Home RV Electric Primer

About 1,000 people in the United States die each year as a result of electrocution.

Welcome

This document is intended as an overview to basic electrical mechanics as applicable to the RV world.  5th-wheel and trailers are in much of the same needs but the separation of chassis and house power is more obvious.   Reading this document from front to back is better than skipping around as the Glossary contains more information than straight definitions.

Caveats

I tend to have favored locations for things.  In general when I specify a store name, stores of the same genre are included in the reference.  For example, when I say Camping World, I include other RV supply stores.  When I say Wal-mart, I include other general merchandise stores.

This document is meant as an overview and not as a step-by-step repair manual.  It contains some warnings.  Some warnings are to dumb to include so if you attempt to repair anything based upon what is said here, remember that this is only a guide and you are absolutely on your own for such repairs – I am not liable for omissions or inaccuracies.  I do welcome comments and corrections. (email me)

Glossary

We need to agree on some words here.   I have arranged the words in an order that I think builds upon itself.

Electricity

Electricity is a form of transportable and convertible power used for the creation of pleasure in various devices.  My analogy throughout this document is that electricity is like water going through a pipe where the size of the pipe controls the current and the pressure is the voltage.  Water flows from uphill to downhill.  Electricity flows from positive to negative.

Resistance

Resistance is the measure of the effort it takes to push electricity through a medium.  Resistance is measured in Ohms.
A conductor is something through which electricity will flow with very little resistance.  Silver, gold, platinum, and copper are very good conductors.  Children and dogs are poor choices as conductors.  In general, conductors are wires since the lesson object is minimum power loss over a long distance. 
An insulator is something through which electricity will flow with much resistance.  Glass, ceramic, and air are good insulators.  By definition, an insulator is an exceedingly poor conductor.

Appliance

In this document, an appliance is anything that causes electricity to be consumed with the expectation that the consumption will generate pleasurable results, such as producing light, heat, or sound.  An appliance consumes electricity when it permits an electric flow through it with some resistance.  An appliance when off is an insulator and when on is a poor conductor.

Circuit

A Circuit is the path from the positive power supply side to the negative power supply side.  This path is composed primarily of a conductor wire, a fuse, a switch, a receptacle, an appliance, and a conductor wire to the return side.  In general, multiple receptacles are wired in parallel to the same circuit with the presumption that the maximum circuit capacity will not be exceeded or the fuse will blow.

Ground

Electricity follows a path.  That is, voltage is positive from the source, goes through whatever wires, through some device (hopefully not human) and returns to source on the negative side.  A break anywhere in the line/circuit causes no electrical flow to occur.  The concept here is that the physical earth (ground) is sort of an electrical black hole for the negative side.  For DC power (AC too, sort of) there is always a hot side and a ground side.  You always switch the hot side for obvious reasons (i.e. you want to live, you make a good conductor, are frequently grounded, and believe that wires on the downstream side of the switch are safe to touch).

Voltage

Voltage can be thought of as the amount of pressure or ‘push’ of electricity.  Electricity is measured in Volts -- the higher the voltage, the more dangerous.

Current

This can be thought of as the size of the pipe or the capacity of the device using the electricity.  Current is measured in Amperes (Amps).

Power

Power is energy consumed (i.e. the product of the Voltage and the Amperage).  One Volt against one Amp is one Watt of power.  You can think of power as a lot of pressure in a small pipe or a lower pressure in a large pipe.  It is easier to drown in the output of the large pipe.  It is easier to be damaged by the stream from the small pipe.  In either case, you may be dead.

Switch

In this discussion, a switch is a 2-position device such that one position places a conductor through the device and the other position places an insulator through the device.

Parallel Wiring

To increase current capacity on a DC line, power supplies of the same voltage can be wired side-by-side.  Multiple 12-volt batteries can be wired side-by-side to produce 12 volts for an extended duration.  
Parallel means that:

Series Wiring

To increase voltage on a DC line, power supplies can be wired end-to-end.  For example, 2 6-volt batteries can be wired end-to-end to produce 12 volts.   Series means that

DC – Direct Current

The voltage is carried through 2 wires.  One wire contains the positive (+) power.  The other contains the negative (-) power.  Typically the negative is thought of as ‘Ground’.  DC is generated at a specific voltage and this voltage is reduced by line loss.  You can think of DC as water through a pipe and the energy is produced by the water flow.

Batteries and generators produce DC power.  DC is NOT transformable and suffers line loss at a much greater rate than AC.  For RV use, the “not transformable” is the major problem as different devices use different voltages and most power-consuming devices need AC.

