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# 15 amp Circuit: How Many lights

## 15 amp Circuit: How Many lights

#1
12-11-13, 06:32 AM
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15 amp Circuit: How Many lights

My situation involves the limit of a 15amp circuit.

I am planning on putting up 30 of six 32w bulb, Metalux HBL 632 RT2 fixtures in my 2932sf garage. Each fixture has two ballasts one for 4 bulbs the other for 2.

I will have separate switches for the separate ballasts. Ideally I would have the garage separated in half or thirds of the garage. But it looks like I need four 15amp circuits, with no good way to split it up. Any suggestions?

#2
12-11-13, 06:43 AM
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My situation involves the limit of a 15amp circuit.
Any suggestions?
Use 20 amp circuits. .......................

#3
12-11-13, 07:42 AM
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What do the ballasts draw?

Without seeing the fixtures that sounds like a lot of light for a garage. Is this commercial?

#4
12-11-13, 09:27 AM
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My situation involves the limit of a 15amp circuit.
Assuming the load - your lights - will be on for more than three hours at a time, one 15A circuit can safely power up to 12 amps, or 1440 watts.

Use the rated draw of the ballasts in your fixtures to calculate the load, not the wattage of the lamps.

If the ballasts draw 40W per lamp, which is not unheard of, that's a total of 7200W. You will need 5 15A circuits. One 20A circuit can safely power up to 1920 W of continuous load, so you will need 4 of those.

At 32W per lamp, the total load is 5760 watts. That's 4 15W circuits or 3 20W circuits, but it's unlikely that that will be the actual load.

6 32W T-8 lamps will emit at least 12,000 lumen per fixture, and they could put out more than 18,000 lumen, depending on which tubes you use. That's 360,000 lumen, minimum, up to 540,000. Why are you planning to install that much light?

#5
12-11-13, 09:31 AM
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That's 360,000 lumen, minimum, up to 540,000. Why are you planning to install that much light?
So his house plants will be healthy?

#6
12-11-13, 10:11 AM
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I think it's his garage plants.

#7
12-11-13, 06:12 PM
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Why are you planning to install that much light?
They are 6-lamp high bay fixtures with reflectors and will put out a lot of light.

Metalux HBL632RT2 4' 6 lamp T8 Fluorescent High Bay at Menards

How high will these fixtures be mounted?

#8
12-14-13, 12:34 PM
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That is 1.95 watts per sf. That is the average people said we should have.
Flouresent Shop Lighting, Watts per Square Foot

I have 12' ceilings, light will be surface mounted.

I want to have flexible usage; maybe auto mechanics, maybe just storage.

#9
12-14-13, 02:36 PM
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Unless that group was tied to lamp manufacturers, I can't see all that light being necessary. 24 ea 4 lamp fixtures for a 20 x 24 shop!!! I have 10 ea t-8 s and have more than adequate general lighting. Why would you need so much lighting for storage? Light travels at 186,000 miles per second, so 12 foot ceilings pose no problems.

#10
12-14-13, 02:43 PM
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my shop is 46.5'x63.5' and I am installing thirty 6 bulb x 32watts. 1.95watts per sf.

#11
12-14-13, 02:49 PM
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You should have adequate lighting with that configuration. Still need ballast ratings in order to advise regarding circuit limitation. Ohm's law will help . V x A = Wattage, so you can mathematically. Wattage requirements, divide by the voltage and ,come up with the amperage.

#12
12-14-13, 03:00 PM
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I can't find any amps or watts on the ballasts. What do I look for?

#13
12-14-13, 03:27 PM
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Input Watts:
EB Ballast and STD Lamps
432=109
632=167
Here is the spec sheet:

http://www.cooperindustries.com/cont...81930_sssx.pdf

I think 12 feet mounting height is a little low for high bay fixtures (Cooper calls them F-Bay), but you won't have any trouble seeing.

#14
12-14-13, 04:01 PM
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Might want to look for a low bay fixture.

