SPDT double-throw switch

Discussion in 'Electrical Forum discussion & Blog' started by Ken Tannenbaum1, Dec 27, 2010.

  1. Ken Tannenbaum1

    Ken Tannenbaum1 New Member

    Messages:
    7
    Location:
    Catskill, NY
    I ran a 12/2 cable to use for 240v baseboard heaters in one room and would like to split one of the legs to use ONLY during the summer for an A/C. Can I install an in-line, single-pole, double-throw 20amp
    switch for that purpose? Seems right but want to do the correct thing. It's awfully expensive but should work, right?

    Thanks very much.
  2. jbfan74

    jbfan74 Electrical Contractor

    Messages:
    131
    Location:
    Newnan, GA
    With 12/2 cable, you only have 240 volts and not 120v.
    You do not have neutral wire to use for 120v.

    The only way to do this is buy a pure 240 AC unit.
  3. Ken Tannenbaum1

    Ken Tannenbaum1 New Member

    Messages:
    7
    Location:
    Catskill, NY
    Thanks for the response...Oops, my error...the cable is 12/3, NOT 12/2...it's got a R, B, W and copper wires. Also, nothing's hooked up to the panel yet. Now, just to be sure...at present, the two hots (B+R) run to the 240v heater + the copper ground. There is no neutral necessary from what I gather. Back to me question, can I use the white neutral and split one of the hot legs (B or R) with a SPDT 20amp switch to get to the 110v A/C in the same room? Sorry for the confusion.
  4. drick

    drick In the Trades

    Messages:
    392
    The right thing to do is pull a separate circuit for the A/C. 12/2 wire isn't that expensive.

    And yes what you are suggesting would work. And SPDT 20-amp switches are more $$ but shouldn't be that expensive as they are commonly used in commercial buildings.

    -rick
    Last edited: Dec 27, 2010
  5. Ken Tannenbaum1

    Ken Tannenbaum1 New Member

    Messages:
    7
    Location:
    Catskill, NY
    Thanks.....guess my life would have been easier if the box stores carried 12/4....I should have gone to a supplier direct. HD and Lowes also don't carry that switch.
    But you probably knew that. Happy New Year.
  6. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    You did not need the 12 - 3 for the heater as you discovered, 2 runs of 12-2 would have solved your issue much cheaper than 12-4.

    Maybe I'm missing something, but a spdt switch isnt enough, you need a switch with two poles normally off and 2 poles normally on, so that throwing it disconnects the heater completely and engages a 120v circuit to the AC, and the two may never intermix.

    But then you have a 120v circuit on 1/2 of a double breaker.

    The NEC guy will likely be here soon to read you the law.
    Last edited: Dec 27, 2010
  7. Ken Tannenbaum1

    Ken Tannenbaum1 New Member

    Messages:
    7
    Location:
    Catskill, NY
    Yes, the 12/3 was a waste. About "missing something", you know better than me...that said, based on what you've contributed, I'm going to make another run with 12/2 and not mess with doing it incorrectly. Also, the cost of the 20amp SPDT is probably as much as or more than the 12/2 cable! Anyway, safety first...I live there!
    Thanks.
  8. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    Why bother with a switch at all?
  9. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    This is my question also. the heat and AC will not be in use at the same time so why not wire the AC to the same circuit as the heat but be sure to use a single receptacle instead of a duplex
  10. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    So the NEC allows you to install a double pole breaker in a panel and label it
    "20 amp 240 volt wall heater, with 120 volt AC receptacle, drawing 20 amps on one leg" ?

    Wonder what the inspector will have to say to that one.

    Wow! That makes me rethink my deep respect for the NEC.

    Sure. By that curious assumption, I suppose I can wire my rooftop AC on a 50 amp double pole breaker to my seperate heat pump with seperate thermostat, also with a 50 amp rating, because they will not be on at the same time.

    You guys had too much food at Christmas and got a little light headed?

    Would you take a 120 volt leg off your 240V pool pump to operate a pump house outlet for a electric heater "because they won't be on at the same time"?

    BE WISE! Wire safe circuits.
    Last edited: Dec 28, 2010
  11. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    I don’t think that anyone has posted anything that could be closely related to this statement. Did you have to much food at Christmas and get a little light headed and start seeing things?

    I would suppose that you was into the eggnog just a little to much as this is one of your jokes is it not.



    Do you not know what a heat pump is? A heat pump is a dual action air conditioner. In one mode it cools the inside and heats the outside and in the reverse mode it heats the inside and cools the outside. What you purpose is having two air conditioners on one circuit.

    Someone sure did, see above.

    Now are you making another joke? This does not even come close to heat and AC now does it/

    Finally after many attempts you make a smart post. I know that this took some effort on your part. I am so proud of your effort.

    210.4(C) Line-to-Neutral Loads. Multiwire branch circuits shall supply only line-to-neutral loads.
    Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

    Ever see a receptacle that had both a 240 volt and 120 volt receptacle on the same yoke?
    http://www.leviton.com/OA_HTML/ibeCCtpItmDspRte.jsp?item=8976&section=10085&minisite=10026
  12. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    This whole post is a joke. Even the last line, since it is obvious you don't even know what a "safe" circuit is.
  13. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Yes, but that is not how his system will work.

    Well at least you guys are starting to appreciate some irony and humor. But I don't think you get the point, or do not want to.

    This OP was smart enough to know that if his AC and bases board heater were on at the same time, he would gravely overload one half of his 20 amp breaker. The base heat is a dedicated, permanently installed appliance controlled by a thermostat and it does not lock out in summer.

    The AC might be permanently installed in a hole in the wall like mine, and is then also a permanently installed appliance. It is also not locked out in winter.

    I can't make anything of the NEC nonsense, but even a layman would not want his electrician to wire up a circuit to save 4$, and then guarantee it will be overloaded under some very possible circumstances.

    You would hardwire a base board heater and then pull a jumper to a dedicated A/C outlet?. I just don't think so. Or hope so.
  14. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    First why would anyone need a lock out between the two?

    Second one can’t overload half of a two pole breaker. The breaker is either overloaded or it isn’t.

    Third what damage would be done should the breaker be overloaded? Would it not trip and prevent and damage?
  15. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    Disagree. Try "extremely unlikely situation".
    Besides, like JW said, SO the breker gets overloaded because in the middle of summer someone spilled a bucket of ice on the heat thermostat. It trips, you reset it, you clear the ice off the t-stat and go back to your party.
  16. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    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.

    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: Dec 29, 2010
  17. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    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.
    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.
    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: Dec 29, 2010
  18. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,684
    Location:
    Cave Creek, Arizona
    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.
  19. Bird Doo Head

    Bird Doo Head New Member

    Messages:
    19
    Location:
    Detroit
    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
  20. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    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.
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