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  1. #1
    Terry Beck's Avatar
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    Default Does 2 x 120 volt = 240 volt wiring?

    Odd ball wiring, but I have seen it once before. This home is 15 years old, and was approved by the state electrical inspector - although, the breakers described below are probably newer than the original panel wiring.

    The metal enclosure in the wall is what used to be a Cadet electric wall heater (yeah, I know all about the recalls, that's not my question).
    You'll see that they have run double hot conductors, double neutral conductors, and double grounds. Every other existing Cadet in the house are 220-volt heaters (I did not remove them to see how they were wired, but assume that at least one other is done this same way).

    At the main electrical panel I see this breaker wiring configuration. A 20-amp duplex-Square D breaker, with pairs of hot conductors. The Square D breakers are rated for 2 copper conductors. Could not trace where they went, but the poor labeling indicated "spare heat".

    Though the Square D breakers are rated for multiple branch circuits, this seems like a non-compliant installation, but What are the electrical dangers here?

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  2. #2
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    Default Re: Does 2 x 120 volt = 240 volt wiring?

    Those double breakers that take up on breaker slot are not allowed in some municipalities, you'll need to check with yours.
    You only have 220 if each hot wire to the unit is being fed by each incoming service leg. Depending on the panel this will be alternating or opposite breaker slots.

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  3. #3
    neal lewis's Avatar
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    Default Re: Does 2 x 120 volt = 240 volt wiring?

    At the wall heaters, it's not double wiring. One pair of wires is run into the heater and the other is going out to the next heater. That's why they're twisted together with the heater gone.

    BTW it's 240, not 220 volts.

    Marcus, you're saying that tandem breakers are not allowed?


  4. #4
    Jerry Peck's Avatar
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    Default Re: Does 2 x 120 volt = 240 volt wiring?

    Most likely ... the top breaker has 240 volts across the black/white conductors.

    The second breaker down only has 120 volts from those black conductors to ground or neutral.

    The white conductors on the top breaker are required to be permanently re-identified from white to (black/red/brown/some hot color) by painting or other effective means (tape is not a permanent method, though there is not even any tape there).

    Jerry Peck, Construction / Litigation Consultant
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  5. #5
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    Default Re: Does 2 x 120 volt = 240 volt wiring?

    No 'mini/two circuit' breakers allowed in Chicago. I've gone over it with the city insp and they write it all the time. The theory being if someone starts throwing in a bunch of mini's there may be overload issues requiring a new panel or larger service.

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  6. #6
    Jerry Peck's Avatar
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    Default Re: Does 2 x 120 volt = 240 volt wiring?

    Quote Originally Posted by Markus Keller View Post
    The theory being if someone starts throwing in a bunch of mini's there may be overload issues requiring a new panel or larger service.
    That does not make any sense.

    I could put just as much load on a bunch of 40 amp breakers and overload the main disconnect.

    Sure, *BOTH* would overload the main, and both would be just as wrong. You are only allowed to install those in specific locations in many panels.

    If you do something based on people ignoring the instructions, then base it on them 'ignoring the instructions' - which includes installing too many large breakers.

    Jeez, what a lame reason for disallowing them.

    Sorry, no 40 amp or larger breakers allowed either.

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  7. #7
    Richard Moore's Avatar
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    Default Re: Does 2 x 120 volt = 240 volt wiring?

    Square-D lists its load centers for the number of allowable circuits (up to 42). That may include listed spaces for tandem breakers. The first JPEG is the breaker mounting diagram for a couple of very common Homeline 200-amp panels (QOs and smaller panels are similar). The left one is a "20/40" panel allowing tandem breakers in every one of the 20 full-size positions. The right one is a "30/40" allowing tandems only in the bottom 10 of the 30 full-size positions for a total of 40 "circuits".

    The second JPEG shows the difference at the bus bars to prevent mounting tandems where they are not supposed to go.

    Those "preventions" might be overcome by off-brand breakers or deliberately...ummm...modifying the Square-D breakers, but then any panel can be screwed up or overloaded by some idiot willing to ignore the instructions.

    I agree with Jerry; not allowing tandems where the panel is clearly listed for their use makes no sense other than it probably creates more work for the local electricians' union.

    BTW, I also agree with Neal's assessment..."At the wall heaters, it's not double wiring. One pair of wires is run into the heater and the other is going out to the next heater. That's why they're twisted together with the heater gone." Based solely on the photos, I don't see any issues (as long as the whites are identified as hots, particularly at the heater box, and the grill cover is put back on).

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    Last edited by Richard Moore; 07-16-2008 at 04:22 PM.

  8. #8
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    Default Re: Does 2 x 120 volt = 240 volt wiring?

    Please Jerry, like that's the first weird municipal reasoning either on of us has heard? From my experience, I'm not sure how (except for brains and years of experience) the muni insp would know if the panel is rated for mini's or not.
    a) they don't open panels; b) they generally don't have time or inclination to do research and c) they leave the burden of proof on the property owner.

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  9. #9
    Jerry Peck's Avatar
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    Default Re: Does 2 x 120 volt = 240 volt wiring?

    Quote Originally Posted by Markus Keller View Post
    I'm not sure how (except for brains and years of experience) the muni insp would know if the panel is rated for mini's or not.
    a) they don't open panels;
    They (I being one at times) don't open the panels either ... ... we simply tell the electrician that if the panel cover is not removed and nearby (usually hanging from one corner screw), that we will not inspect the panels, oh, and there will be a re-inspection fee too.

    b) they generally don't have time or inclination to do research
    No research required, it is either so stated in the panel schematic or they are not allowed.

    and c) they leave the burden of proof on the property owner.
    No, they leave the burden of proof on the electrical contractor, if that contractor wants to pass his inspection.

    Jerry Peck, Construction / Litigation Consultant
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  10. #10
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    Default Re: Does 2 x 120 volt = 240 volt wiring?

    a) you are assuming coordination among the parties
    b) you are assuming they can read
    c) you are assuming new install by an electrical contractor
    All very noble and proper ideas that at least around here are the exception rather than the norm.

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  11. #11
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    Talking Re: Does 2 x 120 volt = 240 volt wiring?

    ec jerry,
    kudos on post #9. i work on both sides of the fence also and make it a point to not trash either side.


  12. #12
    Jerry Peck's Avatar
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    Default Re: Does 2 x 120 volt = 240 volt wiring?

    Quote Originally Posted by brian schmitt View Post
    i work on both sides of the fence also and make it a point to not trash either side.

    Brian,

    I trash BOTH sides ... when it is deserved.

    And sometimes just for fun. (kidding, maybe)

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