With DC, the ground is always an acceptable negative side (acceptable does not mean not preferable).

AC – Alternating Current

The voltage is again carried through 2 wires.  In AC however, at rapid, regular intervals the power sign is reversed such that the net voltage on the line is 0.  This reversing frequency is referred to as Hertz.  In North America (NA), this is 60hz.  This means that the current goes 0 → +120v → 0 → -120v → 0 at 60 times in one second.  You can think of this as a pipe full of water being vibrated at 60 times per second.  With AC the vibration of the water -- not the flow produces the energy.  AC power has reduced line loss (the energy bumps along but nothing really flows).  AC current has the ability to be transformed between higher and lower voltages.

Alternators and inverters produce AC power.  The negative side is NEVER an acceptable ground.  Because of this, all high-power devices contain a third wire for ground to prevent the power from taking unintended shortcut routes to ground.  AC power transformers produce 240v.  This transformer is center-tapped to produce two circuits each containing 120v.  The center wire is ‘neutral’ and has some of the characteristics of ground making it such that two-wire connections are generally, relatively, safe.

Sine

Sine is a specific mathematical function continuously and smoothly varying between 0, +1, 0, -1, and returning to 0.  Clean AC current makes the full sine range many times per second with no deviations from the sine functional curve.  The sine functional curve is referred to as a sine wave.  If household AC power does not match the sine wave, the power is referred to as ‘dirty’.

Line Voltage

Line voltage in North America is specified at 120V 60hz AC.  Worldwide Line voltage is 240V 50hz AC.

Machines

Engine

An Engine converts chemical to mechanical energy as in a car.  A combustion engine expounds this power in a rotating shaft.

Motor

A Motor converts electric to mechanical energy.  A typical motor also expounds its power in a rotating shaft.  A motor will generate DC voltage.  It may have an integrated inverter so that the combination produces AC voltage.

Devices

Rectifier

A rectifier is an electronic device that permits electricity to flow only in one direction. A combination of rectifiers and condensers (electricity buffers, sort of) can be arranged to convert AC voltage to DC voltage. A diode is a rectifier.

Converter

A Converter converts AC electrical energy to DC electrical energy.  A converter typically contains at least one rectifier.  A plug-in-the-wall battery charger is a converter.  Almost all RVs have a converter hidden somewhere in a storage area near the inside fuse panel.  This converter permits the charging of the batteries and the usage of 12v appliances in the RV when the RV is using park power or the generator.

Inverter

An Inverter converts DC electrical energy to AC electrical energy.  Typically an inverter plugs into your battery or cigarette lighter and contains 120v outlets on it for household appliances.

An inverter operates by interrupting or breaking the DC voltage at regular intervals, in our case 120 times per second.  It also inverts the voltage polarity each time it breaks the line.  This generates a sequence of 0 → +12v → 0 → -12v → 0. 

DC voltage is difficult to control:  without serious electronic devices, you do not raise DC voltage .  You lower it by using it up.  But you do not raise it.

This is the primary advantage oa AC current.  AC current causes magnetic fields.  It turns out that taking advantage of these magnetic fields permits the 'transforming' of AC from one voltage to another.  Once our inverter takes the 12v DC into 12v AC, we can transform the 12v to 120v.  There is a price to pay.  There is always a price to pay.  You know this.  The inverter is not 100% efficient.  85% to 90% is really great and we can get that with the latest technology.  The lost 15% is the heat that we feel from the inverter. Ergo, inverters have fins.  There is another reason for the fins: transforming is also not 100% efficient.  This loss also generates heat.

AC voltage (0 → +V → 0 → -V → 0) can be transformed to various voltage levels and since the average voltage is 0, line loss is minimized.  Historically an inverter was mechanical and was composed of a wheel with metal contacts that rotated at a precise speed.  The wheel has contacts that touch the input and output wire sets to create the alternating sequence.  There are 2 problems: guaranteeing that the wheel rotates at the precise speed and shape of the voltage curve.  The standard AC line is a sine wave and the wheel-generated voltage is closer to an erratic square-wave.  Some electrical equipment is sensitive to the shape of the wave.  Some equipment is sensitive to the cycle count.  Recent electronic engineering has produced solid-state inverters with neither of these problems.  Solid-state devices cost rise rapidly as the power requirements rise.  Solid-State devices are also relatively efficient (~85%) compared to their old mechanical counterparts.

