Length Considerations of 50-amp Extension Cords

[DaveGalt]

I've tried to research this on the internet, but I'm not confident enough in my electrical knowledge to feel safe to make a decision.

I'm considering having a 50-amp outlet installed at our house so that visitors can stay in our 38-ft Holiday Rambler Endeavor. In the summer, the weather can get in the high 90's so they'll definitely need air conditioning.

The problem is, I would need to install the 50-amp outlet by the house and run an extension cord to the MH because putting the outlet close enough to the MH would cost more than $2,000 (maybe much more if the diggers encounter rock).

This is what I'm unsure about though: If the extension needs to be 75 feet long, what type of extension cord could handle running both roof air conditioners without excessive voltage drop-off or risk of overheating or fire?

Thanks.

[Biljol]

Maybe a stupid question why not put in a pole and do a overhead line?

Other than that they make 75’ cords so I think just get one from a good company.

[Argosy]

50 amps @120v #6 wire is 116.62v out. 3.3% drop.


The problem I see is everything electrical has a maximum permitted temperature rise. Stringing 75 feet of cord across the ground in hot sun then drawing a bunch of power through it is going to make a really hot cable. Biljol might have the solution, get it up in the air.

Not to mention you don't have to drag 75 feet of that cable around. That has to be worth something.

[TexasTom]

Hoping some electrical experts comment, but I didn't have very good luck with this. I did essentially the same thing but with a 25' extension. Worked fine until I started running all 3 ACs. The plugs which connected the two power cords together got very hot after a day or so, and they both eventually started to melt before I noticed. It is my understanding that is caused by a bad connection, so I replaced both ends, but have not tried it since.

[Crasher]

The best long term solution is to bury the wire and install a pedestal. I did that at our WI home. It was easier for me, as we had a Mini-Sneaker that knifed the wire in the ground about 12" deep. I even had to cross a blacktop driveway. I then installed a 50 amp RV receptacle of one of the RV port posts. There must be some contractor in your area with a small vibrating plow that could knife the wire in for you. That's a far better way than laying a cord on the ground. That also allows you to keep the RV plugged into power and keep the batteries up to 100%.

[NXR]

What will the total cord length be? 75' extension plus how long a coach cord?

How long will the electrical run from your home circuit breaker box to the RV outlet be?

That will be the total length you need to calculate the voltage drop for. If the run from the breaker box to the RV outlet is long, consider having the electrician go to the next size wire, maybe 4 AWG, to minimize that part of the voltage drop.

I carry a 30' extension and my coach cord is about 25' from the plug to the automatic transfer switch. The run from the home breaker box to the RV outlet is just under 50' for a total run of about 100' of 6 AWG if I use the extension cord.

I don't normally run the extension cord at home but I did use it for a month in Florida in March this year, so 55' of cord.

38' motorhome and two 15,000 BTU air conditioners turned on 24x7. Plus the 12 amp electric water heater. Plus the 4 amps for the RV fridge. Plus a Splendide washer/dryer used almost every day.

The cord never got hot and it was laying on the dirt. I wrapped a plastic bag around where the RV cord and the extension cord join and put a rock underneath it to keep the connection out of any rain and flowing water.

I do have an internally mounted Hughes Autoformer and a hard-wired PI EMS. The Autoformer never went into "boost" mode that I saw, but the Hughes does provide a 2% voltage boost all the time.

Hope this helps,

Ray

[twinboat]

Folks are calculating your voltage drop at the full 50 amps or 12,000 watts. Your likely not going to use that much energy

How many watts is your generator, probably not 12,000 watts, and it runs everything.

Base your calculations on that.

[Country Road]

Originally Posted by Biljol

Maybe a stupid question why not put in a pole and do a overhead line?

Other than that they make 75’ cords so I think just get one from a good company.

To answer your question, using 75’ of quality rv cord will work ok. Voltage drop is calculated by every 100’ meaning if you extend length past that, you need to bump up one wire size.

Now this is assuming that your outlet is installed close to your breaker source and you’re not running a long distance to install the outlet.

Of course, it would be best to bury a good Uf wire and put your pedistal near your rv.

Whatever you do, check your voltage in your rv when all is done to verify voltage is sufficient.

[jacwjames]

I have had success using a 50' extension cord added to the original 25' cord that I normally use and have not had an issue with voltage drop or cords getting hot.

A lot depends on the connection, how well does the two ends mate. If there is a problem it will be on the female side not clamping tightly onto the male portion.

My original 25' cord uses a twist lock type connector that attaches to the motorhome, this provides for good connection. I just replaced this with a 50' cord with the same type connectors. This should eliminate having to used an extension cord in most cases. I also carry another 40' extension cord. Both cords are in good condition and I do not see any significant voltage drop.

[Fiesta48]

Many of the inexpensive 50A extentions cords are only 10 gauge wire. That's only 30A.
After almost burning the house down over loading it, I found my extension cord was only 30A 10 gauge. Replaced male and female connections right afterwards too.

[Argosy]

Originally Posted by twinboat

Folks are calculating your voltage drop at the full 50 amps or 12,000 watts. Your likely not going to use that much energy

If the full 50 amps has a 3.3% drop anything less still won't be a problem. Way easier than trying to figure the max possible use, then which leg everything is on. He basically can't overload a 75 ft cord, that's not a concern.

[Props2]

Use the tools below and make your own determination. Too many variables without knowing your complete electrical installation.
https://www.southwire.com/calculator-vdrop


Also look at this. You will be using column B.

https://up.codes/s/ampacities-for-fl...lexible-cables

[jacwjames]

Originally Posted by Fiesta48

Many of the inexpensive 50A extentions cords are only 10 gauge wire. That's only 30A.
After almost burning the house down over loading it, I found my extension cord was only 30A 10 gauge. Replaced male and female connections right afterwards too.

Good point,

When I was looking for an extension cord I did see many that were advertised as 50 amp but did not have 6 awg wire. I actually bought a cord normally sold for a cord reel so there was no plug on one end so it was easy to verify. If you buy a cord with plug ends installed you would never know.

[BOOZE TRAVEL]

I would just put underground rated cable in conduit and bury it 15" deep. That way you don't have to move it to mow or damage it in some other way.
Just my opinion, not a professional recommendation.