12V distribution question

[jjrbus]

Here is a sketch of what I want to do for 12V for review. Will the #8 wire with a 40A breaker from the isolater be an issue? The #8 wire is original.

The schematic for the PD9145A shows 18" max to the 12V fuse panel with no breaker, is that OK?

Any input on this greatly appreciated. Jim

[jjrbus]

OK, upgrade 1 wire, fuses protect to 60 amps, I will have to reread this a few times to get it all!

On wire to battery with 50-A breaker on each end is not right? Converter charger, charges house battery using that wire so should be protected on converter end, battery supplies power on that wire to fuse panel, so should be protected on that end? Or so it seems to the non electrician. Would it hurt anything to have the 50A breaker on both ends?

With the length and size of the wires if the math is done taking into consideration voltage drop it appears that the vehicle alternator does not charge the house battery. That is the way it came from the factory! When time permits I will add a #2 wire from vehicle battery to house battery with CB and isolator and such.

50A breaker at house battery is a marine type breaker/switch.

Thanks for the input always greatly appreciated. Jim

[DrewE]

The fuses on converters are called "reverse polarity" fuses because that is typically the only time they blow, but they protect against overcurrent in either direction. Fuses are not directional. A converter with two 30A reverse polarity fuses won't be able to output more than 60A without the fuses blowing, so no additional circuit breaker or fuse is required provided the wire can safely carry that current.

[GordonThree]

enblethen wrote:
To the right of the 50 amp circuit breaker is a terminal where #8 wire connects to the #6. That is why the circuit breaker should be reduced to 40 amp to protect the wire leaving the terminal.

good catch! downgrade CB or upgrade that one little piece of wire 🙂

[enblethen]

To the right of the 50 amp circuit breaker is a terminal where #8 wire connects to the #6. That is why the circuit breaker should be reduced to 40 amp to protect the wire leaving the terminal.

[jjrbus]

It is a WFCO 8900 series, there are 2 30A fuse in it for the VCC lug. I thought they are only for reverse polarity? The PD9145 is reverse polarity protected by 2 30A fuse.

The #8 wire is MTW type rated at 55A at 90° C.

Thanks for the responses, greatly appreciated. Jim

[DrewE]

The general setup looks more or less reasonable, but there are several details I don't really like.

I would suggest using heavier wire for your six inch wires, or even a little buss bar. If you don't have a main fuse on the fuse panel, note that with the setup you show the power you have available there will have rather significant differences depending on whether you're running off the house battery (50A max), or plugged into shore power (95A max in theory). 95A is more than 6 gauge wire can carry safely. Some of the other wires could in theory under some (rare) circumstances also be overloaded when multiple sources are on line at the same time.

The 50A breaker near the junction point on the battery wire is pointless and unnecessary. Leave the breaker or fuse as close to the battery as possible. Likewise, the breaker on the line to the isolator is unnecessary if you have a breaker or fuse of an appropriate size close to the chassis battery (as you should).

The 6 gauge and 8 gauge wires to the battery and isolator are rather long for their size in terms of voltage drop. Heavier wires will help with battery charging in particular. If possible, I would prefer to mount the converter at or near the battery rather than at the fuse panel, but that's possibly more a personal preference than anything. (If you have an "emergency start" switch associated with the isolator, you should have much heavier wire between the batteries and the isolators and much larger fuses/circuit breakers for it to be very effective. The starter needs much more than 40A.)

Do you have a battery disconnect switch planned? That would presumably go between the battery and the rest of the world.

Do you have a generator installed in the RV? That would need another heavy wire lead from one or the other of the batteries, of course with an appropriate fuse or circuit breaker.

[GordonThree]

I suppose it's OK to have a breaker at both ends of your house battery wire, but in my opinion, you only need the one at the battery. the converter is going to have overload/overcurrent protection built in, protecting the pathway between it and the battery, therefore only the battery side needs protection, preventing the battery from a runaway discharge.

Rest of it looks good. Make sure your distribution terminal is somewhere you can easily re-torque it every year or two.

[ronfisherman]

jjrbus wrote:
Here I am befuddled again! When I posted I believe I saw the sketch, now I am sitting looking at the sketch with my post. But it says post was edited by administrator?

Someday I will figure this out, what am I doing wrong? Jim

Your drawing was edited because it exceeded recommended 640 width. Some notepads will not properly download a drawing/picture that is to wide.
If you look at your original post within edit you will see that "width=640" was added to your img link.

[Bobbo]

I don't think you need to reduce the breaker to 40 amps. The 8g wire is either protected by a 40 amp breaker, or is in the section that is not protected except by the converter and battery's breaker. The 50 amp breaker is only protecting 6g wire.

The wire from my PD4655V does not have a breaker between the converter and 12v distribution board, but the wires to the battery come off that board, not off of a juncture between the board and the converter. The wires from the converter to the 12v board are a home run (aka a straight shot).

[enblethen]

You do not need breaker coming out of the converter.
Your battery circuit breaker should be reduced to a 40 ampere as there is #8 wire in the circuit which is not rated for that much.
Drawing shows 50 amp in battery circuit. You only need the one adjacent to the battery.
What kind of DC distribution panel. Some have main fuses for battery feed and converter feed. If you get this style, you drawing would be incorrect. If you plan on just getting fuse block style then you would be OK. Protected fuse block

[BobandShaz]

I see the drawing but have NO IDEA to answer your questions.

[jjrbus]

Here I am befuddled again! When I posted I believe I saw the sketch, now I am sitting looking at the sketch with my post. But it says post was edited by administrator?

Someday I will figure this out, what am I doing wrong? Jim

[GordonThree]

your sketch didn't make it