Replies

1. 
   davidmeiland | May 17, 2004 03:45am | #1

   All the circuits in my house are 20 amp or higher. It makes it harder to use pancake boxes for ceiling fixtures but I can't think of any electrical reason you wouldn't do it.

2. 
   WayneL5 | May 17, 2004 04:35am | #2

   There was a lot written here since the article came out.  Check the archives if you wish.

   I believe the resolution was that the article was incorrect.  You are not supposed to put lights on the two 20 amp circuits that are required for kitchen outlets, but there is no general prohibition against putting lights on 20 amp circuits in general.

1. 
   panda | May 20, 2004 04:09pm | #4

   The article was in the November 2003 No. 158 page 63. They are talking about low voltage lighting. (I don't think it makes a difference) On page 65 they say "When tapping into the power source, Keep in mind that the National Electrical Code (NEC) requires lighting to be on a 15 amp circuit." This makes no sense to me because the amount of current that goes through any electrical circuit, even the human body, is dependent on the resistance of the item and the voltage applied, not the current available. I=E/R I don't think the formula has changed since I learned it. Why would the NEC require a 15 amp circuit?

   Thanks again for everyone's comments.

   Dennis

3. 
   Houghton123 | May 17, 2004 04:38am | #3

   Granted, it was some years ago, but our building inspector was THRILLED that I used 20 amp (12-ga.) circuits for the lights.

4. 
   Sancho | May 20, 2004 05:17pm | #5

   You didnt mention the gage of your wireing. 20 amp would be ok I think as my older home has it but it has 12 ga wireing. if you have 14 ga wireing then its a definate no no

    

   Darkworksite4:

   El americano pasado hacia fuera ase la bandera

1. 
   panda | May 20, 2004 05:38pm | #6

   All wiring is 12 guage on 20 amp circuits.

   Dennis

5. 
   DanH | May 20, 2004 05:55pm | #7

   Keep in mind that fixtures may not be designed/rated to be on a 20-amp circuit. Code generally allows fixtures to use lighter wiring than the circuit ampacity would require, but there's a limit to how much this allowance can be safely pushed.

   Having said that, has anyone tried recently to find a 15A Edison fuse? They're scarcer than hen's teeth, so any house still on fuses likely will have 20A circuits.

1. 
   BillHartmann | May 20, 2004 06:25pm | #8

   "Keep in mind that fixtures may not be designed/rated to be on a 20-amp circuit. Code generally allows fixtures to use lighter wiring than the circuit ampacity would require, but there's a limit to how much this allowance can be safely pushed."

   Does not have anything to do with it.

   The lighting fixture is designed to support the size of lamps that are approved for use in it.

1. 
   DanH | May 23, 2004 11:38pm | #10

   A light fixture must be capable of sustaining a temporary overload long enough to trip the fuse/breaker. If it only had to be able to support the design load then there would be no point in fuses in the first place, since faults are almost always in fixtures, not in the in-the-wall wiring.

   Availability of 15-amp fuses appears to vary by locale. Couldn't find them in Tennessee or Kentucky, even in "old-fashioned" hardware stores. Seem to be readily available in Fargo, ND, for what that's worth.

1. 
   BillHartmann | May 24, 2004 01:01am | #11

   What is the fusing current of #18 wire?

1. 
   DanH | May 24, 2004 04:16am | #12

   Depends on how big a fire you want to start.

2. 
   JohnSprung | May 24, 2004 10:21pm | #13

   > What is the fusing current of #18 wire?

   It depends on the application.  It depends on how much heat the insulation can stand, and how much heat the wire can dissipate.  A service drop from a utility pole can dissipate a lot more heat than a piece of Romex buried in blown-in cellulose. 

   NEC doesn't allow anything smaller than #14 for power lines in buildings, so there isn't an entry in their table in the code for #18.  I have seen a table for SJ cords that gives the same 20 amps for #12 and 15 amps for #14 as the code, and it has 13 amps for #16 and 10 amps for #18.   So maybe that's where it would be if it were allowed.  But it isn't.

