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Old 11-21-2018, 07:28 PM   #1
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Default Some basic electrical questions

I have some questions about electrical wiring in general. My plan is to put a cutoff switch for the cabin battery in my 97 PW and adding to that electrical the Victron battery monitor. I知 running a cable from the battery negative to the switch預 cable from the switch to the Victron shunt預 cable from the shunt to a bus bar that will have the cabin load/grounds. So here goes:

1. Switch: Blue Sea. The m-series is 300A; The e-series is 350A. With my single battery setup I figure the greatest draw is probably the 12v heater element on my old Dometic fridge. I have no inverter and the rest of the loads are the usual suspects (water pump, heater fan, ceiling fan and interior lights). Are the amp ratings of either switch acceptable?

2. Busbar: Currently there are 3 wires connected to the battery negative. Do I need to get a 4-post bus bar or will a single-post or double-post be ok? I don稚 need the cabin load/grounds separate. They never were. Again I値l be going with Blue Seas product. They have ones rated at 250A and 600A. Would the 250A work ok?

3. Cables: Amp ratings on the Blue Sea products assume 4/0 wire. Is that a good choice or is it over kill? I知 estimating the total wire loop will be 8 feet. But is 4/0 a safe bet for minimizing loss? Also does anyone have any recommendations for brand?

4. Currently I have wires going from the battery neg and pos to a cable that exits the battery box and terminates in MC-4 connectors at the hitch on the rear of the van. I plug my solar suitcase into these connectors when I hook it up. Do you recommend including this in the 田ut-off switch loop or just leaving them? There痴 never any load unless I connect up the solar panel.

I think that痴 it and, as always, appreciate greatly any advice.

thanks.glenn
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Old 11-21-2018, 08:55 PM   #2
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It seems unlikely that the house loads in your van would exceed 40A. Even that would likely require the fridge to be on DC, the water pump running, the furnace fan running and some lights. That's also assuming that the charger you choose is rated 40A or less.

6 gauge wire would be adequate.
4 gauge wire would be more than adequate.

I think you've already mentioned that you have no plans to add a second battery or large inverter.

The 250A rated stuff is fine.

I like the idea of using a 4 post or buss bar.

These terminal fuse blocks are easy to use:
https://www.bluesea.com/products/519...k_-_30_to_300A

or dual fuse block https://www.bluesea.com/products/215...k_-_30_to_300A

The dual fuse block would mount on the battery positive terminal. One fuse could be coach main wire and the second fuse could be for the wire from the isolator / separator.
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Old 11-21-2018, 10:52 PM   #3
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Don't have advice; but curious as to why switch the negative as opposed to switching the positve?

Is there a reason that switching negative is required or advantageous; Done a lot of electrical work over the years but the only RV I've worked is mine.

Just wondering
Paul J
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Old 11-22-2018, 12:10 PM   #4
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What is the actual amps you expect? What is the distance for the battery cable? 4/0 sounds very heavy. My max amps are 200 and I use 2/0 for 4 feet over all one way. I went with the larger Blue Sea 600 amp bus bar and the Blue Sea M series switches. It is about voltage drop. Note; 4 awg (21 sq mm) is not 4/0 awg (107 sq mm).
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Old 11-22-2018, 02:05 PM   #5
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@Paul J. Now that you bring it up: I'm not sure. When putting the RV in storage I always disconnected the battery negative. That probably comes from the car procedure that I follow where you don't want a disconnected positive cable accidentally touching the grounded chassis/frame. With a switch, however, that wouldn't be the same issue. Blue Sea's wiring diagram does show it connected to the positive, between the battery and the boat engine. I'm not sure that it makes a difference. Anyone else have thoughts?
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Old 11-22-2018, 02:07 PM   #6
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@markopolo. Many thanks! I know from your other posts that you've done a lot of wiring and your advice is greatly appreciated.
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Old 11-22-2018, 02:08 PM   #7
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@Sehc. Yes! I did mean simply 4ga wire.
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Old 11-22-2018, 02:17 PM   #8
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I switch positive. If you are literally disconnecting everything, I don't see where it matters one way or the other. However, I have two items upstream of the master switch: (1) the solar controller, and (2) the Trik-L-start. I want these always connected, since I park outdoors and want them doing their job all the time. If anything remains connected, I think it is important to maintain the integrity of the chassis ground, which means positive switching.
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Old 11-22-2018, 04:42 PM   #9
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Most systems if not all systems that I've work on disconnected the load from the source on the hot side (hot in relation to neutrals and grounds); and most maintain solid connection on grounds and neutrals.

If a system starts getting a little complex it seems like things might get a little confusing.

Again not giving advice so much as just talking about normal practices.

Thanks for your response,
Paul J
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Old 11-29-2018, 04:30 PM   #10
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Default switching negative

Quote:
Originally Posted by mck150stone View Post
Don't have advice; but curious as to why switch the negative as opposed to switching the positve?

Is there a reason that switching negative is required or advantageous; Done a lot of electrical work over the years but the only RV I've worked is mine.
lll
Just wondering
Paul J
swtching negative is standard practice in automotive systems as it prevents arcing
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