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Old 02-28-2020, 12:01 PM   #1
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12V questions

We ran our 110v wire (12/2) and we now are hoping to the 12v off of our solar system batteries, through our 12 circuit blue sea fuse block.

My questions arise from determining wire gauges. I have been using a chart that has led me to a conclusion the i can run simply 18 Gauge wire to all my appliances.

- LED strips
- Water water pump
- 12v TV
- LED fridge control panel
- 12v receptacles
- Propane Hot water heater
- etc.

Now, would I be gauging to the amperage of the appliance or the fuse circuit that I am wiring the appliance to. There should be some breathing room right? (2.5 amp LED is on a 5 amp fuse)

Also, would i be wise to use 16 gauge just to be safe? instead of 18.

Lastly, when gauging for the length of wire, if the connection to an LED strip is at 27ft, is that the length I calculate? or do i add on the length of the LED strip aswell? (27ft of wire + 35ft of Light strip)

Thank You!
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Old 02-28-2020, 12:29 PM   #2
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Originally Posted by Shawn & Ash View Post
Now, would I be gauging to the amperage of the appliance or the fuse circuit that I am wiring the appliance to. There should be some breathing room right? (2.5 amp LED is on a 5 amp fuse)
Fusing? If so, the fuse is to protect the wire, not the device, so fuse according to what the wire can handle (or less, never more).

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Also, would i be wise to use 16 gauge just to be safe? instead of 18.
Depends on the current and wire length. If you have a circuit where 18ga is just barely adequate, 16ga is a good move. If 18ga is already overkill, no reason to overkill it again. There is nothing wrong with using the same wire size everywhere (in this application) but it typically results in some very oversized wire since the current requirement of each circuit can vary quite significantly.

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Lastly, when gauging for the length of wire, if the connection to an LED strip is at 27ft, is that the length I calculate? or do i add on the length of the LED strip aswell? (27ft of wire + 35ft of Light strip)
Just to the wire strip connection - no need to add the length of the strip. LED's/SMD's are generally such a low current circuit (milliamps) that the wiring is not critical (assuming you are not using some super tiny wire that is nearly impossible to work with (30ga, for example).
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Old 02-28-2020, 12:55 PM   #3
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I really question that 18 is big enough for any of that with the exception of the LEDs and maybe the fridge control panel. Definitely not the water pump and recepticals. Probably not the TV.
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Old 02-28-2020, 10:02 PM   #4
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Originally Posted by Shawn & Ash View Post
Lastly, when gauging for the length of wire, if the connection to an LED strip is at 27ft, is that the length I calculate? or do i add on the length of the LED strip aswell? (27ft of wire + 35ft of Light strip)

Thank You!
Remember, the length you have to use is the total circuit length out to the device/appliance and back. Thus in your example above, the length is 2'x27'=54'.
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Old 02-29-2020, 04:34 AM   #5
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I suspect you might be reading/interpreting that chart wrong unless you have really short wire runs. Can you show us the chart you are referring to?
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Old 02-29-2020, 06:22 AM   #6
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You generally size your wire for the maximum amperage of the breaker/fuse +25%. There's nothing wrong with slightly oversizing your wiring.

PM me if you would like.
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Old 02-29-2020, 07:17 AM   #7
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You generally size your wire for the maximum amperage of the breaker/fuse +25%. There's nothing wrong with slightly oversizing your wiring.
You size your wire for amperage draw of the device and distance of wire, then size the fuse to protect the wire.
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Old 02-29-2020, 07:33 AM   #8
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You size your wire for amperage draw of the device and distance of wire, then size the fuse to protect the wire.
Exactly. You want the over current device to fail before the wiring can overheat.
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Old 02-29-2020, 06:24 PM   #9
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Here is a page with some helpful charts and a wire size calculator


Here is a great resource and reference on wiring from Victron


And a couple short introductory videos (one and two) on wiring, and calculating wire size, fuses, etc


And for a much more comprehensive overview of mobile/marine electrical systems, this 6 part series a great resource.
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Old 02-29-2020, 08:57 PM   #10
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This was the chart I was referring too. I was definitely off with all 18awg throughout considering what has been said.

