Basement subpanel issues

Discussion in 'Electrical Forum discussion & Blog' started by docpops, Oct 30, 2008.

  1. docpops

    docpops New Member

    Messages:
    13
    I'm finishing a basement, and currently have an unused 20 amp breaker once dedicated for a washer, a well as a 240V outlet for an old dryer long since moved upstairs. The 240 outlet is hooked into my main panel at a twin 30 amp breaker. My plan is to use the 20 amp for the bathroom, and then put in a subpanel where the 240V was, so I can run three circuits:
    1 - spare bedroom (lights/outlets/small TV)
    2 - small 120V 1000W cadet heater
    3 - dedicated outlet for a treadmill (around 1100W at peak)

    The electrician was out today and mentioned he could only put in a 30 amp breaker where that 240V outlet is. I already ran 2 lines of 12G romex to the area where the washer/dryer outlets were (one each for the bath and bed), and was going to run 2 more lines - one for the heater, and one for the outlets.

    Something tells me I'm going about this all wrong - I couldn't quite get an answer as to why we couldn't put in more than 30 amps at that old 240 - my hope was to run three separate 20 amp circuits from it (I thought 2 30 amp breakers at the main meant I had 60 amps total - stupid of me) so I could dedicate one 20 amp breaker each to the bedroom, heater, and treadmill.

    All/any input and advice appreciated.
  2. docpops

    docpops New Member

    Messages:
    13
    Also, I don't plan to ever be running the heater and the treadmill at the same time, or certainly not at anything near peak capacity.
  3. Basement_Lurker

    Basement_Lurker One who lurks

    Messages:
    668
    Location:
    Victoria, BC
    You have a double 30A breaker in your main panel; which is not the same as two single breakers. The double breaker still pulls only 30A, but it uses two hots to give you 240v. I assume that the reason why you couldn't use anything larger than 30A for the sub-panel is because you plan on re-using your 3-wire dryer wire for your sub-panel. That wire is only rated at 30A; so if you wanted a larger main breaker on your sub-panel, you would have to run a larger service wire.

    I think 30A should be ok for the 3 circuits you plan on wiring from the sub-panel. The bedroom sounds like a rarely used guest room, so it's hardly a factor for the small amount of power it will use, and the heater is a fixed draw at like half of a 15A circuit, and so is your treadmill, which would never be in use at the same time when one of the other two circuits would be in max use. If this is going to be inspected, you don't have to tell them that the treadmill circuit is dedicated specifically for a treadmill, it can just be normal outlet.
  4. drick

    drick In the Trades

    Messages:
    392
    This is most likely the reason. If you are planning on reusing the dryer wire you cannot change out the 2 pole 30 to anything but a single pole 30 IF the wire is only 3 conductor (most pre 1997 dryer wires are 3 conductor instead of 4) because you don't have enough conductors to install a split phase sub panel and take advantage of both halves of the two pole 30 amp breaker.

    Based on your load calculation it won't matter though. Just buy a small sub panel and feed it off of a single pole 30 at the main box. You should be fine.

    -rick
  5. docpops

    docpops New Member

    Messages:
    13
    Thank-you so much, so far.

    But, can I physically run three strands of 12G romex out of this subpanel (bedroom, heater, trdmil)? This, in my inexperienced mind, is what I'm blanking on. My associate says I have to run all of this on a single strand of 10G, but since I've got the 12 in already I was hoping there was a different way.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,917
    Location:
    New England
    If you run new wire all the way back to the original panel, remove the 30A CB, and then run new wire, as long as the wire is the proper size and you have room in the panel for the new breakers you are installing, you should be golden (assuming all of the workmanship is up to code). If you want to reuse the original wiring for the dryer for something, anything you put on it cannot exceed the original wire's power rating; so, unless that wire was oversized upon installation, what is attached to it can't exceed the original rating. But, if you use that 30A with a 30A breaker, and feed a subpanel, the total of the breakers on that subpanel can exceed the 30A (just like it likely does on your main panel). But, given what you are planning, you'd get the subpanel's breaker tripping.

