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Thread: SPDT double-throw switch

  1. #16
    General Engineering Contractor ballvalve's Avatar
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    I really do not get you guys. Is it just the contrarian view?

    Under your suggestions, it seems we could hook up the AC, the baseboard heat, and the microwave all on one breaker because the breaker will take care of it in case someone turns them all on at once.

    Second one can’t overload half of a two pole breaker. The breaker is either overloaded or it isn’t.
    So the NEC allows a double pole 20 amp breaker [simply two singles ganged togther] to be wired with 2 wires or circuilts on one half of it that is sure to be loaded to 40 amps at some indeterminate time?

    I am sure any electrician, including the building inspector, will insist that the 2 permanently installed appliance be on seperate, independant circuits.
    Last edited by ballvalve; 12-29-2010 at 03:34 PM.

  2. #17
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by ballvalve View Post
    I really do not get you guys. Is it just the contrarian view?
    Under your suggestions, it seems we could hook up the AC, the baseboard heat, and the microwave all on one breaker because the breaker will take care of it in case someone turns them all on at once.
    No, I don’t believe anyone has said anything about a microwave until now. I believe what has been said to this point is that two noncoincident loads can be on one circuit such as heat and air conditioner. I also believe that a picture of a 240/120 volt receptacle was also posted to show that the two can be connected to the same overcurrent device.
    Quote Originally Posted by ballvalve View Post
    So the NEC allows a double pole 20 amp breaker [simply two singles ganged togther] to be wired with 2 wires or circuilts on one half of it that is sure to be loaded to 40 amps at some indeterminate time?
    And sometimes even mandate that this be done. By the way should a 20 amp breaker be loaded to 40 amps guess what is going to happen.
    Quote Originally Posted by ballvalve View Post
    I am sure any electrician, including the building inspector, will insist that the 2 permanently installed appliance be on seperate, independant circuits.
    Well there is at least two electricians that is not requiring this and as far as an inspector is concerned he can not require something to be done any different that is allowed by the NEC.

    I am sorry if you don’t understand this concept and your lacking of understanding goes to prove how important that someone working on an electrical system have some kind of knowledge of what they are doing other than what they read posted on the web. It is also why so many states require a license for someone entering the electrical contracting field.
    Last edited by jwelectric; 12-29-2010 at 03:51 PM.

  3. #18
    Moderator & Master Plumber hj's Avatar
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    Along with what everyone else has posted, it should be a DPDT switch so the baseboard is COMPLETELY removed from the circuit, not just one leg to it. The AC would be wired to ONE of the two poles on the other side of the switch.

  4. #19
    DIY Junior Member Bird Doo Head's Avatar
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    Hi All
    It looks like this thread got kind of grouchy! (Hopefully all in good fun!)
    It also looks confusing. The writer, Ken, has lots of great responses from you folks. If you all don't mind, I'd like to offer my thoughts on the matter for Ken to also consider:

    My Thoughts:
    A) I absolutely would not share the heater circuit with a receptacle outlet. If you look at NFPA 70 you will see a prohibition against connecting the built in receptacles on a baseboard heater to the heater circuit. (I don't have the code book in front of me right now, but I believe it is 424.9) Logic would dictate that the AHJ would also object to a "not-built-in" receptacle outlet wired from the heater circuit. You can always ask for "Special Permission" (See 424.10, I believe it is)

    B) Watch where you locate the receptacle outlet. Most, if not all, heater manufacturers prohibit receptacles directly above the heater. This is required for them to receive listing by UL or other testing agencies for their product. (And it is a safe idea. After time, the constant heat will deteriorate the jacket on SPT lamp cord. It will get dry, brittle and crack.)
    If you do install the receptacle above the heater, against the manufacturer's requirements, you are have voided the listing by an approved testing agency- It's a code violation to install it without the listing. (And, perhaps an excuse for your fire insurance carrier to deny a claim.)

    C) Also, you may need this receptacle protected by an Arc Fault Interrupter, depending what room it is in. If that's the case, you're probably going to have a less expensive project by running the receptacle's wiring from an existing circuit that's AFCI protected, if the capacity is sufficient for what you want to do with the receptacle.

    If you have the receptacle protected by AFCI on the same circuit as the heater, I would expect nuisance tripping. It is hard to believe that AFCI's and line voltage thermostats would get along. When the bi-metal is cold, the stat's internal arcing could be a long enough duration to open the AFCI. <Great! Now I have to know. Time to experiment around a bit>

    D) If you do get approval & plan to go ahead and share the heater circuit with the receptacle outlet, remember that the capacity may not be enough on the 20 amp circuit. Fixed electric heating equipment must be calculated as continuous loads. That's also in Article 424 somewhere. (424.3B? 4B?) If you're getting a permit, this may be an issue if the heater is close to the circuit's permissible total load (even if you don't plan to run the heater and use the receptacle simultaneously).

