Simple MH Power questions

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.

Tiercel

Well-known member
Joined
Jul 20, 2021
Posts
430
Location
Pennsylvania
I appreciate your concern but I am running a 7’ run from a bolt-on connection straight to the 400 WATT inverter. The wire gauge far exceeds the inverter capacity.

Although I have no experience with DC, I have wired thousands of AC receptacles, light switches, and lights. The MH manufacture put no fuses in the 30’ run between the battery and the panel. What if that connection going into the panel arcs. What if I took the inverter cable with clips on the end and clipped it straight to the battery? That cable has no fuse.

Maybe I am still missing something.
 

JayArr

Well-known member
Joined
Jun 13, 2020
Posts
788
Location
Mission British Columbia Canada
The wire gauge capacity has to exceed the blade fuses not the inverter capacity. The fuses are for protection in the case of a catastrophic failure, like if all the power transistors in the inverter shorted. When this happens the fuses have to be the weakest link and they have to blow before the wire heats up and starts a fire.

Take a look at the picture, that's what the inside of an inverter looks like when the power transistors short out. The fuse needs to keep that short from turning the wires leading to it into red hot elements.

I'll keep saying this until everyone understands, fuses protect wiring, don't size a fuse based on the load. Size it based on the smallest wire leading to it.

Smart wiring puts a fuse at the battery so that if the main run to the fuse box shorts there is protection. There is no wiring code for RVs that I know of so it's not always there.

The cables with clips aren't meant for permanent attachment and they aren't meant to be hidden under or in anything so the rational is that you'll see them burning and that you'll disconnect them when not in use.

Do what you want, it's your RV. I don't think you're missing anything I'm just more careful than you think is necessary. We don't have to think alike and my advice is free so you can ignore it.
 

Attachments

  • PA270028.JPG
    PA270028.JPG
    171.9 KB · Views: 5

Henry J Fate

Well-known member
Joined
Jun 14, 2018
Posts
1,634
Generally you should protect the wire from the point of power. What makes the best sense is to put an inline fuse at the connect point which appears to be the stud and nut fastener. That protects the wire in case something out of the ordinary occurs. I did something similar with my hard wired 750 watt inverter. I ran #2 wire directly from my battery bank to the inverter inside the living area. I bought a fuse (100amp) that bolted to the battery bank then connected the #2 wire to the other end of the fuse. This protects the wire from the battery to the inverter and it makes me feel a whole lot safer. 100 amps was a little bigger than I wanted but that was all the supplier had on the shelf. They had a 75amp which is borderline so I settled with the 100

Manufacturers do some things that are not healthy. Any runs of wire unprotected is not a good thing. Especially large wires capable of lots of power.

Always protect the wire first then protect the device.
 
Last edited:

Tiercel

Well-known member
Joined
Jul 20, 2021
Posts
430
Location
Pennsylvania
If I connect the negative terminal from the inverter to any piece of grounded metal it will work. Is there any reason it is preferred to wire directly back to the negative post on the battery? Labor-wise it makes very little difference.
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
4,941
Location
Auburn, CA or Reno, NV
Is there any reason it is preferred to wire directly back to the negative post on the battery?
With a 400W inverter, it won't make any difference. If a lot larger, I would want to be sure the neg connection from the battery to the frame was nice and thick, which most likely is anyway.

-Don- Reno, NV
 

Isaac-1

Well-known member
Joined
Dec 3, 2016
Posts
5,271
Location
SW Louisiana
Resistance in steel will be higher than resistance in copper so you will see more voltage drop, probably not a big deal on a 400 watt inverter, but can be on larger models, which may cause the inverter to cut out on low voltage sooner.
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
4,941
Location
Auburn, CA or Reno, NV
True, that is why it is not as big of deal with a 400 watt inverter, vs a larger one
Well, I am saying it won't be a big deal even with a much larger inverter. I would be more concerned with the house neg battery wire to the frame than the frame itself.

The frame is a pretty thick wire! Can handle a lot of current because the resistance is very low when that much metal.

-Don- Reno, NV
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
4,941
Location
Auburn, CA or Reno, NV
Take a look at the picture, that's what the inside of an inverter looks like when the power transistors short out.
Looks much like any other switched mode power supply when any one part shorts out.

Usually one part shorting out takes several other parts with it, in any switching power supply circuit. Burnt up boards in such are common when just about any part shorts out in those.

-Don- Reno, NV
 

Tiercel

Well-known member
Joined
Jul 20, 2021
Posts
430
Location
Pennsylvania
The frame is a pretty thick wire! Can handle a lot of current because the resistance is very low when that much metal.
Very true. I remember the several years when aluminum house wire was legal.

The increase in resistance of aluminum over copper meant that you we had to go up a gauge in wire size. Steel might have a higher resistance but the frame goes up a thousand times in wire size which off sets resistance.
 

Latest posts

Forum statistics

Threads
121,220
Posts
1,221,106
Members
126,226
Latest member
Hqcustomdesign
Top Bottom