Inverter size is measured in Watts.  Costco and Sam’s Club sell 500 Watt inverters for about $40.  Flying J sells inverters up to 2KW at reasonable prices and a good brand name.  Camping World sells the same inverter as Costco for $60-80 dollars.  Costco also sells 1000-1500W inverters.

Remember that the inverter is draining your 12v battery.  This is OK if you have lots of 12v battery or it is being recharged.  On many RVs, the cigarette lighter on the RV dash panel is connected to the engine battery and not the living area batteries.  It is easy to drain the engine battery by watching TV and a VHS tape or satellite dish for a few hours on the inverter.  If you do this, you will not be able to start the RV.

Remember also that many appliances (e.g. TV, refrigerator) have a startup current requirement greatly in excess of their operating/specification requirement.  The inverter may not be able to handle the starting load even for a short time unless its capacity is greatly larger than the rating of the offending appliance.

Think about this.   A 1200w inverter is drawing 10 120v AC Amps.  Watts is the product of voltage and amps.  Easy.  WIth 100% efficiency, 10 120v Amps is equal to 100 12v amps.   A very large battery is good for 80 Amp-hours.  If you use 1000k (1kw) for  1 hour, you will drain the battery to zero.  1kw is a microwave or a water heater or your refrigerator and TV with dish.  In other words, if you use the inverter for normal household use, you can almost hear the slurping sound of your battery being leached.  12v batteries do not like to be slurped.  They like to be drained nice and slowly.  In fact this is one of the main differences between an RV battery and a car battery.  RV batteries like slow.  They do not like slurp.

Battery

A chemical device which when voltage is applied, causes a chemical reaction such that the electric power can be released at a later time.  The amount of output voltage is dependent upon the chemical combination.  The amount of power is based up the size of the battery, usually measured in ampere-hours.  All commercially viable batteries contain harmful chemicals.

Most package batteries are 1.5 volts and a letter indicates its capacity and size – the higher the letter, the bigger.  There are 9-Volt batteries that are rectangular the size of a small matchbox with 2 metal snaps on one end.

Acid batteries run 2 Volts per cell.  In general acid batteries are set up to be 6-Volt, 12-Volt, or 24-Volt.  We shall ignore 24-volt batteries in this discussion as if you have one, you know more than I do.  6-Volt batteries are referred to as Golf Cart Batteries and are also the battery of choice by RV manufacturers for RVs.  2 6-Volt batteries wired in series produce 12-Volts.

Battery Charger

This is a DC device (maybe with a front end converter so that AC voltage may be input) producing voltage from 10% to 50% higher than the battery that is to be charged.  When connected to the battery, the charger reverses the battery’s normal chemical process such that the power is ‘stored’ in the battery.  It is critical that batteries only be charged which have a chemical composition permitting this.  Batteries not intended to be recharged have a tendency to explode and disperse chemicals in an unsatisfactory manor.

Generator

A Generator converts mechanical energy to DC electrical energy.  For all practical purposes you can think of a generator as a reversed DC motor that, when its shaft is rotated (mechanical energy), its power leads expound a DC voltage.

Alternator

An Alternator converts mechanical energy to AC electrical energy.

Fuse

A device which will break the circuit if its rated current is exceeded.  In general the fuse is composed of a thin metal strip that will melt when overloaded.  This makes it a one-time device.  See Circuit breaker.

Circuit Breaker

A circuit breaker is a device that breaks/opens the circuit under excessive current flow.  A circuit breaker is placed as early (close to the positive source) in the circuit as possible to reduce downstream shock hazard.

Ground Fault Detector (GFD)

A Ground Fault Detector measures the current flow between the 2 wires in a circuit and monitors the ground line.  If the ground line is not properly grounded or it carries a current to ground, the GFD will break the main circuit.  Some GFDs will also monitor current polarity and flow and if incorrect also break the circuit.  In most cases, a GFD is found in the bathroom posing as a standard electric outlet.  It is identifiable by the test/reset buttons between the plugs.  A GFD not only protects the appliances plugged into it but also protects all devices plugged into outlets downstream on the same circuit.

Line Monitor

This is a device inserted into a circuit (e.g. plugged into a receptacle) that indicates the status of the circuit.  This will at least measure the line voltage.  It will also generally indicate the ground and polarity status.  In an RV these are critical.  A line monitor with LEDs indicating polarity, ground, and LEDs for line voltage can be purchased at Camping World or similar store.  When you initially plug into park power, you inspect the Line Monitor to make sure that the power to the RV is good.  Open grounds, reversed polarity, and low voltage are all good reasons to leave the site for another.  If you have an autoformer, you can increase the voltage but not correct the other problems.