    But, to be honest, in my own home I have a non-standard installation. There's an enclosed porch with one fixed electric baseboard heater & a line voltage wall stat. We rarely use it. ($$$$) The receptacle outlets, lighting outlets and such are NOT connected to the heater circuit- But this circuit is not "dedicated" for the heater. Also on it is a NEMA L6-20 (240 volt 3 Wire) receptacle at my experimental bench (not on the porch). No neutral is required for the receptacle's intended purpose. That receptacle is part of a group of power taps for testing & evaluation purposes. I know the load each time I use it. If the porch heater is on, I'll turn it off.

    Is it 100% code compliant? I'd bet many people on this forum could find reasons that it is not, if we wanted to. (Starting right at 424.9, moving on over to 210.8A-5, etc) Is it safe for MY purposes? Yes. Would I leave it if I sell the house? No! Absolutely not. I'd eliminate the receptacle outlet.

    Ken: I hope I was able to add some ideas for you to consider. I sincerely hope I didn't confuse you more. I'd leave the heater(s) on a dedicated circuit.
    Paul

  5. #20
    General Engineering Contractor ballvalve's Avatar
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    Thank you. Finally a response of reason, knowledge, and practicality. Circuit breakers are not designed to correct obtuse and unneeded circuitry. Do it right from the start, and your breaker will only trip when a unexpected and dangerous event happens.

    I am surprised that Marne rock, such a stickler for laws and safe circuits has been advocating this odd wiring scheme.

  6. #21
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by ballvalve View Post
    ........................ this odd wiring scheme.
    Odd, yes, sort of.
    Legal and SAFE, also YES!

    Just because you don't understand this stuff fully please don't criticize those of us that do!

  7. #22
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Bird Doo Head View Post
    If you look at NFPA 70 you will see a prohibition against connecting the built in receptacles on a baseboard heater to the heater circuit.
    True, but it specifically refers to the fact that a built-in receptacle can be used in place of one specified in 210.52(B), meaning they don't want the heater shared with a general use receptacle.
    In this case we are talking about a receptacle dedicated to an air conditioner.

    IMO there are a BIG difference here.

  8. #23
    DIY Junior Member Bird Doo Head's Avatar
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    I suppose your interpretation of the reason the paragraph exists could be valid. But, as we all know, each AHJ has their own take on things. I'd be more inclined to pass a shared circuit if the outlet sharing with the heater was a single receptacle outlet on the yoke and it was blocked by the air conditioner. (Alternatively, a twist lock.) It might fly if the A/C was the indoor unit from a split system (again, placing the receptacle so it can not be used by anything but the A/C). I'd also have to calculate the circuit, consider motor load, etc.

    Yes, the built-in receptacle may always, always be counted as one of the 210.52(A)(1) required receptacle outlets. This paragraph is provided so the "no receptacle outlet above the heater" requirement of the manufacturer does not prevent a residence from having the required 210.52(A)(1) outlets. Picture a room with electric baseboard heaters from end-to-end on one wall. Since you may not install a receptacle above an electric heater, how would you be compliant with "no point along the floor line shall be more than 1.8 meters from ... "? That is why the sentence allowing the built in to count is in the NEC. (Floor receptacles aren't necessarily the answer. One could still drape cords over the heater, going up to a table lamp and they can be very impractical, costly to install & possibly not approved to count as one of the required.)

    I know for an absolute fact any 120 volt receptacle on the heater circuit would not pass in Detroit; commercial or residential. I can also name several other jurisdictions where 424.9 (or is it .10? I forgot) has been firmly judged to mean no receptacle outlets on the heater circuit.

    Electric heaters' receptacle outlets are often the subject of questions because electric baseboard heat is popular around here in older homes with hydronic or steam heat. People add rooms and don't want to (or can't) tap the wet system. Or, like me, have a room that is allowed to freeze and don't want to send the hydronics out there, thus requiring glycol.

    Please don't forget about the possibility of this receptacle outlet being in a room requiring protection by an arc fault device. I suggest you keep it simple and straight forward. I'd separate the heater circuit.

    Since you have to get tools out, drill holes, pull & staple NM, bash your head on joists, put the tools away & clean up the mess anyway, you might as well pull in two circuits. But this is your house and you are the one paying for the cable and doing the work while I'm sitting at home with my feet up, reading a good book and enjoying a deelicious glass of Kool-Aid!

    Thanks for letting me give my thoughts on the matter,
    Paul

  9. #24
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Bird Doo Head View Post
    I know for an absolute fact any 120 volt receptacle on the heater circuit would not pass in Detroit; commercial or residential. I can also name several other jurisdictions where 424.9 (or is it .10? I forgot) has been firmly judged to mean no receptacle outlets on the heater circuit.
    Well, it is obviously not clear cut so that gives an AHJ quite a bit of leverage if they choose.
    Thankfully the whole country is not Detroit.



    Quote Originally Posted by Bird Doo Head View Post
    Please don't forget about the possibility of this receptacle outlet being in a room requiring protection by an arc fault device. I suggest you keep it simple and straight forward. I'd separate the heater circuit.
    What I or we would do is irrelevant here IMO. The question has become is it legal to have 120v A/C and 240v electric heat load share a common MWBC. IMO yes.

