Discovered a 10 AWG Cable

Discussion in 'Electrical Forum discussion & Blog' started by GoldMaple, Oct 7, 2009.

  1. GoldMaple

    GoldMaple DIY Junior Member

    Messages:
    26
    Location:
    Canada
    I live in an old house and I have been doing some renovating. I was looking for a way to get to my electrical panel because I'd like to run a couple of new circuits into my basement. Given the location of the Panel it was not going to be an easy task. While looking for a route I discovered a wire coiled up and stuck in the joists. It was brand new and disappeared so I opened up the panel upstairs and there was the other end coiled up in the Panel box. It was not hooked up. :) How handy! So, the wire is fairly thick and it has "10 AWG 300 volt" stamped on it. So, I think it's 10 gauge and capable of handling 30 amps? My question is.... Can I attach a very small panel box in my basement to this wire and add one 10 amp and two 15 amp breakers? Or am I constrained to the 30 amps, so only two 15 amp breakers? I'm not sure what this cable is capable of handling. Thanks!
  2. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    992
    Location:
    NY State, USA
    30A does NOT mean "two 15a breakers". Also, there are no 10a breakers. If you find one it is an oddball and most likely for industrial use.

    Let's get the basic info first. What conductors are in this cable? If it is black, white, red and GROUND (bare or green), then you can effectively install a sub-panel.
    If it is just black, white and ground then you can install a sub-panel, but it would be a bit hacky as you would be limited to a 120v panel.
  3. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    You can provide any number of breakers provided that you don't exceed the 30A of the cable (which is protected by the panel's main breaker). You'll need to do load calcs to ensure that your loads are within 80% of 30A.

    You'll have a tough time finding a panel with a 30A main. Most likely you'll need to backfeed the panel through a breaker which has some requirements (labeling and hold down, I believe).
  4. GoldMaple

    GoldMaple DIY Junior Member

    Messages:
    26
    Location:
    Canada
    Wires

    Okay, good. The cable has 4 wires, a red, black, white and a bare wire. I'm hoping that I could add a small panel with 4 breakers. I mentioned a 10 amp breaker because I would like to run a dedicated circuit into the bathroom I'm renovating and use it for the heated floor. All the manufacturers stated that it must be on a dedicated circuit or the GFI will be tripping all the time. The heated floor will take less than 4 amps because the bathroom is so small. Another breaker I'd like to run to my washing machine because someone connected the current circuit to the kitchen upstairs so when my microwave goes on and the washer is on the breaker trips. The third breaker I'd like to save for when I redo my upstairs bathroom and use for the heated floor. Again, it will draw less than 4 amps when running. Both heated floors won't be running all the time. Probably run then on a programmable timer for times we know we'll use it. I would then like to have the option of adding one more circuit for future use. Does this seem reasonable?
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,539
    Location:
    Cave Creek, Arizona
    wires

    I would use a small sub panel without the main since the 30 amp breaker in the main panel would provide the "master" breaker function.
  6. Ian Gills

    Ian Gills Senior Robin Hood Guy

    Messages:
    2,777
    Location:
    USA
    It can't be done with what you are intending to do, but if my needs were more modest (two 15 or 20 amp circuits) I would be tempted to use that cable as a shared neutral and run two circuits directly from the panel using it.

    Of course you cannot very easilly use GFCI or AFCI breakers with a shared neutral and these are very often required with certain types of new wiring work.
  7. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    Sounds reasonable to me.
  8. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    992
    Location:
    NY State, USA
    He does NOT need a 30A main.
    He can use any panel. Typically a small sub-panel will have a 60 or 100A rating. They can be fed with anything from 30A up to their rating.
    Also, no main breaker is required since this sub-panel will be within the same structure as the main panel. A main-lug panel would be a typical install.
    Last edited: Oct 8, 2009
  9. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    992
    Location:
    NY State, USA
    Why can't it be done?? Sounds like it will to me.

    Also, two-pole GFCI breakers are very common, and two-pole AFCI breakers are getting more common.
  10. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    You're right. :)
  11. GoldMaple

    GoldMaple DIY Junior Member

    Messages:
    26
    Location:
    Canada
    Another Question

    Thanks for all the replies. I really appreciate it.....:)

    Here's another question. It seems to me that the simplest way to do this is to add a lug sub panel that uses the breakers in the main panel. I understand that I could power the sub panel with a 3 wire cable but it's better with a 4 wire cable and with the 4 wire cable I would use a double pole breaker. What I don't understand is why is it better to use a 4 wire cable in this configuration? Whether I use a 3 or 4 wire cable it's 30 amps so there must be something else?

    (I have a 4 wire cable and will use a double pole breaker)
  12. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    992
    Location:
    NY State, USA
    A 3-wire cable would give you 30A @ 120v, or 3600 watts.
    A 4-wire cable would give you 30A @ 120/240v, or 7200 watts.
  13. GoldMaple

    GoldMaple DIY Junior Member

    Messages:
    26
    Location:
    Canada
    Okay, so given...

    A 3-wire cable would give you 30A @ 120v, or 3600 watts.
    A 4-wire cable would give you 30A @ 120/240v, or 7200 watts.

    and "Watts = Volts x Amps" and

    3600 = 120 * 30 3 wire
    7200 = 240 * 30 4 wire

    then by using a 4 wire cable we double the volts which doubles the watts. Based on what I see here is that with a four wire cable I draw twice the power before I utilize all the amps. Is this correct? If so, it's a far superior setup.
  14. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    992
    Location:
    NY State, USA
    A 240v panel is actually a typical setup. A 120v panel is extremely odd.
  15. Ian Gills

    Ian Gills Senior Robin Hood Guy

    Messages:
    2,777
    Location:
    USA
    I did not realise you were so rich Petey. I wish I could afford one of those.
  16. alternety

    alternety Like an engineer

    Messages:
    650
    Location:
    Washington
    This may be an excessively paranoid question, but is the found cable copper?
  17. GoldMaple

    GoldMaple DIY Junior Member

    Messages:
    26
    Location:
    Canada
    Yes, it's copper.
  18. Ian Gills

    Ian Gills Senior Robin Hood Guy

    Messages:
    2,777
    Location:
    USA
    I wish it had been gold.
  19. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    992
    Location:
    NY State, USA
    I don't get this comment. If you are required to use AFCIs what does it matter how much they cost?

    A two-pole AFCI is only slightly more expensive than two single-poles. And if the home run is very long you are saving money on wire.

    If you cannot afford a project or renovation, don't do it. :rolleyes:
  20. Ian Gills

    Ian Gills Senior Robin Hood Guy

    Messages:
    2,777
    Location:
    USA
    Crucially, I prefer single pole for 120 volt circuits because I wouldn't want a dual pole breaker tripping two circuits if a fault caused by just one of them was detected.

    If that means spending more money on cable, so be it.
    Last edited: Oct 10, 2009
Similar Threads: Discovered Cable
Forum Title Date
Electrical Forum discussion & Blog Two 12-4 Romex cables through the same floor joist holes Jul 5, 2014
Electrical Forum discussion & Blog Would this cable run down face of beam to wall (under beam)be up to code (Wisc)? Jun 5, 2014
Electrical Forum discussion & Blog Armoured Cable - Ground Mar 27, 2014
Electrical Forum discussion & Blog Wagobox to splice (2) 12/2 with ground cables Jul 22, 2013
Electrical Forum discussion & Blog 2 12/2 NM cables in one hole through top plate into attic cellulose Jul 13, 2013

Share This Page