4 Wire Range and Oven to 3 Wire SE Cable

Discussion in 'Electrical Forum discussion & Blog' started by rjschwar, Jul 11, 2020.

  1. rjschwar

    rjschwar New Member

    Joined:
    Jul 11, 2020
    Location:
    Washington
    I found this thread and have a similar setup but had a couple clarification questions:
    https://terrylove.com/forums/index.php?threads/question-on-3-wire-kitchen-range-4-wire.67912/

    We replaced a couple cabinets so I had to remove and reinstall our oven/microwave combo and the cooktop.

    I have AA-8000 6 Gauge Aluminum SE Cable with insulated black, insulated black with red stripe, and bare aluminum strands running from a 50 Amp 240 breaker in my panel that goes to a oven/microwave combo with 4 wires, and then continues to my island cooktop/vent fan, again with 4 wires. The referenced thread says you can connect the 4 wire to 3 wire using the bare aluminum for both neutral and ground of the appliances. This is how it was done previously.

    Elsewhere I've been told this can be unsafe if something causes the neutral to float at a hot voltage. The proposed solution to this they suggested would be to use a GFCI breaker and intentionally dead end the ground from the appliances avoiding at all costs tying the neutral to ground at the appliance else I'll lose GFCI protection.

    I see a couple options, from the multiple sources I've seen.

    1. Just connect everything back how it was previously. Black to black, red to black with red stripe, ground and neutral to bare aluminum at both appliances.

    2. do 1 but add a GFCI. I'm leaing toward this assuming wiring ground and neutral together at the appliances doesn't mess with GFCI protection

    3. same as option 1 except I don't connect ground and neutral at the appliance, instead cap the ground and connect neutral to bare aluminum at both appliances. The problem I see with this is the ground from the appliance is bare copper in metal conduit and metal junction box. I don't see how this would be much different than connecting the ground to the neutrals, as the SE cable is bare without insulation on the neutral as well.

    4. I have a nearby spa panel that is connected with 6/3 to my main panel, so I have the option to "steal" ground from my spa circuit though I don't know if this is allowed, or how that might mess with my spa GFCI.

    Any thoughts would be helpful.

    Additional question. Is there anything special I need to do to connect Aluminum wire to copper? The previous connections just used wire nuts, but I thought I had seen before you need some anti-corrosive stuff to do that.

    Thanks,

    Richard
     
  2. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    You have a lot going on and it gets confusing at the beginning. As I understand its three wires? Ground as the bare wire, then you state it is four wires? Does the cable to the oven is it three or four wire? L1, L2, Neutral (an insulated current carrying wire ) and ground (bare or green wire).

    You cannot take a ground (green wire) from one circuit to work on another. A microwave and range hoods needs a neutral and ground.
     
  3. Sponsor

    Sponsor Paid Advertisement

     
  4. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Here is the governing section of the 2014 NEC. If the 2017 or 2020 NEC are in force in your area, you should check to see if the section has been changed. If not, and your installation meets all the requirements in the exception, you can use the bare conductor as your grounded (neutral) conductor, and you can bond the frames of the equipment to the grounded conductor. But pulling a new 4-wire cable from the panel would result in a superior and safer installation.

    Cheers, Wayne

    250.140 Frames of Ranges and Clothes Dryers. Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.
    Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be connected to the grounded circuit conductor if all the following conditions are met.
    (1) The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.
    (2) The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.
    (3) The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a
    Type SE service-entrance cable and the branch circuit originates at the service equipment.
    (4) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment
     
  5. rjschwar

    rjschwar New Member

    Joined:
    Jul 11, 2020
    Location:
    Washington
    To clarify I have 3 wire SE insulated, black with red stripe insulated, and uninsulated aluminum strands running from panel to oven/micro combo then to cooktop. Both appliances are 4 standard wires. I can't pull a new wire without topping my walls apart so I guess I'm stuck with the grandfathered method.

    Would adding a gfci help anything?

    What about pulling a ground from my spa panel if allowed?

    Thanks,
    Richard
     
  6. Bannerman

    Bannerman Well-Known Member

    Joined:
    Mar 19, 2014
    Location:
    Ontario, Canada
    You need a neutral wire from the panel for 120 volt devices such as a microwave. Although it may work, using ground as a neutral is not typically permitted.

    Can you route a new 4 conductor cable from the panel to the appliance location? While you may not be able to install the new cable within the wall without removing drywall, perhaps a new 240 volt outlet box could be surface mounted on the wall behind or beside the appliance, with the new cable routed through a hole in the floor directly beside the baseboard.
     
