Wiring for Oven and Cooktop

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Old 07-26-12, 01:24 PM
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Wiring for Oven and Cooktop

I am in the process of a kitchen remodel which involves moving and replacing my Oven and Cooktop.

The current wiring for them is as follows:

1. The wiring from the panel in the corner of my basement is Aluminum (6-Gauge I think), Stabiloy Type SE, Style U. This is connected to a 40A breaker in the panel.

2. This wire runs about 50ft to the other side of the (unfinished) basement in to a junction box where it is junctioned with 2 branches of 8-3 Copper Wire (I am assuming it is using the correct wire nuts for Aluminum to Copper).

3. One 8-3 runs to the Cooktop, the other runs to the Wall Oven.

I believe this is not appropriate because everything I read suggests that Ovens and Cooktops should each have a dedicated circuit. The Oven requires 30A per the User Manual, and the Cooktop requires 40A.

Fortunately I have an unused 30A breaker in the panel, so my plan for rewiring is as follows:

1. Run a dedicated 10-3 line from the unused 30A breaker in the panel to the new location for the Wall Oven

2. Now I finally get to my question..... In an ideal world I would probably run a new 8-3 Copper line from the 40A breaker in the panel to supply the Cooktop. However, I would need close to 70ft of wire, and based on Lowes prices that would cost me close to $200 just for the wire.

Therefore, I am wondering if it is OK to leave the current line and junction box in place to provide a dedicated 40A service to the Cooktop (in other words I will remove the 2nd 8-3 wire from the junction box to make this a dedicated circuit).

Any advice would be appreciated.

Thanks,

Chris
 
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  #2  
Old 07-26-12, 06:29 PM
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(I am assuming it is using the correct wire nuts for Aluminum to Copper).
Safety first! You should NEVER use any type of twist-on wire nut or connector to directly connect aluminum and copper wire and especially on high amperage connections! Aluminum and copper wire should always be isolated from each other using an approved connector. Next, what is voltage rating of both cooktop and oven? I fully agree with a new circuit for the oven and a 10-3/G NM B cable would be just fine if the oven's voltage is 120/240 volts. The installation manual should tell you the required voltage. I would also recommend a new copper circuit for the cooktop and getting rid of the aluminum.
 
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Old 07-26-12, 10:13 PM
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Next, what is voltage rating of both cooktop and oven?... The installation manual should tell you the required voltage.
Recognizing that you may not have the installation manuals for these appliances you are relocating, what does the nameplate on each show?
 
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Old 07-27-12, 08:33 AM
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Since you need to extend the circuits the new wiring would need to meet the current code requirements. Unless both are straight 240 volt units you will need new wiring.
 
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Old 07-27-12, 11:46 AM
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Thanks for the responses.

The Oven will be new. It is a GE Oven / Microwave Combo (JKP90SP). According to the specifications it is 208V or 240V. In either case the specification requires a 30A circuit. The specific instructions are "You must use a single-phase 120/208 VAC or 120/240 VAC 60 Hertz electrical system".

The cooktop is older and I don't have the install manual. Looking at the unit itself it states "Connect only to a 3-Wire 120/240 V electrical supply". It goes on to say that the neutral wire is not required. Looking online at equivalent newer models (it is a Dacor 36" 5-burner unit with no ventilation) I am pretty sure it requires a 40A circuit.

I am not sure where this leaves me with regards to the wiring?

I am assuming that I should move forward with my plan for a dedicated 30A circuit for the Oven by running a new 10-3 line to the panel (which already contains an unused 30A breaker)?

However, I am still not sure where I stand on the Cooktop and whether I can use the existing 40A circuit (knowing that it contains a junction box for the transition from Aluminum to Copper), or whether I need to run a completely new line. I am always a fan of doing the job right, but in this particular case, I want to make sure of the requirements before I drop $200 on the 75ft of 8-3 Copper wire that I would need.
 
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Old 07-27-12, 12:10 PM
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You wrote:
According to the specifications it is 208V or 240V.
But then you contradicted that by writing:
You must use a single-phase 120/208 VAC or 120/240 VAC 60 Hertz electrical system
The second probably better describe what you need and that means a 4-wire feed so you plan of a 10-3 feed on a 30a breaker should be good.

I am always a fan of doing the job right, but in this particular case, I want to make sure of the requirements before I drop $200 on the 75ft of 8-3 Copper wire that I would need.
Given the known problems with aluminum a $200 one time fee is cheap insurance in my opinion.
 
