong Range/Dryer Outlet?
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: 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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