Complete Rewire Wire Size

Hi all, I feel pretty competent about this since I am a journeyman electrician and I have good experience with 12v wiring. Its just that I have never rewired a travel trailer, just class B RVs.

All wiring will be gutted except exterior clearance lights since the trailer was a kit and built by someone who didn't know what they were doing at all. Anyway...

Plan is for 2 golf cart GC-2 6vs in series on the tongue, progressive dynamics 4000 45A DC mighty mini converter/and AC DC load center, 30 amp ac service.

The DC loads are going to be:

-refrigerator DC element 10 AMPS ( very small old manual change 3 way)
-water pump 4 AMPS
-4 x interior light fixtures 4 AMPS (12W standard bulbs) bulbs
-outdoor light 1 AMP
-fantastic fan 3 AMPS
-furnace 3.5 AMPS
-2 cig lighter ports 30AMPS ( fuse each at 15 amps, probably will never see that level of current)
-300W samlex Pure sine wave inverter (fused 30 amps)

Total 85.5AMPS max theoretical including 30A combined from some imaginary high current cig lighter load.

put a terminal style MRBF 80A fuse on positive of battery. Run #4 wire from fuse about 6 ft to positive bus bar inside a trailer compartment near the mighty mini (probably blue sea brand). Run 2 negative cables from the battery, one #4 from battery negative to the trailer frame and another #4 to a negative bus bar (close to the positive one)

Have a #6 wire going from bus bar to 50A auto reset breaker and then to the mighty mini's positive fuse compartment lug. Attach a #6 positive wire from mighty mini converter output to the second positive lug in the mighty mini fuse board lug. Attach matching size negative wires from bus bar to mighty mini lug and converter output respectively.

Install #8 wire from positive bus to 30A auto reset breaker and then to samlex inverter, with a matching negative wire from negative bus. total wire length 2 feet probably.

consolidate all 12 v branch circuit negative wires onto negative bus bar, all positives to each respective fuse terminal in the mighty mini.

for 120v, put the 30 amp service cord onto a 30A breaker, which in turn supplies and protects the AC bus. 15A breaker for converter supply, 15 amp for convenience receptacles, 15A for an electric on demand hot water. Neutral wires of branch circuits to neutral bus, bond wires to ground bus. Jumper from ground bus to trailer frame. I recall something about having to take a separate chassis bond wire from converter case to trailer frame, but that is for discrete converters like a PD 9100 series I think, not a combination panel like the mighty mini.

phew. A bit of an Essay. Is this more or less what everyone else would do?

22 Replies

JamesJudasPries
Explorer
Mar 21, 2015
Bend,

Ya 10 should work too. It's weird to think of what the rating is. My 2009 Ford ranger has 2 cig lighter ports, each fused at 20 amps individually. That seems high to me.
Bend
Explorer
Mar 21, 2015
tenbear wrote:
I only saw one mention of fuses, that by BFL13.

If you decide to use smaller wire, be sure to decrease the fuse rating to match the wire size.

Speaking of which:

"-2 cig lighter ports 30AMPS ( fuse each at 15 amps, probably will never see that level of current)"

IIRC, cig ports are rated at 100w. A 10 amp fuse each might be better.
tenbear
Explorer
Mar 20, 2015
I only saw one mention of fuses, that by BFL13.

If you decide to use smaller wire, be sure to decrease the fuse rating to match the wire size.
DrewE
Explorer II
Mar 20, 2015
enblethen wrote:
I would suggest using XHHW for the larger conductors.
NM-2 would be the best to use for the 120 volts system, and especially not loose THHN. THHN would be good for the 12 volt.
Some of walls may not be thick enough for standard boxes. You may need to get shallow boxes in some locations, but remember the GFCI takes standard depth boxes.
I would run a separate 120 volt circuit for the refer.

Instead of GFCI outlets, it may be easier to use GFCI breakers. You can't get tandem (skinny) GFCI breakers so far as I know, but that shouldn't be a big problem here.
enblethen
Nomad
Mar 20, 2015
I would suggest using XHHW for the larger conductors.
NM-2 would be the best to use for the 120 volts system, and especially not loose THHN. THHN would be good for the 12 volt.
Some of walls may not be thick enough for standard boxes. You may need to get shallow boxes in some locations, but remember the GFCI takes standard depth boxes.
I would run a separate 120 volt circuit for the refer.
BurbMan
Explorer II
Mar 20, 2015
Roy, makes sense. The underside of our TT is covered in coroplast so no loose wires. The only thing below the coroplast is the propane line.
BFL13
Explorer II
Mar 20, 2015
I added a few more wire sizes to my post above. I suppose you can infer the DC wire size for the main circuits from their fuse sizes. That would be 15a fuse goes with #14 wire it seems (same as with 120v as was mentioned)
MEXICOWANDERER
Explorer
Mar 20, 2015
Strain Relief

I used one for each cable. 1"

I smeared silicone dielectric grease onto the cable where the SR grabs it to seal it tight against acid fumes. The stuff in the next compartment is just too expensive. Del City is sorta screwed-up in their catalog. Go to the flexible pigtail page then a submenu link allows the user to click on regular SRs. I also used these SRs in the converter compartment, shore power cord - all over... the big job came with tail and clearance lights and nutserts. Stainless steel with stainless steel pan head Torx Screws. I put shakeproof external tooth lockwashers on each screw. Trucklite sealed lamps. 22-years never replaced a bulb. No streaks down the paint :)
time2roll
Nomad
Mar 20, 2015
westend wrote:
FWIW, I pulled AWG 14 THHN for branch circuits, both 120V and 12V (principally light circuits), mainly because I have miles of it laying around. I don't regret that, it is working well.
As long as there is no confusion between 12vdc and 120vac circuits.
RoyB
Explorer II
Mar 20, 2015
BURBMAN - It sure did but the way the factory guys did it was drill out a 4-ionch hole in the floor of a cabinet and ran any and all wiring thru this big hole and then when you looked under the trailer there as wires and cables going in all direction strapped to whatever they found close by.

Mt first trip out OFF-ROAD I snagged a bunch of cables with under brush haha...

My OLD ELIXIR Power Converter used wire nuts to tie all my 120VAC and 12VDC circuits together behind the unit. What a RATS NEST of WIRING that was. This ELIXIR only had ONE 120VAC Circuit Breaker and FOUR each 12VDC FUSEs.

I had a roof mounted Air Conditioner installed on the roof when I purchased the unit and the guys used my only 30AMP Circuit Breaker for that wired in reverse of course and the trailer didn't have a MAIN CIRCUIT. I guess they figured the pedestal 30AMP Breaker would trip haha...

I wrote them a nice letter about that. It was dangerous as far as i was concerned.

When I replaced all of this with the more modern WFCO 8900 Series Power Distribution Center I now have a spot for five large size 120VAC breakers which I have filled with one large size 30AMP main Breaker and then 8ea half size 15-20AMP breakers. It also has ELEVEN Fused Circuits plus TWO REVERSE POLARITY fused circuits.

Best way out for me was to REWIRE the whole thing. You know how it goes -one thing leads to another haha.

I certainly don't have a problem snagging wires under the trailer anymore. It is also very easy to route new wiring in all the flexible conduit paths that feeds all areas inside the cabinets.

Turned out to be good and useful/safe project for me.. My POPUP trailer does not have the underbelly cover so it was a easy project...

Now all my electrical mods all get from Point A to Point B using flexible conduit... You know how we RADIO GUYS are. lots of RG cables going everywhere hehe...

Roy Ken