Volt/Ohm Meter (VOM)

This device available at Radio Shack or Wal-Mart that is useful in determining voltage similar to a line monitor.  In addition it can be used to check fuses and track down wiring problems.  It has a meter and not LEDs and requires more expertise than the line monitor.  It does not make a good fuse tester for fuses that are plugged in already.

Surge Suppresser

Although clean power is 120v 60hz AC under a standard sine wave, many things can happen to the line carrying it such that the voltage may vary drastically.  For example, lightning (gross electricity of gross voltage) may hit the line.  Another example is that there is another appliance on the line that uses serious power when activated (for example, an air conditioner).  A surge suppresser looks like a funny extension cord and contains solid-state devices which detect the voltage aberrations/spikes and either break the circuit or absorb the spikes when they occur.  Putting a heavy usage device on the appliance side of the surge suppresser defeats the purpose of the surge suppresser.

Transformer

A transformer takes an AC input and produces an AC output of a different voltage.

Autoformer

An autoformer is a device that transforms the line voltage to within the acceptable range.  Primarily the acceptable range is 110v to 130v.  Line voltages outside this range will cause serious damage to major appliances (e.g. Air Conditioners) and electronic devices.  RV parks are notorious for having low line voltages.  The autoformer capacity generally is measured in Amps ranging from 30 to 50 Amps. An Autoformer costs from $300 to $500 dollars.  Unlike the UPS, major appliances are supported.

Remember that your appliances trust you to supply proper power.  If you do not, your appliances will die.  When you turn on an appliance, it draws current.  If your circuit is poorly wired (i.e. the appliance draws excessive current for the circuit) the voltage will drop for all other appliances on the same circuit.  The wiring in question may be either that in your RV, the connecting cord to the park, or the park wiring itself.  You decide – quickly.  If it is the connecting cable, replace it. If it is the park power, use an autoformer.  Your line monitor may indicate good voltage until you turn on the appliance.  Be ready with the Autoformer if the line is in doubt. 

Your appliances need a certain amount of power.  Power is the product of voltage and current.  When you increase the voltage to your appliance through an autoformer, the park side of the autoformer increases its current.  If the park voltage is low and your appliances draw close to 30 Amps, the autoformer will draw more than 30 Amps and break the circuit.  You have no remedy for this except to not use that appliance or go to another park site.

My experience with the Hughes Autoformer indicates that the unit performs its intended purpose but it does it so mechanically that it becomes necessary to have a serious UPS or at least surge suppresser downstream from it to protect computer and electronic equipment.  The autoformer does not produce a clean, continuous output.  Instead it shunts from one voltage to another within the required range in steps of 5 to 10 volts depending upon its input.  Each time it changes, you can hear the AC drift up and down.  A UPS will scream like it is being attacked at these changes and I wonder what the impact of this shunting is on my other equipment.  If your line voltage is low and you do not have an autoformer, your AC will eventually burn out.  The problem can be so bad that the AC will draw the copper right off of the power cord.

Device Combinations

Circuit

Defined above but placed here to clarify it variability.  For example, if a circuit is closed with no appliance in the circuit, it is referred to as a short circuit and will either blow its circuit breaker, deplete the power source, or burn itself up.

UPS – Un-interruptible Power Supply

This is a combination of devices that is effectively:
Line cord → Surge Suppresser → Converter → Battery charger → Battery → Inverter → Wall outlet.
This permits you to have an appliance run continuously while there is either line power or battery power or both.  For example, a computer can be connected to a UPS so that when the house loses power, the computer runs on the battery until the house power is restored.  The price of a small UPS is low enough that may replace a surge suppresser as the device of choice for computer protection.  The more Watts the UPS is rated and the lighter the protected load, the longer the UPS can operate without house power.  In general for household purposes, 10 minutes is a good time.  In 10 minutes the user has the ability to gracefully stop what he is doing, save his results, and shutdown the computer.

The largest distributor of UPS devices is APC.  They make a wide range of UPS in various qualities and with various levels of software.  For the RV computer, a good UPS is almost required.  This is because RV power is very dirty and very unreliable.  Unless you have a late-model, electronic generator (e.g. Honda), the shape of the electric curve is dirty (i.e. not a Sine wave), it is not exactly 60hz (my Onan varies from 58-62 every time the load changes), the voltage varies seriously with load until the generator recovers, and the power may randomly shut off.  House power in an RV park varies seriously between parks and time of day.