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Old 07-27-12, 01:00 PM
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Thanks for all the input!

Any thoughts on whether I should run an 8-3 line or an 8-2? The current supply line is 8-3 but the neutral line is simply capped in the junction box where it connects to the cooktop input wiring. Would an 8-3 give me more flexibility for the future (i.e. would a new cooktop in the future want an 8-3 supply)?

The price difference appears to the reasonably substantial (8-3 being around $1 per linear foot more expensive than 8-2).

My final question is more of a "for interest" question, but, when I looked up the Aluminum wiring online it seemed to suggest that it is still used for residential service lines. Is there a reason for this given, if Copper is widely agreed to be better? Is it a cost thing?
 
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Old 07-27-12, 01:07 PM
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Any thoughts on whether I should run an 8-3 line or an 8-2? The current supply line is 8-3 but the neutral line is simply capped in the junction box where it connects to the cooktop input wiring. Would an 8-3 give me more flexibility for the future (i.e. would a new cooktop in the future want an 8-3 supply)?
Only the 8-3 will give you both a neutral, for controls, and an equipment ground, for the frame of the cooktop.

Plus, that will comply with current code requirements.
 
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Old 07-27-12, 02:13 PM
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You might want to price out using conduit and THHN individual conductors.

In larger sizes it is common to use aluminum for feeders because of cost. The problems with aluminum were mostly in branch circuits and their smaller wires.
 
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Old 07-27-12, 03:40 PM
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My final question is more of a "for interest" question, but, when I looked up the Aluminum wiring online it seemed to suggest that it is still used for residential service lines. Is there a reason for this given, if Copper is widely agreed to be better? Is it a cost thing?
Aluminum is a fine conductor and yes, is is less expensive than copper. The residential service lines you're asking about are outside, and relatively easy to keep isolated from direct contact with copper.

Experience has taught never to splice or otherwise directly aluminum to copper and energize that connection. Too often, bad things happen.
 
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Old 07-30-12, 10:41 AM
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So I took all of your advice and purchased some 8/3 wire to run a new line direct to the Cooktop and remove the Aluminum completely.

In the past I have added several new 15A and 20A circuits to a panel, but never a 240V circuit. Is there any specific advice anyone would give on any differences with doing this compared to adding a new 15A/20A circuit to a panel?
 
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Old 07-30-12, 11:46 AM
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The process is the same. The only difference is that you connect two hots to the 2 pole breaker.
 
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Old 07-30-12, 12:44 PM
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Thanks. I'm also going to get a homeowners permit for the work, so that an inspector can take a look after I am done and verify it is all done correctly
 
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Old 07-30-12, 12:59 PM
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I'm also going to get a homeowners permit for the work, so that an inspector can take a look after I am done and verify it is all done correctly
Sounds good. Be sure to leave everything visible and unpowered until after the inspection. Well, cover the panel, just be there to open it quickly when the inspector arrives!
 
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Old 07-30-12, 02:56 PM
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One final question I have is around the connection to the appliances. As always seems to be the case for me, what I have right now serves only as the example of what not to do, not as an instruction on the correct approach.

I discovered recently that the current line to oven was simply punched through the drywall and connected with wire nuts to the oven power cable. This strikes me as very dangerous because it means that the spliced wires were sitting directly on top of the metal shell of the oven. The line to the Cooktop was at least run in to a junction box, although this was rather haphazardly attached to part of the inside of the kitchen cabinet beneath the Cooktop.

Given that I have excellent access to all of the wiring, my current plan for both appliances in their new location is to run the feed wires in to recessed device boxes and then connect them to the appliance power leads within the junction box (both appliances are direct wire). The question I have on this are:

1. Does this sound like a good plan?

2. Is it OK to use the heavy duty blue plastic boxes, versus using metal ones?

3. What type of faceplate can I use for the junction box, given that the appliance power wire will be entering from the front, and not from the back as it usually the case with recessed boxes?
 
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Old 07-30-12, 09:23 PM
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What type of faceplate can I use for the junction box, given that the appliance power wire will be entering from the front, and not from the back as it usually the case with recessed boxes?
Set a 1900 or a 4-11/16" box in the wall and use a flat cover with a center KO and a 90[SUP]o[/SUP] connector.

 

Last edited by ray2047; 07-31-12 at 08:57 AM. Reason: Add image.
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