3 and 4 wire stove

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  #1  
Old 10-19-05, 09:34 PM
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3 and 4 wire stove

I have a built-in oven and a cook top I am installing in the kitchen, the oven has a red, black, white, & ground wire, someone clipped the white and the gound together, is this ok? The cook top only has a red, black, & ground. My supply line, 220 line, only has red, black & ground, how do I connect everything to this and make it code/correct? I can connect the oven & cooktop to the same 220 line correct?
 
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  #2  
Old 10-20-05, 05:44 AM
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No, you cannot connect the devices to the same 240 volt line. They likely have different current requirements, and besides, you would not want to be limited to only using one at a time.

Your supply line is a straight 240 volt line. It does not have a neutral. What size is the breaker protecting the line and what size are the wires? This circuit, perhaps with a new breaker, will probably be okay for the cook top.

Your oven requires a four wire circuit. You need to run a new line for the oven.

before, proceeding, you need to determine the current requirements for the stove and cook top. They should be listed on them, or you can find them in the owners manuals. The owners manuals will discuss installation. If you don't have the owners manuals, you can probably find them on line.
 
  #3  
Old 10-20-05, 05:47 AM
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You _may_ be okay on both points, but more information is needed.

1) The _best_ way to install an electric cooking appliance is with a four wire circuit (2 hots, 1 neutral, 1 ground).

2) A 'three wire' circuit (2 hots and a ground) to an electric cooking appliance was permitted in earlier editions of code. If this circuit was installed when it was code compliant, then it is 'grandfathered' in and you can use it. You should note that only _some_ wire types are permitted to be used in this fashion. For example, the ground wire in NM cable (romex) is _not_ sufficient for this use.

3) Because of the two possible circuit configurations, _many_ appliances have instructions for how to connect them to either a three wire or four wire circuit. Generally this installation involves connecting the ground and neutral lines somewhere, either using a special jumper in the appliance, or by connecting both wires in the junction box. To determine if this is permitted for your appliance, and how to make the connection, you need to see the appliance installation manual.

4) You cannot simply connect a couple of appliances to a circuit. You must make sure that the circuit has sufficient capacity for the appliances. You need to determine the following: the current consumption of the appliance(s), the size and current rating of the wire, and the rating of the circuit breaker/fuse protecting the wire. Overloading a circuit is a great way to start a fire.

5) You cannot simply connect any 220 appliance to any 220 circuit. Not only must the circuit have sufficient capacity to feed the appliances, but the appliance must be listed as being safe on a circuit of that capacity.

6) If all of the requirements are met, then yes, you can place an oven and a cooktop on the same circuit. But it requires the combination of a circuit sized to feed both appliances, combined with both appliances being permitted to be connected to a circuit with that rating.

7) Both appliances should have a nameplate that specifies their KW rating, the maximum breaker, different connections, etc.

Questions that you _must_ answer:
A) What sort of wire/cable is feeding this circuit? Is it NM, SE-R, or some other type? What gage of conductors?
B) What is the rating of the circuit breaker/fuse feeding this circuit?
C) What are the instructions on the range for connecting to a three wire circuit?
D) What is the KW rating of the oven and the cooktop?
E) What is the maximum circuit rating (fuse/breaker) that the oven and cooktop are permitted to be connected to?

-Jon
 
  #4  
Old 10-21-05, 09:21 AM
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There's no way these 2 permanently installed 220V appliances can go on one circuit. As racraft said, you might be able to use the existing circuit for the stove, but definitely need to run a new 4-wire circuit for the oven.

Doug M.
 
  #5  
Old 10-21-05, 09:47 AM
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Doug,

I do not believe that you are correct.

210.19(A)(3) Exception 1 discusses 'tap conductors' for household cooking appliances. This clearly indicates that a circuit of greater ampacity than needed by a single appliance. It basically says that you can have a 50A circuit for cooking appliances, and that a cooking appliance that only needs 20A could be connected to this circuit with 20A conductors.

This exception would only be useful if you ran a single 50A branch circuit to a location, and then connected two separate appliances to this circuit, each with its own (suitably rated but less than 50A) conductors.

The McGraw-Hill NEC 'Handbook' shows a specific example in their discussion of 210.19(A)(3) Exception 1, where they have a wall oven and a cooktop both connected to the same 50A circuit. Note: the Handbook is _not_ code, but is instead a professional interpretation of code.

Again, this would only apply if A) The circuit has sufficient capacity for _both_ appliances and B) the appliances are listed for operation on a circuit of this capacity. In other words, if I have an oven that requires 20A, but is listed as suitably protected on a 50A circuit, and I have a cooktop that requires 30A but is listed as suitably protected on a 50A circuit, I believe that I can use both of these together on a single 50A circuit.

I additionally see the following issue with the original post: if the supply line has hot, hot, and ground, and the ground is a bare wire in romex, then the original install was not to code, and the three wire circuit not 'grandfathered'. On the other hand, the 'black, red and ground' makes me wonder if the original install is in conduit, in which case a neutral could be added.

And it does all come down to needing more information. Without knowing the ratings and limits of the appliances, and the size and wiring method of the supply conductors, we are all just guessing.

-Jon
 
  #6  
Old 10-21-05, 10:09 AM
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I'm not an electrician nor do I have access to a code book. I'm very surprised that any appliance would be rated for 20 amp and allow connection to 50 amp, but apparently some do. I'm also quite amazed that basically putting wiring rated for 20 amps on a breaker rated for 50 is okay too. If that's the case, and I certainly can't argue, I humbly stand corrected, BUT I don't feel that this is good practice and would still advise jonesdx to run at least 1 new circuit.

Doug M.
 
  #7  
Old 10-21-05, 10:16 AM
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I am not an electrician, but I do have access to a code book. I would personally advise jonesdx that any advice which he gets for free on the internet is worth what he pays for it. *grin*

I agree that 'tap conductors' are perhaps less than ideal; on the other hand you do this all the time when you plug a 10W electric clock with 18ga zip cord into a 15A receptacle on a 20A circuit.

-Jon
 
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