30 Amp RV electric wire size question

[rfuerst911sc]

Our new used 5th wheel is now home under the RV carport we had installed last week . I want to run a 30 Amp line from my man cave garage to the carport . A 30 Amp RV electric connector looks like a 220 volt dryer outlet but in fact is 110 .

So a single pole breaker . Now what size wire to use ? The run is 75 ' . Online searches have stated 10/2 is sufficient . While that may be true I am thinking 8/2 to be safe . Thoughts ?

If # 8 is the right answer would you go romex or THNN ? If I go 8/2 romex UF then I only need conduit on the outside of the man cave the rest can be buried . If THNN then all of it has to be in conduit .

The biggest energy eaters is the roof AC ( 15000 btu ) and the water heater . Everything else is piddly . I will probably also add a few lights to the building but they will be LED . So what do you guys think ?

[Tim Hancock]

Here is 30 amp one on Amazon that is 75' lg and uses 10 GA.

https://www.amazon.com/Parkworld-886184-Extension-Lighted-Handle/dp/B07CGDVGPQ?th=1

edit They also sell in 100' max length.

[rfuerst911sc]

Tim I should have stated I already have an RV extension cord . It looks like a 50 footer . I am asking about the wire size to run from my man cave building circuit breaker box to the carport building . That run is 75 ' . Sorry if that wasn't clear .

[CurtEgerer]

There's an 80% rule of thumb that would make the design amps 37.5 (30 divided by .80). This is mainly for safety and accounting for energy losses. Another rule of thumb is that the amps increase about 10% per 50 feet of run. So, I'd use the 8.

[Tim Hancock]

Originally Posted by rfuerst911sc

Tim I should have stated I already have an RV extension cord . It looks like a 50 footer . I am asking about the wire size to run from my man cave building circuit breaker box to the carport building . That run is 75 ' . Sorry if that wasn't clear .

I knew that.... My link was to show that a "store bought" 30 amp RV cord uses 10ga wire for up to 100'. So you should be "ok" using 10ga romex for your application.

[Tim Hancock]

All that said... I would have guessed your "5th wheel" would have been 50 amp service. I ran some heavy 6ga in my shop for my 50 amp motorhome. I was fortunate and got my hands on some used wire from a machine rebuild from work. Just had to buy the new circuit breaker and a female plug/box.

Wire (along with everything else) is getting stupid expensive these days.

[MysticLlama]

If you can swing the few extra $$, do a small outdoor subpanel and run 240 to it with 8/3 and you'll have all the flexibility for whatever. That gives a voltage drop of <2.5% @ 50Amps.

This way you have 240v/50A for the future, 120v/30A for now, and can drop a 120V box there also for whatever comes up.

I'd did something very similar with 10/3 Romex at a shorter distance that was also a combo of in-wall and in-conduit.

[CurtEgerer]

^^^ I like this idea. Most 5th wheels these days are 50, so if you upgrade in the future you're all set!

[rfuerst911sc]

Originally Posted by Tim Hancock

I knew that.... My link was to show that a "store bought" 30 amp RV cord uses 10ga wire for up to 100'. So you should be "ok" using 10ga romex for your application.

My mistake sorry about that . Should never assume

[dad911]

Originally Posted by rfuerst911sc

....... Thoughts ?

......romex or THNN ?.......

My thoughts? I'd run a 60A 220v sub panel with conduit so you can add a car charger, etc in the future. Not much more expensive, but leaves options open. Also not supposed to run romex through another conduit.

[rfuerst911sc]

It's a 2014 5th wheel and 26 ' and is definitely 30 amp . Only one AC unit on the roof , I think twin roof AC needs 50 amp . Or longer campers use 50 . Anyway I will move forward with # 8 wire . Thanks guys

[rfuerst911sc]

Originally Posted by MysticLlama

If you can swing the few extra $$, do a small outdoor subpanel and run 240 to it with 8/3 and you'll have all the flexibility for whatever. That gives a voltage drop of <2.5% @ 50Amps.

