new lights in shop, need help wiring

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  #1  
Old 02-10-05, 03:28 PM
mach1dad
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new lights in shop, need help wiring

I plan to install and wire a number of 48” 4 tube fluorescent light fixtures in my shop. My plan is to have 2 rows with 7 fixtures each. I’ll call them row A and B. For this example I will number the fixtures in both rows from left to right 1-7. Now for the fun part! I would like to control the fixtures as follows: Fixtures A2, A4, A6 on one switch. A1, A3 on another switch. A5, A7 on yet another switch. Same idea for Row B. Power should come from switch side. All switches will be located at same spot. Runs will be in conduit. Would someone like to tell me the most efficient way to wire this mess? Thanks
 
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  #2  
Old 02-10-05, 03:57 PM
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OK, I'm just another DIYer, so any pro who wants to step in feel free.

I think we need to know a couple things first...

How many circuits do you plan for this? What is the max wattage tube that can be used in the fixtures?

---EXAMPLE---
Suppose the fixtures use 40 watt tubes. In that case, you would have:

7 fixtures X 4 tubes/fixture X 40 W/tube = 1120 Watts X 1 A/120 V = 9 1/3 A

Two rows then gives you 18 2/3 A. This is well over 80% of a 20A circuit, so in this example, you should plan for two circuits, one for each row of lights.
---END EXAMPLE---


Answer the questions above and we'll go from there...
 
  #3  
Old 02-10-05, 03:59 PM
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One other thing...I am assuming you are planning 6 total switches, three per row, right?
 
  #4  
Old 02-10-05, 04:08 PM
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And yet a few more questions:

How do you plan to connect to the fixtures? Will they be hard wired or do they have plug-in cords? Do the fixtures hang from chains, or are they mounted to the ceiling?
 
  #5  
Old 02-10-05, 05:55 PM
mach1dad
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chirkware thanks for your interest.

The fixtures are rated to 40 watt max for each tube. The amp rate on the ballasts reads .73. As there are two ballasts per fixture I'm guessing I should plan for no less than 1.46 amps per fixture. I have not decided on the number of circuits yet as I look to learn from the forum what is best.

Yes I would like 6 total switches. Using this configuration I expect to be able to control the lighting to the area in the shop where I am working and keep the electricity use down when possible.

The fixtures are to be installed in a metal building. I was thinking that I would screw them directly to the metal framing members with sheetmetal screws. Then they would be hardwired, with all wire inside EMT conduit.
 
  #6  
Old 02-10-05, 06:28 PM
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OK, at 1.46A per fixture, one row of 7 fixtures is roughly 10 amps.

I would plan for two circuits. One 20 amp circuit should only feed MAX 16 amps (80% of its capacity). You could run #14 and go with 15 amp circuits, but I'd go ahead and use #12 and 20 amp so you have room to grow.

For simplicity sake, I'll assume you decide to use a circuit per row. From here on out, I'll just deal with one row of fixtures and their three switches. I am ignoring the second row, it will be done exactly the same...


CONDUIT: Run conduit from the breaker panel to the triple box for your three switches. From there, run conduit to fixture A1, then from A1 to A2, etc. until all fixtures are connected together. This assumes you can go in one end of a fixture and out the other--we'll adjust this part if we have to. The wiring will pretty much stay the same.

WIRING: Run #12 (or #14) black, white, green from panel into switch box. Wirenut three black pigtails to your black from the panel and connect them to your three switches. From the box, run a black, red, BLUE, white, and green to A1. Connect the black to SW1, red to SW2, and blue to SW3. Wirenut the two whites together. Pigtail greens to ground screws of switches and to box (assuming you are using a metal box).

Now, since all the fixtures are on the same circuit, you just need one neutral wire. Connect it to A1's neutral, then run it to A2 and connect to A2's neutral, etc. all the way to A7. Same with the grounds...

Now for your hot leads...Black needs to connect to the hot side of A1, bypass A2 (run though A2 but don't connect to A2), and connect to A3. Red will bypass A1, connect to A2, bypass A3, connect to A4, bypass A5, and connect to A6. Blue will bypass A1, A2, A3, and A4, connect to A5, bypass A6, and connect to A7.


That should do, and should look very neat. This makes the first switch control A1 & A3, the second controls A2, A4, & A6, and the third controls A5 & A7. If you want to change which switch controls which set of fixtures, just change where you connect the black, red, and blue at the switches.


Now, repeat all this for the other row and you're in good shape!
 
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Old 02-10-05, 07:31 PM
mach1dad
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This is a real help. Thanks

Only have one hopefully minor change. If possible I would like to run to the middle and fan out with the wiring. Example: from switch box run wires toward A4, the take black wire to A1 and A3, take red wire to A2, A4, A6, and blue wire to A5 and A7. Still passing through (not connecting) to others where necessary. Will this work? Would single neutral (white) still work ok.

Fixtures do not have green wire. Is this ok? Will the fact they are hardwired to the EMT work for this?
 
  #8  
Old 02-11-05, 04:14 AM
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Run your conduit from the switch box into A4. Hopefully, you can go into the side or top of A4. You will need one conduit leaving A4 going to A3-A2-A1, and another leaving A4 going to A5-A6-A7. Your black now passes through A4 into the conduit to A3, connects to A3, then bypasses A2 and connects to A1. Same idea with the blue wire, just going into the opposite conduit that goes into A5.

Your Red wire will connect to A4 as before. Then pull a red wire from A4 through A3 and connecting to A2, and another from A4 through A5 and connecting to A6. So the red coming in and the two going out will connect to the hot side of A4.

Whites will similarly split off each direction. White in and two whites out connecting to the neutral of A4. One white goes to A3-A2-A1, and the other goes to A5-A6-A7.

I would still run the greens. Do them just like the whites. Look at the installation instructions for the fixtures and connect your greens however it says to ground. There may be a threaded grounding screw hole somewhere on the fixture shell.

While the conduit itself may be an adequate ground (if so, you may not need the green wire for any of this), I would not recommend simply counting on it to do the job (a loose conduit connection at any point will compromise the ground bonding). You might ask the local electrical inspector or a local electrician whether your area allows you to just use the conduit for the grounding.
 
  #9  
Old 02-11-05, 12:06 PM
mach1dad
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Thanks for all your help!
 
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