    If you must know. Would I do it? I have to say maybe. Depends on the situation.
    Under "normal" conditions of course not.

  10. #25
    General Engineering Contractor ballvalve's Avatar
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    I am sorry if you don’t understand this concept and your lacking of understanding goes to prove how important that someone working on an electrical system have some kind of knowledge of what they are doing other than what they read posted on the web. It is also why so many states require a license for someone entering the electrical contracting field.
    Posted by marne rock.....

    I intuitively and historically understand electric circuits so well that I do not hide behind obscure and worthless quotes from the NEC. For you to pursue this obtuse circuit as being "allowed", makes me think you may be imbued with knowledge of the law but inept when it comes to pulling a wire and thinking about how it will interface with actual, daily use.

    I would never subject my customers or self to a "doubled up" circuit breaker, certain to be overloaded by a customers actions at a later date.

    An advocate of correct, failsafe circuits as yourself should have told the original poster that he needed to simply pull a 12-2 wire for the AC and spend and extra 8$ To protect his family and follow the law and adhere to the best practices. I believe Mr.Birddo has given you sufficient information to retract the previous defenses.

    If anyone else bothered to read this forum, you would have many more detractors in what seems to be a private club of dubious distinction.

    Once again in the hopes of getting you to understand, you proposal seems to be the same as saying that your rooftop AC drawing 40 amps, might as well also have 2 more wires on the same breaker feeding a 40 amp electric wall heater, "because they won't be on at the same time"

    Its not going to be accepted by any inspector or electrician with a scant bit of sense.

    And thanks HJ for the switch idea backup, which started this whole thing. I originally said he needed total disconnect of the two circuits, OR 2 seperate wire runs, of which only the seperate breaker and wire run made any practical sense.
    Last edited by ballvalve; 12-31-2010 at 12:09 AM.

  11. #26
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by ballvalve View Post
    I intuitively and historically understand electric circuits so well that I do not hide behind obscure and worthless quotes from the NEC. For you to pursue this obtuse circuit as being "allowed", makes me think you may be imbued with knowledge of the law but inept when it comes to pulling a wire and thinking about how it will interface with actual, daily use.
    What a complete and utter JOKE!! I literally LOL'd when I read this!


    I intuitively and historically understand electric circuits,......So that means you know everything that is safe and legal to install? Or you just know how things work?

    "obscure and worthless quotes from the NEC"......you HAVE to be #@$* kidding me!!

  12. #27
    DIY Junior Member Bird Doo Head's Avatar
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    To All Who Took The Time To Post On This Thread,
    This thread was a fun one! Thank you for letting me join in.
    It is nice when people can have differing opinions and enjoy a pleasant back-and-forth!
    (Somehow, the NEC seems to instigate this often.)

    I want to wish all who read this a Happy, Safe and Blessed New Year!

    Paul

  13. #28
    General Engineering Contractor ballvalve's Avatar
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    That might be a good ending. But an ad for BASEBOARD HEATERS just popped up here. Now that is humorous!

  14. #29
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by ballvalve View Post
    Posted by marne rock.....

    I intuitively and historically understand electric circuits so well that I do not hide behind obscure and worthless quotes from the NEC. For you to pursue this obtuse circuit as being "allowed", makes me think you may be imbued with knowledge of the law but inept when it comes to pulling a wire and thinking about how it will interface with actual, daily use.
    Through out the 1980s I wired multifamily dwellings all up and down the Eastern Seaboard. In quite a few of these units I would pull a 20 amp circuit to a single receptacle for an air conditioner and from there to multiple thermostats for baseboard heat. Not only was this passed by the local inspector but also by the Federal HUD inspector as some of these units were low rent projects.
    Now it might that none of us, inspectors both state and federal or contractors have as much intelligence as some lowly well pump installer but we did it anyway. If you think it necessary I will get a dispatch out immediately to these individuals that this issue needs to be addressed but I think that it would be about thirty years too late.

    By the way the Rock of the Marme is the 3d Infantry Division and part of the XVIII Airborne Corps and is directly responsible for you being able to sit and debate your feelings here.
    Do a Google search of Rock of the Marme

  15. #30
    General Engineering Contractor ballvalve's Avatar
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    Yes it is 30 years too late. They probably rewired the circuits after 200 trips to the circuit breaker. In 1980 we didnt even have a building department here, so I would'nt give it a shot today. And your circuit is different from what is in this thread, its 20a 120v on one leg, not a shared load on 2 wires.

    Dad speared, burnt, and shot his share of our pacific enemies in the big war, island by island, so I won't require any education about the military, especially since he spent the next 15 years as a drill sargeant. Saved you from eating rice and writing left to right and inside out with little squiggly lines. Thanks to the guys in Europe too, but they did'nt have to sleep with 3 foot long centipedes and spiders the size of a 200 amp entry panel.

    http://www.32nd-division.org/history/ww2/32ww2-1.html

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