  7. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    You cannot take a ground (green wire) or neutral (wht wire) from one circuit to work with another. A microwave and range hoods needs a neutral and ground. If they work as you found it, it appears these were not installed correctly. As stated in the older post you found, you cannot use a ground as a neutral. wwhitney comments from the NEC book addresses the ground, not a neutral.

    The entire purpose of a ground is for safety. A ground is connected to the chassis of an appliance, should a hot lead touch the chassis it's a path to ground (a short) to cause the circuit breaker to trip. It is not suppose to carry current. A neutral wire (white) is an insulated conductor to carry the current of the appliance back to the circuit panel. If the microwave draws 10 amps, its 10 amps on the white lead.

    220 volt appliances do not need a neutral, especially electric water heaters. Overtime as electric ranges, oven and dryers became electronic, the electronics need a neutral. In the days of two wired homes, (two prong outlets), major appliance would be tied to a ground with a strap around a copper pipe and to a screw connection such as on the washer or dryer, all for safety.
     
  8. rjschwar

    rjschwar New Member

    Joined:
    Jul 11, 2020
    Location:
    Washington
    Running a full new run would be very difficult. My panel is in a bad position across the house from my kitchen. It sounds like I'm grandfathered based on the code above, but I'm curious if a GFCI would help anything, or whether it is worth/allowed pulling a ground from my spa circuit.
     
  9. Bannerman

    Bannerman Well-Known Member

    Joined:
    Mar 19, 2014
    Location:
    Ontario, Canada
    Why? Your cooking appliance wiring is already equipped with a ground wire which is grounded at the panel. You require an insulated neutral conductor and connection to the panel.
     
  10. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Sorry to quibble, but per the NEC section I posted, the existing SE cable is being used as an ungrounded supply with a bare neutral. And that NEC section allows bonding the case of the equipment to the neutral, rather than to an EGC. Part of the reason to think of it as a neutral conductor is that the equipment is actually using it for the circuit for the 120V loads, so it a current carrying circuit conductor, unlike an EGC.

    Cheers, Wayne
     
  11. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Just to confirm, the existing SE cable originates at the service panel? I.e. the panel closest to the utility, where you can shut off power to the whole house?. As opposed to some indoor panel, when you also have an outdoor disconnect.

    Cheers, Wayne
     
  12. Bannerman

    Bannerman Well-Known Member

    Joined:
    Mar 19, 2014
    Location:
    Ontario, Canada
    No worries!

    I have not seen SE cables installed beyond the service panel in a residential setting unless feeding a subpanel. I assumed that cable may have been installed as a 240 volt service with only an un-insulated grounding conductor and no Neutral.

    As the NEC allow using an uninsulated conductor as both a neutral and grounding conductor, the cooking appliance frame (chassis) will be grounded in compliance to NEC requirements, so an additional grounding conductor from the Spa circuit would be redundant at best.

    If a grounding conductor may be easily added to the cooking appliance' outlet box without tearing walls apart, I anticipate running a new 4 conductor cable
     
  13. rjschwar

    rjschwar New Member

    Joined:
    Jul 11, 2020
    Location:
    Washington
    Yes, the existing SE cable originates at the service panel. The spa panel is a separate circuit that also originates at the service panel. The service panel is indoors but has the 200 amp breaker to shut off power to the whole house.

    It would be difficult to run a new 4 conductor cable to the service panel. It would be possible to run cable to the spa panel potentially.
     
  14. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    The issue I'm having is yes, NEC using a bare wire for a neutral/ground is acceptable for million of homes with three wire 220 volt appliances, but not to add an appliance like a microwave. A 220v volt electric range has no current requirements on the ground wire and any current from a 120 v motor or the electronics are so small that UL & NEC must deemed it safe. But a microwave usually takes a 1000w or more @ 120v. That is a lot of current on 240 circuit unprotected ground. Yes it does sit inside the cable jacket for protection.
     
  15. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    From the section I quoted it seems that if it's a microwave/oven combo unit, and comes from the manufacturer as a 240V oven component with a receptacle on it for plugging in a 120V microwave component, that's still allowed for existing conditions. I agree that it puts a lot more current on the neutral than a typical electric range or clothes dryer.

    Cheers, Wayne
     
  16. Bannerman

    Bannerman Well-Known Member

    Joined:
    Mar 19, 2014
    Location:
    Ontario, Canada
    It would then seem the exemption quoted may not necessarily apply to the cooktop as that is a separate appliance, not integral to the oven/microwave.
     
  17. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    OK, but the cooktop is itself surely 240V, and the 250.140 exception would apply separately to it. I was talking about a 120V load, such as possibly the microwave or the vent hood.