18awg should be good for led strips even at 54ft? For everything else, Iíll reconsider.
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Old 02-29-2020, 10:22 PM   #11
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Do you have a link, there are generally 2 or 3 tables used when gauging wire (ampacity, 3% voltage drop, and 10% voltage drop tables). Its unclear which table this is.
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Old 02-29-2020, 10:38 PM   #12
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You should read this page, and consult those charts. You want to make sure the gauge you choose is meets the standards for both ampacity (current carrying capacity) and voltage drop. Personally I would go off the 3% chart, but you may be willing to go off the 10% voltage drop chart for non-essential, non-sensitive loads.


According to that chart, for a 5A load you would need to use 10 AWG for <3% voltage drop at 60 ft. This is the lowest amperage on the chart.



But if you input your numbers into the calculator I linked to earlier it shows 14 gauge wire @ 54ft for a 2.5a load is a <3% voltage drop, 16 gauge wire keeps you under 5%
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Old 02-29-2020, 10:42 PM   #13
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Do you have a link, there are generally 2 or 3 tables used when gauging wire (ampacity, 3% voltage drop, and 10% voltage drop tables). Its unclear which table this is.
I do not, I canít remember when I took the screen shot but, the charts you showed me helped. Thank You!

So the Wire Gauge is conducive to the voltage drop correct? And you should always be shooting for 3% drop or less, just to be efficient.

What qualifies as a sensitive load? Anything over 10 amps? Mostly because I already bought 100ft of 18awg (black and red) and the same for 16awg. Not sure if Iíll need anything lower gauge considering my hook ups. Possibly the pump.
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Old 02-29-2020, 11:14 PM   #14
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10 amp Water pump- 10 gauge wire 10ft
2.5 ampLED Lights - 16 gauge wire 60 ft
2.5 amp Closet light - 18 gauge wire 10ft
2.5 amp Bathroom light - 18 gauge wire 10ft
1 amp Fridge 12v- 18 gauge wire 10ft
12 amp TV- 6 gauge Wire 60ft
5 amp 12v receptacles - 10 gauge wire 50ft

At 3% this I what I came up with. Iím sure Iím forgetting something but I this looks alright.

Where do you recommend. Purchasing the different size wires? Order off amazon? auto zone?
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Old 02-29-2020, 11:42 PM   #15
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Originally Posted by Shawn & Ash View Post
I do not, I canít remember when I took the screen shot but, the charts you showed me helped. Thank You!

So the Wire Gauge is conducive to the voltage drop correct? And you should always be shooting for 3% drop or less, just to be efficient.

What qualifies as a sensitive load? Anything over 10 amps? Mostly because I already bought 100ft of 18awg (black and red) and the same for 16awg. Not sure if Iíll need anything lower gauge considering my hook ups. Possibly the pump.

To be honest I can't give adequate answers to some of your questions, I'm not an expert when it comes to wire sizing, I'm still learning myself.


But yes, as I understand it, voltage drop is a function of wire gauge and wire distance. To compensate for longer distances (and thus higher resistance) larger diameter wire needs to be used to minimize voltage drop and heat.


As for what constitutes 'sensitive electronics' I'm not sure, my assumption is voltage sensitive digital devices like computers, maybe marine navigation or comms equipment. But honestly I'm not sure, its just a disclaimer I've seen in a number of articles about voltage drop/wire size. I plan to just err on the side of caution and keep things under 3%.


But regarding LED's I've been told that:
Quote:
For DC LEDs, voltage is not critical (but can effect the brightness of the LED). In this case you can get away with greater than a 3% voltage drop.
So if you are okay with wasting a bit of your energy as heat, and a little dimmer LEDs, you could get away with using 16 AWG in a 54ft run, this would be about a 9% voltage drop.


