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    Page 1 of 1

    Dual-fuel range electrical hookup question

    New postPosted: Tue Jul 26, 2016 12:25 am
    by tedcohen
    I bought a dual-fuel COSMO range, which is apparently foreign (Chinese?) made. The oven is electric and the cooktop is NG.

    Anyway, the instruction manual says it must be wired with a "three-phase, four-PRONG cord." (Three phase? Residential? Is that how the Eurpoeans do things?)

    My house was built in 1961 and has a three-wire range configurement, No. 8 cable going from the main panel to a three-prong receptacle in the kitchen.

    OK so far...?

    I uncrated the range and looked at the back, from which protrudes a three-wire armored cable. Not four wires, but three.

    A tag on the cable says "no neutral required," and I see two hots and a ground.

    Why the instructions say I need four prongs? God knows.

    Anyway, can I buy a three-pronged plug and attach the hots on the sides (either side, either hot) and the ground on the top?

    I ask that, assuming that the third wire on my existing three-wire range cable in my house is connected to the ground bar in the main panel. (Ground and neutrals in the main panel's kind of the same, right, since don't they go to the same grounded busbar?)

    Thanks much.

    Range voltages: 220-240V/50-60Hz, 35 Amps

    link to installation instructions: http://www.homedepot.com/catalog/pdfIma ... cb7aa8.pdf

    Re: Dual-fuel range electrical hookup question

    New postPosted: Tue Jul 26, 2016 9:10 am
    by Jerry Peck - Codeman
    I found the answer in the installation manual you linked to:
    - Yes, that is designed for 3-phase wiring systems.
    - And, yes, it may be connected to single-phase wiring systems.

    Page 34 of 51 see Figure 24.jpg


    Newer construction (since around 1996 or so) have four-wire circuits (four-prong plugs/receptacles) for ranges and dryers, before that time, ranges and dryers were only wired with three-wire circuits (three-prong plugs/receptacles).

    With three-wire circuits, there were two-hot conductors and one neutral/ground conductor (the metal appliance cabinet was not really 'ground', it was 'neutral') and that lead to many instances of electrical shocks.

    The wiring change to four-wire circuits added a separate ground, there were two-hot conductors, one-neutral conductor, and one-ground conductor (the metal appliance cabinet is now 'ground' and not 'neutral').

    You will need a four-wire cord and plug to match the four-wire receptacle which is installed (presuming that the house is new enough to have a four-wire circuit).

    You will not need to use the neutral connection according to Figure 24, so make sure that wire is capped off so it cannot accidentally make contact with any of the other wires or terminals.

    Re: Dual-fuel range electrical hookup question

    New postPosted: Tue Jul 26, 2016 9:26 am
    by tedcohen
    Jerry,

    I am not proficient enough to understand electrical phases.

    But sounds as though you say I'm OK to use the three-wire range cable that is currently in the house, employing the third wire as the ground instead of a neutral?

    My house was built in 1961, so it has a three-wire receptacle.

    Do I need to open up the service panel to see whether that third wire is grounded (assuming it's OK to use that wire as I have specified above)? (The service panel is new - less than a year ago when electrician put in a new panel and new breakers.)

    Thanks!

    Re: Dual-fuel range electrical hookup question

    New postPosted: Tue Jul 26, 2016 10:25 am
    by Jerry Peck - Codeman
    As you have a three-wire circuit and matching receptacle, you will need to use a three-wire/prong range cord.

    The drawing shows that one hot conductor is connected to a terminal which apparently is marked as L1, the other hot conductor would be connected to a terminal marked as L2, and the third wire in the cord, which in the receptacle is neutral/ground, is connected to the ground terminal.

    DO NOT connect the white/neutral terminal to anything according to Figure 24.

    Back at your panel, if we presume that your panel is the service equipment with the main service disconnect, then the neutral is bonded (connected) to ground at that panel, so the neutral/ground wire in the three-wire circuit is connected to ground at that panel.

    However, if that panel is not the service equipment panel and does not have the main service disconnect, then the neutral is likely not (should not be) bonded (should not be connected) to ground.

    In 1961, I am guessing that the panel is the service equipment panel which has the main service disconnect in it, if so, the connection of the circuit to the panel should be okay.

    The above is based on Figure 24 in the installation instructions.

    Re: Dual-fuel range electrical hookup question

    New postPosted: Tue Jul 26, 2016 12:59 pm
    by tedcohen
    OK, so, I will buy a three-prong PLUG for the THREE-WIRE armored cable coming from the back of the stove. (No need for a so-called range cord since the range has its own armored cable that simply needs a plug.)