    To the OP, 250.130(C)(4) does allow you to extend the EGC from the spa panel to the oven and to the cooktop, assuming the spa panel has a sufficiently large EGC (25-60 amp breakers all require a minimum of #10 Cu EGC). What you would then need to do is insulate the bare neutral conductor anywhere it is exposed outside the service entrance. Because the EGC and the neutral can only be interconnected at the service entrance, never downstream of it. So you don't want a bare neutral conductor to contact a metal junction box or wiring compartment within a piece of equipment, which would now be bonded to the EGC as normal. And you'd need tor remove the neutral/case bonds that should currently exist at the oven and cooktop.

    Cheers, Wayne

    250.130(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:
    (1) Any accessible point on the grounding electrode system as described in 250.50
    (2) Any accessible point on the grounding electrode conductor
    (3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates
    (4) An equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates
    (5) For grounded systems, the grounded service conductor within the service equipment enclosure
    (6) For ungrounded systems, the grounding terminal bar within the service equipment enclosure
     
  18. Bannerman

    Bannerman Well-Known Member

    Joined:
    Mar 19, 2014
    Location:
    Ontario, Canada
    The wording of the OP makes it unclear, but since the cooktop is installed in an island, I anticipate the vent fan is then a separate appliance unless an extractor is built into the cooktop in which case, mention of a vent fan would not be required.

    I understand a range circuit is to be dedicated to one appliance, and no other branch circuits maybe wired from it. I have since read NEC does allow a range circuit to be utilized for both a seperate cooktop and wall oven IF local codes permit, but no additional outlets or separate hard wired appliances such as a range hood may share that circuit.
     
  19. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    If the vent fan is on the same circuit as a cooktop, then I assume it is a downdraft and may well be built in to the cooktop. Even if not, I would say one could argue that the vent fan is still a household cooking appliance.

    To my knowledge there is no requirement in the NEC for an individual branch circuit for a cooktop or a wall oven. Indeed, as a range served by an individual branch circuit is not uncommonly replaced with a separate wall oven and cooktop, in that situation it is typical to power them both from the same branch circuit. (2014) 210.19(A)(3) addresses this in part. [The word "tap" here means a conductor without normally sized OCPD at its point of supply.]

    Cheers,
    Wayne


    210.19(A)(3) Household Ranges and Cooking Appliances. Branch circuit conductors supplying household ranges, wall mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8 3/4 kW or more rating, the minimum branch-circuit rating shall be 40 amperes.
    Exception No. 1: Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units shall have an ampacity of not less than 20 amperes and shall be sufficient for the load to be served. These tap conductors include any conductors that are a part of the leads supplied with the appliance that are smaller than the branch-circuit conductors. The taps shall not be longer than necessary for servicing the appliance.
    Exception No.2: (omitted, about downsizing the neutral conductor)
     
  20. rjschwar

    rjschwar New Member

    Joined:
    Jul 11, 2020
    Location:
    Washington
    The cooktop is 4 wire on the 240 circuit with a built in downdraft fan. Same with the oven/microwave. 4 wire 240 appliance and somewhere internal the microwave is getting the 120V. There is nothing else on the circuit except the 2 240V appliances.

    Here's maybe another dumb question. The original installation just used wire nuts (blue) to connect the aluminum to the copper appliance wire. This isn't right correct? What is the appropriate way to attach 6 gauge aluminum to copper? I think the appliance wire is 12 gauge but I'd have to double check.
     
  21. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    So the old SE cable goes to the wall oven, and then modern 3 conductors plus ground goes from there to the island cooktop? The proper thing to do with the separate neutral/grounds in the new cable is not 100% obvious. Hopefully they got that and the case bonding at the oven and the cooktop correct.

    As to the aluminum to copper connection, I'd suggest Polaris-style insulated mechanical connectors, they are typically rated for both aluminum and copper. E.g. (3) 3-port connectors, incoming aluminum, outgoing copper, and pigtail to wall oven. Space in the wall oven wiring compartment might be an issue, but a junction box with blank cover could be set behind the wall oven, I think.

    Cheers, Wayne
     
Similar Threads: Wire Range
Forum Title Date
Electrical Forum discussion & Blog Question on breaker, wire, and outlet for Oven/range Aug 29, 2019
Electrical Forum discussion & Blog Question on 3-wire Kitchen Range > 4 wire Nov 24, 2016
Electrical Forum discussion & Blog Strange question..maybe. Combining wires from two circuts Jun 30, 2012
Electrical Forum discussion & Blog 4 wire range to 3 wire receptacle Dec 26, 2011
Electrical Forum discussion & Blog Sizing Kitchen Range Breaker Size & Wire Gauge Apr 12, 2011

Share This Page