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Old 08-02-2016, 04:12 PM   #1
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12v circuits

Trying to learn about making a 12v circuit - I am quite the novice at this. When laying out the circuit, trying to decide how it must be done - everything in straight series (bottom pic) or can I put tags off the main wire (top pic). This would be for one circuit of lights, for example. Red is + below and black is -; the diamonds are lights. Does it matter which way I do this?
Thanks,
Greg
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Old 08-02-2016, 04:19 PM   #2
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The diagrams you have pictured are both considered "in parallel". "In series" would have each light in one side of the circuit only, i.e. cut the red lead (or black lead) and insert a light.

To answer your question, either way is OK. A subtle difference is the top configuration could have smaller wire running from the main line to the lights while the bottom one should have wire capable of carrying the entire load.

Al
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Old 08-02-2016, 04:41 PM   #3
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If it is physically possible use the lower configuration. The fewer the connections the better.
Of course this is only practical for something like ceiling fixtures.
Match the wire size and fuses to the full load of the branch circuit. It does not hurt to run larger wire. Even if the load does not require it.
Keep in mind; the individual fixtures will have smaller wire and the fuses are there to protect the wire. Just because you use #12 or #14 wire for the branch circuit it does not mean you install 20 amp or 15 amp fuses respectively.
For example: if you use LED fixtures it might be possible to install 5amp or 7.5amp fuses. Do the load calculations.
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Old 08-02-2016, 04:47 PM   #4
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Both will work. Personally I like the top method better, especially for incorporating remote switches, etc. Also depending on location of the lights themselves it's easier to run a central wire down the center line and branch off of it. IMHO.
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Old 08-02-2016, 05:29 PM   #5
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Thank you Joe and TG. For practicality sake, I am going to run branches. It does make it easier to incorporate switches as well, I believe.

TG - I assume your comment means that even if I run a 14AWG wire, if one of the lights has a wire that is 16 AWG, I need to have a fuse appropriate for the smallest wire, correct? I guess the principle is the fuse should be appropriate for the smallest wire in the circuit?
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Old 08-02-2016, 06:01 PM   #6
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Short answer yes. This means you must be conscious of how many devices are on each circuit and how many you perceive to use at the same time.
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Old 08-03-2016, 08:55 PM   #7
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"TG - I assume your comment means that even if I run a 14AWG wire, if one of the lights has a wire that is 16 AWG, I need to have a fuse appropriate for the smallest wire, correct? I guess the principle is the fuse should be appropriate for the smallest wire in the circuit?"

Not correct, if you had a main run of 14 gauge which can safely handle 15 amps, and then tapped off of that with a bunch of lights that each used say one amp, you'd want to be sure that the number of lights/loads on that line didn't exceed the 15 amp total. This is as long as the lights/loads are wired in parallel, which they'll need to be to work.
Even though the lights will probably have tiny pigtail wires in the 18-20 gauge range you'd still fuse for the overall 14 gauge amp limit and be sure your total loads on the circuit won't exceed the 15 amps in this example.

If they were series then you'd have to fuse for the smallest wire, but if you did that your loads wouldn't all get 12v and wouldn't work.
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