Unlike the autoformer, the UPS is a sensitive device and expects to handle fairly small appliances (e.g. computer or TV).  If you have an autoformer, you need a UPS.

I have used various APC UPS devices with varying results.  Any unit less than 500 Watts is not prepared to handle generator electricity.  If nothing else, the varying Hertz will cause the UPS to quickly disable itself.  The 500-Watt APC I have found to be unreliable and had to have my first one replaced.  The second one cannot handle the generator.  The APC 650-Pro did a real good job handling the generator electricity.  The software that came with the earlier models was very good at reporting the line condition.  The latest APC that I purchased supplied software not operable on the latest Windows (XP).  Since XP supports this unit directly, this is not a serious problem but you lose the reporting software and therefore do not have any idea what the UPS is doing -- and what it is doing is anything from beep tones going on and off, Green/Red LEDs going on and off, and a clicking sound come from somewhere inside the box.  If any of these things happen, the UPS will ultimately disable itself.

So now, I use the UPS when I use park power.  When I use my generator, I use a surge suppresser and only my laptop.

Tying the words together in a meaningful manner

Line Voltage

North America uses 120v 60hz AC as its standard although the norm seems to be 110 volts.  Lower than 110v tends to burn things out.  In the USA excess of 125v is rare.  I have found up to 135v in Mexico (that burns the toast).

Except in rare instances (e.g. standing in a puddle of water), 120v will not hurt you.  It can shake you up.

Appliances expect the 60hz.  Computers and clocks will run funny if frequency is off by just a little.  Household wall outlets do not significantly vary from exactly 60hz.  Generators can easy vary by several Hertz.

Europe (and everywhere except North America) uses 240v at 50hz.  240v can and will kill you.

A plug adapter is a simple device permitting one set of prongs to fit another set of prong-holes – the plug adapter makes no attempt to determine whether this is a sane thing to do.  There are plug adapters to make the conversion between various plug types -- be very careful.  PC battery chargers will usually take either voltage.  Norelco shavers will take either.  Some appliances have a switch specifying which voltage is expected.  Make sure what you plug into such an adapter will accept the alternate voltage and any switch is set BEFORE you plug in the appliance.

The various line voltages are not interchangeable: you cannot just get a plug adapter for anything and plug things in.  If you attempt to do this, you burn out your favorite toy.  Things designed to use 120v will instantly erupt in sparks if you plug them into 240v (too much push, too small of a pipe).  Similarly, things designed for 240v will burn out although not necessarily with sparks) if you plug them into 120v (too little push, too big of a pipe).

North American Connector Conventions

15-Ampere

Usage:

Household – your small electrical items use these.

Identify:

2 vertical slots ONLY.  Maybe one larger.

History:

Many years ago there were only two wires running around your home on little, white, ceramic pedestals.  These connected to outlets each having two equal-sized holes.  By convention (see the American Fire Standards), the left hole is neutral and the right hole is hot.

As electric usage matured and people died, this arrangement grew to be the standard.  The electrical appliances that really needed to know the difference grew larger plug legs on the ground side.  Toasters fall into the group with larger ground-side plugs.  Computer battery chargers do not.

As we used more electricity, we outgrew the 15-amp circuits and went to 20-amp.  As we really did not want to die, we added the third, round hole for serious ground and no longer trust the neutral to be ground.

In the USA, anything using serious power has a 3-prong, 20-amp grounded plug.  Toasters seem to be the exception.  Canada has stricter laws in this area.  For example, the last time I was in Canada, waterbed heaters needed 3-wire plugs.  In the USA, 2-wire is normal for these heaters.

Anything designed for a 2-hole plug will work in a 20-amp 3-hole outlet.

20-Ampere

Usage:

Household – your appliances use these.

Identify:

2 vertical slots - left side usually larger, 1 round hole below

The left slot, neutral line, is larger on contemporary outlets.  The round hole is the ground.  The right slot is the  ‘hot’ side of the circuit.

In North America, the standard 20-AMP plug receptacle has two blade prongs and a round prong.  The blade prongs are at the top of the plug and are parallel to each other.  The round prong is at the bottom of the plug and is generally slightly longer than the blade prongs.  This is to assure that a good ground is made before any current flows through the blade prongs.   The bigger left-side prong also helps to make sure the line is grounded before it is hot.

All high-power devices and devices intended to be used near water will have all three prongs. 