#15
12-14-13, 04:36 PM
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#16
12-14-13, 05:07 PM
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Your fixture catalog number is: HBL 632 RT2

The HBL fixtures use either 4 - F32T98 OR 6 - F32T8 lamps - Yours use 6 lamps

Input Watts:
EB Ballast and STD Lamps
432=109
632=167
The 4-lamp fixture uses 109 watts - includes both lamps and ballast
The 6-lamp fixture uses 167 watts - includes both lamps and ballast.

It's on the spec sheet on the right hand side under Energy Data:

http://www.cooperindustries.com/cont...81930_sssx.pdf

#17
12-14-13, 05:54 PM
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How do the ballast s use less than the lamps?

#18
12-15-13, 06:38 AM
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bkvanbek

How do the ballast s use less than the lamps?
I am not sure quite how to answer your question other than to say the electronic ballasts only use a few watts and you have 6 lamps. If that's not enough information you could call Cooper-Metalux. The information I gave you came from the spec sheet.

#19
12-15-13, 03:57 PM
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The ballast for the 4 lamps are AB4-32-IP-UNV-HBF with "input power" of 147-108 watts, depending on the F32 lamp used. Which of course is more than 32watts a lamp.

And for the 2 lamps are AB2-32-IP-UNV-HBF with "input power" of 76-57 watts, depending on the F32 lamp used.

If I wire these 30 fixtures (and five fans) with 5 circuits, then they could be switched an acceptable way. But one circuit with 20 of the 2 lamp ballasts would have a max of 1520 watts and the three circuits with 10 of the 4 lamp ballasts each could have a max of 1470 watts. Is this acceptable?

#20
12-15-13, 04:12 PM
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If I wire these 30 fixtures (and five fans) with 5 circuits, then they could be switched an acceptable way. But one circuit with 20 of the 2 lamp ballasts would have a max of 1520 watts and the three circuits with 10 of the 4 lamp ballasts each could have a max of 1470 watts. Is this acceptable?
That would probably work fine or you could just use 20 amp circuits and remove all doubts.

#21
12-15-13, 04:22 PM
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I already have the 14/2 and 14/3 cable. And with the three-way switching 12 ga gets expensive.

#22
12-17-13, 03:18 PM
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I already have the 14/2 and 14/3 cable. And with the three-way switching 12 ga gets expensive.
Have you done the math? If the #14AWG cable you have is returnable and you could run one less circuit, would you cpend more or less to do this with 20AQ breakers and #12 AWG cable?

one circuit with 20 of the 2 lamp ballasts would have a max of 1520 watts and the three circuits with 10 of the 4 lamp ballasts each could have a max of 1470 watts. Is this acceptable?
Originally Posted by Nashkat1
Assuming the load - your lights - will be on for more than three hours at a time, one 15A circuit can safely power up to 12 amps, or 1440 watts.
The three circuits that draw 1470W each are marginal. The one that draws 1520W is overloaded.

#23
12-17-13, 03:37 PM
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If the load is not continuous, on for more than 3 hours, you can load it higher. The 15 amp could support 1800 watts, the 20 amp could support 2400 watts.

#24
12-17-13, 04:18 PM
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What I don't get is the ballast ratings. If we used the bulb wattage, 32, the 1520watt circuit would only be 1280. And the 1470 would also be 1280watts.

#25
12-17-13, 04:55 PM
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The ballast also use some energy above the bulb wattage.

#26
12-17-13, 05:14 PM
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Yikes!

I can't resist.
Is this a sun bathing garage or an indoor greenhouse?
You may need an air conditioner as well.

#27
12-17-13, 07:27 PM
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Or I could just use ES bulbs, then I would be at 80% or less of max with my configuration, for five 15amp circuits.

Mike, in a woodworking forum the members did a pole and the majority of them thought 2 watts per sf is what is needed for lighting. I have these same lights in another area at 1.16 watts a sf and I could use more. So I don't think 1.95 watts per sf is too much.

For growing I think they use HID. And I don't tan.

