Ground for Wall Oven

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  #1  
Old 08-17-07, 10:30 AM
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Ground for Wall Oven

I'm replacing my wall oven and just discovered the old wiring doesn't have a ground. Whoever installed the original oven connected the oven ground wire to the neutral (white) supply wire!

This is a 30A line with #10 (black, red, white). For the new oven, can I run a ground to a nearby cold water pipe?
 
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  #2  
Old 08-17-07, 11:34 AM
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No you cannot just run a line to the water pipe.

Your oven should have instructions on how to wire it into a 3 wire setup.
 
  #3  
Old 08-17-07, 12:18 PM
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> Whoever installed the original oven connected the oven ground wire to
> the neutral (white) supply wire!

This is legal for existing (pre-1996) electric range/oven and dryer wiring. Follow the oven manufacturer's instructions for a 3-wire installation. If the manufacturer does not allow connection to a 3-wire ungrounded source, then you'll need to install a new 4-wire circuit for the oven. Most manufacturers allow 3-wire, but you may need to call their 1-800 number if it's not printed in the manual.

> can I run a ground to a nearby cold water pipe?

No.
 
  #4  
Old 08-18-07, 12:01 PM
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Yes it is pre-1996. I was surprised it was wired like that, but I did look back at the installation guide for the old oven and sure enough, the instructions for a 3-wire installation do say to connect the appliance ground to the white.

Now I'm just trying to understand the concept of grounding better. If a ground is connected to the white, as in the old oven, it's really not a legitimate ground, is it?? If not, why connect it at all? Or is it simply for protection against any failure in the neutral?
 
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Old 08-18-07, 12:32 PM
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240 volts does not require a neutral. So for pre 1996 installations you have two hot wires and a grounding wire. In newer installations there is an additional grounding wire to bond the frame of the appliance to the grounding system as well. So for your application, use the red and black for the hot connections and the white for the grounding/neutral wire.
 
  #6  
Old 08-18-07, 12:55 PM
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It may be 2 ways of considering this:

1 Follow the code (who is made for making safe installations)

2 Making it safe whitout conserning about the code.

Re 2

Grounding is made to bond all metal or conductive parts witch may be reached at same time to get a voltage difference so small as it is totally harmless.

Grounding is by code color-coded, and bounded to N (white) in fusebox.
If the normal current in white = 0 Amps the voltage drop = 0 volts, and is harmless. The white will serve as ground and give protection.

If this white is serving an outlet, or other device who may cause a high current in the same white lead, this idea may be dangerous.

If you leave the ground terminal with no connection, it will be safe until an fault makes connection between live and metal frame of the heater. When this error occurs you or anye else have to reach this surface and other conductive surface bounded to ground before it may harm anybody.

dsk
 
  #7  
Old 08-18-07, 06:00 PM
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"240 volts does not require a neutral...for pre 1996 installations you have two hot wires and a grounding wire."

Now (post-1996), 240 volt circuits come with a neutral (white) AND a ground wire. Obviously this must be an improvement (I assume in safety) over the old standard. How so? Is it primarily to protect the circuit in case someone decided to add a new receptacle to the dedicated oven circuit? I'm trying to understand how electricity travels in a 240 volt circuit that makes it so different from a 120V.

Thnx.
 
  #8  
Old 08-19-07, 10:09 AM
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Originally Posted by walks View Post
"240 volts does not require a neutral...for pre 1996 installations you have two hot wires and a grounding wire."

Now (post-1996), 240 volt circuits come with a neutral (white) AND a ground wire. Obviously this must be an improvement (I assume in safety) over the old standard. How so? Is it primarily to protect the circuit in case someone decided to add a new receptacle to the dedicated oven circuit? I'm trying to understand how electricity travels in a 240 volt circuit that makes it so different from a 120V.

Thnx.
The electricity travels the same just in the same way, as far as you operate on only one voltage. The difference is witch point of the supply who is deemed to be Neutral. The trouble is when you use both 120 and 140 volts on the same 3 wires.

I do not know if it is allowed by NEC, But in Norway It wold be allowd with a remarking of that white wire with putting on a hose og green + yellow color
(European ground color) in all ends of the cabel, and connecting the remarked wire to the ground bus in the fuse box.
Then you have your 2 wires Live, and ground.

I do not even know if you have different bars for ground and N, or it is common in your fuse box.

The main reason for different systems in US and Europe is probably when the networks was designed in Europe the Y shaped 3 pase system was well known, and the US had their old 110+110V system all over. A new system would cost to much. Almoast as changing from right hand driving to lefthand driving or visa versa.

dsk
 
  #9  
Old 08-19-07, 12:51 PM
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There is 120 volts between the "Live" wire in a circuit and the "Neutral" ( White wire) ,AND also 120 volts between the "Live" wire and "Ground".The White wire/ Neutral conductors of a circuit is the "Grounded" ( connected to "Ground" at the Service panel) circuit conductor.

In your house, the metallic water lines to a washing machine are considered to be "Ground". Because there is 120 volts between the "Live" ( Black wires) in the appliance wiring and the White wires, and also 120 volts between the "Live" wires and the water lines , both the White wires and the water lines are at "Ground" voltage relative to the "Live" wire.

