1. Home
  2. Tech
  3. DIY
  4. The Shocking Truth About AC Power

The Shocking Truth About AC Power

Originally Published in MotorHome Magazine

If you spend enough time in your motorhome you’ll eventually encounter a problem with the
AC power supplying your coach. Even if you don’t plug into a bad AC circuit, chances are
good that you might experience electrical problems due to lightning (even nearby strikes
can cause problems) or other types of electrical irregularities that can find their way
into your motorhome. Recently, we heard about a motorhome that was damaged to the tune of
$2,400 due to a nearby lightning strike. When these events occur, every electrical device
in your coach is a candidate for damage, including your microwave, TV, DVD player, stereo,
air conditioners, converter and/or inverter. So, protecting them should be a high priority.

In addition to lightning, other common issues that can cause damage include voltage on
ground, open neutral, high or low voltage, and reverse-polarity conditions. Another
important point is that your motorhome is at risk while parked at home or in storage. Any
time your coach is plugged in to 120-volt AC current, it should be protected. While these
problems are more common than you may expect, they are also very easy to protect against.
So rather than taking chances with a coach full of electronics, our suggestion is to simply
install a UL-listed surge protector.

There are several units available on the market,
including portable models that can be plugged in between your shorepower lead and the AC
pedestal, as well as hard-wired units that mount inside the electrical cabinet of your
motorhome. There are disadvantages to the portable units, such as the possibility of theft
and the exposure to weather, so we opted for the hard-wired version. The model we selected
is the TRC Surge Guard model 50-Amp Hardwire #34560, which is available through Camping
World and other RV retailers. It is a UL-listed device and offers 1750 joules of surge
suppression and handles a spike current of up to 6500 amps. It is a 50-amp device and, if
needed, will work with 30-amp adapters. At the time this article was written, the unit was
available at Camping World for $355.55 ($319.99 for President’s Club members).

the unit is fairly straight forward if you are familiar with basic wiring. Assuming you
have room in your electrical bay, you should be able to install your own. If not, Camping
World can install it for about $158. Once in place, the Surge Guard acts as a filter to
continuously protect your coach from a variety of threats. As soon as you plug your
motorhome into an AC receptacle, it automatically checks for faults such as an open
neutral, voltage on the ground wire and reverse polarity, and prevents the power from even
being passed through to the coach until corrected. During its use the Surge Guard also
senses voltage irregularities continuously and if the voltage drops below 102 volts or goes
above 132 volts for more than eight seconds, power will be removed.

Once proper conditions
are present the device has a built-in 135-second delay before it allows power to pass
through to the motorhome. This allows the AC compressor to bleed off the high pressure
before attempting to restart after a surge. The unit also has four LED lights on the
display that allow you to inspect conditions and see at a glance the current state. If a
fault exists, the lights allow you to determine the exact type that has occurred.
Considering the cost versus benefits, it is clear that a quality surge protector is one of
the very first accessories that should be added to any motorhome. If you decide to install
your own, these tips – along with the manual for your specific surge protector – should
allow you to install the unit in a safe and effective manner. Before beginning any
installation of this type, be sure the coach is completely disconnected from shorepower and
that the AC generator is manually turned off (check any auto-start function as well) and
that the inverter is off. If you are not competent and comfortable with 120-volt AC
electrical wiring, have this done by a professional.

 Installing the Surge

 A Surge Guard can be installed before or after the transfer switch; after
talking to the manufacturer we opted to install our model before the transfer switch. Not
only is this an easier install due to the wiring involved, it is also the most common
location. However, this does allow the generator power to remain unprotected. Generators
are generally very stable these days and rarely cause problems; thus the manufacturer
advised it is perfectly safe. First, locate your electrical bay and identify the shorepower
line that feeds it. Shown here is the wire in question

Next, determine a suitable location
to mount the Surge Guard. The only caution from the manufacturer is that it should not be
mounted horizontally with the face point up toward the sky. Any other orientation is fine,
but remember you will want it located so that it can be easily viewed. We mounted ours
vertically beside the transfer switch using sheet metal screws. It is also a good idea to
look behind the mounting wall and make sure your screws are not going to cause any problems
on the back side of the mounting location. You will then need to cut the large 50-amp power
cord in the location you selected for proper mounting. Be sure to leave enough slack on the
transfer switch side to allow the wires to attach to the Surge Guard. The shorepower line
will now be loose so its length is not an issue.

Next, strip the four wires (1/2-inch) and
mount them to the Surge Guard as shown in the installation manual of your device. Tighten
the screws according to the manufacturer’s instructions; in our case 16 inch-lbs. The
stripped portion of the wires should be completely contained in the terminal block housing.
Because there are only four wires and they are color coded, it should be easy to find the
proper location for each one. Pay attention to the direction of the wiring and make sure
you connect the load/output side of the Surge Guard wires to the transfer switch side, and
the line/input side of the Surge Guard to your shorepower wire that connects to the AC

After establishing all the connections for the Surge Guard, use strain relief
clamps to hold the wires in place to prevent them from pulling out of the terminal
connections. Once connected, double check all the wires as well as the mounting of the
Surge Guard and the strain relief clamps. If everything checks out, first turn off all AC
devices in the coach, then connect the shorepower cord to an approved AC receptacle. Next,
verify the “line” lights are illuminated and that the danger light is off. At this point
the delay light will flash for two minutes and 15 seconds, then the power connection will
be made, allowing AC power to flow to the motorhome. If there are problems with the wiring,
the lights will help you troubleshoot and make corrections. Now you will be able to enjoy
your coach and have one less thing to worry about when plugging into a campground
receptacle, or when the weather gets rough.

Subscribe to Wildsam Magazine today, Camping World and Good Sam’s magazine of the open road.

Just $19.97 for a year’s subscription.


Please login or register to view archived articles.

Sign In

Do not have an account? Create New Account