Notes on Electrical 110/240 Volt Shore Power
Here is a little review of the basics that help get our RVs energized with Household
type electrical power.
Most motor homes and travel trailers have what is called "A 30 Amp 110 Volt Shore Power Cord".
This cord is usually a heavy extension containing 3 #10 gage wires, one end is wired
directly to the RV and the other end terminates at a male plug designed for
connecting to a 30 amp 110volt receptacle. This plug/receptacle combination is
oddly shaped, as there are 2 angled flat prongs for the power circuit and one round
prong, which is the Ground Connection. Lots of time this plug is mistaken for older
type 220/230-volt electric dryer or electric range connection and a receptacle
or adapter is wired up and when connected to the higher voltage it is likely to damage
the RVís electric components, and create a dangerous situation. This happens
often enough to mention here and is one of the first things to pass on to someone
new to camping vehicles.
When at most commercial campgrounds we usually are provided with a 30-amp 110-volt
receptacle to plug into. When at most other locations an adapter will be required to
connect to the electrical power source. The most common is the small round or triangular
adapter that will allow you to connect to most standard 110-volt wall receptacles. When
using the adapter we downgrade the limit in power to the RV to the power available to
the outlet/receptacle we plugged into, usually 15 or 20 amps. The adapters are usually
rated for 15 amps only and are not usually of good quality.
An alternative is the Dog Bone type adapter given itís name for having the shape
more or less of what with a stretch of imagination could be compared to a large bone.
Dog bone adapters eliminate strain by being flexible and usually are of higher
Larger Motor homes and travel trailers may be equipped with a 50-amp power cord
that has 3 #6 wires for power and 1 #8 wire for ground. This power set up is said to
have 2 legs, (or circuits) of 110 volts each. The plug is the now standard 4 prong 50
amp 240 volt type found on modern electric ranges. All kinds of
power adapters are available for this plug configuration, the most important thing
to note is that most adapters, dog bone or other simply put the same 110 volt
power from the 110 volt wall receptacle on to both legs, (circuits) of the power
cord. This limits total usable power to the power available at the wall receptacle
or outlet. 50-amp service can be connected to a properly wired 50-amp 240-volt receptacle,
which will utilize the 2 legs of 110 volts. Typically there is no 240-volt
electrical equipment installed in production RVs until we get into the bigger rigs,
Bus conversions, custom units, etc. So for the most part we see 110-volt washer
dryers, air conditioners, and electric cooking appliances.
In any case there are many possible configurations to manage power inside the
RV as well as many devices designed to help with power management tasks. Throw into
the mix an onboard 110-volt generator and manage to be totally self-sufficient. The
most interesting system is the load shedding power management system that will
disconnect or "shed" circuits in a prioritized order. This system asks you to select
your available power and will prevent overloading by monitoring total amp load
and disconnects circuits so you wont trip a circuit breaker from your source of power.
The big topic is safety mostly concerning the use of extension cords to connect
your RV to a source of power. It is always stressed that you use a proper 3-wire
extension cord of appropriate size "Wire Gage". The ground prong not only connects
the RV to ground at the power source it also aligns the other prongs as to be in
proper polarity. Now one of the most important things about the internal wiring of a
RV is that the neutral wire is floating, or in other words is not connected or "Bonded"
to Ground. One of the reasons why is that if anything were making a connection
between the RVís ground and neutral circuits and the polarity of the extension cord
was reversed, or that the polarity of the source power was reversed, the RV would
have a HOT SKIN condition or meaning that anything connected to electrical ground
via the wiring including the vehicle chassis the siding if metal, door
frames, etc. could be on the Hot or dangerous side of the 110-volt.
This is aggravated by how well the tires insulate the RV from earth ground. This
scenario may seem a little far-fetched but Hot Skin conditions happen and there is
still a lot of backwards wiring out there.
When planning any electrical switching for your RV always switch the Neutral as
well as the Hot or "Hots".
In most cases the internal wiring of your properly installed onboard Genset has its
Neutral bonded to Ground. This case the source ground "The Genset", and the RV Ground
is electrically the same.
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