This thread addresses a similar situation to yours, and explains the factors in better detail than I can (specifically posts #10-12)
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Old 03-01-2020, 12:05 AM   #16
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Where do you recommend. Purchasing the different size wires? Order off amazon? auto zone?
There are a few sources I trust for wiring:
Bay Marine Supply
Genuine Dealz
And the products featured here

The first two links are for Marine Grade tinned copper wire which is a bit more pricey but guaranteed high quality, thin strand wire (which is more flexible and important for mobile and marine applications).

The third link should be somewhat more affordable automotive grade wiring. All three are either sources I trust, or recommended by sources I trust. I'm sure there are many other trustworthy sources out there, these are just the 3 that I know of.

In general I try to follow marine standards/practices as they generally have much more developed best practices and standards, higher quality products, and design for harsher conditions and place a premium on reliability/durability. But this is overkill for many people.
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Old 03-03-2020, 02:01 PM   #17
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This might be a dumb question but is it normal to wire certain items in parallel on the same wiring loop. For example does it make sense to wire all the ceiling and LED light strips that I am using to the same circuit (all in parallel). Or wire both my ceiling fans together? I realize I would need to double the amps being used so thicker gauge wire would be needed.
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Old 03-03-2020, 03:10 PM   #18
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Just a few observations. I've been troubleshooting and repairing automotive electrical systems since cars had generators.

Looked at dzL_ calculator it seemed a bit hard to read. I like this one. https://www.wirebarn.com/Wire-Calculator-_ep_41.html

It's quite normal and acceptable for automotive wiring to use chassis ground as long as grounding points are good connections. Doing it that way you only need to calculate for one-way.

Consider running a fused heavy cable with tie in points along one side with easy access. Then you can tie into that with a fuse for branch circuits. I have one in each room. It's quite easy to add new circuits at a later time if needed.

Quote:
What qualifies as a sensitive load? Anything over 10 amps?
Amps has very little to do with sensitive load. Over voltage will likely kill electronics. Under voltage, they probably just wont work. If a load (amps) is too high for a given wire size/distance the voltage will drop and the wire will heat up. The hotter it gets the more the voltage will drop. Very basically, a fuse is just a smaller wire that melts when the amperage (temperature) gets too high for it's size.

Quote:
10 amp Water pump- 10 gauge wire 10ft
2.5 ampLED Lights - 16 gauge wire 60 ft
2.5 amp Closet light - 18 gauge wire 10ft
2.5 amp Bathroom light - 18 gauge wire 10ft
1 amp Fridge 12v- 18 gauge wire 10ft
12 amp TV- 6 gauge Wire 60ft
5 amp 12v receptacles - 10 gauge wire 50ft
Wiring for one way with chassis ground I don't see that you will end up with anything near these distances.
I couldn't find any kind of 12V Fridge that was as low as 1 amp.
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Old 03-03-2020, 06:02 PM   #19
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10A water pump? Eh... when mine kicks in its drawing something between 170W-250W (16A-20A). I ran subpanels to the front and back with 12ga on 30A fuses for the runs.



The LEDs in my ceiling are wired with 16ga, and there's about 12 different runs each with 1-4 LEDs and 5a fuse for the run. Don't put 10+ lights on a single 16ga wire. 60 ft sounds like a huge run, too.



The 12V fridge we have for the van uses something like 40W on eco mode, 60W-80W ish normal. Even though that's really low power, its not 1A, its more like 3A-7A.


The longer runs, consider positioning DC fuse panels in the front, back and middle of the rig, hidden behind things. Then tap off of those for local loads. Its easier than doing huge runs to a central area.
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Old 03-05-2020, 07:56 AM   #20
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Good ideas.
One thought is to use a Sq. D, Type QO, Breaker panel for DC. They are rated to 46 VDC if memory serves. Sure makes it easy for wiring, testing, and load shedding. But they take up more space than a fuse panel.
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