15 Amp circuit capacity

[JosephM]

Hello, I'm adding some recessed lighting in my basement. The wiring that is there consists of some 14/2 wire and 12/2 wire for the existing recessed lights. There are 4 of them right now. I was wanting to add 6 more on one 15 amp circuit. The bulb themselves would be 65 watt spots. Will one 15 amp circuit handle 6 lights? Can I get away with using 14/2 NM wire or should I use the heavier 12/2 on the new circuit? When all is done I would have 2 -15 amp circuits that have 6 recessed lights each. Is this safe?

Thanks in advance, Joseph Indiana

[Tom Horne]

A fifteen ampere circuit will carry a continuous load such as lighting of 1440 volt / amperes. A twenty ampere circuit will carry 1920. Do the math. Divide the circuits available VA capacity by the VA of the installed lamps and you will get the number of lamps that the circuit will carry. As long as the lamps are incandescent the wattage of the lamps can be used as the VA of the lamps.

-- Tom

[I-zheet M'drurz]

Absolutely.

15A @ 120V = 1800 watts, so if the fixtures themselves were rated as such (they usually aren't) you could run 6 * 250 watt bulbs without going over 15A (6*250=1500W=12.5A)

That's -exactly- the type of circuit that 14 guage wire is made for. Actually, you could put all 12 fixtures on one circuit (and break them up into as many switched branches as you want to.) If you would use a 100W bulb in each, you're still only be talking about 1200W = 10A @ 120V. There's really no need to tie up a 2nd breaker for two circuits.

[TURTLE]

this is turtle.

It seem here your over killing here a good bit. The 12 -- 65 watt lite will pull about 4 to 5 amps and you can combine the 12 lite on 1 -- 20 amp / 1 --

15 amp circuit with #12/2 and cut down on all the circuits in your home. Less circuits / less trouble down the road. Now you can't have a bunch of other stuff on here too and add the 12 lites together.

Now you could just use the 14 wire and 1 -- 15 amp breaker to run the hold thing.

TURTLE

[Tony Hwang]

Hi, VA is not equal to Watts. Reason? Power factor, Cosine Phi. As far as math is concerned. Tony

[Doug Miller]

As far as a purely resistive load such as an incandescent lamp is concerned, they are indeed equal.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

[Doug Miller]

You forget that, for continuous loads, the circuit is limited to 80% of its rated capacity. This is the calculation you should have used:

15A @ 120V x 80% = 1440 watts.

He's still within the limit, of course, but the limit isn't as high as you claim.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

[volts500]

Probably why Tom Horne specifically stated "as long as the lamps are incandescent..." For calculating purposes, the PF of a resistive load (such as an incandescent light) is PF = 1, thus VA = Watts, for a resistive load. If an inductive load is served (such as fluorescent light fixtures), _then_ the PF must be considered, in which case, to calculate VA one must use the amp draw printed on the fluorescent light _ballast_ label, _not_ the amp draw as "calculated" from the wattage of the fluorescent lamp(s).

[Zaf]

LMAO. What do you suppose the power factor of a light bulb is?

[Tony Hwang]

Hi, Since you used word PURELY, even the filament of incandescent bulb has inductance, how could it be pure R without X? I still stick my gun on my statement. Watts is not equal to VA, better give some margin. Tony

[Tony Hwang]

Hi, That kind of thinking could cause problems in the field. I said math. As long as one knows what it is. Tony

[Tom Horne]

I didn't say it was equal in all cases. What I said was that for incandescent bulbs the value given in watts can be used as the VA value.

-- Tom

[Doug Miller]

OK, why don't you do the math, and tell us how much difference there is between watts and volt-amperes for, say, a 60-watt incandescent light bulb?

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

[Tony Hwang]

Hi, Also wiring has inductance. If I install 15A circuit, I'd let it carry ~13A and have peace in mind. Are you going to give full load in your case then? Tony

[volts500]

Tony, your argument holds about as much water as a tiny piece of pork (fat) in a can of "Pork" and Beans.......interesting how the pork is always listed _first_.

The reason why the NEC limits a continuously loaded lighting circuit (defined by the NEC as a circuit expected to remain on for 3 or more hours) to 80% (that's 12 amps for a 15 amp circuit) is because the circuit breaker will start to nuisance trip when left on for an extended period of time if the full 15 amps is applied continuously, _not_ some ridiculous argument about the minuscule amount of inductance in an incandescent lamp.

[I-zheet M'drurz]

Uh huh (snicker). And any discussion of this subject (inductance, AC power factor and phase relationships, Xl and Xc) is beyond your area of knowledge, you've already told us that when I brought it up months ago.

I get it now, Volts. You donut understand it, it becomes "ridiculous" and "miniscule".

Stick to wiring whips for air conditioners, you won't strain yourself that way.

[volts500]

Yeah, I remember tried to tell us that a toaster is an inductive load and a fan motor was a capacitive load. BRAHAHAHAHAHA, I'm still laughing about that. Doesn't surprise me that you also think that an incandescent lamp is a significant inductive load just because the filaments are coiled. ROTFLMAO.

[Boden]

For a resistive load cosine(phi)=1.

Boden

T>

[Boden]

Have you ever measured the inductance of a lamp filament? It's insignificant.

Boden

T>

[Tony Hwang]

Hi,

15A breaker won't trip at 15A. Depending on what kinds, it has to be over 15A. The delay time is different. Just like fuses, fast blow vs. slow blow. Like 15A fuse does not blow at 15A. Hardly any electrical load is pure resistance. They're mostly inductive load. Never saw a phase correcting capacitor banks in commercial buildings? Inductance causes surge when power is turend on. Tell me one pure resistive load in any utility grid. In non-DC circuit we talk about impedance(combination of resistance and reactance; sum of inductive and capacitive reactance) As an example, again I emphasize example, not real figures, a 60W light bulb has 6 Ohm resistance and 1 micro Henry reactance. Impedance at 60Hz is root of 6+(2 x Pi x 60 x 1/1000,000). Definitely more tahn 6 Ohms. This thread is closed for me. Tony