Oven neutral or not

Users who are viewing this thread

Sleepless

New Member
Messages
10
Reaction score
0
Points
1
I will soon be remodeling our kitchen. The present wall oven location will be moved about 10' across the room. The present 8/3 wire (40 amp circuit) runs in the ceiling. The ceiling sheet rock will have to be removed anyway so I planned to just pull the existing wire to the new location (resulting in a shorter run).

The problem is that we are going from a 1978 3-wire oven to a 4-wire (convection) oven (why can't they use 220 fans and transformers!!!). (The new oven will only need a 30 amp circuit.) The installation information from the manufacturer allows for a 3-wire installation "where codes permit" -- see attached file. I had a discussion with the salesman at the (large) appliance store, he talked in a very large circle, but implied that an existing 3-wire circuit would be acceptable, but a "new" installation would require a neutral.

I certainly want to comply with code, but running a new wire in an existing house will be a real pain.

Do I need to run a new 4-wire circuit to the new location?
 

Attachments

  • 3-wire.jpg
    3-wire.jpg
    94.6 KB · Views: 7,072
Last edited:

PatrickH

New Member
Messages
21
Reaction score
1
Points
3
Location
Virginia
The exception to this is applicable to existing installations with no grounding conductor in the box. :(
 

Jadnashua

Retired Defense Industry Engineer xxx
Messages
32,770
Reaction score
1,190
Points
113
Location
New England
This is my understanding...if you are putting a new stove/oven in the same place, and it is wired with three wires, you can install the new one IF the appliance allows it. Otherwise, you must run a new cable with 2-hots, neutral, and separate ground. The old unit probably does have some 120vac stuff in it, and internally tied the neutral and ground point together. That is not allowed in a new install...the ground and neutral must be separate. All new units internally have neutral and ground separated, but if being installed on a three-wire circuit, they tie the ground and neutral back together. It is safer to have an independent ground wire to trip the breaker if there's a fault.
 

Sleepless

New Member
Messages
10
Reaction score
0
Points
1
The old unit probably does have some 120vac stuff in it, and internally tied the neutral and ground point together.
Yes indeed, the existing oven has a timer and light bulb that are 120vac. I haven't pulled out the old unit, but since there is no neutral from the panel, it must have its ground and neutral joined.

That is not allowed in a new install...the ground and neutral must be separate.
The question is -- would this be classified as a new install or a replacement.
 

hj

Master Plumber
Messages
33,602
Reaction score
1,038
Points
113
Location
Cave Creek, Arizona
Website
www.terrylove.com
quote; I haven't pulled out the old unit, but since there is no neutral from the panel, it must have its ground and neutral joined.

You are mistaken. It DOES have a neutral, but it does NOT have a dedicated ground.
 

Speedy Petey

Licensed Electrical Contractor
Messages
1,108
Reaction score
9
Points
38
Location
NY State, USA
Just to clarify. Older "3-wire" 120/240V range and dryer circuits ALWAYS required a neutral. It was the ground that was allowed to be omitted. The neutral served both purposes.
 

Sleepless

New Member
Messages
10
Reaction score
0
Points
1
I do understand that the neutral and ground are shared, or one can say that the case ground is not dedicated.

The question is more practical, does moving the oven location require a new 4-wire circuit?

(I still don't understand why these are built as 120/240, they could easily be built as 240. Certainly any appliance exported to Europe is not going to be 120/240!)
 
Last edited:

Jadnashua

Retired Defense Industry Engineer xxx
Messages
32,770
Reaction score
1,190
Points
113
Location
New England
Generally, moving things requires it to be brought up to current codes...a direct replacement may not. Best directed to your local inspector.
 

hj

Master Plumber
Messages
33,602
Reaction score
1,038
Points
113
Location
Cave Creek, Arizona
Website
www.terrylove.com
quoe; Certainly any appliance exported to Europe is not going to be 120/240!)

And WHY would it be, since they do not have 120 v power. A customer from the "old country" put out all his Christmas decorations and could not understand why they were all "yellow", until I told him they were for 220 but were running on 120 and he would need to buy new decorations.
 

Reach4

Well-Known Member
Messages
38,796
Reaction score
4,412
Points
113
Location
IL
Sleepless's point was why would a US oven that did not have an AC outlet on it even use a neutral? I think the answer would have been because 240 volt oven light bulbs would be hard for a US customer to get. I wonder if they will figure out how to use LEDs for ovens. Not for a while, I expect due to the temperatures.
 

