Wire Calculations for low bay LED lights

[lilsparky]

Hi, I need assistance on how to get started. We are installing 9 low bay 80 W, 75 lumens/watt LED lights at 120 v. I need to size the conductors and conduit but I don't see anything in the code to help with LED. Is it the same as incandescent or HID lights?

I believe, I must find my amp, then go to the ampacity table, then size the conduit. Am I correct? I'm having trouble getting started. Can someone help me.

Thanks,
just need a kick to get started lol!! :?

 

[maghazadeh]

Hi, I need assistance on how to get started. We are installing 9 low bay 80 W, 75 lumens/watt LED lights at 120 v. I need to size the conductors and conduit but I don't see anything in the code to help with LED. Is it the same as incandescent or HID lights?

I believe, I must find my amp, then go to the ampacity table, then size the conduit. Am I correct? I'm having trouble getting started. Can someone help me.

Thanks,
just need a kick to get started lol!! :?

9 x 80W = 720W / 120V = 6A, then go to ampacity table, and then size your conduit.

 

[lilsparky]

Duh, thank you! I got as far as the 720VA and then thought it should be a little harder because of the lumes/watts. Sometimes it's just so simple.:dunce::jawdrop:

 

[n1ist]

Lumens per watt just tells you how efficient the light is...
/mimke

 

[lilsparky]

Ok thanks

 

[broadgage]

Calculate as above, but IMHO an allowance should be made for voltage drop resulting in extra current being drawn.
Most LED lights contain a constant wattage electronic power supply, that is at lower than nominal line voltage, extra amps will be used to provide the same watts.

Remember that the utility voltage may be 5% low at 114 volts actual, and that additional voltage will be dropped in the branch circuit.

In the absence of any more detailed data I would be inclined to allow an extra 10%.
6.6 amps instead of 6 amps in the example given. In this case it most unlikely that the extra 10% will matter since 6 amps or 6.6 amps are both well within the capacity of a 15 amp or 20 amp branch circuit.
If the lighting is going to be a continous load, as is probable, then the branch circuit can only be loaded to 80%, as with any other continous load. Still no problem with a worst case case current of only 6.6 amps.

The allowance for extra current drawn at low supply voltages may be more important for large installations.

Also for large installations, a higher voltage would be preferable, but for only 720 watts I would not worry.

 

[steve66]

Hi, I need assistance on how to get started. We are installing 9 low bay 80 W, 75 lumens/watt LED lights at 120 v. I need to size the conductors and conduit but I don't see anything in the code to help with LED. Is it the same as incandescent or HID lights?

I believe, I must find my amp, then go to the ampacity table, then size the conduit. Am I correct? I'm having trouble getting started. Can someone help me.

Thanks,
just need a kick to get started lol!! :?

Sorry, but it doesn't sound like you are close to being on the right track.

You start with the branch circuit size - 15 or 20 amps. You size the wire for the branch circuit size. Then you size the wire for the conduit size.