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JamesJudasPries's avatar
JamesJudasPries
Explorer
Mar 20, 2015

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?
  • Dave-Sparky's avatar
    Dave-Sparky
    Explorer
    Mar 20, 2015
    that's quite a list!

    I don't see any major issues overall, but some of you loads do seem light.

    Your interior lite fixtures depending on the bulb my need up to 2 amps each and your furnace load may be closer to 7 amps form my experience.

    The buss structure sounds good and reasonable, but I would draw it out and look for potential issues.

    From my reading I don't think you are bonding the neutral to the ground, this is good! The panel in a trailer is esentially a subpanel and this is the correct way to wire it.

    Good luck and pay attention to the torque of the connections to the wires as they will need to withstand more vibration than any other wiring you have ever done.

    Dave, WA ME-01
  • westend's avatar
    westend
    Explorer
    Mar 20, 2015
    Really good plan, the 12V bus path will allow easier installation and upgrade, if necessary. Do not bond the 120V neutral to ground, it should float. I used 12V (-) phase bus and 120 V ground to a single frame ground. That was on the advice of one of our Forum electrical wizards. If you will be installing a battery monitor, allow for the 12 V ground to travel through the shunt when locating frame ground. Not totally necessary but I'd suggest to install the largest possible wire to the inverter. Things just seem to work out nicely with the largest wire.

    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.

    Good luck with your wiring project!
  • JamesJudasPries's avatar
    JamesJudasPries
    Explorer
    Mar 20, 2015
    Thanks guys!

    Yes, that is the plan isolate neutral and ground on 120v. The specs I listed for current draw came from the manuals of the appliances, but the appliance are old probably from the mid 1980s so maybe the modern equivalents draw more? Not sure.

    I think i will install a simple 5 led battery meter voltmeter . You know, one of those empty , low ,med ,full/charging idiot lights. Probably 18 gauge wire and a 1 amp fuse in the panel. I think that's all the guy will care about.

    Yes that is the plan, use 14/2 stranded rv cable for the 12v branch circuits , maybe use some. 12 gauge for the fridge.

    I will find out the max size wire for the samlex 300w inverter terminals. Maybe #6?
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Mar 20, 2015
    I agree. Stranded THNN is hard to beat. I used 12-gauge with #6 spade terminals for the receptacles. Makes wiring a whole lot easier. Spec grade receptacles throughout. Cole-Hersee rocker switches. Red + yellow for the 12-volt stuff - same as YSB yacht color coding.

    Battery compartment is for batteries only. Passed cables through a bullhead and used Del City plastic strain relief threaded bushings. Buss bars and inverter on the other side. Zero corrosion. Converter charger, Klixon switch breakers with LED fault indicators across both AC and DC breakers.

    Looks like you're going to have a nice setup. The way you want it and trouble-resistant. Have a blast - it's fun!
  • JamesJudasPries's avatar
    JamesJudasPries
    Explorer
    Mar 20, 2015
    Hey Mex,

    should I use 2 waterproof plastic strain relief connectors, one for Neg and Pos, to penetrate through the fiberglass of the trailer? Is that what you mean? Or should I get a single multi conductor strain relief connector and drill a bigger hole?
  • azrving's avatar
    azrving
    Explorer
    Mar 20, 2015
    Go to LED bulbs.

    If possible leave room for 2 more six volt batteries.

    Consider the 14 speed model 6600R fantastic vent. It can run much slower if needed and draw even less. .2 to 1.9 amp draw
  • VintageRacer's avatar
    VintageRacer
    Explorer
    Mar 20, 2015
    The ampacity of the wire is about the same for 12Vdc and 120Vac, so your training will see you through. On high amp DC loads always look for the voltage drop over distance as well as the ampacity, this is particularly important for inverters. Your inverter is quite small, I would think about wiring it for a 1,000 watt inverter just for ease of possible future upgrade. I used 14 gauge stranded wire for all my low current DC loads - radio, lights, etc, 12 gauge for the fridge and furnace (the voltage drop thing), and did all home-run grounds to a dedicated ground bus. To make it really easy I color coded the wiring, and ran out 50 foot spools, tied one end off and made them twisted pairs with my electric drill. Took seconds to put a really nice twist into the pair of wires, and made it neat and easy to run. You know of course that low voltage DC and 120VAC can never share any fixture, must always be in separate boxes and conduits. Chaseways I think are OK to share. You also know to treat the RV AC panel like a Pony panel and float ground vs neutral. The bond is always provided by the source of power, be that plug on a pole, generator or your inverter (if you wire inverter loads through your panel, which that inverter is not rated for). Always tie all grounds to the chassis of the RV.

    Brian
  • BurbMan's avatar
    BurbMan
    Explorer II
    Mar 20, 2015
    Remember that ampacity for wiring is independent of voltage, so even at 12v the max for #14 is 15a, 20a for #12 and 30a for #10, etc.

    Most of the lighting in my TT is all #12, mostly white zip cord with a red tracer on one conductor for polarity. All of the lighting is #12 wire. Example: there are 4 fixtures in the slideout, total of 7 bulbs (1.2a) with potential total draw of around 8.4a. From the fuse panel, it's about a 25' run to the first fixture the way the wire is run. Then 13' down the slide to the last fixture. As it is, if you turn on all 4 fixtures, you can see the first 3 dim slightly when the 4th is turned on. Problem is gone now that I have LED bulbs that draw a fraction of the current.

    12v is lot more sensitive to voltage drop over a run than 120v is...so when you choose your wiring size, consider the distance to the source as well as the load. Note the numbers in the table below are the maximum run distances at load and wire gauge to maintain acceptable voltage drop.

  • RoyB's avatar
    RoyB
    Explorer II
    Mar 20, 2015
    I used what is called Marine BOAT WIRE 2-cond #12 gauge in a covered sleeve enclosure for all of my 12VDC lite wiring. Every cable carried its own ground wire. Although some DC wiring is to the trailer frame all of it comes from the DC Power Distribution Center with 2-conductors. One +12VDC and the other -12VDC. All of my 12VDC Battery wiring was 4 GAUGE ANCOR BRAND marine wiring which always had ANCOR ring terminals on both ends where possible. All of my BATTERY WIRING components were BLUE SEA products that has STUD connections.




    I also cut my own battery cables and use a 8-ton hand crimper to properly install the ring terminals which have adhesive type heat shrink ends...




    Being for my OFF-ROAD POPUP trailer I included all of the under floor wiring in PVC FLEX TUBING which was routed the whole underside of the trailer and came up through the floors with PVC electrical junction boxes mounted up-side down with weather tight covers. All sealed for no bugs etc...

    Better explained with this trailer floor plan for my trailer.


    My wiring is based for the WFCO 8900 series Power Distribution center..




    My 1500WATT PSW AIMS INVERTER 120VAC ouput terminates in the panel mounted receptacle. This is my manual transfer switch for runing my trailer 120VAC items from my inverter.



    Roy Ken
  • BFL13's avatar
    BFL13
    Explorer II
    Mar 20, 2015
    There are some wiring sizes shown in this drawing from the Komfort's (a 5er) manual for some of it. Might help a bit, but of course your RV will have its own needs.



    EDIT: Some more wire sizes from the Komfort manual's drawings

    Monitor panel:
    #14 to water pump
    #18 to each water tank
    (doesn't say for the fan and light, but goes to a 15a fuse.)

    DC fuse panel- all 15a fuses (no wire sizes given) except 10a to Winegard TV panel

    Thermostat etc:
    Air conditioner relay kit to Furnace- #14
    Power Centre to AC relay kit: #14
    Power Centre to furnace: #14

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