#28
12-17-13, 08:17 PM
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n a woodworking forum the members did a pole and the majority of them thought 2 watts per sf is what is needed for lighting. I have these same lights in another area at 1.16 watts a sf and I could use more. So I don't think 1.95 watts per sf is too much.
A watt is a unit of power. It's a convenient measure for billing purposes. It doesn't mean anything in terms of light.

If you want more light, what you're looking for is a light source that emits more lumens (or lumen). If you want to increase the efficiency of your lighting, look for sources that produce more lumen per watt.

#29
12-18-13, 06:42 AM
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Are you suggesting there is a better lighting choice for my application, than T-8 fluorescent?

#30
12-18-13, 06:56 AM
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Are you suggesting there is a better lighting choice for my application, than T-8 fluorescent?
A watt is a unit of power. It's a convenient measure for billing purposes. It doesn't mean anything in terms of light.

If you want more light, what you're looking for is a light source that emits more lumens (or lumen). If you want to increase the efficiency of your lighting, look for sources that produce more lumen per watt.
No, I think he's just telling you that watts per sq foot means nothing because light isn't measuerd in watts. Lighting levels are measured in footcandles. Lumens is how much light you'll get from a lamp.

We typically buy things based on how much of it we get, right? When buying milk, we buy it by volume (gallons). So, why should light be any different? For decades, we have been buying lightbulbs based on how much energy they consume (watts) -- no matter how much light they give us (lumens).
What's a Lumen?

Lumens measure how much light you are getting from a bulb. More lumens means it's a brighter light; fewer lumens means it's a dimmer light.
Lumens and the Lighting Facts Label | Department of Energy

Shop Lighting For Woodworkers | The Wood Whisperer

Last edited by CasualJoe; 12-18-13 at 07:18 AM.
#31
12-18-13, 07:23 AM
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I would not say watts has nothing to do with how much light you get. When discussing tube fluorescent lights the difference between lamps of the same watt is negligible.
I am using T8s and those cooper fixtures and the discussion is watts per circuit, so watts per sf is most relevant.

#32
12-18-13, 11:18 AM
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I would not say watts has nothing to do with how much light you get. When discussing tube fluorescent lights the difference between lamps of the same watt is negligible.
Really?

Let's take one type of lamp, one manufacturer and one wattage, and see if there are any real differences. Sticking with Phillips bi-pin 4 ft. T8 32W tubes, there are two different ratings for design lumens in their extra long life lamps:

28115-4 or 26116-2, 2700 lumens
28120-4, 2800 lumens

Then there are their Advantage High Lumen lamps:

28080-0, 28081-8 and 28085-9, 3000 lumens
28089-1, 2900 lumens

Four of their PLUS 800 Series Long Life T8 Fluorescent Lamps are rated as having 2800 design lumens and one is rated as having 2710 design lumens. Their PLUS 700 Series Long Life T8 Fluorescent Lamps range from 2550 to 2660 design lumens. Phillips plain 800 Series T8 Fluorescent Lamps are all rates at 2710 design lumens and plain 700 Series T8 Fluorescent Lamps are rated at either 2600 or 2750 design lumens.

A Phillips Rapid Start 32W T8 Fluorescent Lamp is rated as having 1860 design lumens.

Same company, same tube style, same wattage, and a difference of 1140 lumens, or almost 40%.

Originally Posted by CasualJoe
watts per sq foot means nothing because light isn't measured in watts. Lighting levels are measured in footcandles. Lumens is how much light you'll get from a lamp.
Originally Posted by Nashkat1
If you want more light, what you're looking for is a light source that emits more lumens (or lumen). If you want to increase the efficiency of your lighting, look for sources that produce more lumen per watt.
[SUP]Data: Phillips Lighting Catalog - Lamp Specification Guide 2013[/SUP]

#33
12-18-13, 12:49 PM
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I am using T8s and those cooper fixtures and the discussion is watts per circuit, so watts per sf is most relevant.
I don't think so. Try looking at the catalog for lumens under the 4 foot F28T8 lamps.