Wattage for 15A light legs

[AC-DC]

15A at 117VAC, gives you: 1755 W. If I figured about 1000-1200 W. per 15A leg, would that be overkill, or is that a good range to be in?

 

[gudguyham]

Re: Wattage for 15A light legs

Usually 80% of the available total is acceptable. So your figures of 1000 to 1200 is quite conservative.

 

[iwire]

Re: Wattage for 15A light legs

Originally posted by gudguyham:
Usually 80% of the available total is acceptable. So your figures of 1000 to 1200 is quite conservative.

Actually 100% loading is fine unless you believe that 100% of the load will be continuous.

I am also curious why Angus (AC-DC) chose 117 volts.

220.2 requires the use of 120 as the voltage for computations.

A 15 amp 120 volt circuit can be loaded to 1800 watts.

A 20 amp 120 volt circuit can be loaded to 2400 watts.

Unless that full load will run 3 hours or more.

Continuous Load. A load where the maximum current is expected to continue for 3 hours or more.

What that means IMO is that some of the load can stay on forever as long as some of the load stops at least once every 3 hours.

If you decide your load is continuous then

A 15 amp 120 volt circuit can be loaded to 1440 watts.

A 20 amp 120 volt circuit can be loaded to 1920 watts.

Now that is code and code is a minimum standard for safety.

Most of the commercial jobs I work lighting circuits are 20 amp circuits and only loaded to 8 to 12 amps, that leaves room for changes and assures the breakers in the panels are running cool.

Meeting code and providing a good design are not one in the same.

[ October 08, 2005, 07:26 AM: Message edited by: iwire ]

 

[iwire]

Re: Wattage for 15A light legs

By the way you are figuring the load based on the fixture rating and not the lamp wattage?

Ten 150 watt fixtures equipped with 60 watt lamps have to be counted as 1,500 watts, not 600 watts.

 

[infinity]

Re: Wattage for 15A light legs

Ten 150 watt fixtures equipped with 60 watt lamps have to be counted as 1,500 watts, not 600 watts.

It that true? Would a 200 amp disconnect with 125 amp fuses count as 200 amps?

 

[iwire]

Re: Wattage for 15A light legs

Originally posted by infinity:

Ten 150 watt fixtures equipped with 60 watt lamps have to be counted as 1,500 watts, not 600 watts.

It that true? Would a 200 amp disconnect with 125 amp fuses count as 200 amps?

Here is the rule, it actually only applies to recessed fixtures, I thought it applied to all fixtures.

220.3(B)(4) Recessed Luminaires (Lighting Fixtures). An outlet supplying recessed luminaire(s) [lighting fixture(s)] shall be computed based on the maximum volt-ampere rating of the equipment and lamps for which the luminaire(s) [fixture(s)] is rated.

 

[infinity]

Re: Wattage for 15A light legs

Thanks for the reference bob. I threw in the disco thing as one of "Bob's rules". Actually I love your reference to the disconnect. Good call with the Angus reference.

[ October 08, 2005, 08:20 AM: Message edited by: infinity ]

 

[iwire]

Re: Wattage for 15A light legs

Originally posted by infinity:
Good call with the Angus reference.

I have always been an AC-DC fan, when my wife first got pregnant everyone was driving me nuts asking what name had we picked.

I told everyone that if it was a boy they would be named Angus. That usually shut them right up.

 

[AC-DC]

Re: Wattage for 15A light legs

Thank you so much for the replies. I picked 117 as a mean voltage, wasn't aware of 220.2. And yes, I'm using fixture ratings, not actual wattage. Thanks! Just as an aside, at what voltage does a 75W bulb actually draw 75W? I would assume @ 120, (220.2), otherwise you'd run into problems when the line voltage went up some. Si?

 

[iwire]

Re: Wattage for 15A light legs

Originally posted by AC-DC:
at what voltage does a 75W bulb actually draw 75W? I would assume @ 120, (220.2), otherwise you'd run into problems when the line voltage went up some. Si?

I doubt lamps are made that precise and the temperature of the filament will change the resistance.

But in general a 75 watt lamp labeled 120 volt will draw 75 watts @ 120 volt.

You can also get 130 volt rated lamps which will of course not draw full wattage at 120 volts.

 

[AC-DC]

Re: Wattage for 15A light legs

Gotcha.
Thank y'All very much.