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Thread: 15 amp and 20 amp circuits in same box

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    DIY Junior Member LHO's Avatar
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    Default 15 amp and 20 amp circuits in same box

    I have added a partition wall in an existing space (next to kitchen). I will be adding one outlet extending the existing 20 amp circuit. Also, I want to have one of these outlets switched with the overhead light circuit. I am wondering if there is a problem with cutting the "hot" tab on the side of the receptacle and having the top outlet switched 15 amp, the bottom 20 amp? My concern would be if someone plugged in a surge protector (like below) or other device that gangs the upper and lower outlets. (I don't plan to do this here, but I use two such devices in other rooms.) If the two circuits are on opposite sides of the phase it could get ugly if one of these is plugged in.
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    Electrical Contractor/Instructor jwelectric's Avatar
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    But nothing would be wrong with installing a second receptacle on the 15 amp circuit right beside or above or below the 20 amp circuit.

    If you split one receptacle then there is some other issues other than the one you posted that would need to be addressed so do as I suggested for simplicity

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    DIY Junior Member LHO's Avatar
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    I could put two duplex recepticals -- I presume that I can put them in the same box (yes, I know, connect all neutrals and grounds).

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    Electrical Contractor/Instructor jwelectric's Avatar
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    connect all grounds yes

    each neutral goes with its own circuit so do not connect all neutrals

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by LHO View Post
    ... having the top outlet switched 15 amp, the bottom 20 amp?
    As I understand things, either would still only be a 15A outlet as far as its actual rating is concerned unless the outlet was specifically configured/designed/engineered for 20A (with one horizontal blade, I think) in the first place. In other words, multiple 15A outlets are typically used in 20A circuits.

    Quote Originally Posted by LHO View Post
    My concern would be if someone plugged in a surge protector (like below) or other device that gangs the upper and lower outlets.
    I have never seen one of those multipliers ever gang the uppers and lowers together (although that might not be true of an actual surge-protecting multiplier). In fact, I occasionally use one of them on the end of an extension cord and have never found the unused blades on the back energized. So then, the upper and lower parts of the multiplier would still act just like their places of actual connection whether or not the upper and lower were separated at the wall receptacle.
    Last edited by leejosepho; 10-24-2011 at 09:50 AM.
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    DIY Junior Member LHO's Avatar
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    Quote Originally Posted by jwelectric View Post
    connect all grounds yes

    each neutral goes with its own circuit so do not connect all neutrals
    Just so I understand -- Are the neutrals not connected because of the different amperage of the circuits? I ask this because several of the switch boxes have switches from different 15 amp circuits. In this case the neutrals are all connected.

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    DIY Junior Member LHO's Avatar
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    Quote Originally Posted by leejosepho View Post
    As I understand things, either would still only be a 15A outlet as far as its actual rating is concerned unless the outlet was specifically configured/designed/engineered for 20A (with one horizontal blade, I think) in the first place. In other words, multiple 15A outlets are typically used in 20A circuits.


    I have never seen one of those multipliers ever gang the uppers and lowers together (although that might not be true of an actual surge-protecting multiplier). In fact, I occasionally use one of them on the end of an extension cord and have never found the unused blades on the back energized. So then, the upper and lower parts of the multiplier would still act just like their places of actual connection whether or not the upper and lower were separated at the wall receptacle.
    It's not the outlet that would be 20 amp, it's the circuit and of course, the 20 amp circuit has #12 wire.

    I did get out a multiplier and a surge protector multiplier. You are right the top and bottom blades are not connected.

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    Electrician ActionDave's Avatar
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    Quote Originally Posted by LHO View Post
    Just so I understand -- Are the neutrals not connected because of the different amperage of the circuits? I ask this because several of the switch boxes have switches from different 15 amp circuits. In this case the neutrals are all connected.
    The neutrals from different circuits should not intermingle. The current that leaves the panel on circuit A should return on wiring associated with circuit A only, not circuit B or C or any other.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by LHO View Post
    It's not the outlet that would be 20 amp, it's the circuit and of course, the 20 amp circuit has #12 wire.
    Yes, and I had missed the part about your wanting to switch the other part of the receptacle with a light circuit. So, I had thought you were intentionally trying to have different amperages available at that outlet where both halves are rated at 15A. Please excuse!

    Quote Originally Posted by LHO View Post
    I did get out a multiplier and a surge protector multiplier. You are right the top and bottom blades are not connected.
    I suspect the safety engineers were way ahead of both of there since what you are doing is common, and since I am likely not the only one to ever attach a multiplier to a single-ended extension cord.

