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Discussion Starter · #1 ·
Hello, I am looking for some help in choosing the right size wire for a 200' run in order to power my travel trailer and shed.

Description of Run:

1. (Electrical Box) >>>>> 50ft. >>>>> (Sub Box, Small Shed / 4/20 amp. -120v outlets) >>>> 100 ft. >>>> (Travel Trailer 30 amp. Circuit)

Can someone please help.. I got the basics down, but not sure how to calculate voltage drop and other factors.
 

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You need to know what the total load on the circuit is. A single rooftop air will draw 10-12A, the micro can be about the same. Lighting is all 12V, and the convertors usually max out around 5A on the 120V side. Fridge is the unknown(12V/120V/propane). You need some extra available ampacity for your creature comforts(TV/coffee maker/etc).

I have a building lot I set my toy hauler on for the ATV riding season. Trailer is placed about 150' away from a 400A service I set. I have an 8/6 cord I drag out. Two bellboxes on the end. One is 30A/120V for normal house power. The second is a 20A/120V circuit for a second air conditioner.
 

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Discussion Starter · #4 ·
Thanks for your response...but I'm not concerned to much with extra Amps other than making sure i get the recommended 30 amps to the trailer without loosing any due to the long run. I only have one plug and am also starting with a 400 amp service.

I understand #10 is good to about 100' plus..what should i use to make sure i dont loose anything at 200'.

I was thinking of starting with #8 to the shed and then #10 to the trailer. Dp you think this will get me what i need.
 

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Thanks for your response...but I'm not concerned to much with extra Amps other than making sure i get the recommended 30 amps to the trailer without loosing any due to the long run. I only have one plug and am also starting with a 400 amp service.

I understand #10 is good to about 100' plus..what should i use to make sure i dont loose anything at 200'.

I was thinking of starting with #8 to the shed and then #10 to the trailer. Dp you think this will get me what i need.
I guess I'm not understanding your measurements but if it's a 200' run 120V 30A I would use #4 copper. That would give you less then a 3% drop over the distance. Amperage is constant. If you start with 30 you end up with 30 or whatever size over current device you are protecting the circuit with.
 

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You start by figuring out the total load (what lights, air conditioner, appliances, etc.) you are going to run in order to figure out how many amperes you need.

Given the amperes you move right on to wire size. You don't need to figure out the total load all over again.

Since you chose 30 amps we figure resistance equals allowable loss within the wires (3% is 3.6 volts). Allowable resistance of the wires (400' round trip) is volts divided by ameres or 0.12 ohms. Since resistance is usually published as per 1000 feet we scale up the allowable resistance to 0.30 ohms. The needed wire size for the run from main house panel to shed panel and on to the trailer is #4 copper at 0.24 ohms per 1000;. (No. 5 wire is 0.31 ohms per 100'.).

You can do the internal shed wiring with 12 gauge for lighting and receptacle branch circuits.

You can use a main panel breaker of 40 amps with the #4 wiring leaving some headroom for lights, etc. in the shed itself and the worst case voltage drop will be just a smidgen over 3%. While the #4 wiring will support a main panel breaker as high as 75 amps, there is no useful reason for that because at such a high amperage the voltage drop will be much greater.
 

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Or you can take 30 amps at face value for the trailer (as you stated) and not bother to figure out what appliances in the trailer you will be running and when.

You will still have to add up the amperes or watts of things in the shed you will be running.
 

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Or you can take 30 amps at face value for the trailer (as you stated) and not bother to figure out what appliances in the trailer you will be running and when.

You will still have to add up the amperes or watts of things in the shed you will be running.
Pretty sure that all rvs with 30 amp cords have a 30 amp main breaker in their on board panel. So the OP won't be pulling more than 30 amps through that 30 amp outlet no matter what appliances he uses in it.


But yes he needs to add the expected amperage use in the shed and not plan for only 30 amps to the shed.
 
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