Alwayslearningelec
Senior Member
- Location
- NJ
- Occupation
- Estimator
120 or 277v Fixture Calc
- Thread starter Alwayslearningelec
- Start date
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winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
You need to know the fixture input current, which is not specified in the information provided.
If you know the power factor then you can calculate current from wattage and voltage.
You may also need to know starting inrush current if large banks of these will be turned on at once
Jon
If you know the power factor then you can calculate current from wattage and voltage.
You may also need to know starting inrush current if large banks of these will be turned on at once
Jon
kwired
Electron manager
- Location
- NE Nebraska
Watt's Law states that: Power (in Watts) = Voltage (in Volts) x Current (in Amps) P = V I
That gets you close, power factor will change actual draw, the higher the power factor the less it will be an impact.
That gets you close, power factor will change actual draw, the higher the power factor the less it will be an impact.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Figure out the current at each voltage (74/120 or 74/277) and see how many of those loads you can fit on your circuit.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Power factor, in-rush current aside:
120V
74W/120V=.62A
20A circuit
20A/.62A each light=32.26 lights
32 lights x .62A=19.84A
277V
74W/277V=.27A
20A circuit
20A/.27A each light=74.07 lights
74 lights x .27A=19.98A
120V
74W/120V=.62A
20A circuit
20A/.62A each light=32.26 lights
32 lights x .62A=19.84A
277V
74W/277V=.27A
20A circuit
20A/.27A each light=74.07 lights
74 lights x .27A=19.98A
Flicker Index
Senior Member
- Location
- Pac NW
- Occupation
- Lights
It's odd the fixture doesn't show you the amps. Even screw-in bulbs do.
For example, one here says 120Vac, 9W, 110mA.
Another says 120V 90mA 11W
For example, one here says 120Vac, 9W, 110mA.
Another says 120V 90mA 11W
Keep in mind commercial lighting is normally a "continuous load".. adjust accordingly
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
That doesn't compute.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Oh, we weren't expecting the inspector to show up!
The first example does compute with a PF of 0.68!That doesn't compute.
The latter however is questionable!
Flicker Index
Senior Member
- Location
- Pac NW
- Occupation
- Lights
From DOE EnergyStar specs
7.1.5. Test report(s) shall be available from EPA-recognized laboratory(ies) for the tested representative model and the variant(s) demonstrating that variant performance for the following parameters varies by no more than the percent indicated while meeting this specification’s requirements:
i. Input current and input wattage: ±10%
ii. Power factor: ±5%
iii. Maximum overall length, except as affected only by variations in lamp base or envelope shape: ±5%
iv. Maximum overall diameter: ±5%
Then, they have rounding allowances.
7.1.5. Test report(s) shall be available from EPA-recognized laboratory(ies) for the tested representative model and the variant(s) demonstrating that variant performance for the following parameters varies by no more than the percent indicated while meeting this specification’s requirements:
i. Input current and input wattage: ±10%
ii. Power factor: ±5%
iii. Maximum overall length, except as affected only by variations in lamp base or envelope shape: ±5%
iv. Maximum overall diameter: ±5%
Then, they have rounding allowances.
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