Sizing Wire to 12v Fuse Block ? - Ram Promaster Forum
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post #1 of 11 Old 05-17-2017, 04:21 PM Thread Starter
El Guapo
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Sizing Wire to 12v Fuse Block ?

I'm trying to determine what size wire and fuse/breaker to use between my house battery and the Blue Sea 12v fuse block. My 12v load circuits are as follows:

1. TV - 2.3 amps
2. Two Rigid scene lights - 1.5 amps total
3. Fantastic Fan - 1.8 amps
4. MaxxAir Fan - 4.2 amps
5. LED 3w Lights, 9 total on three circuits (main, over bed, over counter) - 2.25 amps total
6. Fridge - 5.0 amps
7. Water Pump - 7.0 amps max
8. Two USB iPhone chargers - 2.0 amps?
9. One cigarette type charger (possible occasional use) - ??? amps
10. Composting toilet fan - ??? amps

Everything listed comes to about 19 amps. It could be slightly more if adding the last two items. The distance the wire will run from my battery to the fuse block will be about 6'. I typed it into the BlueSea calculator and it says I need to use #12 wire (12v, 20amps, 2% drop, 90degree, 6' run). Does that sound right? That seems kind of small. I wired my whole van using #12 , maybe I went way overboard.

Last edited by El Guapo; 05-17-2017 at 04:40 PM.
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post #2 of 11 Old 05-17-2017, 07:49 PM
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1) On wiring, "overboard" is good! Just more space for all those electrons to move around in!

2) For your main feeds to a panel, I would put in (3) #12 's in parallel. It's easier wire to work with and terminate, offers extra capacity for not yet discovered accessories you may want to add, and you probably have some extra #12 around.

Just MHO,
ed

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post #3 of 11 Old 05-17-2017, 08:08 PM
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Hi,
It seems like sum of the loads you list is more 26 amps?

But, I'd use more than that -- you may want to plug a 15 amp device into that lighter socket, or you may want to add a heavier duty 12 volt appliance later. I'd go for at least 50 amps, which could be a #8 wire. Does the info on the BlueSea panel say anything about the max size of the wire/fuse coming into it?

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post #4 of 11 Old 05-17-2017, 08:30 PM Thread Starter
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Originally Posted by GaryBIS View Post
-- you may want to plug a 15 amp device into that lighter socket, or you may want to add a heavier duty 12 volt appliance later. I'd go for at least 50 amps, which could be a #8 wire. Does the info on the BlueSea panel say anything about the max size of the wire/fuse coming into it?

Gary
All I could find on the fuse block was no more than 100 amps total and no more than 30 amps for any particular circuit.
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post #5 of 11 Old 05-17-2017, 08:39 PM Thread Starter
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Originally Posted by proeddie View Post
1)
2) For your main feeds to a panel, I would put in (3) #12 's in parallel. It's easier wire to work with and terminate, offers extra capacity for not yet discovered accessories you may want to add, and you probably have some extra #12 around.
ed
3 #12 wires in parallel? Would that be to make up three separate wires, all full length and all three going from the battery to the fuse block? I wasn't even aware you could do that. I'm learning as I go.
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post #6 of 11 Old 05-17-2017, 10:31 PM
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Another word for amps is current or flow.

If a #12 wire provides a path for 20amps to flow without any overheating, etc., then (2) #12 wires will let 40 amps flow.

If wire is like a pipe, then 2 pipes let twice as much water flow, right?

On some occasions, I have found it easier to get 2 or 3 smaller wires from point to a to point b than 1 big thick wire.

Some of the high power ham radios I have are provided with a power cord that has 2 smaller wires for + and 2 smaller wires for -

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post #7 of 11 Old 05-18-2017, 09:06 AM
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If the Blue Sea will take it, stranded #4AGW is available at H-D in custom cut lengths and very cheap. Consider overbuild big time! If red is not available tape each end with red electrical tape to indicate that it is a positive wire.

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post #8 of 11 Old 05-18-2017, 12:34 PM
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The #8 is good up to 40A at 3% V drop on 10' length.
Blue Sea site gives all data https://www.bluesea.com/resources/1437
Been working with DC power for over 40 years now and the hardest part is to deal with the terminal lugs and connections, so if it's true bigger is better, over sizing if not required it's a pain.

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post #9 of 11 Old 05-18-2017, 09:42 PM
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I also used a Blue Sea Fuse Block and ended up with #6 stranded cable connections. My Victron 50/100 solar converter and 45 amp PD charger also needed connections so I purchased #6 welding cable from Amazon for all the runs. My high amperage connections to the 460 amp battery pack, 2kw inverter and engine battery link are all 1/0 welding cable. Where crimped lugs are involved it's simpler not to have too many wire sizes even if there is some overkill involved. It's also a lot cheaper to buy bulk length cable.

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post #10 of 11 Old 05-19-2017, 02:29 PM Thread Starter
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Originally Posted by wbullivant View Post
Where crimped lugs are involved it's simpler not to have too many wire sizes even if there is some overkill involved. It's also a lot cheaper to buy bulk length cable.
That's how I ended up using all 12 gauge for the individual load wiring. It was cheaper to buy a roll of it than buy smaller quantities of two or three different size wiring.
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