    Basically, no protected circuit can have an undersized wire between the source and the protection device...30A breaker, must have wire that can support 30A service. As long as all of the wires are protected properly, the aggragate total can be higher (you may have 150A worth of breakers in your main panel, but only a 100A main breaker, for example, but each branch must have the proper sized wire for its individual breaker regardless of whether if you turn everything on it doesn't overload the individual branch, but trips the main).
  7. docpops

    docpops New Member

    Messages:
    13
    So if I understand what you are saying, Jadnashua, I could conceivably place three separate 20 amp breakers in my subpanel, even though the main circuit is only 30 amps, and as long as the sum total load doesn't exceed 30 amps at any given time (which seems inconceivable to me) I won't be tripping the circuit?
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,508
    Location:
    Cave Creek, Arizona
    sub panel

    If you can take care of grounding, then the dryer wire to a sub panel will give you 30 amps on each leg, in effect 60 amps at 120 v.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,917
    Location:
    New England
    A CB sets the maximum current on that individual circuit. As long as the wires feeding that CB are also properly fused or run through a CB, the weakest point must be protected...if it is exceeded, it will trip, protecting anything downstream.

    An HJ's point is also correct, but needs to be done right.
  10. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,532
    Location:
    North Carolina
    215.2 Minimum Rating and Size.
    (A) Feeders Not More Than 600 Volts.
    (1) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

    All this bull you are being told means nothing. Your asnwer lies above
  11. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    Why is the answer always so easy, yet so hard. :D
  12. drick

    drick In the Trades

    Messages:
    392
    >>Why is the answer always so easy, yet so hard.

    Try not to fall asleep reading article 220:) ZZZZZZZzzzzzzzzzz. Oh, sorry I accidentally flipped to page 102.

    I think you skipped a math class somewhere jwelectric if you actually think the 30A breaker is going to trip.
    1200W Heat +0.25 (that is your only continuous load) = 1500W
    1100W for the treadmill (noncontinuous load ) = 1100W
    that leaves 1000W for a single guest bedroom! You could hook up a 50 inch plasma TV and have a 500w lamp on your nightstand (better tell the guests to bring their sun shades) and that breaker will still hold!

    However, if you throw in the fact that your not supposed to exceed 80% capacity on the #10 then things do start to get a little too tight. The breaker will still not trip though.


    -rick
  13. drick

    drick In the Trades

    Messages:
    392
    This is totally wrong. You can't even wire standard residential switches and outlets to 10GA wire. And yes, you can run 3 20A circuits out of the sub panel that is protected by a 30A breaker back at the main panel.

    -rick
  14. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,532
    Location:
    North Carolina

    Now wouldn't that be three watts per square foot instead of a lamp on the table and a TV?
    Ain't no wonder he don't know what is going on with all these people telling him everything but how to do it the right way.
  15. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT

    Yeah, sure ya can, wanna give me the code section that would allow that?
  16. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    Sure... I think you skipped a few electrical classes, but what do I know?
  17. docpops

    docpops New Member

    Messages:
    13
    Thanks for all the help. I think I have it sorted out.
  18. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    Best advice yet
  19. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,532
    Location:
    North Carolina
    Thank you for the kind words although now my hat wont fit my head :D:D
Similar Threads: Basement subpanel
Forum Title Date
Electrical Forum discussion & Blog Wire to Subpanel - through basement Jul 23, 2009
Electrical Forum discussion & Blog finishing 1500 sq ft basement, wiring from scratch to subpanel Jan 15, 2008
Electrical Forum discussion & Blog Basement electrical wires Feb 5, 2013
Electrical Forum discussion & Blog GFCI in unfinished basement on a 220v motor load Oct 8, 2010
Electrical Forum discussion & Blog Running Wires From Basement Question Jun 10, 2010

Share This Page