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Old 12-20-2008, 07:23 AM   #1
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Fluorescent Light Ballast


Hi, I'm from Canada (eh). I want to install a fluorescent light fixture http://www.homedepot.ca/webapp/wcs/s...k=P_PartNumber I want to connect it to a light-switch that controls power to an electrical wall outlet. Is this possible? Cheers.

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Old 12-20-2008, 07:57 AM   #2
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1. The power feed with neutral for the receptacle must first enter the existing switch box in question and then you add a cable going up to your new light. Note that you will have to choose one of:
1a. Have the switch control both the new light and the receptacle.
1b. Change the receptacle wiring to always-on and use the switch for the new light,
1c. Install a duplex switch unit.

Alternative:

2. You run a power feed going to your light and then you can run a cable down to the existing switch box. You still have to make a choice,
2a. Install a duplex switch unit,
2b. Change the receptacle wiring to always-on and use the switch for the new light.

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Old 12-20-2008, 03:24 PM   #3
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Originally Posted by gatzke View Post
Hi, I'm from Canada (eh). I want to install a fluorescent light fixture http://www.homedepot.ca/webapp/wcs/s...k=P_PartNumber I want to connect it to a light-switch that controls power to an electrical wall outlet. Is this possible? Cheers.
Fo shizel. You can buy a fluorescent light fixture that has a cord or "pigtail". They are made to plug into outlets that are already in your ceiling. Most of them come with chains to suspend the fixture from the ceiling with hooks.

Or, I think that you might be able to remove the outlet from the box, and then install a new fixture over the box and run the wires through a knock out on the fixture if you want it hard wired. (Depending of course that the position of the outlet is where you'd like your light fixture to be centered.) But you might want to look into that, I'm not an electrician and I am sure I'll get hammered for that.
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Old 12-20-2008, 03:30 PM   #4
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Sorry, I see now that you wrote "wall" outlet, I was thinking the outlet was on the ceiling.

Good advice has already been given. If it were me I would run new cable from the switch, and then it's up to you if you want to do a little rewiring to make the outlet "always on" or you can leave it to be controlled by the switch if you don't use it much. Just make sure your existing switch box has the capacity for the new wires.
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Old 12-20-2008, 03:41 PM   #5
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If it's not grounded it may not always "start", it's something about capacitance from the metal shell to the tubes 1/2" away.
I'd scrape the paint away from the grounding screw.
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Old 12-20-2008, 03:57 PM   #6
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Be careful about the box fill. Assuming a metal box:
Table 314.16(A) of the 2005 NEC dictates the number of conductors you are allowed.
You will certainly need a deep (probably 75x50x70mm) box to meet this requirement.

Also, if your branch circuit is 20A, with #12 AWG wire, your new wiring to the light will also have to be #12, and you fill up the box really fast.
If you have NM cable running into the box, and you are permitted to use nonmetallic outlet boxes, I think you could get more conductors in that than in a metallic one. I don't see a chart in the 2005 NEC for nonmetallic box fill.
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Old 12-20-2008, 03:59 PM   #7
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If it's not grounded it may not always "start", it's something about capacitance from the metal shell to the tubes 1/2" away.
I'd scrape the paint away from the grounding screw.
I think you mis-placed this post. Unless I'm missing something here
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Old 12-20-2008, 04:05 PM   #8
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I think you mis-placed this post. Unless I'm missing something here
I think he was just pointing out that it is important to have the fixture grounded because some fluorescent fixtures can't start properly without a ground.

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Old 12-20-2008, 04:21 PM   #9
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I think he was just pointing out that it is important to have the fixture grounded because some fluorescent fixtures can't start properly without a ground.

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Old 12-20-2008, 04:34 PM   #10
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I think he was just pointing out that it is important to have the fixture grounded because some fluorescent fixtures can't start properly without a ground.

Jamie
Sorry about that.
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Old 12-20-2008, 06:50 PM   #11
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Be ... I think you could get more conductors in that than in a metallic one. I don't see a chart in the 2005 NEC for nonmetallic box fill.
(Non-metallic boxes use the same box fill rules in terms of cubic inches of space inside. Many have the cubic inch volume embossed somewhere on or in them. Be aware that some have spring finger clamps that protrude inside and you need to count "clamps" as one unit of box fill.)

I never realized that fluorescent light fixtures needed to have their framework grounded to work properly; I would have guessed at first that a defect existed. Now if the fixture relies on capacitance to ground, doesn't that imply leakage and a GFCI would trip?
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Last edited by AllanJ; 12-20-2008 at 06:54 PM.
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Old 12-20-2008, 06:59 PM   #12
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(Non-metallic boxes use the same box fill rules in terms of cubic inches of space inside. Many have the cubic inch volume embossed somewhere on or in them. Be aware that some have spring finger clamps that protrude inside and you need to count "clamps" as one unit of box fill.)

I never realized that fluorescent light fixtures needed to have their framework grounded to work properly; I would have guessed at first that a defect existed. Now if the fixture relies on capacitance to ground, doesn't that imply leakage and a GFCI would trip?
I don't think leakage is great enough for one or two, but whole rows may trip a GFCI. Have you ever noticed a fluorescent that wouldn't quite light, but lit right up when you touched it? I have seen this on several occasions, and every one of them was ungrounded. Yeah, it doesn't happen alot, but it does happen. Grounding isn't just for kids any more.
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Old 12-20-2008, 07:03 PM   #13
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if the fixture relies on capacitance to ground, doesn't that imply leakage and a GFCI would trip?
The tube capacitance is on the ballast secondary winding, and I'm not sure how much capacitance you'd get from a tube 1/2" from ground.
You could assume a parallel plate capacitor and use the "8.85 formula" in this link
http://en.wikipedia.org/wiki/Capacitance
and convert all distances to meters.

You need .09F at 60 Hz and 120v to trip a GFI.

I'd think there'd be way more capacitance from the primary winding to the grounded metal ballast case. Electronic ballasts without large windings may have much less capacitance to ground unless they put in an RFI filter.
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Old 12-20-2008, 08:37 PM   #14
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This discussion reminds me of a time when one of my flourescent lights in my unheated garage wouldn't work in the winter! It turned out to be a bad ground! Worked OK in the summer though! Must have been because of the capacitance wasn't suitable to ionize the lamp gas!
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Old 12-20-2008, 09:22 PM   #15
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This discussion reminds me of a time when one of my flourescent lights in my unheated garage wouldn't work in the winter! It turned out to be a bad ground! Worked OK in the summer though! Must have been because of the capacitance wasn't suitable to ionize the lamp gas!
I recall an online discussion with an engineer that designed the fluorescent lights on the space shuttle. He said that was one of the problems. They couldn't get the lights to work consistently. Finally, they tried grounding the reflector, and Bingo!

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