Check my assumptions-CFL floodlights for the Backyard

Hugh R · 01-01-2009, 03:11 PM

I have a really big backyard and am thinking about CFL floodlights, 120 volt, not low voltage. Too much voltage drop for the distances I want to run for 12v. I want to uplight some oak trees and really see the lights from the house which could be several hundred feet away.

Currently, I have a dedicated 15 amp breaker going to ten lights around the pool with 60 watt incandescent bulbs which is 600 watts, or about 5 amps, excluding line losses. They are all in a loop meaning the wires go from one light to the next. . I want to tap into one existing light in the middle of the loop and run outdoor-rated flex out and branch out to about 8 CFL outdoor fixtures.

The CFL's that are equivalent to a regular 75 watt incandescent are 18 watts, so 8 x 18 = 144 watts, if I convert the existing ten 60 watt bulbs to CFL's as well then I'm looking at 140 watts (they're 14 watt CFLs), and thus about 284 watts total, or around 2-1/4 amps, plus voltage drop on about 300 feet of outdoor wiring. It looks like I'll be well under the load rating of the 15 amp breaker. Any thoughts? Are my assumptions correct?

Eric Coffey · 01-01-2009, 05:12 PM

The only thing I would add is that some of the CFL-to-incandescent equivalency ratings seem to be a bit optimistic regarding lumens/output. In other words, those 14w CFL's are probably closer to 40w incandescent. To equal a 60w incandescent, you probably need a 20w+ CFL.

Hugh R · 01-01-2009, 06:45 PM

Thanks Eric, but even with that, I think I'm still well under the rating of the breaker. I never did this project because the wattage to get some decent lumens in the trees always seemed to dictate a bigger breaker, hence maybe a subpanel. But with the CFL's it looks like it's definitely doable.

carambola · carambola's Garage

dude, given the values you have stated your voltage drop should be 2.1 A and using a given of 120v we then apply ohms law.
248/117.9=2.1
2.1 is definately within the 80% allowed of 15

hope this helps

fingpilot · 08:33 PM

Hugh;

I just changed everything in the house over to CFL's. Did not change the dimmables, but I see now that there even models for that.

I discovered two 'surprises'. The lumens on the 100 and 120 watt comparable ones are probably brighter than described. The lower lumens are close to, or even 'conservative' on brightness.

Second discovery. When cold, they start after a 2 second or so delay, and come on very dim, rising to full luminescence after a minute or so.

The only other consideration would be waterproofing; they are not rated 'outdoor' unless specifically stated. Some of the larger flood-looking ones have base up or down restrictions, and some seem to run fairly warm, not the bulb part, but the transformer / starter part. Check bulb dimensions carefully if going into an enclosure. The CFL's are sometimes longer, especially the larger 'flood' types.

My electrical consumption is noticibly down. PG&E paid a fair share of the changeover costs, I'd say 15% or so.

Hugh R · 01-02-2009, 08:24 AM

Cool, thanks guys.

competentone · 01-02-2009, 04:08 PM

Quote:

Originally Posted by Hugh R

Currently, I have a dedicated 15 amp breaker going to ten lights around the pool with 60 watt incandescent bulbs which is 600 watts, or about 5 amps, excluding line losses. They are all in a loop meaning the wires go from one light to the next. . I want to tap into one existing light in the middle of the loop and run outdoor-rated flex out and branch out to about 8 CFL outdoor fixtures.

The CFL's that are equivalent to a regular 75 watt incandescent are 18 watts, so 8 x 18 = 144 watts, if I convert the existing ten 60 watt bulbs to CFL's as well then I'm looking at 140 watts (they're 14 watt CFLs), and thus about 284 watts total, or around 2-1/4 amps, plus voltage drop on about 300 feet of outdoor wiring. It looks like I'll be well under the load rating of the 15 amp breaker. Any thoughts? Are my assumptions correct?

I'm no electrician, but are the new fixtures designed to only accept the CFLs?

If you are using standard flood light fixtures that can support standard flood bulbs is it acceptable (code), or advisable to have a circuit that could be overloaded by someone simply swapping the CFL bulb (18 of them, if I'm understanding your description) with larger (100+ watt) bulbs?

Hugh R · 01-02-2009, 04:47 PM

Good point compentenone, I'll check my calcs, but I'm pretty sure that I'd still be way under. The new lights can only take the CFL bulbs, and if someone load up the other ten with 60 watters, I'd still be under. The turning point for me doing this now, not ten years ago was the advent of inexpensive CFL. I wouldn't have the load capacity running a bunch more 60 or 100 watt floodlights out there.