    Why the instructions say range "must be wired with a three-phase, FOUR-PRONG cord" escapes me - since the armored cable coming from the rear of the stove is a THREE-WIRE cable.

    A tag on that armored cable says, "Frame grounded by connection of grounding lead to neutral lead. If local codes do not permit grounding through neutral, open the connection and use grounding lead to ground unit. Connect neutral lead to branch-circuit neutral conductor in usual manner."

    A second tag says, "No need to use neutral. The potential at the power supply electrical connections shall be 150 volts to ground or less."

    So, I assume that since I am using a three-wire receptacle since my house is pre-1996 that I should leave the armored cable connection as it came from the manufacturer and not open it up and split the ground and the neutral?

    Photo attached (with luck) of armored cable coming from stove.

    Re: Dual-fuel range electrical hookup question

    New postPosted: Tue Jul 26, 2016 2:50 pm
    by Jerry Peck - Codeman
    That photo helps a lot - it is already factory wired for a single-phase connection such as we have here in the US.

    tedcohen wrote:OK, so, I will buy a three-prong PLUG for the THREE-WIRE armored cable coming from the back of the stove. (No need for a so-called range cord since the range has its own armored cable that simply needs a plug.)


    Correct.

    Why the instructions say range "must be wired with a three-phase, FOUR-PRONG cord" escapes me - since the armored cable coming from the rear of the stove is a THREE-WIRE cable.


    They probably printed up one set of installation instructions and then tried to adapt it to different wiring systems.

    A tag on that armored cable says, "Frame grounded by connection of grounding lead to neutral lead. If local codes do not permit grounding through neutral, open the connection and use grounding lead to ground unit. Connect neutral lead to branch-circuit neutral conductor in usual manner."

    A second tag says, "No need to use neutral. The potential at the power supply electrical connections shall be 150 volts to ground or less."


    Yes, that does mess with the mind as that is not what is shown in Figure 24 of the installation instructions and the two statements contradict each other to an extent (no neutral is 'needed' because there are apparently no 120 volt loads, which means all the light bulbs (lamps) will be 240 volt, as will all the controls, fan motors (if any), etc - so a neutral is not "needed" for anything, however, the neutral connection within the range is apparently bonded (connected) to ground, which means that they could (should not, but 'could') be using the neutral-bonded-to-ground-as-a-neutral-connection for 120 volt lamps. If your lamps are 120 volts, then the neutral SHOULD NOT be connected to ground, and that would mean re-wiring the circuit to a four-wire circuit ... except that your house was built in 1961 when a three-wire circuit was allowed, and the neutral current was permitted to be on the ground conductor - not the safest wiring, but what was allowed 'back then' and one more reason it is no longer allowed.

    Be that as it may be, the photo shows a 'factory supplied' 'pig tail' with 'red' (hot), 'black' (hot), and a 'green' (ground) conductors to be connected to the circuit. HOPEFULLY ... all factory wiring beyond what is shown in the photo is correctly done. If so, your dual-fuel range is wired for connection to a 240 volt ONLY circuit, with a ground for the metal case of the range.

    So, I assume that since I am using a three-wire receptacle since my house is pre-1996 that I should leave the armored cable connection as it came from the manufacturer and not open it up and split the ground and the neutral?


    Options:
    1) IF ... you do not already have a three-wire (three-slot) receptacle installed, make the pigtail connection directly into the electrical box with the appropriate cover which has a connector to receive that pigtail.

    2) IF ... you have a three-wire (three-slot) receptacle installed, then remove that pigtail and replace it with a three-wire range cord which has a three-prong plug on it.

    Options 1) and 2) are the proper ways to connect that range as that pigtail is not intended or designed to have a plug installed on the end of it.

    You need a disconnect for that range, a cord and plug into a receptacle serves as that disconnect; if you directly wire that pigtail into the electrical box, then a disconnect is needed either there or at the panel, I will presume that your 1961 house has breakers, and if it does, then get a 'breaker lock out' device (available for different many types of panels, but may no longer be available for some older discontinued panels). A breaker lock out device fits over the breaker behind the panel cover (so it stays in place at all times) and when the breaker is flipped 'off', a small lock can be installed so you can safely work on the wiring without anyone turning the breaker 'on' while you are working on it ... no need to cook you while trying to hook up the range to cook dinner ... not a good thing to do.

    The above may sound like a silly additional precaution to you (or others), but it is neither a silly nor a little precaution if you ask the surviving spouses of those who thought it was a silly little thing to do.

    Re: Dual-fuel range electrical hookup question

    New postPosted: Tue Jul 26, 2016 3:06 pm
    by tedcohen
    Fascinating!

    Thanks much Jerry for your diligence.