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Formula for changing lights to recessed bulbs?

7K views 12 replies 5 participants last post by  jwhite 
#1 ·
In our kitchen we have a one light similar to this:

http://www.lowes.com/lowes/lkn?action=productDetail&productId=80719-13537-PKWL432RC&lpage=none

I'd like to get rid of the fluorescent light and add recessed lights and a couple of pendant lights like this: http://www.lampsplus.com/products/4...2522&cm_mmc=NXTG-SH-_-Chandelier-_-NA-_-42522

How do I figure out if the existing wiring going to the fluorescent light will support the pendant lights and recessed lights? What is the max # of recessed lights that I can install?

Thanks for your help.

Jeff
 
#2 · (Edited)
Start by mapping the circuit to see what all is on it now. To do this turn off all your breakers one at a time till the kictchn lights go out. Next turn on every breaker but the kitchen light circuit. Next go around the house and make a note of everything that is not working. Include all light fixtures and recepticles.

You need to add up the wattage of everything. If you have recepticles on the circuit, the code says that you do not need to count them, but common sence says to add a value for what may be plugged into it.. TV, Vacume, etc.

If any of your kitchen or dining room recpticles are on this circuit, you have a code issue and you should pull a new circuit to start.

Next deduct the light fixture that you plan to remove from the total, and add the wattages for all the things you want to add.

Now do the math. 120v is the nominal number we use for this. So multiply 120 times the amperage associated for the wire size. number 14 is for a 15 amp breaker. number 12 wire is for a 20 amp breaker.

never load a circuit beyond 80 percent of its capacity.

So: 120 volts x 15 amps = 1800 watts x .80 factor = 1440 watts.
......120 volts x 20 amps = 2400 watts x .80 factor = 1920 watts.

Do not load the circuit beyond this value.

Lighiting in a home is not considered to be continous load the way it would be in an office or other building. If it were you would need to muliply the lighting load times 1.25 in the middle of your calculations.
 
#3 ·
Thanks so much for the quick reply. Let me see if I have this right:

If the existing light has (4) 40 watt bulbs, I would subtract 160 watts.

The two pendant lights are 35W each = 70 W
Typical recessed lights (approx. 50-75W each) x 6 = 300-450 W

Total = approx. 370 - 520 W

Maybe there are some low voltage recessed lights that I can find? Otherwise, this probably isn't a DIY project? :mad:

Jeff
 
#4 ·
ooops, sorry JWhite. I didn't scroll down all the way and see the end of the message where you made the sample calculations.

Once I determine which breaker the kitchen lights are on, could I see the value for the breaker (15A or 20A) and use that for the calculation?

I see now though that I need to find out everything that is on that circuit and add it all up. Looks like I might have enough wiggle room.

If I determine that there are 5 receptacles on that circuit, how do I estimate the wattage for the receptacles? I don't think anything more than a coffee pot, blender, etc would be used on those plugs. How many watts do those types of appliances require?

Sorry for all the questions.

Jeff
 
#5 ·
For flourcent lights, read the ballast. The wattages may not work out the way you would expect.

If the coffee pot or blender is on that circuit, then go back and read what I posted above. Unless you use these in some room other than the kitchen or dininng room you have a code violation. Kitchen and dining room recepticles are supposed to be on a small appliance circuit. Nothing else can be on this circuit. The lights being on that circuit would be a violation.

You can generally speaking use 180 VA or watts for all other recepticles. That is unless you know something larger is on the circuit, for example an entertainment center, or freezer on the back porch. If that is the case look on the appliance and find the actual load.
 
#6 ·
You can generally speaking use 180 VA or watts for all other recepticles.
I agree. For non continuous loads that is the number. For continuous loads use the rating of the equipment connected.

Typical recessed lights (approx. 50-75W each) x 6 = 300-450 W
I cant seem to find it in the code, but someone told me before that interior lights are typically 65watts max and exterior are typically 75 watts max, that doesnt cover special fixures just a rule of thumb.

Im no electrician but that seems to apply to every fixture Ive worked on.
 
#13 ·
Joules,
I have to agree with Pete. In this thread and others you have shown that you need to back away from giving too much advice.

The OP asked about a specific install that did not require dedicated recepticles, and you inserted a comment that does not apply, in a way the was misunderstood by me, and possibly others.

I am not trying to be too harsh on you, but it is important to be as accurate as we can when giving advice.
 
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