    Quote Originally Posted by ActionDave View Post
    The neutrals from different circuits should not intermingle. The current that leaves the panel on circuit A should return on wiring associated with circuit A only, not circuit B or C or any other.
    Unless, of course, two circuits (drawing from the same leg, I think) are specifically wired with a shared neutral, correct?

    Note: My washer/dryer combo is 240V, but I suspect its neutral is shared internally since the appliance likely has 120V circuits/components inside.
    Last edited by leejosepho; 10-25-2011 at 06:52 AM.
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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by leejosepho View Post
    Quote Originally Posted by ActionDave View Post
    The neutrals from different circuits should not intermingle. The current that leaves the panel on circuit A should return on wiring associated with circuit A only, not circuit B or C or any other.
    Unless, of course, two circuits (drawing from the same leg, I think) are specifically wired with a shared neutral, correct?

    Note: My washer/dryer combo is 240V, but I suspect its neutral is shared internally since the appliance likely has 120V circuits/components inside.
    When wiring multiwire branch circuits it is important to know and understand what is happing or an overload can and will occur.

    Multiwire circuits that are installed to items such as dryers and ranges are not something to worry about as the cable and over current devices are pretty straight forward.
    210.4 of the NEC mandate that all ungrounded (hot) conductors must be opened at the same time on multiwire circuits. With a dryer the two pole breaker will do this as well as the breaker for the range. The cable will have the appropriate size conductors and no problems.

    When wiring something such as these receptacles the same rule applies. The breaker must open all ungrounded conductors at the same time and the two ungrounded conductors would need to share the same neutral.

    What will happen here is one 20 amp 2 wire cable and one 15 amp 2 wire cable will be installed which will result in two neutral conductors of different size. These neutral conductors will land on the same terminal bar in the supplying panel and should they again terminate together would constitute a parallel conductor and then would have to comply with 310.4 and be;
    (1) Be the same length
    (2) Have the same conductor material
    (3) Be the same size in circular mil area
    (4) Have the same insulation type
    (5) Be terminated in the same manner
    Which a 12 and a 14 wouldn’t meet the criteria for a parallel circuit.
    Another danger is if both are on the same leg of the panel. This would make the current add on the neutral which will result in an overload and damage the conductor.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Understood ... and some of this has recently been on my mind since there seems to me to be a difference between two legs running 240V to something like a welder (with an equipment ground, of course) and then two legs and a neutral going to my 240V washer/dryer combo (which also has an equipment ground). The washer/dryer seems to need a common neutral internally where a welder does not, so where a 240V welder would have a black, a white and a bare wire, the washer/dryer combo needs four wires: black, red (or whatever), white and bare, correct?

    I am not sure whether one of the three wires running to my 240V dual-fuel (gas top) range/oven is bare, but I think it is ... and that would mean the oven's "equipment ground" actually also doubles as a neutral (via bonding at the supply panel) for its clock and controls (that I assume are 110V).
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    Electrical Contractor/Instructor jwelectric's Avatar
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    Appliances such as dryers use two voltages in order to do their functions. The heating element on the dryer is a 240 volt component and the motor that turns the tub in most cases is a 120 volt component along with the controls.

    Most ranges will have 240 volt heating units with a 120 volt light and clock.

    Appliances such as welders, well pump motors, water heaters, electric heating, air conditioners and the such are just 240 volt appliances that needs no neutral for anything 120 therefore only two conductors.
    The NEC and good common sense tells us to re-identify the white conductor by encircling it with tape, paint, marker, or just a tag to let everyone know that it is an ungrounded conductor.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by jwelectric View Post
    The NEC and good common sense tells us ...
    What would bad common sense have to say?! (wink)

    In any case, and in my simple ignorance that has nothing to do with any kind of sense, I had thought it was okay to use tape or whatever to mark and/or to label wires, but that a wire's color could not be changed by tape.

    So, thanks for the info.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    Electrical Contractor/Instructor jwelectric's Avatar
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    We are not changing the color of the wire we are re-identifying it so it won’t be confused with a grounded neutral conductor but instead a person would see the tape around the white conductor and know that it is being used as an ungrounded (hot) conductor.

    The same re-identification is allowed when using the white conductor of a cable in switch loops.

    In the event of using single strand conductors in a raceway such as EMT or conduit then we are not allowed to re-identify a conductor simply because we are able to install the proper color conductor.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by jwelectric View Post
    In the event of using single strand conductors in a raceway such as EMT or conduit then we are not allowed to re-identify a conductor simply because we are able to install the proper color conductor.
    Ah, now I see. My concern was about whether the electrician might be required to run a new line to my range (as part of our service-entrance update) if the existing third conductor is only bare, but the allowance you have just explained answers that question.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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