PatrickH

New Member
Messages
21
Reaction score
1
Points
3
Location
Virginia
We don't distribute power the same as European Countries. In Europe 230 volts is from the conductor to ground (i.e. Neutral), as where here in the states, it's usually 240 volts between the two conductors, and 120 volts to ground. It really doesn't matter though. Appliance companies likely don't create, at least in large numbers, appliances that can operate in either grid. You could take it up with the local inspector if you aren't able to pull a new feed for the range. Or you could tell us where the panel is, if you need some tips on running a new range circuit to it.
Jadnasua is right that adding the dedicated ground will yield a safer installation for you and the family. Connecting the neutral and ground at the appliance means that the case will be part of the circuit. If the grounded leg is severed or loose and you or someone else provides a better path to ground via the sink faucet etc, then you could get a shock from the case of the range. GL.
 

hj

Master Plumber
Messages
33,602
Reaction score
1,038
Points
113
Location
Cave Creek, Arizona
Website
www.terrylove.com
I may be wrong, but I have heard that some countries, like Australia, only have a single 240v wire coming in to the building. The "neutral" is taken care of by an "earth/ground" connection.
 

Reach4

Well-Known Member
Messages
38,796
Reaction score
4,412
Points
113
Location
IL
If you were worried enough about a shock with the shared neutral, you could put in a 30 Amp 2 Pole Ground Fault Circuit Breaker into the breaker panel to replace the breaker you have now.
 

Sleepless

New Member
Messages
10
Reaction score
0
Points
1
If you were worried enough about a shock with the shared neutral, you could put in a 30 Amp 2 Pole Ground Fault Circuit Breaker into the breaker panel to replace the breaker you have now.

Interesting -- how does the GFCI know there is an imbalance between the two poles and ground if the common and ground are connected at the oven?
 

Reach4

Well-Known Member
Messages
38,796
Reaction score
4,412
Points
113
Location
IL
huge2.png
Interesting -- how does the GFCI know there is an imbalance between the two poles and ground if the common and ground are connected at the oven?
The worry would be if there was a current between the stove and something else. The GFI runs the three conductors through a small sensing transformer that only looks for the algebraic sum of the 3 currents (ideally zero). http://www.schneider-electric.us/support/index?page=content&country=US&lang=en&id=FA115047
http://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf page 11.
 
Last edited:

Sleepless

New Member
Messages
10
Reaction score
0
Points
1
This oven has two fans (110VAC) -- is a motor load on a GFI circuit a potential problem?
 

Reach4

Well-Known Member
Messages
38,796
Reaction score
4,412
Points
113
Location
IL
This oven has two fans (110VAC) -- is a motor load on a GFI circuit a potential problem?
No.

What could trip the breaker is if the neutral is connected to the oven frame, AND also some external ground or source connects to that frame and that connection passes over 4 milliamps of current. Now there is a path of current in addition to the 3 wires going through the differential current transformer.
 
Last edited:

Sleepless

New Member
Messages
10
Reaction score
0
Points
1
What could trip the breaker is if the neutral is connected to the oven frame.

But that is the recommendation of the manufacturer (for three wire connection), neutral is connected to the oven cabinet via the green wire (see illustration in first post).

I will have other grounds available in the area (cooktop and dedicated circuit for microwave above oven).
 

Reach4

Well-Known Member
Messages
38,796
Reaction score
4,412
Points
113
Location
IL
I edited my previous post to turn the first two sentences into a single sentence. It would take both things to trip the GFI breaker.

If the wire that would have connected to the green in a 4-wire setup is connected to nothing rather than the white neutral, then touching the oven frame with an outside ground would not trip the GFI. If the wire that would have connected to the green in a 4-wire setup plus the oven neutral is connected to the white neutral in your cable, then touching the oven frame with an outside ground or other connection might trip the GFI. It would depend how much current flowed.

In regular convenience outlets, it is not required that the chassis/protective ground be connected if there is a suitable GFI. I don't know what the rules would be according to code. I think I know what I would do. I would not connect the chassis to ground. I would let the terminal that would have gone to the green float. However don't do it because I would do it. I am not a electrician. I tend to look at circuits from an electronics point of view and not a NEC code point of view.
 

Sleepless

New Member
Messages
10
Reaction score
0
Points
1
I would let the terminal that would have gone to the green float.

Seems like it would be preferable to pull a ground from the microwave circuit for the oven case ground. (Bare wire in 3-wire 120/240vac "R0mex" connects to oven neutral only)

Not sure this would jive with the NEC!!

I do understand how the GFI would protect IF the case is not connected to the neutral.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks