Replies

1. 
   UncleDunc | May 09, 2002 07:40pm | #1

   Assuming one hot wire is connected to each side of the 220, you can't overload the neutral. If one side is loaded to capacity and the other side is idle, the neutral current matches the hot current. If the load is balanced, there is no current at all in the neutral. And anywhere in between, the neutral is carrying less current than the most heavily loaded hot wire.

   If both hot wires are connected to the same side of the 220, then yes, you would need a heavier neutral.

   
   

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   Edited 5/9/2002 1:33:37 PM ET by UNCLEDUNC

2. 
   BossHog | May 09, 2002 08:40pm | #2

   2000 watts of lighting at 110 volts equals about 18 amps. I'd split up the lighting circuit - Do you really need that many lights on all the time ?

   The world's full of apathy, but I don't care

1. 
   jbwilly | May 09, 2002 09:49pm | #3

   The area in question is 20' X 40'.  I was going to put in about 12-15 four bulb 4' fixtures.  The bulbs are 40 watts each. 40 X12 =480 X 4=1920watts.  I think the math is correct.  Is this too much lighting for the area?  I have not been able to find any reference material on the subject.  While I was planning to put every other light on a seperate switch, I would expect to have them all on while working at night.

1. 
   BossHog | May 09, 2002 09:58pm | #4

   I don't really know about how much light you'll need - Maybe someone else can address that.

   I was just thinking about the power meter spinning with all those lights going. I would consider splitting the shop into halves or thirds, and having only the ones you need turned on. Or maybe have fewer lights on the ceiling, and add a couple over a workbench that could be turned on as needed.

   If there's one thing I can't stand, it's intolerance.

2. 
   BillHartmann | May 09, 2002 10:36pm | #5

   [Boss - Nominal voltage is 120, not 110.]

   JB

   On 20 amp circuit you can have a 2400 volt-amps of load. But for continous load (which this would be) you are required to limit it 80% or 1920 VA.

   A couple of months ago FWW had an article on shop lighting. On Badger Pond (www.wwforum.com) there was a discussion about the amount of lighting that people has in their shops. I **THINK** that the average was about 3 watts per sq ft, but I may not remember correctly. You might search the archives over there.

   If that is correct then the number of lights that you have is a little shy.

   Now are you SURE that you are using 40 watt bulbs. While there are still some 40 watt bulbs if you get the special color corrected one, most common ones are 32-34 watts. And if you go with the newer T8 bulbs I think that is all of them are 32 watts (for a 4footer). But you really need to look specs for the bulbs, they are is wide range in the light output.

   BTW, the "shoplight" bulbs are only rated for 25 watts and to work with a special shoplight ballast. They only output about 1/2 of a candles worth.

   But to the bulb rating you need to add some for losses in the ballast. Sorry, but I don't have any numbers at hand.

   Anyway you are pushing the limit. I would also suggest some combination of either zoning the lights and/or alternating them. Depends on the shop layout and how you work.

1. 
   DaveRicheson | May 09, 2002 11:24pm | #8

   Bill, believe it or not ,a lot of office spaces are going back to the true 40 watt bulbs. We have been going to long life (44,000 hours) bulbs with the bright daylight color. The newer T10 bulbs will fit the stsandard T12 bi-pin sockets. The T8 will not and the ballast of the T12 or T1o fixture is not ussually compatable with the T8.

   I was ammazed at the difference thes new bulbs made. Compared to a standard 40W bulb, these things are about 30% brighter. We recently did our main first floor hallway leading to the elevators in our building. I watched smiles break out on peoples faces as the lighting improved ( what do you call those people that sudy that type of stuff?). Those that did not see the work in progress ask if we had repainted the hallway. Wild,huh?

   These new long life bulbs cost about $14.00 each for the T12. We just found out from another supplier that he can furnish the same warrenty in a T10 bulb at $8.00 each. Want to guess which one we are now purchasing?

1. 
   BillHartmann | May 10, 2002 12:15am | #9

   Dave

   I believe, I BELIEVE.

   I replaced my 8ft 60watt CW's with a 75 watt "designer series natural light". Not only is the color much better, but they are also much brighter.

   Looking around in the catalogs you can find all kinds of better bulbs.

3. 
   DaveRicheson | May 09, 2002 11:05pm | #7

   Boss is right.

   If you use energy efficient bulbs and standard ballast you will draw about 0.63 amp per bulb pair, or 1.26 amp per four light fixture. If you use 15 fixtures your total amp draw is 18.45 amps. To much for one twenty amp circuite. Drop the number back 12 fixtures and you only pull 14.76 amp. Maximin loading is 80% of breaker rating, so you are under the 16 amp reccomended loading max for a 20 amp circuit.

   Your best bet is to pick out your fixtures and read the ballast label, and then figure your load accordingly. High efficientcy ballas and bulbs or electronic ballast might allow more lights.

   Dave

3. 
   TLRice | May 09, 2002 10:48pm | #6

   JBW,

   Thats all perfectly safe and legal (by the NEC) as long as the 12 AWG wire circuit is protected with a 20A or less breaker/fuse. As someone else mentioned, you can share a neutral if the hots are on opposite phases.

   20 x 40 space used a work shop, , 800 sf, 1200 - 1600 watts of lights seems about right. 1.5 - 2w/sf is the equivalent of a well lit office (the lighting guys will tell what lighting levels need to be in foot-candles).

   Something to consider, put about 1-1/2 watts per sf for general area lighting and put bright, locally switched, task lights over specific work areas.

   
   

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   Edited 5/10/2002 8:30:06 AM ET by Tim

4. 
   4Lorn1 | May 13, 2002 05:23am | #10

   The 3 wire circuit you describe will work well and is, to my knowledge, well within NEC guidelines and most codes. On long runs you can save a substantial amount of money on the cost of Romex.

   The only problem I see and the reason I limit using this configuration is that if for any reason the neutral connection is compromised the two sides of the circuit will rebalance the voltage in potentially hazardous ways. One side may get something just shy of 240v while the other gets the remainder of the 240v. Any impedance limited devices, small motors, transformers and especially florescent ballasts can overheat and catch fire.

   If you do use this technique I recommend that you run the 3 wire cable into a dedicated box. A well grounded metal 4by4 box located in the attic, don't get me started on attics, or crawl space with the other two runs of 12/2 going to the loads would be cheap insurance. The dedicated box, one without a device or other circuits, ensures that the neutral connection will not be manipulated and possibly damaged during repairs to any devices.

   The dedicated box eats up so much of the savings in running 1-3wire cable vs 2- 2wire runs that unless the runs are extremely long or someone insists I usually avoid the shared neutral configuration.