[A/S] Re: Generator Question

["bleipper" <rv@xxxxxxxxxxx>]

Thanks, Maurice, for a good one on the genset grounding. Here's
another few ideas that may help folks (I hope).

First, if you really want to know to true dope, go to your local
library and take a look at the electrical code. There is a whole
section on RV's and another on grounding and another ... :-).

2) AC outlets have three connections: A hot, a neutral, and a safety
ground. The hot and neutral are the working electricity lines. The
safety ground is strictly for safety and not used to carry electricity.

3) A GFI (ground fault interuptor) trips a fuse if it thinks there is
any leakage from the working electricity lines. These are supposed to
be used on any 'outside' circuits, including those feeding RV's.

4) The hot and neutral working electricity lines are not connected to
anything else except at one very special point (the service entrance)
where the neutral is connected to ground and both are well connected
to earth ground.

5) Gensets (generator and motor sets to produce electricity) are not
service entrances so they keep the electrical working lines completely
separate and isolated from everything else. 

6) There are two ways to connect your genset to your RV. One is via a
transfer switch and the other is via the electrical feed cord.

7) The RV fuse box is not a service entrance so it keeps safety ground
and neutral isolated. A good transfer switch not only switches the
electrical feed to your genset but will also make the service entrance
ground to neutral connection. This way, when plugged into shore power,
the service entrance is back at the camp or household fuse box. When
on genset power (with a transfer switch) the service entrance is at
the transfer switch.

8) When you plug your RV into the genset rather than using a transfer
switch, you should, theoretically at least, connect the chassis ground
of the genset to the electrical safety ground. Most of the time this
is done by using the three prong plug on the genset. There will be no
connection or electrical relationship between either working
electrical line and ground in this case.

9) Using a genset will not create shocking skin conditions unless (a)
one of the working electrical lines is connected to ground somewhere
and (b) the other working electrical line is connected to your trailer
safety ground. This is two gross wiring errors working in unison to
generate dangerous conditions.

10) Ground is never used in modern circuits for a return path. A
neutral is used instead. This is why 50 Amp RV service has four wires. 

The ground may be connected to one, and only one, working electrical
line and at one, and only one, particular and carefully specified
point. This is for safety reasons and to provide a common referent, only.

Where some campers get in trouble is when two errors work together.
First the neutral and hot get swapped between the campground service
entrance and their RV fuse box. And, second, there is an improper
neutral to safety ground connection in their RV. When both of these
errors happen at the same time, the RV chassis can complete a circuit
back to the service entrance grounding point causing a potential shock
hazard.

And be careful in discussions about who is grounded to what where
because a lot of electricians are thinking household and not RV. You
need a competent electrician familiar with RV code and even then it
probably helps to check the code yourself (especially check stuff like
this message as I might have got it backwards myself).

Oh, and by the way, With your RV unplugged, check the resistance
between ground and neutral (use the pins on your power cord). It
should be infinite or open, right? Same as between ground and hot,
right? Neutral to hot will show the resistance of any loads you have
on line (converters, lights, detectors, or whatever).