Replacing a 3 prong receptacle with a 4 prong one


  #1  
Old 11-16-02, 12:56 PM
moechris
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Question Replacing a 3 prong receptacle with a 4 prong one

Hello,

In the process of replacing a 13 year old electric range (in a 13 year old house) with a dual fuel range, I noticed that the new range has a 4 prong plug. The old range had a three prong (and of course a 3 prong receptacle). I think it is a foregone conclusion that I need to replace the receptacle.

I would appreciate any help anyone has to offer.

Thanks,

Moe
 
  #2  
Old 11-16-02, 01:23 PM
J
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No, you may NOT replace the receptacle, unless you are prepared to replace the entire cable from the kitchen to the main panel.

Look carefully at your new range's installation instructions. They will certainly tell you what to do if you only have a three-wire receptacle. All range instructions give two sets of electrical installation instructions -- one for 3-wire service and one for 4-wire service. You will need to go back to an appliance or home improvment store and buy a 3-wire range cord.
 
  #3  
Old 11-18-02, 10:36 AM
moechris
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Thanks John

You could have responded with four letters; RTFM. Thanks for not doing so . You are right, the instruction for dealing with my situation are in the installation manual which, obviously, I had not read before posting. It is a reflection of my dependence on this sight and good advice I have gotten in the past.

Thanks, again.
 
  #4  
Old 11-18-02, 11:36 AM
P
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John-if the existing branch-circuit cable contains 3 branch-circuit conductors and a Equiptment Grounding Conductor why can't a 4-prong receptacle be connected? I'm presuming the Ground prong on the cord-plug connects to the Ground slot in the receptacle which is connected to the EGC on the cable. A residential installation 13 yrs. old suggests either Non-metallic cable or Armored cable as the wiring method.Each wiring method has an EGC.--Cheers, PATTBAA
 
  #5  
Old 11-18-02, 11:47 AM
J
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PATTBAA, you are theoretically correct. However, I've never seen a three-hole recepacle used when four wires were present in the box. So I just assume that there are only three wires in the box. It's a good assumption almost all the time.
 
  #6  
Old 11-18-02, 01:24 PM
winkleal
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John,

I recently replaced a three prong dryer outlet w/ a four prong in a house built in 1974. The electrician ran 10/3 w/G but did not connect the ground to anything in the receptacle box. This house has been in the same family the whole time, so I know it is the original wire. All I had to do was make sure the ground wire was connected correctly in the panel and it was. Now I have the added safety of a four wire 220 outlet. I guess that thinking at the time was that 3 prong was the way to go. Just my 2 cents on the subject.


Tony
 
  #7  
Old 11-18-02, 05:01 PM
J
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Thanks winkleal. Now at least I've heard of such a thing. Guess the moral of the story is that there is no harm is looking in the receptacle box to see if you have three insulated conductors plus a grounding wire. If so, you can make the installation safer by replacing the receptacle with a 4-hole receptacle and using the 4-wire instructions. But if you don't have all four wires, leave the receptacle alone and use the 3-wire instructions.
 
  #8  
Old 11-19-02, 07:27 AM
moechris
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Question Follow-up question

Well, I looked in the receptacle box and found three hefty insulated wires and a grounding wire that is "attached" to the box itself. All three insulated wires are of same color. Keeping in mind that I am not an electrician at all but do not consider myself stupid, can someone help me with the installation of a four hole receptacle.

Thanks,

Moe
 
  #9  
Old 11-19-02, 07:51 AM
HBB
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Is the receptacle box metal?

Does the "grounding" wire connected to the box continue back to the panel, or is it simply attached to the box and stops there?

Can you tell if the heavy cables are contained in flexible (or rigid) metal conduit, which would be connected (making contact) to the box?

Do the instructions clearly show you diagrams for the two wiring situations -- three-wire and four-wire?

Do the instructions say anything about removing or adding a jumper wire from the neutral to the appliance frame in either or both of those scenarios?
 
  #10  
Old 11-19-02, 08:04 AM
moechris
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Hello HBB,

The receptacle box is metal.

The grounding wire is terminated at the metal receptacle box. I assume that it comes from the panel.

The best I can figure, the three hefty cables are not contained in any conduit. They enter the box along with the braided grounding cable "loose." If the answer to this question is critical, I can scrape off the drywall around the box to get a definitive answer.

Thanks,

Moe
 
  #11  
Old 11-19-02, 08:22 AM
HBB
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Okay, I assume that grounding wire is bare and it enters the box WITH the other cables.

Hopefully, you haven't taken the three-wire receptacle loose yet. When you do, you'll need to mark, tape or somehow be able to differentiate between the two hot wires and the heavy neutral wire when you install the new four-wire receptacle.

You didn't answer the question about jumpers in the instructions for the new range.

That's important and we need to know the situation on it.

And you didn't say if the instructions offer diagrams for both scenarios.
 
  #12  
Old 11-19-02, 08:33 AM
moechris
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Premature post

I did not answer all of your questions. Sorry.

With the four wire, there is nothing to do as the range is ready to be plugged in.

For the three wire, yes it does have instructions regarding attaching one of the terminals (i think that is what it is called) to the appliance frame using a metal piece provided.
 
