How many lights on a 15 amp breaker

Discussion in 'Electrical Forum discussion & Blog' started by Zenman, Mar 18, 2010.

  1. Zenman

    Zenman New Member

    Messages:
    58
    Location:
    New Jersey
    Redoing the basement lighting circuit. Is there a code or general rule of thumb when it comes to how many lights can be put on a 15 amp circuit?

    I am familiar with how to convert between watts and amps. And I know how to figure out how many 100 watt bulbs can be on simultaneously before blowing the breaker, but was curious what the pros do. Do I max it out since it is unlikely that all the lights will be on at the same time OR leave 20% of the available 15 amps unused???

    Thanks!
  2. Lightwave

    Lightwave New Member

    Messages:
    98
    Location:
    Vancouver, BC
    Full load draw on a lighting circuit should not exceed 80% of the breaker rating. For example, no more than 14 100w fixtures on one 15a circuit.

    You have to take ballast inefficiency into account if you're using fluorescent lights.
  3. Zenman

    Zenman New Member

    Messages:
    58
    Location:
    New Jersey
    Ok... I thought I remembered hearing an 80\20 rule on this but wasn't sure... I do have some florescent fixtures, so I'll look into that as well. Thanks!
  4. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    999
    Location:
    NY State, USA
    There is no 80% rule with regard to residential lighting, unless the circuit is heavy and us expected to be on for 3 hours or more. ALL lighting general use receptacles are taken into account in the load calculation
    Common sense just prevails here.

    I know Canada has different rules on this than the US. So to the OP keep this in mind.
  5. Zenman

    Zenman New Member

    Messages:
    58
    Location:
    New Jersey
    Thanks for the reply. And yes I'm in the US.
  6. andrew79

    andrew79 Licensed Electrician

    Messages:
    18
    Location:
    Ontario Canada
    i'm pretty sure i recall somewhere that a pure lighting load can be loaded to 100%.....having said that i'm not positive and the general rule of thumb is always 80%....which is 12A not 14A as mentioned above. We normally run a max of 11 lights on a circuit.
  7. Michael Faltas

    Michael Faltas New Member

    Messages:
    1
    Location:
    Montreal
    Hi Andrew79,
    I live in Montreal so I want to respect the Canadian codes and standards. I would like to know if I have 5 general use outlets (receptacles) and on a 15A circuit, and I would like to add some recessed lights on that circuit, how many lights can I add if they are each 50W? I heard that the maximum number of items on a 15A circuit is 12. Is that a rule in Canada and Quebec more specifically?
    Thanks
  8. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,561
    Location:
    North Carolina
    According to the National Electrical Code there can be no more than 3 watts per square foot in residential wiring. This would equate to 600 square feet per 15 amp circuit. There is no mandate on the number of receptacles on a 15 amp circuit but 210.19(A)(1) says that a circuit shall have an ampacity not less than the load served. This would mean that no more than 1800 watts of lighting load could be on one 15 amp circuit even in a residential setting.

    If a lighting fixture that incorporates some sort of ballast then the wattage of the bulbs would not be used but instead the load of the ballast would be used in the calculation.

    There is no 80% rule in residential wiring except for a couple appliances such as water heaters as outlined in 422.13 and motors in 430.22 ect…
  9. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Lighting is a sort of crapshoot because a homeowner can instantly change watt draw from 10 to 150 on EACH screw in fixture.

    Then there is the guy who puts a screw in light to plug adapter, and hangs his 1500 watt harbor freight halogen heater from the garage ceiling. Or a dozen grow lights for pot.

    That's why god made circuit breakers.
  10. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,561
    Location:
    North Carolina
    give us information backing up this statement please
  11. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    jw.

    Do you not mean to say no LESS than 3 watts per sqft?

    In my 1770sqft house supposedly I need a minimum of three 15 amp general use circuits (plus 20 amp circuits in the kitchen and bathrooms, laundry, etc) but of course I have several more than that. I'm pretty sure I have five general use circuits in the house, but it has had an addition to the original 1000 sqft.
  12. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,561
    Location:
    North Carolina
    This is correct.

    In your case 3- 15 and 4-20 would be code compliant but not very practicable
  13. Chad Schloss

    Chad Schloss Member

    Messages:
    330
    Location:
    USA
    that is another spammer. you can always tell two things: they have a quote they copied from somewhere (copied partially from post #2) and they have a website link in the post that is clickable.
  14. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    As ever, the code is a minimum.

    What house gets built with the minimum circuits? Cheap tract homes.
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