There have been a lot of discussions about what 50 amp service
really is. I hope that these pages clear up some of the confusion.
On shore power 50 amp service is 120/240 volt power. This means
that you can access 120 volts or 240 volts, but the key is you have
12,000 watts of power.
The minute somebody tells you that 50 amp service is a 30 and 20
breaker you can be sure that they don't know what the heck they're
When somebody tries to convince you that the RV parks only wire
up one leg, that's even worse. If they did that only 1/2 of a 50
amp coach would work.
When some guy tries to convince you that the RV mfrs. only use
1 leg of the 50 amp, he's wrong. I have contacted Winnebago, Monaco,
Fleetwood and Newmar. All use both legs of the 50 amp service. I've
talked to tech reps in 4 RV service shops and at Camping World in
Wilsonville, OR. None of them have ever seen a rig that uses only
one leg. Chris Bryant of Bryant RV services posted the NEC codes
for 50 amp RV service to the newsgroup rec.outdoors.rv-travel and
the code calls for 120/240 double pole installation.
I have heard that there is an RV park some place in Arizona that
the park owner has tied 1 leg of power using a 4/0 wire for the
hot to both busses in a RV receptacle panel. He has then put in
a double pole 50 amp breaker. By doing this he is really delivering
50 amps at 120 volts to the customer. When RVers who are used to
using a lot of power pop the breakers, he blames this on the power
company. In my opinion this is dishonest. If you pull into a park
and are told you are going to have 50 amp service, it should be
240 volts, not 120 volts. If anyone runs across this type of problem,
you should notify the City or County Electrical Inspector for that
area as well as the Better Business Bureau for that town, and if
the park is a Good Sam Park, notify Good Sam.
My suggestion is to carry a volt meter and always check the power
at the post before you plug in. If it's 50 amps it WILL BE 240 VOLTS.
What would be more dangerous than jumping the hot would be to run
2, 50 amp service wires from the same bus on the main service panel
in the park. If a park ever did this, when you test the receptacle
with a volt meter, you would see zero volts from hot to hot, and
120 from either hot to neutral or ground on the RV Park service
box. This would be an extremely hard error to make because of the
way the service panels work, but could be done by a totally inapt
Now, why is that so important? If a park has made this kind of
error, here is what will happen. The power is coming from a service
panel in the RV park to the post at the RV site. The first safety
breaker is at the service panel and could be as high as a 200 amp
breaker. The next breaker will be at the site post, and will be
a 2 pole 50 amp breaker. The service will come into your RV across
2, 6 gauge wires for hot, one 6 gauge wire for neutral and a ground
wire, and feed into a double pole 50 amp breaker on the main breaker
panel in your RV.
The way that these breakers work is that you have 2 hot legs, 120
volts on 1 bus and 120 volts on the other bus. When you're using
240 volt service the hot legs cycle out of sync with the neutral.
This means that the current going back across the neutral wire will
null out, or be canceled by the each other. So, if you have 40 amps
on one bus and 40 amps on the other bus the current return on the
neutral is zero! The only line that has a breaker is the hot, not
the neutral. Put too much current across either hot and the breaker
120 volt from the same bus, is additive. This means that with the
power being fed from the same bus from the park service, to the
2 poles of the 50 amp breaker and feeding each bus of main with
120 volt power, if you put 40 amps on each bus you have 80 amps
going back across the neutral. Good way to have a fire. Now, all
that being said, I've been in hundreds of RV parks in over 30 states
and 2 Canadian Provinces, and have never found such a condition
to exist, but that doesn't mean it can't.
Don't believe it? Check with an Electrical Inspector. That's what
A WORD OF CAUTION!!!
Unless you have a better than average working knowledge of electrical
service, how it works and understand what the safety procedures
are while doing wiring, I STRONGLY recommend you not try to do this
on your own. If you wire something wrong you can cause serious damage
to your RV, you and your loved ones.
Electricity is dangerous, treat it with respect.
In closing, Steve Wolf has a page that is very clear on how to
wire a rig so that you can use 30 amps of shore power for the rig
and 20 amps for the rear AC. To find out how he did this go to http://www.wolfswords.com/.
Steve has several pages of extremely good information on RV stuff.