HELP: wiring electric cooktop

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  #1  
Old 10-24-07, 09:22 PM
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HELP: wiring electric cooktop

Sorry for the newbie question - I searched the forums, but didn't find an answer I fully understood so...

I'm replacing an older Jenn_air C206 cooktop with a new Kenmore 42733 cooktop, and the re-wiring has me confused.

From the power supply, I've got 3-wire cable (white, black, and bare copper). At the breaker box, there are two 30-A breakers joined together. Original installation occured in 1991. The metal junction box by the cooktop isn't formally grounded, but the copper wire probably rubs inside the box (it's a tight fit).

From the new cooktop, I've got 4-wire cable. I've got the installation instructions, and they indicate for the 4-wire to 3-wire connection:
Cooktop-to-Power Supply
black-black
white(neutral)-white
Green(ground)-white
red-red

The red is throwing me. What are the proper connections for my situation?

I would think that I'd want:
Cooktop-to-Power Supply
Black-black
Green-copper
white-copper
red-white

Can you advise?

Thank you for any help you can offer!
 
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  #2  
Old 10-25-07, 05:14 AM
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You need to run a new cable from the panel to the cooktop. Your old cooktop was 240 volts, your new one is 120/240 volts. Your existing setup has no neutral wire. Install the proper size (or physically larger) cable and use the proper size circuit breaker.
 
  #3  
Old 10-25-07, 08:26 AM
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The specifications on the Sears website indicate that this unit requires a 40A circuit; you have a 30A circuit. Unless the installation instructions that came with the unit allow a 30A circuit, you need to install a new 8/3 cable with a 40A breaker.

If the unit can operate on a 30A circuit, then your guess as to the wiring layout is correct.
 
  #4  
Old 10-25-07, 10:33 AM
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Just to clarify, you have "two wire" right now (don't count the ground). It is wired as two hots with no neutral. Fine for the 220 load, not ok for the 120.

I disagree with ibpooks, you do need a new wire. The way you're thinking of hooking it up, it will work, but it won't be right.
 
  #5  
Old 10-25-07, 05:01 PM
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Thanks you guys and thanks for the clarification Fubar411 - I understand now! Can you point to a discussion on how to rewire for 120/240 at the breaker box? Physically pulling the wire might be a pain, but I guess there's no better time to learn!

-denalidog
 
  #6  
Old 10-25-07, 07:22 PM
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The metal junction box by the cooktop isn't formally grounded, but the copper wire probably rubs inside the box (it's a tight fit)...........................

240 volts @ 40 amps????Probably isnt even in the ballpark.

In your ckt panel ....install whatever the Mfr reccommends for supply in a Double pole breaker.

8/3 with ground NM-B cable will have ...white , black, red and ground(Bare copper).

At the panel, red and black go to the breaker poles(One each..and the breaker doesnt care which screw gets which wire)..White to neutral buss , bare to ground buss.

Once the wire is in the box, ground the box(Using a pigtail off of the bare) and continue using the installation instructions.

Your local code may require a receptacle , or "Hard wire", But once the wires are in the junction box, the rest is just following instructions.
 
  #7  
Old 10-26-07, 01:58 AM
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Considerations about electric and practical use, with no thoughts about codes.

The stove has a max wattage of 9.1 kW
This will be near 38 Amp at full load.

The absolutely full load situations are just of short time.
The 30Amp beraker will acept this for at least 1/2 hr.

The need for the 120V if real is only for controlling device, and will probably not be able to make a voltagedrop to be conserned about, then it will be safe to connect the ground and grounded wires to ground from supply.
To avoid risk of fire caused by load in the wires a cu wire awg no 9 or greater will probably be safe even with long time full load.

If you do so, you will probably experince problems at all. If you use full power the breaker may trip.

BUT You may violate codes, and whats following by this.
 
  #8  
Old 10-27-07, 10:19 AM
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Originally Posted by denalidog View Post
From the power supply, I've got 3-wire cable (white, black, and bare copper). At the breaker box, there are two 30-A breakers joined together. Original installation occured in 1991. The metal junction box by the cooktop isn't formally grounded, but the copper wire probably rubs inside the box (it's a tight fit).

You need a Grounded (neutral) conductor in the circuit to operate the 120V controls on the cooktop.

On older homes with a existing 3 wire range circuit, your allowed to use a insulated 3rd conductor as the grounded (neutral) conductor.

The only exception where you can use a bare 3rd conductor as the grounded (neutral) is if it's part of a existing type SE cable.

None the less, if the circuit was installed in 1991, it's not "grandfathered" (a exception), because the electrical code at that time required a 4 wire circuit.
You will have to replace the circuit with a 4 wire [(2) hots, insulated neutral and ground] to be code compliant.
The wire size will depend on the KW rating (or amperage) of the new cook top

That bare copper rubbing against the metal box is no substitute for a properly connected bonding wire.
All it would provide is probably some serious arcing if you ever had a line to metal (box) fault.
This wouldn't be good.

Just my opinion
steve
 
  #9  
Old 10-29-07, 07:58 AM
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How do you recommend physically pulling the new 8/3 wire? Should I use the existing wire and lash (tape?) the new wire to it, then pull from the house? Is there something barbed on two ends that you hook into the NM sheath to attach the wires together, then tape across the ends to minimize snagging?

In my situation, the breaker box is out in the garage, the line runs overhead from there into the attic (relatively unobstructed), then down an interior wall, into a conduit and through the floor, to the kitchen island with the cooktop. All sharp bends in the course are close to the kitchen island.

I was surprised to find 8/3 wire sells for $2.70/ft - I've got a good 40 ft run...that new cooktop is getting expensive!

Thank you,
denalidog
 
  #10  
Old 10-29-07, 08:05 AM
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No, you cannot pull the new cord with the old one. Abandon the old cable and run the new cable.
 
  #11  
Old 10-29-07, 08:29 AM
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Originally Posted by denalidog View Post
I was surprised to find 8/3 wire sells for $2.70/ft - I've got a good 40 ft run...that new cooktop is getting expensive!
Thank you,
denalidog
Google "www.southwire.com" and look at the "4 conductor Type SER aluminum cable.
It's about half the price of copper cable.
You will need the next size larger than copper if you use aluminum.
Example...if you need #8 copper, you will need #6 aluminum.
Look at the amperage ratings.


Edited to add: Some localities won't allow aluminum to be used for branch circuit wiring.
Check with your local codes office or Authority having Jurisdiction before installing it.

steve
 
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