Breaker loads!

x2jearly

Member
I am circuiting 100 watt Metal Halide fixtures, 277 v, stanchion mounted on exterior platforms and walkways.
What should I use for circuit loading:

a) 100w= 130 input wattage (from ballast chart) or
b) 1.15 max. input amps (from same chart).


I have always (about 50 years) used the input wattage, but have recently been told to use the input amps.

130 input wattage vs 1.15 amps (318 watts) which is about 2.5 times more. Thats a lot more breakers.

Thanks
 

xformer

Senior Member
I am circuiting 100 watt Metal Halide fixtures, 277 v, stanchion mounted on exterior platforms and walkways.
What should I use for circuit loading:

a) 100w= 130 input wattage (from ballast chart) or
b) 1.15 max. input amps (from same chart).


I have always (about 50 years) used the input wattage, but have recently been told to use the input amps.

130 input wattage vs 1.15 amps (318 watts) which is about 2.5 times more. Thats a lot more breakers.

Thanks
IMHO... I would read Section 220 of the NEC. It will tell you what to use... :)
 

iwire

Moderator
Staff member
From 2011.

220.14 Other Loads ? All Occupancies. In all occupancies,
the minimum load for each outlet for general-use receptacles
and outlets not used for general illumination shall
not be less than that calculated in 220.14(A) through (L),
the loads shown being based on nominal branch-circuit
voltages.



(D) Luminaires. An outlet supplying luminaire(s) shall be
calculated based on the maximum volt-ampere rating of the
equipment and
lamps for which the luminaire(s) is rated.
 

kwired

Electron manager
Open circuit current. Now that is going to be an interesting explanation. :)
probably means what it draws when the lamp circuit is open not when the input power is open.

One thing that is not mentioned is power factor, If you have 129 watts and 318 VA your power factor is only .40 - which is very low.

The 318 VA is real to your conductors and overcurrent devices even though 129 watts is all that is doing any useful work.

I am going to assume these are simple reactor type ballasts, and have no capacitor in the circuit, otherwise they would likely have a much higher power factor.
 
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