Low power devices or devices with built-in power constraints have only two blade prongs.  Low power devices that are not polarity sensitive have two prongs of the same size.  Appliances expected to be used by stupid people near water have built-in GFDs.

It is possible to hold the plug in such a manner that your skin contacts the prongs as you insert the plug into the receptacle.  Do not do this.  It is also possible to attempt to insert the prongs with foreign objects, such as other wires, between the prongs as you insert the plug.  Do not do this either.

Very old receptacles have only the blade prongs and no ground hole -- the slots may be the same size (see 15-amp history).  You really do not want to use these.  If you must, you need a grounding adapter.  Make sure that the adapter has a proper ground through the outlet or you may have a serious surprise of the negative sort.  In general, it is better to upgrade the receptacle than to use an adapter.   These old outlets are often reverse wired -- you need a line monitor to verify proper polarity and grounding.

Older receptacles may indicate old circuits.  Old circuits were designed for 15 AMPS and not 20 AMPS.  In this case, the fuse may have been upgraded to 20 AMPS but the wiring not upgraded.  This is a very common, very dangerous practice as you may be seriously overloading badly aged wiring.  The wire may handle this overload but it is likely that aged insulation cannot.  The standard receptacle for 20 Amps is flush to the wall.

WARNING:

Always take 120VAC wiring seriously!  Yes, when I was younger, I learned to wet my finger and stick it into a lamp socket to see if the socket were hot.  I did this wearing tennis shoes  while on a wooden ladder because I worked in old houses where the wiring polarity was, at best, inconsistent.  Luckily I am still alive.

Reversed wiring can kill you.  Always have a meter handy.  You can buy one anywhere -- including Wal-Mart.  In the RV ALWAYS have a voltage meter/indicator plugged into a highly-visible outlet.  I have plugged into RV parks where the park voltage was reversed -- and the ground wire un-grounded!

30-Amp

Usage:

Legacy RV connector to park power
Your RV plugs into external park power with a big black cord to one outside outlet, usually on a gray post with a circuit breaker.

Identify:

3 equi-distant slots: 2 Large angled slots, 1 round hole

A 30 AMP plug also has 3 prongs.  These also contain 2 blade prongs with a circular prong at the bottom.  The 30 AMP plug is identifiable because: the 3 prongs always exist, all prongs are larger than the 20 AMP prongs, and the 2 blade prongs angle towards each other rather than be parallel.  The plugs and receptacles are not interchangeable with their smaller 20 AMP cousin.  The 30-AMP receptacle is also flush to its mount although it is most likely to be found in a separately mounted wall box:  anything expecting 30 Amps should have its own circuit for obvious reasons.

50-Amp

Usage:

Heavy-duty connector
Same usage as 30-amp except for higher usage.

Warning

50-AMP service is really 220VAC!  This puts you in with the big boys and can make you very dead, very fast if not handled properly!  Rather than put 220VAC appliances in the RV, the two 120VAC sides are kept separate.  But the high voltage is there and you will die if you mishandle it.

Identify:

4 slots: 3 Large angled slots, 1 round hole

A 50 AMP plug has 4 prongs and is actually 2 circuits of 25 AMPS each.  Remember that the standard power transformer produces 240v with a center-tap to permit 2 120v circuits.  The 50 AMP plug has prongs for each side of the 240v and one prong for the center-tap.  The fourth prong is for ground. 

Here is the skinny on this.  Let us say that of the two circuits from the transformer, one has a night light and the other has a toaster and they are both off.  There is no power transfer so nothing happens except the transformer hums to itself.  If we turn both appliances on, the one side of the transformer pushes more power than the other.  The loss of balance in the power line causes an excessive power drain.  Think of the transformer as needing to balance and therefore throwing away power on the night light side to balance the needs of the toaster.  It is worse if there is no night light at all.  The idea here is to always balance the load across the transformer.

In your home circuit breaker box, the breakers actually alternate between transformer sides.  A well-designed breaker box will have balanced loading between the circuits. 240v appliances use both sides so they automatically balance. 

Back to the 50-AMP service.  Since a 50-AMP draw on one side of any transformer is a serious balance mismatch, the 50 AMP plug attempts to remedy this. The RV with a 50 AMP service will have a circuit box laid out with balanced usage to balance the line back to the power source or transformer.  Lower AMP connections may cause an unbalance but not as serious.  A series of 30 AMP circuits under similar loads can be arranged such that the total at the transformer approaches a good balance.  Again, it is unlikely that the lower load circuits will damage anything.  Balance is necessary only for efficiency at the lower load.  Efficiency results in a lower electric bill and more consistent voltage levels.

