500 Watt vs Amps?

[NY_Yankees_Fan]

How many 500 Watt lights can I put on a 15 amp circuit?

Thanks

 

[Anonymous Poster]

If you're talking 120 volt units, 3 easily, with a littlle power left over. You might want to turn them on individually though.

 

[NY_Yankees_Fan]

Yes 120 Volt type

 

[Phred]

Tom,

Power = Voltage x Current for a resistive load. More complicated for motors.
So 120 V and 15 A results in 1800 watts.

So 3x 500 watt lights would work.

Fred

 

[NY_Yankees_Fan]

What happens if you go over 1800? Do you pop the breaker?

I have 2- 500 lights ( would like to add one more 500W light), 2-150w lights+ 4-15 watt fluorescent lights plus several plugs on the same line. All are on separate switches. All run through a 20 amp GFI, all wire is 14 G.

Do you see a problem with this? Do you think the last 500W should be on another circuit?

Thanks

 

[ns_in_tex]

Code says you should not load a circuit more than 80% full time. You may get away with running more than 1800 watts for a short time, but if this is a continous load 80% figures 1440 watts. I personally would not worry about 1500 watts, but if more is added, you would be pushing the circuit.

Kind of like running your car at full throttle, it will take it for a while, but not as long as at a slower speed.

 

[kyoders]

Tom,

First of all, I am not a licensed electrician, so don't take what I say as gospel. If memory serves me, 14G is too small for a 20amp breaker. I would suggest, if possible, to swap the breaker with a 15 amp (no need for GFCI if just lights), then put the 3 500 watt lights on just that circuit. You should normally only load a circuit to 80% capacity, which on a 15amp circuit would be 1440 watts, which should be close enough on lights. The suggestion about not turning on all 3 at once, like having 2 on one switch and the third on a separate switch, is a good one. Depending on the temperature and type of light, they can have a bit of a surge on startup until things come to operating temperature.

Then use your 20amp GFCI for the other circuit that has your plugs and misc. lights. Double check me on the wire size, but I believe you will want to go with 12G on a 20amp circuit. If it's not feasible to change the wiring, consider dropping down to a 15 amp breaker.

There is an added advantage to using two circuits. Say you had your lights on and the tool you were using shorted out, popping the breaker. If everything is one circuit, you are left in the dark to figure out what to do. With two circuits, at least you should have light to see what happened.

Kevin

 

[htiek126]

kyoders is correct, you need at least 12 G wire for a 20 amp breaker and at least 14 G wire for a 15 amp breaker. Although the 14 G wire is derated and will probably work fine with the 20 amp breaker, you run the risk of having the wire fail instead of the breaker shutting off the circuit. The warmer the ambient temperature near the wire and the better insulated the area the wire, the less able the wire is to dissipate the heat, and more likely it will fail.

 

[Phred]

Tom,

The other guys have probably answered your question but I will just add....

Yes if you go beyond 1800 watts or very near the breaker should trip.

I assume from your note that the 20 amp GFI is on a 15 amp breaker with 14gauge wire. If so thats fine since you are using the GFI under its rated 20 amps. If this is the case you will be fine with three lights.


I never run anything less than 12 gauge. Cost difference for personal use approaches zero. Different matter if you are doing it for a living. Although if you already have 14 ga no sense pulling out good wire.

Disclaimer: Not a real electrican, just an EE.

Fred

 

[19th_VA]

Yankee,

Don't know if you mentioned the GFI for a particular reason, but I just wanted to point out that GFI will not prevent you from overloading your circuit. Some people have the false impression that GFI"s will prevent circuit overloading. That is not what they are designed for. What they are designed for is preventing you from being electrocuted if you are standing in a lot of water. The GFI works by measuring the voltage through the neutral and comparing it to the hot wire. If they are not pretty close, the GFI trips. If you are standing in a large pool of water and drop a hair dryer in the water, this would allow a LOT of electricity to run into the water and YOU. The voltage would not be returning to ground through the neutral but instead through the water. If you overload a circuit the voltage returns just as it should through the neutral to ground.

