How to Install Underground Electrical Cable for a RV Motor Home

How to Install Underground Cable for an RV Motor Home: Sizing Electrical Cable for an RV Motor Home Panel, Examples for Determining Underground Electrical Cable Sizes. © By: Dave Rongey

Electrical Wiring Video Home Electrical Wiring Videos about this Topic and More Check out my YouTube Channel, and Subscribe!

Learn more with my Home Electrical Video Course: Basic Home Electrical Wiring by Example

Guide to Wiring a Sub Panel for an RV Motor Home
Electrical Question: I’m wiring off of a panel and going to a sub panel with a breaker box that has a 100 amp rated capacity.

• I’m going to be using a maximum of about 30 amps of power at the sub panel.
• The main wire run I’m going to be installing is underground and it is approximately 300 feet away from the main electrical panel. What size wire do I need for this project?
• I will be installing a ground and doing all the necessary things involved for this.
• The approx wattage of the load is 4600 watts, and about 40 amps total with no large appliances.
• This sub panel will be supplying power to a stationary RV motor home. I have looked at all the formulas but this is the most complex part. I just need the size wire for the distance of the wire run.

Thank you in advance.
This area is out in the country.

This home electrical wiring question came from: Tom, from Ft. Pierce, Florida.

Additional Comments: Very Informative.

Dave’s Reply:
Thanks for your RV Electrical Wiring question Tom.

Wiring Underground Cable for an RV Motor Home

Application: Wiring a Motor Home Electric Service Panel.
Skill Level: Intermediate to Advanced – Best installed by a Licensed Electrical Contractor.
Tools Required: Electricians pouch of hand tools and the various power tools necessary for installing the specific electrical service panel.
Estimated Time: Depends on the type of panel and available access to the project area and if trenching will be required.
Electrical Materials and Electrical Wiring Methods must be according to all applicable electrical codes.
Notice: Installing an Electrical Service Panel should be done according to local and national electrical codes with a permit and be inspected.

How to Install Underground Cable for an RV Motor Home

• Sizing Electrical Cable for an RV Motor Home Panel
  • The size of the electrical cable that will be used for an RV Motor Home will depend on the Connected Electrical Load which will determine the size of the electrical sub panel.
  • This will them be that starting point to base the size of the electrical cable that will be installed.
  • The length of the cable is an important factor because long cable runs will produce a lower voltage at the other end.
  • The type of wire that will be used should lower the resistance which will help maintain the voltage.
  • This is why copper wire is best for long cable runs because it has less resistance than that of aluminum wire.

Examples for Underground Electrical Cable Sizes

• Copper Electrical Cable Size
  • A Single Phase 240 volt 30 amp service with a one way distance of 300 feet should have a cable sized no smaller than #4 Copper.
  • A Single Phase 120 volt 30 amp service with a one way distance of 300 feet should have a Cable Sized no smaller than #2 Copper.

• Aluminum Electrical Cable Size
  • A Single Phase 240 volt 30 amp service with a one way distance of 300 feet should have a cable sized no smaller than #2 Aluminum.
  • A Single Phase 120 volt 30 amp service with a one way distance of 300 feet should have a Cable Sized no smaller than 2/0 Aluminum.

• Electrical Cable Size and Cable Type
  • The actual electrical Cable Size and Cable Type selection will also depend on the Voltage and how the cable will be installed.
  • If the cable will be Direct Burial USE or UF Underground Feeder Type cable or individual cables that will be installed into PVC conduit the Cable Type will need to be correct to avoid voltage drop and overheating of the electrical cable.

• Why is Selecting the Right Electrical Cable so Important?
  • The bottom line is that you want your electrical devices to work when you want or need then, so the correct amount of available electrical power must be available.
  • You do not want to burn up or damage the electrical cable or components by installing the wrong electrical service and cable size.

Voltage Readings and Long Distance Cables Tell the Story

• Example of How Electrical Cable Size Makes a Big Difference
  • If the electrical cable is sized incorrectly there may be a full voltage reading at the remote electrical panel when no electrical devices or loads are being used, so a full reading such as 240 volts L1 to L2 may be observed.
  • If a 240 volt load is turned ON such as an air conditioner or other large electrical equipment the voltage may drop down to a lower voltage such as 193 volts L1 to L2 and this lower voltage will cause the equipment to overheat and may cause permanent damage.
  • This is especially important for any motor load, 120 volts or 240 volts, including pumps, swamp coolers etc..
  • Because motors require a large inrush or power when the motor starts the voltage level will drop down if the wire size is not correct.

More about Electrical Service Cables and Wiring

Electrical Calculations and Formulas

The Voltage Drop Calculator found in the Calculations and Formulas section will show how properly sizing the electrical cable is very important for maintaining the correct circuit voltage.

Basic House Wiring Circuits

House Wiring Circuits and Circuit Breakers

This article looks at common 120 volt and 240 volt house wiring circuits and the circuit breakers that are installed identifying the types and amperage sizes used in most homes.
Electrical Panel Circuit Listing

Home Electrical Circuit Breakers

Home Electrical Circuit Breakers

A guide to home electrical circuit breakers and how they work to protect your electrical wiring. When properly installed, your home electrical wiring is protected by a circuit protection device.

Guide to Home Electrical Wire

Electrical Wire for the Home

Complete listing of electrical wire types and parts used for home projects with electrical code information serves as selection guidelines.
Electrical Wiring Codes

Home Electrical Codes

Electrical Code Directory covering AFCI circuit, electrical-boxes, electrical-circuit, electrical-code-outlets, electrical GFCI, electrical-grounding, electrical-project, electrical-services, electrical underground, electrical-wiring, electrical-wiring-code, lighting-codes and smoke-detectors.