Adapters

It is always acceptable to adapt upward.  That is, a low-amp circuit connected to a high-amp power source.  It is generally poor practice to adapt downward: you can cause fires at worst, burnt wiring at best. 

There are adapters for connecting 20/30/50 amp plugs to receptacles in either direction.  Be very careful here.  Connecting a 30 or 50 AMP line to a 20 AMP adapter connected to a 20 AMP electric line will certainly take copper off of your wiring and either melt the 20 AMP line or do worse damage.  Never ever run an AC unit through such a connection!  If you try to run 30/50 AMPS through a cord less than ½ inch in diameter you are seriously overdue at the pearly gates.

If you have a 50-amp rig, you will need a 50 (Female) -> 30 (male) adapter.  These are usually a cord about 16 inches long.  Many parks do not support 50-amps – this is why you need this adapter.  Use this adapter with care -- you are playing with serious Greek fire here.

Most rigs are 30-amp.  You will need a 30 (Female) -> 20 (male) adapter if you want to plug your rig into your house for sustaining purposes.  Sustaining means only those items that keep the RV from dieing.  It does not mean living in the RV from a 20-amp circuit.  Using this to run the AC is a poor choice as you may burn the adapter, burn out the AC unit, and blow fuses. 

You will want a 20 (Female) -> 30 (male) adapter if you want to run a standard extension cord out of the park power box.  Some park power boxes have 20 amp outlets.

RV Park Gray Power Post

To connect your RV to park power, you look for the gray power post.  The best of these are about 3 feet high on a gray steel post with a cover that folds down to cover the connections.  Inside the gray box are a circuit breaker and an outlet for each circuit.  The box may support one or two RVs.

The worst power post is a little outlet box protruding from the ground on a couple of conduit tubes.

The maximum configuration will hold 1 50-amp circuit or 2 30-amp circuits and possibly 2 20-amp circuits.

The RV campsite will have a gray power post at the rear of the site on the driver’s side.  The intent is to be within 20 feet of the power post with the RV power connection.  I have seen the strangest locations of the power box and therefore a 25-foot extension cord may be appropriate.

Cords and Adapters

Things you want

16-18 gauge Cord

You want 2 50-foot 16-18-gauge cords or 1 100-foot 16-gauge cord.  These are needed for using power tools or whatever outside your RV

Never use this cord for RV power when you expect to use any appliances over 10 Amps.  Specifically, never use this cord with the AC: you will not like the results.

Inverter

You want at least one inverter for emergency power.  I would suggest the 500W inverter from Sam's Club at $29.  I use it to charge my PC while driving and to power my breathing machine (CPAP) even when I have park power. Park power is unreliable both for voltage level and for existence.

Extension Cords

We all use them.  We may all need them.  The handy little cords strung around our RV because the manufacturer went cheap and we have too few outlets are necessary and common.

Remember that the copper wire in a cord is a conductor -- this means that electricity flows through it.  You are a conductor -- electricity will flow through you.  But flow does not mean free.  Flowing through you causes serious damage.  Flowing through a copper wire causes friction and heat.  The reason copper is used is because it gives up heat quickly and because it causes little electric friction.


But we have a matter of scale hear when we talk about RVs.  RVs use massive amounts of electricity.  This is why they have 30-AMP and 50-AMP services.  This amount of electricity will power a small house.  An extension cord handling this much current is always at least a half-inch in diameter.  Most of this is insulation.  The rest is thick copper.  If you draw close to the 30 AMPS, this wire gets hot.  The longer the wire, the hotter it gets.


Therefore, NEVER use an extension cord to 30- or 50-AMP service except in an emergency.  When using such a cord, do NOT use your AC.  If you use such an extension cord, hold on to it under your heavy usage and see if it feels warm.  Any warmth at all means you should shut something down -- and I do not mean your dome light!

Surge Suppressers

Buy plug-in surge protectors for your TV, Microwave, etc. when not already protected by a UPS or an inverter.

UPS

I would suggest a small UPS for your electronic equipment. You can buy one at Sam's for $70.  A UPS is much better than a surge protector.  The APC UPS models of less than 650W choke on a generator. The 650W unit does not choke -- it indicates that the generator cycles are 61 and not 60.  If you have a Honda generator with a built-in inverter, the UPS should be unnecessary.