This way you have 240v/50A for the future, 120v/30A for now, and can drop a 120V box there also for whatever comes up.

I'd did something very similar with 10/3 Romex at a shorter distance that was also a combo of in-wall and in-conduit.

That is something to think about . Thanks

[javadog]

I would put it in conduit and run THHN. I would run two hots, neutral and ground. It gives you some flexibility in the future.

I used 8 gauge wire and set a sub panel at the end for my kids RV. About a 75 foot run, like yours. This gives him the ability to plug-in a second air conditioner when needed, as it plugs into a separate, dedicated outlet. He used that capability this summer, when his primary AC failed and had to be repaired. He also has a convenience outlet for other stuff from time to time.

That wire size is good for 50 A in the future, if needed.

As stated previously, if you run underground Romex, you can’t run part of it legally in conduit.

[rfuerst911sc]

If I decide to go with UF the wire will go from the man cave breaker box , through the attic space and exit through the eave . Then down the exterior vertical metal siding and into the soil . If you can't/shouldn't use conduit how do you attach the wire to the metal siding ? You don't leave it exposed correct ? Is there a wire chase that is used instead of conduit ?

[javadog]

I have no idea, I chose not to use it. You’d have to ask an actual electrician…

[Rusty Heap]

how often are you really going to be pulling full 30 or 50 amps, with EVERYTHING turned on.?

10 awg is plenty. negligible voltage drop at the end of 100' ft cord.

when in doubt, simple check with a voltmeter........clamp on Ammeters, that measure AC and DC current, are only $30 on amazon. I went with full instrumentation of my RV house power system. hah, why guess?

[jyl]

Not an electrician, but installed subpanel in my garage and read up on the code at the time. If you do a subpanel, you’ll need to ground it (two ground rods, and separate the neutral from ground bars in panel) and the location has to be code-compliant (requirements for height, clearance to side and in front). In a carport (not enclosed) probably need a weather proof subpanel.

If there is any chance you’ll someday want power out there for more than just a single RV outlet - and your main panel is located where it’s practical to run wire to the carport - I’d do the subpanel. Digging the trench seems, to lazy me, like way too much work to do twice.

Won’t you want the carport to have lights, a standard 15A outlet or two, etc?

The conductor will probably be the biggest expense. That should be similar between the subpanel and running the single circuit for RV outlet. Assuming you don’t upsize subpanel amps.

[javadog]

Another vote (again) for a sub panel.

And if you ever upgrade the RV to one requiring 50 amps...

If you run conduit, you can always re-pull the wire. Not an option with UF.

I'd also run three wires and a ground, not two.

[MBAtarga]

My suggestion - run conduit and THHN. 8AWG is right over 3V drop at 75' - which is borderline.

https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=3&necconduit=pvc&necpf=0.85&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=120&phase=ac&noofconductor=1&distance=75&distanceunit=feet&amperes=30&x=Calculate&ctype=nec

[70SATMan]

Originally Posted by rfuerst911sc

If I decide to go with UF the wire will go from the man cave breaker box , through the attic space and exit through the eave . Then down the exterior vertical metal siding and into the soil . If you can't/shouldn't use conduit how do you attach the wire to the metal siding ? You don't leave it exposed correct ? Is there a wire chase that is used instead of conduit ?

By code, UF wire isn’t required to be in conduit if exposed and depending on local codes can be left exposed like you’re thinking. You just need to use cabling clamps to secure it to the siding. If you wanted a little extra protection, run it inside of open, oversized PVC down to the lower edge of your siding. Clamp the pvc to the siding.

Now, would I use UF for what you are trying to accomplish?? No, for many of the reasons that has already been mentioned. I’d bury conduit and run individual THHN circuit. Along with sub panel grounding, the distance between the feeder panel and sub panel needs to be evaluated for disconnect types.