I want to use two 12v DC transformers. Can I use 3-conductor wire to run them to the "device"[1] being powered? I.e., share the negative return on the third conductor (instead of keeping them seperate with a 4th conductor)?
[1] The powered "device" is something I will make which will switch between those two 12v sources. One 12v source will be "dimmed" using a PWM dimmer. The device will switch between the un-dimmed 12v and the dimmed 12v using a motion sensor (connected to a relay).
I know there are a few ways to do this. I could put the dimmer at the device and use just one 12v power source. But, there will be six of these "devices." So, instead of six dimmers, I thought it might make sense to put the dimmer at the power source, run two sources of power using multiple conductors. (Also, I intend to put the dimmed power on a timer so it goes off after 4 hours. Then, instead of a dim/bright motion sensor, it will be on/off. I would have to put a timer at each device too.).
This isn't related to a car. It's on a house. The "device" will power a segment of LED rope light.
I may end up doing 120v LED floods. But, as a matter of education, I'm curious if 12v DC can share a negative return in the same way 120v AC shares a common neutral). I.e., if the two transformer's negative wires can be connected, and share that third connector.
Thanks in advance!
az2008 wrote:
I'm curious if 12v DC can share a negative return in the same way 120v AC shares a common neutral).
In a house, you can share the neutral with two 120 circuits IF each 120 circuit is a different "leg" of 240. Because it is AC, one leg is active while the other's cycle is 'reversed' and vica versa. The neutral only conducts each circuit half the time. Because of this, both the hot conductors and the neutral conductor can be the same wire gauge.
In DC, current flows at all times. If you have 2 sources of DC with a common ground conductor, the potential current on the ground will be the sum of the sources connected. Ie, two 20amp sources with a common ground, will have the potential to load the ground to 40 amps. The wires size has to be big enough to carry the 40 amps. In this case, the (+) conductors have to be sized for 20 A, and the Ground for 40 A.
Same with a house. If both 120V hot conductors are on the same leg of 240, the neutral will have to be sized to carry twice the load of the conductor. I don't believe NEC allows this.