Line Monitor

You want a Line Monitor.  I like the one with the LEDs as opposed to a gauge.  You permanently plug the line monitor into a very visible outlet.  I have mine in the kitchen.  The LEDs indicate line voltage, polarity, and grounding.  You know you have a problem immediately if you see a red LED and have a potential problem if you see a yellow LED.

If you plug into a park and you get the wrong LEDs, unplug immediately and resolve the problem.

Autoformer

An Autoformer is necessary if you go to parks with low voltage.  This is the majority of parks.

Generator

An engine connected to a generator produces DC energy and consumes gasoline, diesel oil, or propane.  If the engine goes at a constant multiple revolutions of 60 rps, the voltage can be mechanically broken (inverted) to 60hz AC.  This is the historic manner of generator operation for producing household electricity.  Note that the electricity generated in this manner is very dirty.  Although broken and inverted, the voltage curve does not follow a Sine wave.  Moreover, how close it comes to 60hz depends upon how well tuned the generator is.  The voltage varies as the load varies and the generator recovers.

So what is the deal?  The RV runs on 12 volts DC that it obtains from its batteries.  This is converted to 120v AC by an inverter for use on household appliances.  The 120v may also be obtained by park connections or by the generator.

See my brand-descriptions of generators.  See the Care section for generator care.

Refrigerator – see propane

12-Volt Power

There are generally 2 12-volt battery systems in an RV: Chassis power and Coach Power (or whatever names you are comfortable with).

Chassis Power

The manufacturer of the engine and chassis is provides the chassis battery.  It is 12 volts and is similar to a large car battery.  Be careful of this battery or you may not be able to start your RV.  This battery powers the dash panel radio and cigarette lighter.  If you attach an inverter to watch TV, you may not be able to start the RV later.  The chassis fuse boxes are attached to this battery.

Coach or House Power

The coach manufacturer provides the coach battery or batteries.  This is also 12 volts and may be multiple batteries.  The house fuse boxes are attached to this battery.  This battery is attached to the power converter/charger such that park power will charge this battery.  In some cases the converter also charges the Chassis battery but do not count on it.

See the Care section for battery maintenance.

Fuses

In a concrete foundation home, fuses have become obsolete and are replaced with circuit breakers.  Somewhere in the home there is a breaker box to which the power line wires are connected, usually through a steel pipe.  Inside the box will be one or two master breakers and a series of smaller breakers, some paired.  Each breaker has a number printed on it indicating its maximum current capacity.  It also has a switch on one end and a wire connector on the other.

In an RV, there may be a master breaker and there may be individual circuit breakers for the more affluent.  In general there are at least 3 and generally 4 fuse boxes in an RV.

See the Care section for fuse maintenance.

Worldwide Conventions

The standard European plug is round and has 2 round prongs.  The standard European receptacle has a round depression ready to accept the round plug.  The receptacle therefore has recessed holes for the plug and is not flush to the wall when unused.  Because of the recessed jack, it is very difficult to have fingers or other foreign objects touching the prongs when the plug is properly inserted into the receptacle.

There is more.  Other than the same size of plug and same size and spacing of the two prongs, the other characteristics of the European plug vary from country to country.  That is, some plugs/receptacles have ground connections.  In some cases this is a third prong.  In other cases this is a metal spot or spots at the base of the plug.  Therefore when you go to the store to get a European plug adapter for your 120v plug to be used in Europe, you end up with a kit including a combination of European plugs.  In general the primary problem is matching the grounding convention from country to country.  If there is no ground prong on your 120v appliance, you probably need not switch between European plugs very often.

Worldwide uses 220VAC at 50 cycles rather than 120VAC at 60 cycles.  When you buy an adapter kit for your American device and plug it in, you immediately burn up your American device.  If you are lucky, you have a permanently dead device and a small cloud of blue smoke.  Devices meant for international use, have a switch which indicates 120 or 220 volts.  The switch must be in the proper position or you still have a dead device.

With international travel increasing, many electronic devices run internally off DC power at 12V.  The plug input is anywhere from 90 to 250 volts at 50 to 60 cycles and is converted to the necessary 12VDC internally.  This is the purpose of the black box in the middle of your laptop computer power cord.  These are the devices which can use the adapter plug described above.  Those that cannot convert automatically, such as desktop PCs and hair dryers have the 110-220 little switch on the side.

We will not attempt to go into higher Amperage plugs here.  If you need them, look them up as you will need to know more than this document can tell you.

Suggestions?  Questions?  Comments?  Push Home/eMail above.
Written:  2003          Updated:  October 7, 2005          Back To Top