Question on wire size for 30a

NinerBikes wrote:
For runs under 50 feet, 10 gauge wire may be rated for a 30 amp load, but for continuous load, it is derated to 80% of it's value, or 24 amps. This is important to factor in if you ever decide to plug in an Electric car with an EVSE to recharge the car... your circuit is only rated 24 amps. You might want to think about future proofing your installation.

This does not apply to RV pedestals. NEC article 551.73(D) states "feeder-circuit conductors shall have an ampacity not less than the loads supplied and shall be rated not less than 30 amperes." Your RV was built with a #10 supply cord and meets the NEC, no reason a pedestal must have larger wire unless for voltage drop.

60 feet of #10 at 30 amps will drop 3.0-3.5% (3.5-4.0 volts).

MEXICOWANDERER wrote:
Smart decision. You'll never have to regret it.

Calculate twice, pull wire once, and be done with it. Definitely how I would roll, since all the value is added in the labor of the install, materials are minor part of the expense, it's rework labor that gets you.

Ron3rd wrote:
Thanks for all the advice folks, I went ahead with 8ga for a few bucks more.

Thanks for the feedback. You sure are going to enjoy that new hookup!

Jerry

Smart decision. You'll never have to regret it.

Thanks for all the advice folks, I went ahead with 8ga for a few bucks more.

Look at the gauge of the pigtail wire that comes out of your RV. What gauge is it? Mine is 10 gauge and I have a 30 amp service/genny on my RV. The pigtail is about 20 feet long. I also have a 25 foot extension cord which is also 10 gauge which I rarely use. (three conductor) I would not use any further extension cords unless all the extension cords were 8 gauge or less. (larger) You have NO CONTROL over the line voltage at the panel. It may be 125 volts on a slow day, it may be 110 volts (or less) when the electric company is working hard on a hot summer day. W = V X A. Watts equal volts times amps. If the voltage goes down, for whatever reason, the amps must go up to maintain the system. Circuit breakers and wire are sized based on amps. That doesn't even take into consideration derating for LRA (Locked Rotor Amps) or LCL. (Long Continuous Loads)

Is it worth it to save a few bucks on the installation if you have to go out and reset a flipped breaker every other day? Or worse yet, replace a burned up motor, or even worse yet, repair fire damage? I think not! Your choice.

Chum lee

TucsonJim wrote:

john&bet wrote:

TucsonJim wrote:

Jim

You may not use a breaker larger than 20amp on 12/2 with ground romax or a breaker bigger than 30amp on10/2 with ground romax. That is also in the NEC.

Good point - Forgot about the 20A limit on 12/2.

Jim

true for 12/2 romex, not true for #12 THHN in a raceway as long as you meet the requirements for number of conductors and raceway size.

however, the run would need to be short to avoid excess voltage drop. So, for the length the OP is talking about, #10 would be the minimum I'd use, and likely #8

remember, at the end of the run you'll likely have ANOTHER 25-50 ft of #10 cord going to the trailer, making the run near 100-125 ft

What I mean by watch, is so he doesn't trip the circuit breaker in the house.
The connected load with-in the rig should not be over the 30 amp setup.
Do not even try comparing motor loads to other systems.

Marginal cost to go #8 is pocket change. But if I had a piece of #10 taking up space I would use it.

I HATE Romex for near capacity operation where ambient temperatures can approach 40c. Yes it means using EMT.

The way for doubters to learn the hard way (like whacking a mule between the eyes with a 2X4) is to successfully out-smart themselves and actually "do it" the cheap way and suffer the consequences. The first ten years (of fifty) getting whacked until I saw stars, taught me to stop and think before cherry picking the answers and issues I demanded to see out of a MOUNTAIN OF INFORMATION, then proceeded to get a royal butt-kicking. Also known as honorable School of Hard Knocks.

"But I done did it, so you can count on my advice" is one of the lamest forms of advice a person can encounter.

Go to Google and ask an intelligent question like...

TIPS FOR SIZING ELECTRICAL WIRE FOR CIRCUITS WITH ELECTRICAL MOTORS

CORRECT WIRE SIZE is always calculated on a WORST CASE scenario, and NOT on wishful thinking.

WuuWee, down here houses have a 30 amp breaker, on perhaps 12 gauge wire, leading from an 8-gauge service drop.

The single phase 127vac passes to another 30-amp breaker inside the house and from this single breaker passes through the house using 14AWG "Duplex". No earth ground. The house I'm in at the moment is 1/2" plywood over 24" spaced 2X4s and 2X6's. This is a high-wind area.

Thirty amp breakers for 14 gauge wire?

Ever see a box of Diamond brand kitchen matches go up? The house owner laughed and laughed when I substituted a 15 amp whole house breaker. At my expense.

A lot of things can be cured but in the case of my rental house "Stupid" ain't one of them.

Getting back on track, I would select 8 AWG to a straight line distance of 50' at fifty feet one inch, 6-gauge would be used.

When I wired a trucking company shop, 3 phase 257vac a few decades ago, the CFE lineman who showed up almost fell out of his cherry picker bucket.

At the connect-point Black, Red and Blue plus White 4 gauge conductors were waiting for him. The facility was wired with green earth ground. Oh yeah I forgot to mention, down here, transformers are Wye not Delta, hence the white.

More work however I EMT wired 3 phase 600 volts with 240 and 120 transformers, main and sub panels for a large machine shop. Doing the work was no challenge. BALANCING the 3 incoming phase amperage was the challenge. Topping it all off was a 25 horsepower 600 volt DIRECT current bridge crane. Yes I had to do a lot of research. Like how to do a high voltage Scott Connection, and the best legal and intelligent way to convert high amperage AC to DC. The California electrical code inspector arrived and spent 3-hours verifying code. "Flawless" he remarked and the jittery machine shop owner lost a bet and paid through the snot-box for a 5 star 5 course lobster dinner.

I never hesitate to research. It saves lots of money and lots of red faces.