Most shocks are shocks-to- Ground-- If the metal frame of the washing machine is NOT Grounded, and the White wires are insulated from Ground as required by Code, should the "Live" wire of the appliance wiring make contact with the metal frame of the appliance, there is 120 volts between the frame of the appliance and the metal water lines- a definite shock hazard.

THis could be eliminated by an internal "Grounding" connection between the White wire and the metal frame of the washer. Because the White wire/Neutral is a "Grounded" circuit conductor, this connection sets the metal frame at the same "Ground" voltage -level as the metal water-lines.This expedient is seldom resorted to beause washers are equipped with the metal frame connected to a Grounding conductor ,a Green wire, in the line-cord.

Grounding the frame via the Neutal wire is still permissible for certain appliances connected to existing cables.
 
  #10  
Old 08-19-07, 10:42 PM
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Suppose you have a 120Volt line with two wires, black and white, going to one of those old-fashioned ungrounded receptacles. Suppose you replace the receptacle with a grounded receptacle. Since there is no ground wire in the circuit, you pigtail a ground wire from the ground screw in the new receptacle to the white circuit wire.

Is this a legitimate way of grounding some of those old receptacles with no ground? I've never heard of this, yet it appears to be the same concept as the oven wiring described above.
 
  #11  
Old 08-20-07, 03:36 AM
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Originally Posted by walks View Post
Suppose you have a 120Volt line with two wires, black and white, going to one of those old-fashioned ungrounded receptacles. Suppose you replace the receptacle with a grounded receptacle. Since there is no ground wire in the circuit, you pigtail a ground wire from the ground screw in the new receptacle to the white circuit wire.

Is this a legitimate way of grounding some of those old receptacles with no ground? I've never heard of this, yet it appears to be the same concept as the oven wiring described above.
You are thinking the right way, this has been done in Norway, but ar not alowed any more here. Reason: When you are using maximum power, the voltage drop may reach a voltage who may be dangerous.

Eg: ground is always 0 V to ground, just because ground is the reference.
(you may put a volmeter between white and water pipe to test)
When you use no power the voltage betweene N (white) and water pipe shold be almoast = 0V. When you put on hig energy consumer, as heater, cooler etc the resistance in the wire cause a voltage drop of several volts.
The volmeter reads voltage between N and water pipe.
To eliminate this the protectection erth wire is separated, and only connected to N as near the grounding pont of system as possible.

In modern norwegian installations all conductive parts of the building shold be bonded to the ground. (eg water pipes, and even plastic sewer system, due to conductiv enner film of water and polutions.)

dsk

PS Your white wire will act as ground when no power is running thru this.
DS
 
  #12  
Old 08-20-07, 09:42 AM
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> If a ground is connected to the white, as in the old oven, it's really not a
> legitimate ground, is it?? If not, why connect it at all?

You're correct. The old three-wire method of hookup for ranges and dryers is technically an ungrounded circuit. Under normal operation, the grounded neutral conductor keeps the metal frame of the appliance at a safe near-zero volts. The trouble is that when the neutral conductor fails, the metal frame of the appliance can become energized and there's no ground conductor to clear the fault. This situation presents a shock hazard under certain conditions. The story goes that electrical codes were relaxed to allow ungrounded ranges and dryers during WWII to save metal for the war effort; for some reason (probably cheap builders) it took until 1996 to require grounded circuits for ranges and dryers, which was long after grounded circuits were required everywhere else.

Because of the nature of grandfather clauses and ex post facto laws, electrical inspectors cannot require replacement of existing range and dryer circuits until the existing circuit is modified in some way. Relocation or extension of the circuit requires replacement with a four-wire grounded circuit. Replacement of the appliance alone does not constitute modification of the circuit, so appliance manufacturers still have to be compatible with ungrounded circuits.

> Since there is no ground wire in the circuit, you pigtail a ground wire
> from the ground screw in the new receptacle to the white circuit wire.

This is now called a bootleg ground, and it is actually much less safe than leaving the ground unconnected.

> Is this a legitimate way of grounding some of those old receptacles with
> no ground? I've never heard of this, yet it appears to be the same
> concept as the oven wiring described above.

No, it is not legitimate. It is the same concept as ranges however that is a flaw from previous codes as explained above.
 
  #13  
Old 08-20-07, 11:51 AM
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Interesting! You guys are great -- and this is an A-1 web site. I know you get a lot of practical information here and problem solving hints. But it's educational from the big picture view also.

So now I'm back to my practical aspect -- and you've already answered my next question, that I'll need to put in a grounded circuit if I move my oven, which is currently in the plans. The cost of the wire alone is a budget breaker. I'm wondering if there's any way I can just run a #10 ground from the oven connection out to the service panel instead of replacing the black/red/white as well? It's a 30 amp circuit.
 
  #14  
Old 08-20-07, 12:20 PM
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> I'm wondering if there's any way I can just run a #10 ground from the oven
> connection out to the service panel instead of replacing the black/red/white
> as well? It's a 30 amp circuit.

If the existing neutral conductor is white insulated and the existing wire is copper, then you are allowed to run a separate #10 green or bare ground wire back to the service panel ground bar. Most three-wire installations used a bare braided neutral which would need to be replaced entirely, but if yours is white insulated then it is okay.

NEC article 250.130(C) allows the installation of separate ground wires to existing ungrounded branch circuits.
 
  #15  
Old 08-20-07, 01:29 PM
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Terrific! I've got white neutral.
Thanks again!!
 
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