07:35PM | 03/10/01
Member Since: 04/17/00
10 lifetime posts
I am running one 12 gauge NM cable from my panel to a 5 gang switchbox with dimmers. The dimmers collectively control 1360 watts of recessed lighting including 1 100 watt circuit of magnetic low voltage lights. The light are all connected with 12 gauge NM cable. Since 12 gauge NM cable has the capacity to carry 20 amps of current, does this mean that I have to use a 15 amp circuit breaker? The reason I ask is because it doesn't make sense to me to use a 20 amp circuit breaker that will trip at the maximum capacity of the wire. Could the 20 amp rated wire already be melting or on fire by the time the 20 amp circuit breaker trips?


06:00AM | 03/11/01
Member Since: 01/18/99
47 lifetime posts
See if I remeber correctly. I would go with the 15 amp breaker. 15 amps X 120 = 1800 watts, your total load is 1360 watts + 100 watts =1460 watts, well within the limits of the 1800 watts. Some electrician say thaT the circuit most be derated by 85%, but that is usually for commerical applications, but 85% of 1800 watts = 1630 watts well within a 15 amp breaker. HTH


04:08AM | 03/12/01
Member Since: 03/13/00
1675 lifetime posts
bink is right. But you shouldn't worry about 12 guage wire melting or burning from 20 amps of current. 4500-watt water heater elements run on 12 guage wire.


05:47PM | 03/14/01
Member Since: 07/21/00
76 lifetime posts
12 Gauge wire will actually handle 25 amps, However the NEC limits it to 20 amps. If you use a 20 amp circuit breaker you should use #12 wire. It is perfectly acceptable to use a 15 amp breaker with #12 wire. You must use at least #14 wire with a 15 amp breaker but any size wire larger than that is permitted. If you were running a 30 amp circuit for something, then you would need # 10 wire.
Wattage is not what you use to determine wire size, You need to base the wire on the amps. In the example that rpxlpx used for water heater wattage you must consider that the heater runs off of 240 volts not 120. When voltage goes up amperage goes down. Power(watts) = amperage X voltage. So if you had 120v x 37.5amps=4500watts, 240v X 18.75amps also = 4500 watts.
Never load a breaker with more than 80% of its capacity and you will always be safe. 16 Amps is permissible for a 20 amp breaker.
Make sure you use a magnetic dimmer for the low voltage lighting if the lights indicate they require it. They typically require them and also require a neutral to the dimmer. They are also quite expensive. Good Luck, Bill.


05:06AM | 03/15/01
Member Since: 04/17/00
10 lifetime posts
ElectrcBil: Thank you for the practical "how to do it" answers to all 3 of my posts - very helpful.


05:58AM | 03/15/01
Member Since: 03/13/00
1675 lifetime posts
OOPS. Thanks ElectricBil for reminding me about the current(amps) changing with the voltage. Gettin' old, I guess.
In any case, "shouldhave..", to keep wires from melting or burning (and other safety issues) is why we have circuit breakers - so that won't happen.


Post a reply as Anonymous

Photo must be in JPG, GIF or PNG format and less than 5MB.


type the code from the image


Post_new_button or Login_button

These stylish cabinets are a classier way to store laundry goods and give the room a sophisticated, polished look.  It turns out that many bath and kitchen cleansers contain chemicals that are dangerous to the skin and eyes, and often pro... So often we paint tiny nooks white to make them appear larger, but opting for a dark, dramatic wall color like this one—Be... Chocolate-colored walls and large window frames allow the exposed wood beams to take center stage in this small screened p... If you're not crazy about the idea of commingling plants and pool, this modern variation may be more to your liking. The s... Yes, a freestanding garage can become its own tiny house. Artist Michelle de la Vega has all the comforts of a modern resi... There’s nothing like a new set of cabinet hardware to refresh a room. The possibilities are endless: Go modern, rustic, or... Pursue what's known as the stack effect. To achieve it, open the windows on both the upper and lower floors, and as warm a... Like no other floor type, a checkerboard design works wonders to underscore the retro kitchen theme. Vinyl flooring, ceram... Twine lanterns add pops of crafty—but sophisticated—flair to any outdoor setting. Wrap glue-soaked twine around a balloon ... When securely fastened to a tree or the ceiling of a porch, a pallet and some cushioning make the ideal place to lounge. V... Incorporate nature into your lighting scheme by securing a dead tree in a concrete mold and draping your pendant lamp from... For the cost of a can of exterior paint , you can totally transform your porch. Paint the floor a hue that complements yo... In this urban apartment, a standard-issue patio became a serene and green perch by replacing the typical concrete with gro... If you put the washing machine in the mudroom, you can stop the kids from walking through the house in dirty, grass-staine...
Newsletter_icon Google_plus Facebook Twitter Pinterest Youtube Rss_icon