In your case, you are in some danger of starting a fire because (as others have pointed out) 14 gauge wire is not the wire to use with a 20 amp circuit. The GFI will not protect you from this. I would change the breaker to 15 amp. Add another if you need more juice, rather than repulling wires. The added circuit has the benefit of separating your lighting from your receptacles, always a good idea. If I assumed wrong about your impression of what a GFI does, forgive me and disregard the first paragraph of this post.

 

[herbenus]

I had a gfi in my garage. I wanted to be safe. Problem was is it was always going off. Finally replaced it with non-gfi. I was using it for running radial arm saw, electric weedeater, drills, water softener, etc. (not all at same time) I'd like to go back to gfi's someday, but this was frustrating. I have since run some twenty amp services to ther parts of the garage (12 ga) and may consider switching some of those out to gfi's.

 

[Anonymous Poster]

Actually, "GFI" breakers are "NFI" breakers - Neutral Fault Interrupters. As 19th_VA noted, they measure the difference in the current on the neutral vs. the hot. If there is a difference, then it must be going somewhere, i.e. a ground fault. The separate current limiting function of the device acts on the hot only. GFI outlets actually measure the current on the ground, which should be zero. Note that a "GFI" breaker has no ground connection! In fact, both approaches have potential limitations, but are far better than the alternative of no protection. GFI outlets are somewhat more prone to false tripping due to stray eternal currents, while GFI breakers can be fooled by certain inductive loads like motors starting up.

Also remember that consumer grade breakers tend to get more and more sensitive every time that are tripped, leading to more trips, etc. And I have seen holes burned /forums/images/graemlins/shocked.gif right through the side of breakers that have been run "red line" for long periods of time (years). If you have a breaker that trips often, first figure out if there really is an overload condition and if so eliminate it! If it's just continual nuisance trips, its time to retire the tired old breaker or GFI.

BTW, there has been a recent code update that will require arc protection breakers in certain installations. I've read a couple of articles about it but haven't had an opportunity to do any large scale electrical lately, so I haven't bothered really figuring it out yet. /forums/images/graemlins/confused.gif

 

[Inspector507]

Sorry TractorlessSacto,
I have to put my .02 in here. There is no such thing as an "NFI". A GFI breaker or device senses the unbalanced load between the neutral and the hot. If it gets beyond preset limits, it trips off. A GFI device DOES NOT measure the current on the grounding conductor. Why would the NEC® Article 406.3(D)(3)(b) allow you to replace an old non-grounding type of outlet with a GFI when you have no ground available? It doesn't need a ground to even operate.
A GFI breaker does not have a ground connection, because it doesn't need one either. Has nothing to do with the ground.
Just trying to clear any misconceptions up and keep people safe.

 

[Anonymous Poster]

Please, never apologise for telling me when I am wrong, particularly when there is a risk that someone might be affected by my ignorance. /forums/images/graemlins/blush.gif

What I said what was I had been told on more than one occasion, by people I felt were reliable, and I thought was backed up by the evidence. Having been challenged, it took me only a few minutes to absolutely validate that you are correct. Although there are devices for detecting leakage current such as might exist on a ground, GFIs as required by the code absolutely do not utilize the ground.

My apologies to all.

 

[Inspector507]

TractorlessSacto,
No need to apologize to me /forums/images/graemlins/grin.gif
I'm always here to help out when I can. Electricity is dangerous in inexperienced hands and I try to prevent accidents before they happen. Now if I knew as much about tractors........ /forums/images/graemlins/grin.gif

 

[Anonymous Poster]

The terrible thing is that I am not inexperienced with electricity, ranging from low level electronics to high voltage in transmitters. I refered to my ignorance. This was actually worse- bad information. /forums/images/graemlins/blush.gif

What is funny is that a few years ago I had a long conversation on this subject with the director of engineering of a television group- he was the one who "gave" me the term NFI. Now I am trying to figure out who else I passed on this nonsense to over the years. Interestingly, in researching the issue, I found a couple of references to this as a common myth.