  #13  
Old 11-19-02, 08:45 AM
HBB
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Okay. It sounds as if you have everything required coming into the box to simply change the 3-wire receptacle to a 4-wire and plug in the range.

You'll need to buy a 4-wire range receptacle.

The critical fourth wire discussed all through this post is that bare copper grounding wire.

I assume it's size is 10 AWG and it's attached to the box with a screw, possibly stained green.

If so, you'll need to obtain a length of that same wire from a store, attach it along with the wire coming in under the screw and connect it to the grounding terminal on the new 4-wire receptacle.

What you're doing here is creating a pigtail from the grounding wire/screw in the box to the grounding terminal on the receptacle.

You may be able to obtain an already made-up green-colored, insulated grounding pigtail at the store.

You still didn't say if those range instructions show you any diagrams.

And, obviously I hope, you've definitely got the power off on that circuit.
 
  #14  
Old 11-19-02, 08:50 AM
HBB
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BTW: Do you have any way to test voltage in a circuit or at a terminal?

If not, you should at least buy one of those $2 or $3 neon light voltage checkers.

No one should EVER attempt any kind of wiring work without access to a voltage tester.

It's always possible to flip the wrong breaker, think the power to a circuit is off, then get knocked across the room because you flipped the wrong breaker.
 
  #15  
Old 11-19-02, 11:56 AM
HBB
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I finally found some boilerplate I made up a while back to describe to anyone wanting to know the difference between 3-wire and 4-wire range receptacles:

3-Wire vs. 4-Wire Range Receptacles
===================================

In General:
-----------

Ranges operate on both 240- and 120-volts. They require two hot wires and a neutral wire. When the range is operating at 240v both hot wires are conducting power. When a part of it is operating at 120v, one of the hot wires is conducting 120v and the neutral is a return wire, same as in any 2-wire hot/white-return receptacle in the house. These two scenarios may occur simultaneously.

In the event of an electrical short somewhere in the appliance, the appliance case can become energized electrically. If you touch it, you can receive a shock. To prevent this, the case is grounded so that this errant current has a low-resistance path (one better than you) back to the transformer at the electric pole rather than going through you. How this grounding scheme is arranged creates the difference between 3-wire and 4-wire systems.

3-Wire
------

It was previously believed by safety people that it was sufficient simply to ground the case to the neutral terminal with a jumper strap.

Therefore, in this system you'd have two hot hot wires, a neutral wire and a jumper from the neutral terminal on the appliance to the appliance case. In the event of a short, the errant electricity would travel back to the transformer at the pole via the neutral wire.

4-Wire
------

Howevever, attitudes changed and it was determined that that wasn't a sufficient grounding system.

We now have a fourth wire in the system -- a dedicated grounding conductor with its own terminal on the appliance terminal block. This terminal is connected to the case and supplies the same function as the neutral/case grounding jumper in the 3-wire system. In the 4-wire system it's simply dedicated to nothing except grounding.

This fourth wire, the grounding conductor, carries no current, except in the event of a short in the appliance's wiring. And, of course, it continues back to the grounding busbar in the panel, which may or may not be separate from the neutral busbar, depending upon whether it's a main or a sub-panel. In a sub-panel, where the grounding and neutral busbars must be separate, it MUST be connected to the grounding busbar, not the neutral.

Hope this helps.
 

Last edited by HBB; 11-19-02 at 12:15 PM.
  #16  
Old 11-19-02, 12:21 PM
moechris
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Thanks for the education

Appreciate all the information. I feel very comfortable with the task at hand and any apprehension i might had had, disappeared with your last post as it clarified some confusion on my part.

Again, thanks.
 
  #17  
Old 11-19-02, 12:33 PM
HBB
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Great. Glad to help.

Just be sure you make all connections TIGHT !!!.

That's critical and I can't emphasize it enough.
 
  #18  
Old 11-22-02, 11:11 AM
moechris
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Thumbs up One last question

Hi HBB,

I installed the 4-wire range receptacle. One last question I have is regarding the need for a pigtail from the metal box (where the grounding wire is screwed to) to the grounding terminal. I say this because I noticed a brass strip that comes out of the grounding terminal and then runs across the metal plate that holds the receptacle and gets screwed on to the metal box. That says (to me) that the connection a pigtail would provide already is there.

Am I right or am missing the boat altogether.

BTW, I am not trying to be cheap here as I already have the copper wire for the pigtail and am sure will be able to stuff it into the already stuffed box.

Thank you all very much, specially, HBB.

Moe
 
  #19  
Old 11-22-02, 02:05 PM
HBB
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Well, if you're saying what I think you're saying, here's the continuity of the grounding wire:

Case (appliance frame) to case grounding terminal through grounding wire in appliance cord and its grounding prong to grounding hole in receptacle, whose terminal must be connected to the grounding wire all the way back to the ground/neutral busbar of the panel.

Therefore, yes, the grounding wire connected to the screw in the metal outlet box must be pigtailed to the grounding screw of the receptacle.

It could be taken loose from the screw in the box and connected directly to the receptacle grounding screw, but then the grounding would not include the metal box -- hence the pigtail.
 
 

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