Blown circuit breakers?

[Leef]

Ouch!! [img]/forums/images/icons/crazy.gif[/img] Don't pull any punches guys.

I knew there would be a recommended percentage and 80% makes sense. I did put in 3 gang switch boxes and now I'm glad I did. I intended to use the other two switches for outdoor lighting, but they'll be needed to fix my original problem as you recommend. The walls are all bare studs, so more switches and wiring really is no problem.

I'll plan to use 15 a circuits with parallel runs as suggested. Most of all, I appreciate the lesson on proper design and forethought [img]/forums/images/icons/smile.gif[/img] I certainly underestimated the amperage necessary to power 500 watt fixtures.

I assure you it'll be done safely with your advice.

Thanks again,

Leef

[CJDave]

[img]/forums/images/icons/tongue.gif[/img] For the last year-and-a-half I've been involved as a volunteer electrical guy on a church building project. The main lighting; exclusive of the spots and specialty lights; is 15,000 Watts [img]/forums/images/icons/blush.gif[/img] We have a sixteen channel digital dimmer and lots of other good stuff in there. That was my first whack at industrial lighting, and it was a real stretch at times. We have a few channels on the dimmer that are carrying well over 1600 watts per channel. [img]/forums/images/icons/crazy.gif[/img] I just built a shop here at home out of an existing grainery, and since I'm old and need more light to see, my parts rooms have lots of bulbs, but a switch right by the door that is easy to flip off when I'm not in there looking for a gasket or a fitting. [img]/forums/images/icons/tongue.gif[/img]

[dummy]

OK. One more question to add to the confusion. What is the (dis) advantage to running a 20 A circuit when alot of the common switches and outlets are only rated for 15 A?

[GERARD]

Don't have much to add about the wiring aspect but I'll echo the fluorescent question. halogens are nice but take a lot of wattage for the lumes you get. 3600 watts at $.12/kilowatt will cost you about $.43 per hour to run as well as use up 30+ amps of you're capacity. Start some welding out there and you have quite the electric draw. I use fluorescent pretty extensively in our barn (unheated) and have not had a problem with starting, even with the balasts not specifically rated as cold weather. (You have to remember that even though it's -10 outside it's still going to be warmer in an enclosed area unless it stays -10 continuosly for several days.)

[CJDave]

[img]/forums/images/icons/tongue.gif[/img] I'll try and answer that until Inspector 507 can give you a better explaination...... In lighting circuits you could have considerable inrush when the lights are first flipped on. it is momentary, but considerable. That inrush could cause nuisance tripping. The running current on that light circuit could be fifteen AMPs, but inrush would be much more. The fifteen AMP rating of the wall switch would be adequate because as Insp. 507 pointed out, continuous load is technically a load which exists for three hours or more. Inrush is momentary. [img]/forums/images/icons/tongue.gif[/img]

[Inspector507]

dummy,
If I had a circuit that was loaded at 14-16 amps, I'd definately spend the few extra bucks on a 20 amp switch. It's going to last longer.
Breakers are designed to withstand "inrush current" for a short period of time. Motor loads for example will spike a test meter at 2-3 times the rating of the breaker, but as soon as it gets going, everythings fine.

[Phred]

The issue with the small wires in the fixture is that they are short. Remember that the power loss in a conductor is I^2R and that R is proportional to the length and 1/(cross sectional area). What causes a wire to burn is that the power dissipated becomes very large and the wire heats up and melts /ignites something.

So when the code calls for a 12 gauge wire that is a assuming you will run it a relatively long ways.
The wires in the fixture are very short and will not burst into flames with a short current spike of 20 amps.

You would not believe the wires we use in power electronics to handle large currents (>50-100 amps) in tiny little wires. The key is they are very short.

With all this said I tend to over do it on the electrical. No inspector will complain that you used to big a wire or under loaded a breaker.

Fred

[Leef]

This thread has been very informative. As I've contemplated different ways to divide my light fixtures, I've come up with a few more questions. Here is my plan:

-Since I used standard 15a switches, I will use 15a circuit breakers. On the first 3way switch I'll feed three 500W and two 300 W fixtures; however, I've only put 300W bulbs in all five fixtures. Therefore 1500W / 110 v = 13.6 amps which is slightly greater than 12 amps ( 80% of the circuit breaker ).

Q. Is it ok to put smaller bulbs in the 500W fixtures?

Q. Should I buy some smaller bulbs to stay at 80% of the cb?

- On the second switch, I'll feed 3 500W fixtures. Once again I'm at 13.6 amps, so same question applies: change bulbs or leave it.

- I have a lot of 12-3 romex. I am planning to use it from the panel to the two 3way switches mentioned above. It'll be a 20 ft length of romex - red wire in one 15a circuit breaker and the black wire in another 15a cb with the neutral and ground wires shared. I know I've seen this done on the PBS Hometime show which is where I got the idea ( so if it's a bad idea, I didn't think of it [img]/forums/images/icons/blush.gif[/img] ).

Q. Is there too much heat or current to put two 15a circuits through one piece of romex for this distance?

Q. Is it alright to share one neutral and ground between two separate circuits?

Thanks again

Leef

[Leef]

Here's another twist. Temporarily, I have a 20a circuit breaker powering all of these light fixtures. I've been repacing the 500 Watt Halogen bulbs (long and skinny type) with 300W bulbs one at a time to decrease the wattage on the circuit. So far I have one 500W bulb in a fixture I bought rated at 500W, two 300W bulbs in two 500W rated fixtures, and two 300W bulbs in two 300W fixtures.

Here's the twist - the 500W fixtures with 300W bulbs LOOK to be as bright as the 500W bulb /500W fixture. The 300W/300W fixtures are noticeably dimmer. Shouldn't ALL of the fixtures with 300W bulbs look dimmer than the 500W bulb regardless of the fixture rating?

I assume it's the same as my table lamp at home - 100W is brighter than a 60W bulb in the same lamp. Is there something different about Halogen versus incandescent? If I put in a smaller wattage bulb, is the fixture still giving it's rated wattage anyway until the bulb burns out?

Or is it all an optical illusion [img]/forums/images/icons/confused.gif[/img] ?

Confused,

Leef

[Slamfire]

The inspector might not complain, but the equipment on the receiving end can get upset, real quick.