The specs do show that there is a difference in the sensitivity of GFI breakers vs GFI outlets. GFI outlets have a threshold of 5mA, while the GFI breakers have a 20ma threshold. The proximity of the GFI breakers to the bus, and the transients involved, make this neccesary. There should be no effective difference in the protection afforded in either case. It has always been my opinion that the advantage of a GFI breaker is that it protects the entire circuit, while a GFI breaker protects only devices plugged into, or outlets wired downstream of it.

 

[19th_VA]

<font color="blue"> It has always been my opinion that the advantage of a GFI breaker is that it protects the entire circuit, while a GFI breaker protects only devices plugged into, or outlets wired downstream of it.
</font>

TractorlessSacto,

True but you don't always need all the circuits protected. And those darn breakers are expensive!

 

[Anonymous Poster]

Yeah, I have to agree on the expensive part - about $30 vs. $10 for a GFI outlet. And I've had to replace two of mine... /forums/images/graemlins/mad.gif

It just seemed odd to me that in you could have a situation where the GFI trips, but you still have energized conductors half an inch behind the plate.

 

[Anonymous Poster]

just my .02,
Are those 500w lights high intensity discharge (HID) lamps?? HID lamps include metal halide, low/high pressure sodium, and mercury vapor types. Do they glow at first and slowly go to full brilliance?? if so, they are HID. 500w seems to be an odd size. Maybe 400W?? If HID, the circuit breaker(s) must be rated for use w/HID lamps . The marking should be molded into breaker. You need to break out that circuit to a minimum of two or three. I always try to run receptacles on a seperate circuit in a work area so that you don't end up in the dark with a tool still spinning if something trips. The 14 AWG wire is too small for sure. 12 AWG is standard for a 20A circuit. 80% load standard is correct as well as GFI info.

Don't forget that electrical equipment runs on smoke like an old electrician taught me. Once you let the smoke out it doesn't work anymore.
Good luck and be careful.
DaveL

 

[Willie B]

#14 copper can conduct a great deal of current without overheating. failure, (fire) in every case I've seen comes where the solid copper ends and a connection. Imagine a mobile home circuit, wire is as good as any home, outlets are cheap. A pre assembled "daisy chain" branch circuit is run before the outside sheathing is installed. Duplex receptacles are of the backwired variety, a hole in the plastic outlet passes a wire into a spring terminal gripping the wire. A wiring diagram would look like a ladder, the uprights formed by the cable interrupted at each three prong by these back wire terminals.The first receptacle's spring terminals carry the load of the full circuit. UL tests these things new not old. As time passes heated winter air leaks through these outlets to where it is cold. in cooling air relative humidity rises, as it exceeds 100% condensation begins. Net result: all winter these terminals are moist. Corrosion or at least oxidation (tarnish). Oxidized surface isn't as good a conductor. It resists the flow of electricity. As current flows through a resistor heat is produced. As heat is produced oxidation proceeds, more resistance, more heat. These spring terminals loose their temper, gripping the wire weakly, more resistance, more heat. Circuit voltage falls off at this high resistance connection. some voltage is used here in the wall converting electrical energy to heat energy. Less is available for the lamp 60 feet away. When enough heat builds up, a fire ensues.

Bad connections not wire cause most catastrophic failures in electrical circuits. I've never tried it but I bet #14 wire could conduct 40 amps before becoming dangerously hot, nonetheless a weak connection at a wire nut might cause fire at 10 amps. Why do you need to heavily load a circuit.

I take exception to using only #12 circuits, lighting load is predictable, with energy efficient lighting it is possible to light 130 11 watt LED bulbs with a 15 amp circuit. You wouldn't want every light in a house on one circuit. Trip that circuit, it's dark! # 14 or even smaller in future code editions are a good tool to reduce overcrowding in switch boxes. Do lighting only in 14, Use 12 for outlet circuits, it is hard to predict what the occupant will plug in

GFCI outlets sense balance in the "hot and neutral" conductors by passing both through a coil of wire called a current transformer. As the hot flows out creating a magnetic field, the neutral flows in creating a opposing magnetic field. The C.T. senses no field. If power flows from the hot conductor through you to the ground provided by a puddle, less will flow through the neutral conductor, The hot field, stronger than opposing neutral field tells the GFCI to shut off, interrupting power soon enough to prevent electrocution.