   -- J.S.

3. 
   BillHartmann | May 24, 2004 10:39pm | #14

   That was a retorical question, based on this comment.

   "Keep in mind that fixtures may not be designed/rated to be on a 20-amp circuit. Code generally allows fixtures to use lighter wiring than the circuit ampacity would require, but there's a limit to how much this allowance can be safely pushed."

   The fusing current is when the wire melts. For number #18 it is 82.9 amps and 117 for #16.

   But the insulation will be long gone before that.

   And it does not matter what SJ is rated as, because that is not the wire that is used light fixture wiring. I think that MTW is and possilbe some others.

   But you need to go to the UL specs to find out all of that.

   But so what if the #18 is rated at 10 amps. How are you going to get anything near that amount of current through a light fixtured designed for 2 A21 bulbs.

4. 
   davidmeiland | May 25, 2004 01:21am | #15

   "But so what if the #18 is rated at 10 amps. How are you going to get anything near that amount of current through a light fixtured designed for 2 A21 bulbs."

   Maybe you could do it in my brother's house. He had an electrician replace the service (it was a Federal Pacific panel). Now, the light bulb in one room gets incredibly bright and then blows within a second or so of being turned on. I figure that somehow the electrician fed 220 to that fixture...? He's getting it checked out by someone else.

5. 
   BillHartmann | May 25, 2004 01:41am | #16

   Either that or he has a bad neutral connection.

   However, it might not be the electrican's fault.

   One thing that could have happened is that someone jury rigged this light between two circuits. And hot and neutral might have been reversed on one or more circuits.

   Then the electrican might have wired the new pannel "correctly",

   I am intested in know what he does find.

2. 
   archyII | May 25, 2004 02:04am | #17

   Not in chicago.    When we bought our house it had been updated (from fuses) to a new 100A panel with 20A breakers and all 12ga wire. We added two bedrooms and a bath to our attic and upgraded to a 200A service and panel.  The electrical inspector made us change all of the lighting circuits to 15A breakers.  His reason was that the fixtures were not designed for 20A.  I told him that most of the light fixtures wires (wall sconces) were not designed for to handle 15A.  We still had to change the 20A breakers to 15A.

1. 
   BillHartmann | May 25, 2004 02:19am | #18

   I am talking about the NEC.

1. 
   DanH | May 25, 2004 04:03am | #19

   My copy of the NEC is pretty old, but 240-4 lays out overcurrent protection required for fixture wiring. Basically, 20A or less requires at least #18, 30A requires #14, 40-50A requires #12. These numbers are presumably chosen because they make it reasonably likely that the overcurrent protection will kick in before the wire fuses and begins to arc. Ie, the intention is to prevent a fire, not protect the fixture wiring from damage.

   It may well be that later versions of the NEC are more restrictive, and it's certainly possible that local code is more restrictive.

2. 
   BillHartmann | May 25, 2004 07:23am | #20

   "My copy of the NEC is pretty old, but 240-4 lays out overcurrent protection required for fixture wiring. Basically, 20A or less requires at least #18, 30A requires #14, 40-50A requires #12. These numbers are presumably chosen because they make it reasonably likely that the overcurrent protection will kick in before the wire fuses and begins to arc. Ie, the intention is to prevent a fire, not protect the fixture wiring from damage."

   Exactly. The 99 NEC is the same. But you miss labled it.

   That is the limit of the size of the fixture wiring connected to the appropriate branch circuits.

   And 402 covers fixture wiring. Minimum size wiring is #18 and #18 is rated for 8 amps. And the fixture must be designed so that it temp specs of the wire is not exceeded.

   Nothing in 402 or 240 differentiates between fixtures that could be used on 15 amp circuit or on 20 amp circuits.

2. 
   JohnSprung | May 20, 2004 08:07pm | #9

   You can put any fixture on a 20 amp circuit.  15A screw fuses are plentiful at our local HD.  Look in an older part of town where lots of buildings have them, stores there should stock them.

   -- J.S.